feat: add bounded compatible session browser (#8)

Closes #8

docs/api/rendezvous-v1.json

@@ -75,8 +75,68 @@
               }
             }
           },
-          "501": {
+          "400": {
-            "description": "Not Implemented",
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Unauthorized",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "403": {
+            "description": "Forbidden",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Conflict",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "410": {
+            "description": "Gone",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "429": {
+            "description": "Too Many Requests",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
             "content": {
               "application/json": {
                 "schema": {
@@ -85,7 +145,12 @@
               }
             }
           }
+        },
+        "security": [
+          {
+            "PublisherBearer": [ ]
           }
+        ]
       },
       "get": {
         "tags": [
@@ -142,6 +207,13 @@
               "format": "int32"
             }
           },
+          {
+            "name": "excludeFull",
+            "in": "query",
+            "schema": {
+              "type": "boolean"
+            }
+          },
           {
             "name": "cursor",
             "in": "query",
@@ -161,8 +233,18 @@
               }
             }
           },
-          "501": {
+          "400": {
-            "description": "Not Implemented",
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
             "content": {
               "application/json": {
                 "schema": {
@@ -211,8 +293,68 @@
               }
             }
           },
-          "501": {
+          "400": {
-            "description": "Not Implemented",
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Unauthorized",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "403": {
+            "description": "Forbidden",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Not Found",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Conflict",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "410": {
+            "description": "Gone",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
             "content": {
               "application/json": {
                 "schema": {
@@ -221,7 +363,12 @@
               }
             }
           }
+        },
+        "security": [
+          {
+            "PublisherBearer": [ ]
           }
+        ]
       }
     },
     "/v1/sessions/{listingId}": {
@@ -254,8 +401,48 @@
           "204": {
             "description": "No Content"
           },
-          "501": {
+          "400": {
-            "description": "Not Implemented",
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Unauthorized",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "403": {
+            "description": "Forbidden",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Not Found",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
             "content": {
               "application/json": {
                 "schema": {
@@ -264,7 +451,12 @@
               }
             }
           }
+        },
+        "security": [
+          {
+            "PublisherBearer": [ ]
           }
+        ]
       },
       "delete": {
         "tags": [
@@ -295,8 +487,38 @@
           "204": {
             "description": "No Content"
           },
-          "501": {
+          "400": {
-            "description": "Not Implemented",
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Unauthorized",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "403": {
+            "description": "Forbidden",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
             "content": {
               "application/json": {
                 "schema": {
@@ -305,7 +527,12 @@
               }
             }
           }
+        },
+        "security": [
+          {
+            "PublisherBearer": [ ]
           }
+        ]
       },
       "get": {
         "tags": [
@@ -320,6 +547,40 @@
             "schema": {
               "type": "string"
             }
+          },
+          {
+            "name": "contractVersion",
+            "in": "query",
+            "required": true,
+            "schema": {
+              "type": "integer",
+              "format": "int32"
+            }
+          },
+          {
+            "name": "gameId",
+            "in": "query",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          },
+          {
+            "name": "environmentId",
+            "in": "query",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          },
+          {
+            "name": "protocolVersion",
+            "in": "query",
+            "required": true,
+            "schema": {
+              "type": "integer",
+              "format": "uint32"
+            }
           }
         ],
         "responses": {
@@ -333,8 +594,28 @@
               }
             }
           },
-          "501": {
+          "400": {
-            "description": "Not Implemented",
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Not Found",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
             "content": {
               "application/json": {
                 "schema": {
@@ -875,7 +1156,9 @@
           "leaseToken",
           "hostPresenceHandle",
           "hostPresenceCapability",
-          "expiresAt"
+          "expiresAt",
+          "leaseRenewAfterSeconds",
+          "hostPresenceRefreshAfterSeconds"
         ],
         "type": "object",
         "properties": {
@@ -901,6 +1184,14 @@
           "expiresAt": {
             "type": "string",
             "format": "date-time"
+          },
+          "leaseRenewAfterSeconds": {
+            "type": "integer",
+            "format": "int32"
+          },
+          "hostPresenceRefreshAfterSeconds": {
+            "type": "integer",
+            "format": "int32"
           }
         }
       },
@@ -942,7 +1233,8 @@
       "RenewLeaseResponse": {
         "required": [
           "contractVersion",
-          "expiresAt"
+          "expiresAt",
+          "renewAfterSeconds"
         ],
         "type": "object",
         "properties": {
@@ -953,6 +1245,10 @@
           "expiresAt": {
             "type": "string",
             "format": "date-time"
+          },
+          "renewAfterSeconds": {
+            "type": "integer",
+            "format": "int32"
           }
         }
       },
@@ -1115,6 +1411,14 @@
           }
         }
       }
+    },
+    "securitySchemes": {
+      "PublisherBearer": {
+        "type": "http",
+        "description": "Tenant-scoped publisher credential issued during game provisioning.",
+        "scheme": "bearer",
+        "bearerFormat": "rv1 publisher credential"
+      }
     }
   },
   "tags": [

docs/architecture/0004-atomic-ephemeral-state.md

@@ -0,0 +1,101 @@
+# ADR 0004: atomic ephemeral state and single-active availability
+
+- Status: Accepted
+- Date: 2026-07-16
+- Tracking: #6
+
+## Context
+
+Listings, leases, endpoint observations, join attempts, and replay decisions must
+move together. A partially committed authorization can expose an expired listing,
+reuse a capability, or introduce an endpoint that was never authorized. V1 is a
+single-active service, so it needs honest bounded in-memory behavior rather than
+a database-shaped abstraction that implies unavailable durability or scale.
+
+## Decision
+
+`IEphemeralRendezvousStore` is the atomic boundary for directory, lease, presence,
+attempt, endpoint, replay, revocation, and drain transitions. The v1 implementation
+serializes each transition under one process-local lock. This deliberately favors
+simple, auditable correctness at the initial 25,000-listing/10,000-attempt ceiling.
+It retains only immutable listing data, opaque credential fingerprints, observed
+endpoints, monotonic deadlines, and bounded idempotency/replay records.
+
+Every collection has an independent configured ceiling. An operation checks all
+of the capacity it needs before changing any collection. Exhaustion returns
+`CapacityExceeded`; it does not evict live state, partially insert an operation,
+or grow a fallback queue. Policy-provided per-owner listing and per-tenant active
+attempt quotas are evaluated inside the same creation transition, so concurrent
+requests cannot pass a check performed outside the store. New join authorization returns `ServiceUnavailable`
+when the atomic store is unavailable and `Draining` once drain starts.
+
+### Time and cleanup
+
+Expiry uses an injected monotonic clock. Wall time is used only to return an
+informational `ExpiresAt` value. Moving the wall clock forward or backward cannot
+expire or prolong authority. Cleanup runs deterministically at the start of every
+store operation and removes presence, attempts, listings, replay entries,
+idempotency records, and revocations at their deadline. Removal of a listing also
+removes its presence handle and every linked attempt before another caller can
+observe the store.
+
+### Concurrency and idempotency
+
+- Listing registration and join-attempt creation use a tenant-and-owner-scoped idempotency
+  key plus a canonical request fingerprint. An exact duplicate returns the
+  original live result; reuse with different input returns `Conflict`; replay
+  after the resource has expired returns `Expired` until the bounded idempotency
+  record itself expires. Configuration requires idempotency retention to cover
+  every listing and attempt lifetime, preventing a live duplicate after eviction.
+- Lease renewal is compare-and-swap by version. A stale renewal returns the latest
+  version as `Conflict`. Renew/delete races are serialized: renewal either commits
+  before deletion or observes the listing as absent.
+- Host presence refresh is an atomic whole-endpoint replacement because NAT
+  mappings can legitimately change. Attempt capabilities are different: the
+  first endpoint bound for each role wins, an identical datagram is idempotent,
+  and a different replay is rejected. Introduction is consumed once atomically.
+- Cancellation is checked before waiting for the lock and again after acquiring
+  it. A cancellation observed at either point makes no change. Once a synchronous
+  transition starts, it completes atomically and does not expose partial state.
+
+### Visibility and revocation
+
+A listing is visible or joinable only when its lease and authenticated UDP host
+presence are both fresh. Public browsing is tenant/protocol scoped, excludes
+unlisted sessions, and uses a stable listing-ID order with the contract page
+ceiling. Revoking a listing or principal removes every listing, presence, and
+attempt path in the same transition. A revocation is inserted before removal;
+if the bounded revocation pool is full, the operation rejects without deleting
+anything.
+
+### Restart and graceful drain
+
+A process restart creates a new store instance ID and starts empty. Old listing,
+lease, attempt, endpoint, idempotency, and consumption state is not recovered.
+Publishers must re-register; old callers receive typed `NotFound`, `Expired`, or
+`ServiceUnavailable` outcomes rather than an ambiguous success. No database is
+required or supported for the single-active MVP.
+
+Drain is idempotent. It immediately rejects new registrations, attempts, and
+lease extensions, while already-created attempts may bind endpoints and consume
+their introduction during the configured window (at most 30 seconds). At the
+deadline all active state is cleared atomically. Readiness is false while draining
+or unavailable, and application shutdown starts drain before teardown.
+
+## Future shared-store mapping
+
+The interface uses explicit typed outcomes, TTLs, compare-and-swap versions,
+idempotency records, and all-or-nothing multi-record transitions. A future Redis
+implementation therefore requires authenticated transport, tenant-prefixed keys,
+server-side scripts or transactions for each transition, TTLs based on the store's
+authoritative time, and deterministic mediator routing. It must preserve these
+semantics and pass the same contract tests before issue #18 may enable more than
+one active instance.
+
+## Consequences
+
+- V1 has deterministic failure and restart behavior without durable gameplay state.
+- A single lock is a measured capacity constraint, not a claim of horizontal scale.
+- Transport and HTTP modules cannot bypass the store for authorization decisions.
+- Operational code must treat `CapacityExceeded`, `Draining`, and
+  `ServiceUnavailable` as normal typed overload/availability outcomes.

docs/architecture/0005-session-lease-lifecycle.md

@@ -0,0 +1,91 @@
+# ADR 0005: authenticated session lease and presence lifecycle
+
+- Status: Accepted
+- Date: 2026-07-16
+- Tracking: #7
+
+## Context
+
+A host needs to publish a player-facing session without letting an HTTP request
+claim a public endpoint or remain visible after the gameplay socket disappears.
+Registration retries must be safe, credentials must remain opaque, and policy or
+ownership checks cannot race state mutation.
+
+## Decision
+
+The four host HTTP operations require `Authorization: Bearer <publisher credential>`.
+The signed principal supplies the authoritative game, environment, publisher trust
+mode, subject, and allowed regions. Request fields never widen that scope. Creation
+and update apply the enabled `GamePolicy` to exact protocol, region, visibility,
+bounded display/build/capacity values, and the allowlisted metadata schema.
+
+Capacity reported by a host is advisory directory information. Rendezvous bounds
+and publishes it but never treats it as final admission authority; the game host
+still decides identity, bans, reserved slots, and whether a connection may join.
+
+```mermaid
+stateDiagram-v2
+    [*] --> AwaitingPresence: authorized register
+    AwaitingPresence --> Listed: valid host UDP presence
+    Listed --> AwaitingPresence: presence deadline passes
+    AwaitingPresence --> AwaitingPresence: lease renew or data update
+    Listed --> Listed: lease renew, data update, or presence refresh
+    AwaitingPresence --> Removed: lease expiry or delete
+    Listed --> Removed: lease expiry or delete
+    Removed --> [*]
+```
+
+Registration returns a listing ID, lease ID/token, host-presence handle/capability,
+lease expiry, a 30-second renewal suggestion, and a 10-second presence-refresh
+suggestion. The authoritative ceilings remain 60 seconds for the lease and 20
+seconds for presence. Timing suggestions are server-controlled, not client-selected.
+
+The lease token and presence capability are 256-bit opaque values derived with
+HMAC-SHA256 from an in-memory per-process secret, a purpose label, the publisher
+subject, the idempotency key, a canonical request fingerprint, and a random
+per-registration derivation salt. Opaque IDs use separate purpose labels. Exact
+retries read the retained non-secret salt and therefore reproduce the original
+response without retaining plaintext credentials. Once the bounded idempotency
+record expires, a new salt rotates IDs and capabilities so an old token cannot
+regain authority. Metadata order is canonicalized before fingerprinting. The store
+retains the salt and only a second keyed fingerprint of each token. Restart rotates
+the derivation secret while the matching ephemeral state disappears.
+
+Renew, update, and delete require both the same publisher subject and the lease
+capability. Cross-owner or wrong-capability access returns the same not-found shape.
+Update may change display name, build label, advisory capacity, and metadata only;
+game, environment, region, protocol, visibility, trust mode, and opaque IDs remain
+canonical. Delete is idempotent and does not reveal whether another publisher owns
+the supplied ID.
+
+### UDP presence
+
+Only a structurally valid `HostPresence` datagram with the issued capability can
+refresh presence. The public endpoint is the UDP packet's observed source on the
+host's gameplay socket; the HTTP API never accepts one. The bounded local candidate
+comes from the authenticated datagram. Invalid, unknown, or client-presence packets
+receive no response. Presence expiry demotes public visibility but keeps the lease,
+so the same handle can restore visibility without changing session identity.
+
+Public listing responses contain bounded listing data only. They never contain
+public/local endpoints, lease tokens, presence capabilities, fingerprints, store
+keys, or canonical player identity.
+
+## Failure semantics
+
+- malformed or policy-invalid fields return a stable typed `InvalidRequest`;
+- an unsupported gameplay protocol returns `IncompatibleProtocol`;
+- missing/invalid publisher authentication returns `AuthenticationRequired`;
+- cross-scope authorization returns `Forbidden` without resource disclosure;
+- wrong owner/capability or expired state returns the tenant-hidden `NotFound`;
+- idempotency reuse with changed input returns `Conflict`;
+- publisher/global exhaustion returns `CapacityExceeded`; and
+- drain or loss of atomic state returns `ServiceUnavailable` and authorizes no join.
+
+## Consequences
+
+- HTTP registration alone can never make a public session browseable.
+- Plaintext session capabilities are returned to the intended host but are not
+  retained, logged, included in public listing DTOs, or exported as metrics.
+- Re-registration after restart is the recovery path; there is no durable session
+  identity or gameplay state in Rendezvous.

docs/architecture/0006-compatible-session-browser.md

@@ -0,0 +1,51 @@
+# ADR 0006: bounded compatible session browser
+
+- Status: Accepted
+- Date: 2026-07-16
+- Tracking: #8
+
+## Decision
+
+The public list endpoint requires game, environment, and exact gameplay protocol.
+Region is optional, page size is 1–100, and callers may exclude sessions whose
+advisory current-player count has reached the advertised maximum. Lists contain
+public sessions only and only while both lease and authenticated host presence are
+fresh. Unlisted sessions never appear in a list; they may be retrieved directly by
+their 128-bit unguessable listing ID only when the caller also supplies the exact
+game, environment, and protocol scope.
+
+Results use ascending opaque listing ID as a deterministic keyset. A cursor carries
+the last ID plus every compatibility/filter field, a five-minute expiry, and an
+HMAC-SHA256 signature under a per-process key. Tampering, expiry, or reuse with a
+different tenant/protocol/region/full filter returns `InvalidRequest`. Restart
+rotates the key, matching the loss of ephemeral listings.
+
+Pagination is a bounded live view, not a database snapshot. A record that remains
+eligible and whose ID is greater than the cursor is returned exactly once. Records
+removed or made stale disappear immediately. A record created after a page whose ID
+sorts before that page's cursor is outside that traversal; callers refresh from the
+first page to discover new sessions. This avoids skips or duplicates among stable
+eligible records without retaining per-browser snapshot state.
+
+The store reads at most page size plus one record. The service serializes against
+the 256 KiB response ceiling and shortens a page before returning it when metadata
+makes the requested count too large. A continuation cursor is emitted whenever an
+extra or byte-trimmed record remains. All cursor, page, metadata, property, scalar,
+and collection sizes are bounded before untrusted allocation can grow without a
+ceiling.
+
+Browser DTOs are fresh copies containing only opaque listing ID, exact compatibility,
+region, visibility/trust presentation, advisory capacity, build/display labels, and
+policy-validated string metadata. They contain no observed endpoint, lease,
+capability, ticket, credential fingerprint, derivation salt, principal subject, or
+store key. Metadata is display text: JSON encoding escapes markup, but game UI must
+still render values as text and must never execute markup, interpret endpoints, or
+use metadata for authorization.
+
+## Consequences
+
+- Cross-game, cross-environment, incompatible, stale, revoked, expired, unlisted,
+  and optionally full sessions are removed before response construction.
+- Direct unlisted lookup is suitable for an out-of-band invite carrying the opaque
+  ID; human join codes remain future work and require their own bounded abuse model.
+- Host capacity remains advisory. The host makes the final admission decision.

docs/architecture/README.md

@@ -6,6 +6,9 @@ decision requires a superseding ADR and corresponding contract/test updates.
 - [ADR 0001: v1 control-plane boundaries and domain](0001-v1-control-plane-boundaries.md)
 - [ADR 0002: publisher trust, discovery, compatibility, and fallback](0002-publisher-trust-and-connection-policy.md)
 - [ADR 0003: state, privacy, availability, and safety budgets](0003-state-privacy-availability-and-budgets.md)
+- [ADR 0004: atomic ephemeral state and single-active availability](0004-atomic-ephemeral-state.md)
+- [ADR 0005: authenticated session lease and presence lifecycle](0005-session-lease-lifecycle.md)
+- [ADR 0006: bounded compatible session browser](0006-compatible-session-browser.md)
 - [Threat model](../security/threat-model.md)
 - [Security promise and test matrix](../security/control-matrix.md)
 - [Versioned HTTP and UDP contracts](../contracts/README.md)

src/FinalFactory.Rendezvous.Contracts/ContractValidation.cs

@@ -46,10 +46,12 @@ public static class ContractValidation
         value is null || IsVisibleAsciiWithin(value, ContractLimits.DiagnosticCodeMaxCharacters);
 
     public static bool IsBuildVersionValid(string? value) =>
-        IsUtf8LengthWithin(value, ContractLimits.BuildVersionMaxBytes);
+        !string.IsNullOrWhiteSpace(value)
+        && IsUtf8LengthWithin(value, ContractLimits.BuildVersionMaxBytes);
 
     public static bool IsDisplayNameValid(string? value) =>
-        IsUtf8LengthWithin(value, ContractLimits.DisplayNameMaxBytes);
+        !string.IsNullOrWhiteSpace(value)
+        && IsUtf8LengthWithin(value, ContractLimits.DisplayNameMaxBytes);
 
     public static bool IsOpaqueHttpCredentialValid(string? value) =>
         value is not null

src/FinalFactory.Rendezvous.Contracts/Http/SessionContracts.cs

@@ -99,6 +99,12 @@ public sealed class RegisterSessionResponse
 
     [JsonRequired]
     public DateTimeOffset ExpiresAt { get; set; }
+
+    [JsonRequired]
+    public int LeaseRenewAfterSeconds { get; set; }
+
+    [JsonRequired]
+    public int HostPresenceRefreshAfterSeconds { get; set; }
 }
 
 public sealed class RenewLeaseRequest
@@ -117,6 +123,9 @@ public sealed class RenewLeaseResponse
 
     [JsonRequired]
     public DateTimeOffset ExpiresAt { get; set; }
+
+    [JsonRequired]
+    public int RenewAfterSeconds { get; set; }
 }
 
 public sealed class UpdateSessionRequest
@@ -165,6 +174,8 @@ public sealed class BrowseSessionsRequest
     public RegionId? RegionId { get; set; }
     public int PageSize { get; set; } = ContractLimits.BrowserPageMaxItems;
 
+    public bool ExcludeFull { get; set; }
+
     public string? Cursor { get; set; }
 }
 

src/FinalFactory.Rendezvous.Server/Browser/SessionBrowserCursorCodec.cs

@@ -0,0 +1,181 @@
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Server.Browser;
+
+internal sealed class SessionBrowserCursorCodec : IDisposable
+{
+    private const string Prefix = "rvc1";
+    private readonly byte[] _key = RandomNumberGenerator.GetBytes(32);
+    private bool _disposed;
+
+    public string Encode(VisibleListingQuery query, SessionListingId after, DateTimeOffset now)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        BrowserCursorPayload payload = new()
+        {
+            GameId = query.Scope.GameId.Value,
+            EnvironmentId = query.Scope.EnvironmentId.Value,
+            ProtocolVersion = query.ProtocolVersion,
+            RegionId = query.RegionId?.Value,
+            ExcludeFull = query.ExcludeFull,
+            AfterListingId = after.ToString(),
+            ExpiresAtUnixSeconds = now.AddMinutes(5).ToUnixTimeSeconds(),
+        };
+        string encoded = EncodeBytes(JsonSerializer.SerializeToUtf8Bytes(payload, ContractJson.Options));
+        string content = $"{Prefix}.{encoded}";
+        byte[] signature = HMACSHA256.HashData(_key, Encoding.ASCII.GetBytes(content));
+        try
+        {
+            string cursor = $"{content}.{EncodeBytes(signature)}";
+            return ContractValidation.IsCursorValid(cursor)
+                ? cursor
+                : throw new InvalidOperationException("The browser cursor exceeds its contract limit.");
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(signature);
+        }
+    }
+
+    public bool TryDecode(
+        string? cursor,
+        TenantScope scope,
+        uint protocolVersion,
+        RegionId? regionId,
+        bool excludeFull,
+        DateTimeOffset now,
+        out SessionListingId? after)
+    {
+        after = null;
+        if (cursor is null)
+        {
+            return true;
+        }
+
+        if (_disposed || !ContractValidation.IsCursorValid(cursor))
+        {
+            return false;
+        }
+
+        string[] segments = cursor.Split('.');
+        if (segments.Length != 3 || !string.Equals(segments[0], Prefix, StringComparison.Ordinal))
+        {
+            return false;
+        }
+
+        byte[] expected = HMACSHA256.HashData(
+            _key,
+            Encoding.ASCII.GetBytes($"{segments[0]}.{segments[1]}"));
+        if (!TryDecodeBytes(segments[2], out byte[] supplied))
+        {
+            CryptographicOperations.ZeroMemory(expected);
+            return false;
+        }
+
+        bool validSignature = supplied.Length == expected.Length
+            && CryptographicOperations.FixedTimeEquals(supplied, expected);
+        CryptographicOperations.ZeroMemory(supplied);
+        CryptographicOperations.ZeroMemory(expected);
+        if (!validSignature || !TryDecodeBytes(segments[1], out byte[] encodedPayload))
+        {
+            return false;
+        }
+
+        BrowserCursorPayload? payload;
+        try
+        {
+            payload = JsonSerializer.Deserialize<BrowserCursorPayload>(
+                encodedPayload,
+                ContractJson.Options);
+        }
+        catch (JsonException)
+        {
+            payload = null;
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(encodedPayload);
+        }
+
+        if (payload is null
+            || payload.ExpiresAtUnixSeconds <= now.ToUnixTimeSeconds()
+            || !string.Equals(payload.GameId, scope.GameId.Value, StringComparison.Ordinal)
+            || !string.Equals(payload.EnvironmentId, scope.EnvironmentId.Value, StringComparison.Ordinal)
+            || payload.ProtocolVersion != protocolVersion
+            || !string.Equals(payload.RegionId, regionId?.Value, StringComparison.Ordinal)
+            || payload.ExcludeFull != excludeFull
+            || !SessionListingId.TryParse(payload.AfterListingId, out SessionListingId listingId))
+        {
+            return false;
+        }
+
+        after = listingId;
+        return true;
+    }
+
+    public void Dispose()
+    {
+        if (!_disposed)
+        {
+            _disposed = true;
+            CryptographicOperations.ZeroMemory(_key);
+        }
+    }
+
+    public override string ToString() => "[SessionBrowserCursorCodec: key and cursors redacted]";
+
+    private static string EncodeBytes(ReadOnlySpan<byte> bytes) => Convert
+        .ToBase64String(bytes)
+        .TrimEnd('=')
+        .Replace('+', '-')
+        .Replace('/', '_');
+
+    private static bool TryDecodeBytes(string value, out byte[] bytes)
+    {
+        bytes = [];
+        if (string.IsNullOrEmpty(value)
+            || value.Any(static character =>
+                character is not (>= 'A' and <= 'Z')
+                and not (>= 'a' and <= 'z')
+                and not (>= '0' and <= '9')
+                and not '-'
+                and not '_'))
+        {
+            return false;
+        }
+
+        string padded = value.Replace('-', '+').Replace('_', '/');
+        padded += (padded.Length % 4) switch { 0 => "", 2 => "==", 3 => "=", _ => "!" };
+        try
+        {
+            bytes = Convert.FromBase64String(padded);
+            return true;
+        }
+        catch (FormatException)
+        {
+            return false;
+        }
+    }
+}
+
+internal sealed class BrowserCursorPayload
+{
+    [JsonRequired]
+    public string GameId { get; set; } = string.Empty;
+    [JsonRequired]
+    public string EnvironmentId { get; set; } = string.Empty;
+    [JsonRequired]
+    public uint ProtocolVersion { get; set; }
+    public string? RegionId { get; set; }
+    [JsonRequired]
+    public bool ExcludeFull { get; set; }
+    [JsonRequired]
+    public string AfterListingId { get; set; } = string.Empty;
+    [JsonRequired]
+    public long ExpiresAtUnixSeconds { get; set; }
+}

src/FinalFactory.Rendezvous.Server/Browser/SessionBrowserService.cs

@@ -0,0 +1,157 @@
+using System.Text.Json;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Server.Browser;
+
+internal sealed record BrowserServiceResult<T>(RendezvousErrorCode Error, T? Value = default)
+{
+    public bool Succeeded => Error == RendezvousErrorCode.None;
+}
+
+internal sealed class SessionBrowserService(
+    IEphemeralRendezvousStore store,
+    SessionBrowserCursorCodec cursors,
+    IWallClock clock)
+{
+    public BrowserServiceResult<BrowseSessionsResponse> Browse(
+        BrowseSessionsRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+        RendezvousErrorCode validation = Validate(request);
+        if (validation != RendezvousErrorCode.None)
+        {
+            return new(validation);
+        }
+
+        TenantScope scope = new(request.GameId, request.EnvironmentId);
+        if (!cursors.TryDecode(
+                request.Cursor,
+                scope,
+                request.ProtocolVersion,
+                request.RegionId,
+                request.ExcludeFull,
+                clock.UtcNow,
+                out SessionListingId? after))
+        {
+            return new(RendezvousErrorCode.InvalidRequest);
+        }
+
+        VisibleListingQuery query = new(
+            scope,
+            request.ProtocolVersion,
+            request.RegionId,
+            request.PageSize + 1,
+            after,
+            request.ExcludeFull);
+        StoreResult<IReadOnlyList<StoredListing>> found = store.BrowseVisibleListings(
+            query,
+            cancellationToken);
+        if (!found.Succeeded || found.Value is null)
+        {
+            return new(found.Code == StoreResultCode.ServiceUnavailable
+                ? RendezvousErrorCode.ServiceUnavailable
+                : RendezvousErrorCode.InternalError);
+        }
+
+        List<SessionListing> items = found.Value
+            .Take(request.PageSize)
+            .Select(ToContract)
+            .ToList();
+        bool hasMore = found.Value.Count > request.PageSize;
+        while (items.Count > 0)
+        {
+            string? nextCursor = hasMore
+                ? cursors.Encode(query, items[^1].ListingId, clock.UtcNow)
+                : null;
+            BrowseSessionsResponse response = new() { Items = items, NextCursor = nextCursor };
+            if (JsonSerializer.SerializeToUtf8Bytes(response, ContractJson.Options).Length
+                <= ContractLimits.BrowserResponseMaxBytes)
+            {
+                return new(RendezvousErrorCode.None, response);
+            }
+
+            items.RemoveAt(items.Count - 1);
+            hasMore = true;
+        }
+
+        return new(RendezvousErrorCode.None, new BrowseSessionsResponse());
+    }
+
+    public BrowserServiceResult<GetSessionResponse> Get(
+        SessionListingId listingId,
+        GameId gameId,
+        EnvironmentId environmentId,
+        uint protocolVersion,
+        CancellationToken cancellationToken = default)
+    {
+        if (listingId.Value == Guid.Empty
+            || string.IsNullOrEmpty(gameId.Value)
+            || string.IsNullOrEmpty(environmentId.Value)
+            || protocolVersion == 0)
+        {
+            return new(RendezvousErrorCode.InvalidRequest);
+        }
+
+        StoreResult<StoredListing> found = store.GetListing(listingId, true, cancellationToken);
+        if (!found.Succeeded || found.Value is null)
+        {
+            return new(found.Code == StoreResultCode.ServiceUnavailable
+                ? RendezvousErrorCode.ServiceUnavailable
+                : RendezvousErrorCode.NotFound);
+        }
+
+        StoredListing listing = found.Value;
+        if (listing.Definition.Scope != new TenantScope(gameId, environmentId)
+            || listing.Definition.ProtocolVersion != protocolVersion)
+        {
+            return new(RendezvousErrorCode.NotFound);
+        }
+
+        return new(RendezvousErrorCode.None, new GetSessionResponse
+        {
+            Session = ToContract(listing),
+        });
+    }
+
+    private static RendezvousErrorCode Validate(BrowseSessionsRequest request)
+    {
+        RendezvousErrorCode version = ContractValidation.ValidateContractVersion(request.ContractVersion);
+        if (version != RendezvousErrorCode.None)
+        {
+            return version;
+        }
+
+        return string.IsNullOrEmpty(request.GameId.Value)
+            || string.IsNullOrEmpty(request.EnvironmentId.Value)
+            || request.ProtocolVersion == 0
+            || (request.RegionId.HasValue && string.IsNullOrEmpty(request.RegionId.Value.Value))
+            || !ContractValidation.IsPageSizeValid(request.PageSize)
+            || !ContractValidation.IsCursorValid(request.Cursor)
+            ? RendezvousErrorCode.InvalidRequest
+            : RendezvousErrorCode.None;
+    }
+
+    private static SessionListing ToContract(StoredListing stored) => new()
+    {
+        ListingId = stored.Definition.ListingId,
+        GameId = stored.Definition.Scope.GameId,
+        EnvironmentId = stored.Definition.Scope.EnvironmentId,
+        RegionId = stored.Definition.RegionId,
+        ProtocolVersion = stored.Definition.ProtocolVersion,
+        BuildVersion = stored.Definition.BuildVersion,
+        DisplayName = stored.Definition.DisplayName,
+        Visibility = stored.Definition.Visibility,
+        PublisherTrustMode = stored.Definition.TrustMode,
+        Capacity = new()
+        {
+            CurrentPlayers = stored.Definition.CurrentPlayers,
+            MaximumPlayers = stored.Definition.MaximumPlayers,
+        },
+        Metadata = stored.Definition.Metadata.ToDictionary(
+            static item => item.Key,
+            static item => item.Value,
+            StringComparer.Ordinal),
+    };
+}

src/FinalFactory.Rendezvous.Server/Http/ContractEndpoints.cs

@@ -1,4 +1,8 @@
 using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Browser;
+using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
 using Microsoft.AspNetCore.Mvc;
 
 namespace FinalFactory.Rendezvous.Server.Http;
@@ -14,30 +18,52 @@ internal static class ContractEndpoints
         sessions.MapPost("/", RegisterSession)
             .Accepts<RegisterSessionRequest>("application/json")
             .Produces<RegisterSessionResponse>(StatusCodes.Status201Created)
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status401Unauthorized)
+            .Produces<ApiError>(StatusCodes.Status403Forbidden)
+            .Produces<ApiError>(StatusCodes.Status409Conflict)
+            .Produces<ApiError>(StatusCodes.Status410Gone)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("RegisterSession");
         sessions.MapPost("/{listingId}/renew", RenewLease)
             .Accepts<RenewLeaseRequest>("application/json")
             .Produces<RenewLeaseResponse>()
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status401Unauthorized)
+            .Produces<ApiError>(StatusCodes.Status403Forbidden)
+            .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status409Conflict)
+            .Produces<ApiError>(StatusCodes.Status410Gone)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("RenewSessionLease");
         sessions.MapPut("/{listingId}", UpdateSession)
             .Accepts<UpdateSessionRequest>("application/json")
             .Produces(StatusCodes.Status204NoContent)
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status401Unauthorized)
+            .Produces<ApiError>(StatusCodes.Status403Forbidden)
+            .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("UpdateSession");
         sessions.MapDelete("/{listingId}", DeleteSession)
             .Accepts<DeleteSessionRequest>("application/json")
             .Produces(StatusCodes.Status204NoContent)
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status401Unauthorized)
+            .Produces<ApiError>(StatusCodes.Status403Forbidden)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("DeleteSession");
         sessions.MapGet("/", BrowseSessions)
             .Produces<BrowseSessionsResponse>()
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("BrowseSessions");
         sessions.MapGet("/{listingId}", GetSession)
             .Produces<GetSessionResponse>()
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("GetSession");
         sessions.MapGet("/{listingId}/join-attempts", BrowseHostJoinAttempts)
             .Produces<BrowseHostJoinAttemptsResponse>()
@@ -61,20 +87,115 @@ internal static class ContractEndpoints
         return endpoints;
     }
 
-    private static IResult RegisterSession([FromBody] RegisterSessionRequest request) =>
+    private static IResult RegisterSession(
-        NotImplemented();
+        [FromBody] RegisterSessionRequest request,
+        [FromHeader(Name = "Authorization")] string? authorizationHeader,
+        [FromServices] PrincipalCredentialService credentials,
+        [FromServices] SessionLeaseService sessions,
+        [FromServices] IWallClock clock,
+        HttpContext httpContext,
+        CancellationToken cancellationToken)
+    {
+        if (!TryAuthenticatePublisher(
+                authorizationHeader,
+                credentials,
+                clock,
+                out AuthenticatedPrincipal? principal))
+        {
+            return AuthenticationRequired(httpContext);
+        }
+
+        SessionServiceResult<RegisterSessionResponse> result = sessions.Register(
+            principal!,
+            request,
+            cancellationToken);
+        return result.Succeeded && result.Value is not null
+            ? Results.Created($"/v1/sessions/{result.Value.ListingId}", result.Value)
+            : Error(result.Error);
+    }
 
     private static IResult RenewLease(
         SessionListingId listingId,
-        [FromBody] RenewLeaseRequest request) => NotImplemented();
+        [FromBody] RenewLeaseRequest request,
+        [FromHeader(Name = "Authorization")] string? authorizationHeader,
+        [FromServices] PrincipalCredentialService credentials,
+        [FromServices] SessionLeaseService sessions,
+        [FromServices] IWallClock clock,
+        HttpContext httpContext,
+        CancellationToken cancellationToken)
+    {
+        if (!TryAuthenticatePublisher(
+                authorizationHeader,
+                credentials,
+                clock,
+                out AuthenticatedPrincipal? principal))
+        {
+            return AuthenticationRequired(httpContext);
+        }
+
+        SessionServiceResult<RenewLeaseResponse> result = sessions.Renew(
+            principal!,
+            listingId,
+            request,
+            cancellationToken);
+        return result.Succeeded && result.Value is not null
+            ? Results.Ok(result.Value)
+            : Error(result.Error);
+    }
 
     private static IResult UpdateSession(
         SessionListingId listingId,
-        [FromBody] UpdateSessionRequest request) => NotImplemented();
+        [FromBody] UpdateSessionRequest request,
+        [FromHeader(Name = "Authorization")] string? authorizationHeader,
+        [FromServices] PrincipalCredentialService credentials,
+        [FromServices] SessionLeaseService sessions,
+        [FromServices] IWallClock clock,
+        HttpContext httpContext,
+        CancellationToken cancellationToken)
+    {
+        if (!TryAuthenticatePublisher(
+                authorizationHeader,
+                credentials,
+                clock,
+                out AuthenticatedPrincipal? principal))
+        {
+            return AuthenticationRequired(httpContext);
+        }
+
+        SessionServiceResult<bool> result = sessions.Update(
+            principal!,
+            listingId,
+            request,
+            cancellationToken);
+        return result.Succeeded ? Results.NoContent() : Error(result.Error);
+    }
 
     private static IResult DeleteSession(
         SessionListingId listingId,
-        [FromBody] DeleteSessionRequest request) => NotImplemented();
+        [FromBody] DeleteSessionRequest request,
+        [FromHeader(Name = "Authorization")] string? authorizationHeader,
+        [FromServices] PrincipalCredentialService credentials,
+        [FromServices] SessionLeaseService sessions,
+        [FromServices] IWallClock clock,
+        HttpContext httpContext,
+        CancellationToken cancellationToken)
+    {
+        if (!TryAuthenticatePublisher(
+                authorizationHeader,
+                credentials,
+                clock,
+                out AuthenticatedPrincipal? principal))
+        {
+            return AuthenticationRequired(httpContext);
+        }
+
+        SessionServiceResult<bool> result = sessions.Delete(
+            principal!,
+            listingId,
+            request,
+            cancellationToken);
+        return result.Succeeded ? Results.NoContent() : Error(result.Error);
+    }
 
     private static IResult BrowseSessions(
         [FromQuery] int contractVersion,
@@ -83,9 +204,64 @@ internal static class ContractEndpoints
         [FromQuery] uint protocolVersion,
         [FromQuery] string? regionId,
         [FromQuery] int? pageSize,
-        [FromQuery] string? cursor) => NotImplemented();
+        [FromQuery] bool? excludeFull,
+        [FromQuery] string? cursor,
+        [FromServices] SessionBrowserService browser,
+        CancellationToken cancellationToken)
+    {
+        if (!GameId.TryParse(gameId, out GameId parsedGameId)
+            || !EnvironmentId.TryParse(environmentId, out EnvironmentId parsedEnvironmentId)
+            || (regionId is not null && !RegionId.TryParse(regionId, out _)))
+        {
+            return Error(RendezvousErrorCode.InvalidRequest);
+        }
 
-    private static IResult GetSession(SessionListingId listingId) => NotImplemented();
+        BrowserServiceResult<BrowseSessionsResponse> result = browser.Browse(new()
+        {
+            ContractVersion = contractVersion,
+            GameId = parsedGameId,
+            EnvironmentId = parsedEnvironmentId,
+            ProtocolVersion = protocolVersion,
+            RegionId = regionId is null ? null : new RegionId(regionId),
+            PageSize = pageSize ?? ContractLimits.BrowserPageMaxItems,
+            ExcludeFull = excludeFull ?? false,
+            Cursor = cursor,
+        }, cancellationToken);
+        return result.Succeeded && result.Value is not null
+            ? Results.Ok(result.Value)
+            : Error(result.Error);
+    }
+
+    private static IResult GetSession(
+        SessionListingId listingId,
+        [FromQuery] int contractVersion,
+        [FromQuery] string gameId,
+        [FromQuery] string environmentId,
+        [FromQuery] uint protocolVersion,
+        [FromServices] SessionBrowserService browser,
+        CancellationToken cancellationToken)
+    {
+        if (ContractValidation.ValidateContractVersion(contractVersion) != RendezvousErrorCode.None)
+        {
+            return Error(RendezvousErrorCode.UnsupportedContractVersion);
+        }
+
+        if (!GameId.TryParse(gameId, out GameId parsedGameId)
+            || !EnvironmentId.TryParse(environmentId, out EnvironmentId parsedEnvironmentId))
+        {
+            return Error(RendezvousErrorCode.InvalidRequest);
+        }
+
+        BrowserServiceResult<GetSessionResponse> result = browser.Get(
+            listingId,
+            parsedGameId,
+            parsedEnvironmentId,
+            protocolVersion,
+            cancellationToken);
+        return result.Succeeded && result.Value is not null
+            ? Results.Ok(result.Value)
+            : Error(result.Error);
+    }
 
     private static IResult BrowseHostJoinAttempts(
         SessionListingId listingId,
@@ -109,4 +285,72 @@ internal static class ContractEndpoints
         },
         ContractJson.Options,
         statusCode: NotImplementedStatus);
+
+    private static bool TryAuthenticatePublisher(
+        string? authorizationHeader,
+        PrincipalCredentialService credentials,
+        IWallClock clock,
+        out AuthenticatedPrincipal? principal)
+    {
+        principal = null;
+        const string bearerPrefix = "Bearer ";
+        if (authorizationHeader is null
+            || !authorizationHeader.StartsWith(bearerPrefix, StringComparison.OrdinalIgnoreCase))
+        {
+            return false;
+        }
+
+        string token = authorizationHeader[bearerPrefix.Length..];
+        CredentialValidationResult validation = credentials.Validate(token, clock.UtcNow);
+        if (!validation.IsValid || validation.Principal is not IPublisherPrincipal)
+        {
+            return false;
+        }
+
+        principal = validation.Principal;
+        return true;
+    }
+
+    private static IResult Error(RendezvousErrorCode code) => Results.Json(
+        new ApiError
+        {
+            Code = code,
+            Message = ErrorMessage(code),
+        },
+        ContractJson.Options,
+        statusCode: ErrorStatus(code));
+
+    private static IResult AuthenticationRequired(HttpContext context)
+    {
+        context.Response.Headers.WWWAuthenticate = "Bearer";
+        return Error(RendezvousErrorCode.AuthenticationRequired);
+    }
+
+    private static int ErrorStatus(RendezvousErrorCode code) => code switch
+    {
+        RendezvousErrorCode.AuthenticationRequired => StatusCodes.Status401Unauthorized,
+        RendezvousErrorCode.Forbidden => StatusCodes.Status403Forbidden,
+        RendezvousErrorCode.NotFound or RendezvousErrorCode.StaleHost => StatusCodes.Status404NotFound,
+        RendezvousErrorCode.Conflict or RendezvousErrorCode.ReplayRejected => StatusCodes.Status409Conflict,
+        RendezvousErrorCode.Expired => StatusCodes.Status410Gone,
+        RendezvousErrorCode.RateLimited or RendezvousErrorCode.CapacityExceeded =>
+            StatusCodes.Status429TooManyRequests,
+        RendezvousErrorCode.ServiceUnavailable => StatusCodes.Status503ServiceUnavailable,
+        RendezvousErrorCode.InternalError => StatusCodes.Status500InternalServerError,
+        _ => StatusCodes.Status400BadRequest,
+    };
+
+    private static string ErrorMessage(RendezvousErrorCode code) => code switch
+    {
+        RendezvousErrorCode.AuthenticationRequired => "A valid publisher bearer credential is required.",
+        RendezvousErrorCode.Forbidden => "The publisher is not authorized for this operation.",
+        RendezvousErrorCode.NotFound => "The session was not found or is not owned by this publisher.",
+        RendezvousErrorCode.Conflict => "The session changed concurrently; retry with current state.",
+        RendezvousErrorCode.Expired => "The session lease has expired.",
+        RendezvousErrorCode.IncompatibleProtocol => "The gameplay protocol is not enabled for this game.",
+        RendezvousErrorCode.CapacityExceeded => "The configured session capacity is currently exhausted.",
+        RendezvousErrorCode.ServiceUnavailable => "Session state is temporarily unavailable.",
+        RendezvousErrorCode.UnsupportedContractVersion => "The requested contract version is not supported.",
+        _ => "The session request is invalid.",
+    };
 }

src/FinalFactory.Rendezvous.Server/Http/RendezvousExceptionHandler.cs

@@ -0,0 +1,37 @@
+using System.Text.Json;
+using FinalFactory.Rendezvous.Contracts;
+using Microsoft.AspNetCore.Diagnostics;
+
+namespace FinalFactory.Rendezvous.Server.Http;
+
+internal sealed class RendezvousExceptionHandler : IExceptionHandler
+{
+    public async ValueTask<bool> TryHandleAsync(
+        HttpContext httpContext,
+        Exception exception,
+        CancellationToken cancellationToken)
+    {
+        if (httpContext.Response.HasStarted)
+        {
+            return false;
+        }
+
+        bool invalidRequest = exception is BadHttpRequestException or JsonException;
+        httpContext.Response.StatusCode = invalidRequest
+            ? StatusCodes.Status400BadRequest
+            : StatusCodes.Status500InternalServerError;
+        await httpContext.Response.WriteAsJsonAsync(
+            new ApiError
+            {
+                Code = invalidRequest
+                    ? RendezvousErrorCode.InvalidRequest
+                    : RendezvousErrorCode.InternalError,
+                Message = invalidRequest
+                    ? "The request body, route, or query value is invalid."
+                    : "The service could not complete the request.",
+            },
+            ContractJson.Options,
+            cancellationToken).ConfigureAwait(false);
+        return true;
+    }
+}

src/FinalFactory.Rendezvous.Server/Program.cs

@@ -1,7 +1,10 @@
 using System.Net;
 using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Browser;
 using FinalFactory.Rendezvous.Server.Http;
 using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
 using FinalFactory.Rendezvous.Server.Transport;
 using Microsoft.OpenApi;
 
@@ -12,6 +15,7 @@ bool isOpenApiGeneration = string.Equals(
     StringComparison.Ordinal);
 
 builder.Services.AddOpenApi("v1", static options =>
+{
     options.AddSchemaTransformer(static (schema, context, cancellationToken) =>
     {
         Type type = context.JsonTypeInfo.Type;
@@ -31,9 +35,65 @@ builder.Services.AddOpenApi("v1", static options =>
         }
 
         return Task.CompletedTask;
-    }));
+    });
+    options.AddDocumentTransformer(static (document, context, cancellationToken) =>
+    {
+        const string schemeName = "PublisherBearer";
+        document.Components ??= new OpenApiComponents();
+        document.Components.SecuritySchemes ??=
+            new Dictionary<string, IOpenApiSecurityScheme>(StringComparer.Ordinal);
+        document.Components.SecuritySchemes[schemeName] = new OpenApiSecurityScheme
+        {
+            Type = SecuritySchemeType.Http,
+            Scheme = "bearer",
+            BearerFormat = "rv1 publisher credential",
+            Description = "Tenant-scoped publisher credential issued during game provisioning.",
+        };
+
+        HashSet<string> securedOperations = new(StringComparer.Ordinal)
+        {
+            "RegisterSession",
+            "RenewSessionLease",
+            "UpdateSession",
+            "DeleteSession",
+        };
+        OpenApiSecuritySchemeReference reference = new(schemeName, document, null);
+        foreach (OpenApiPathItem path in document.Paths.Values)
+        {
+            if (path.Operations is null)
+            {
+                continue;
+            }
+
+            foreach (OpenApiOperation operation in path.Operations.Values.Where(
+                         operation => securedOperations.Contains(operation.OperationId ?? string.Empty)))
+            {
+                operation.Security ??= [];
+                operation.Security.Add(new OpenApiSecurityRequirement
+                {
+                    [reference] = [],
+                });
+            }
+        }
+
+        return Task.CompletedTask;
+    });
+});
 builder.Services.ConfigureHttpJsonOptions(static options =>
     ContractJson.Configure(options.SerializerOptions));
+builder.Services.Configure<RouteHandlerOptions>(static options =>
+    options.ThrowOnBadRequest = true);
+builder.Services.AddProblemDetails();
+builder.Services.AddExceptionHandler<RendezvousExceptionHandler>();
+
+SystemRendezvousClock rendezvousClock = new();
+EphemeralStoreOptions stateOptions = new();
+InMemoryEphemeralRendezvousStore stateStore = new(
+    stateOptions,
+    rendezvousClock,
+    rendezvousClock);
+builder.Services.AddSingleton<IEphemeralRendezvousStore>(stateStore);
+builder.Services.AddSingleton<IWallClock>(rendezvousClock);
 
 if (isOpenApiGeneration)
 {
@@ -55,6 +115,13 @@ else
     builder.Services.AddSingleton(provisioning.Policies);
     builder.Services.AddSingleton(provisioning.Credentials);
     builder.Services.AddSingleton(provisioning.PublisherAuthorization);
+    EphemeralCapabilityIssuer sessionCapabilities = new();
+    builder.Services.AddSingleton(sessionCapabilities);
+    builder.Services.AddSingleton<ISessionCapabilityService>(sessionCapabilities);
+    builder.Services.AddSingleton(SessionLeaseTiming.From(stateOptions));
+    builder.Services.AddSingleton<SessionLeaseService>();
+    builder.Services.AddSingleton<SessionBrowserCursorCodec>();
+    builder.Services.AddSingleton<SessionBrowserService>();
     builder.Services.AddSingleton(new ProvisioningReadiness(true));
 }
 
@@ -74,7 +141,9 @@ if (!isOpenApiGeneration)
 }
 
 WebApplication app = builder.Build();
+app.Lifetime.ApplicationStopping.Register(() => stateStore.BeginDrain());
 
+app.UseExceptionHandler();
 app.MapOpenApi();
 app.MapRendezvousContractEndpoints();
 app.MapGet(
@@ -85,8 +154,14 @@ app.MapGet(
     .WithTags("Health");
 app.MapGet(
     "/health/ready",
-    static (UdpMediatorService mediator, ProvisioningReadiness provisioning) =>
+    static (
-        mediator.LocalEndpoint is null || !provisioning.IsReady
+        UdpMediatorService mediator,
+        ProvisioningReadiness provisioning,
+        IEphemeralRendezvousStore state) =>
+        mediator.LocalEndpoint is null
+        || !provisioning.IsReady
+        || !state.IsAvailable
+        || state.IsDraining
         ? Results.StatusCode(StatusCodes.Status503ServiceUnavailable)
         : Results.Ok(new HealthResponse { Status = "ready" }))
     .Produces<HealthResponse>()

src/FinalFactory.Rendezvous.Server/Sessions/EphemeralCapabilityIssuer.cs

@@ -0,0 +1,158 @@
+using System.Buffers.Binary;
+using System.Security.Cryptography;
+using System.Text;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Server.Sessions;
+
+internal interface ISessionCapabilityService
+{
+    string CreateDerivationSalt();
+    string DeriveCapability(
+        string purpose,
+        string ownerSubject,
+        string idempotencyKey,
+        string requestFingerprint,
+        string derivationSalt);
+    Guid DeriveGuid(
+        string purpose,
+        string ownerSubject,
+        string idempotencyKey,
+        string requestFingerprint,
+        string derivationSalt);
+    bool TryFingerprint(string? capability, out SecretFingerprint fingerprint);
+}
+
+internal sealed class EphemeralCapabilityIssuer : ISessionCapabilityService, IDisposable
+{
+    private readonly byte[] _key = RandomNumberGenerator.GetBytes(32);
+    private bool _disposed;
+
+    public string CreateDerivationSalt()
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        byte[] salt = RandomNumberGenerator.GetBytes(32);
+        try
+        {
+            return Encode(salt);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(salt);
+        }
+    }
+
+    public string DeriveCapability(
+        string purpose,
+        string ownerSubject,
+        string idempotencyKey,
+        string requestFingerprint,
+        string derivationSalt)
+    {
+        byte[] digest = Derive(
+            purpose,
+            ownerSubject,
+            idempotencyKey,
+            requestFingerprint,
+            derivationSalt);
+        try
+        {
+            return Encode(digest);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(digest);
+        }
+    }
+
+    public Guid DeriveGuid(
+        string purpose,
+        string ownerSubject,
+        string idempotencyKey,
+        string requestFingerprint,
+        string derivationSalt)
+    {
+        byte[] digest = Derive(
+            purpose,
+            ownerSubject,
+            idempotencyKey,
+            requestFingerprint,
+            derivationSalt);
+        try
+        {
+            Span<byte> guidBytes = digest.AsSpan(0, 16);
+            guidBytes[7] = (byte)((guidBytes[7] & 0x0f) | 0x80);
+            guidBytes[8] = (byte)((guidBytes[8] & 0x3f) | 0x80);
+            return new Guid(guidBytes);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(digest);
+        }
+    }
+
+    public bool TryFingerprint(string? capability, out SecretFingerprint fingerprint)
+    {
+        fingerprint = default;
+        if (_disposed
+            || capability is null
+            || capability.Length != 43
+            || capability.Any(static character =>
+                character is not (>= 'A' and <= 'Z')
+                and not (>= 'a' and <= 'z')
+                and not (>= '0' and <= '9')
+                and not '-'
+                and not '_'))
+        {
+            return false;
+        }
+
+        byte[] digest = Derive("fingerprint", capability);
+        try
+        {
+            fingerprint = new SecretFingerprint(Encode(digest));
+            return true;
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(digest);
+        }
+    }
+
+    public void Dispose()
+    {
+        if (_disposed)
+        {
+            return;
+        }
+
+        _disposed = true;
+        CryptographicOperations.ZeroMemory(_key);
+    }
+
+    public override string ToString() => "[EphemeralCapabilityIssuer: key and capabilities redacted]";
+
+    private byte[] Derive(params string[] segments)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        using IncrementalHash hmac = IncrementalHash.CreateHMAC(HashAlgorithmName.SHA256, _key);
+        Span<byte> length = stackalloc byte[sizeof(int)];
+        foreach (string segment in segments)
+        {
+            ArgumentException.ThrowIfNullOrEmpty(segment);
+            byte[] encoded = Encoding.UTF8.GetBytes(segment);
+            BinaryPrimitives.WriteInt32BigEndian(length, encoded.Length);
+            hmac.AppendData(length);
+            hmac.AppendData(encoded);
+            CryptographicOperations.ZeroMemory(encoded);
+        }
+
+        return hmac.GetHashAndReset();
+    }
+
+    private static string Encode(ReadOnlySpan<byte> bytes) => Convert
+        .ToBase64String(bytes)
+        .TrimEnd('=')
+        .Replace('+', '-')
+        .Replace('/', '_');
+}

src/FinalFactory.Rendezvous.Server/Sessions/SessionLeaseService.cs

@@ -0,0 +1,452 @@
+using System.Security.Cryptography;
+using System.Text.Json;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Server.Sessions;
+
+internal sealed record SessionLeaseTiming(
+    int LeaseRenewAfterSeconds,
+    int HostPresenceRefreshAfterSeconds)
+{
+    public static SessionLeaseTiming From(EphemeralStoreOptions options) => new(
+        Math.Max(1, (int)(options.LeaseLifetime.TotalSeconds / 2)),
+        Math.Max(1, (int)(options.PresenceLifetime.TotalSeconds / 2)));
+}
+
+internal sealed record SessionServiceResult<T>(RendezvousErrorCode Error, T? Value = default)
+{
+    public bool Succeeded => Error == RendezvousErrorCode.None;
+}
+
+internal sealed class SessionLeaseService(
+    PublisherAuthorizationService authorization,
+    IEphemeralRendezvousStore store,
+    ISessionCapabilityService capabilities,
+    SessionLeaseTiming timing,
+    IWallClock clock)
+{
+    public SessionServiceResult<RegisterSessionResponse> Register(
+        AuthenticatedPrincipal principal,
+        RegisterSessionRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(principal);
+        ArgumentNullException.ThrowIfNull(request);
+        RendezvousErrorCode validation = ValidateRegistration(request);
+        if (validation != RendezvousErrorCode.None)
+        {
+            return new(validation);
+        }
+
+        PublisherAuthorizationResult authorized = authorization.Authorize(
+            principal,
+            request.GameId,
+            request.EnvironmentId,
+            request.RegionId,
+            request.ProtocolVersion,
+            request.Visibility,
+            request.Metadata,
+            clock.UtcNow);
+        if (!authorized.IsAllowed || authorized.Context is null)
+        {
+            return new(MapAuthorization(authorized.Error));
+        }
+
+        AuthorizedPublisherContext context = authorized.Context;
+        string requestFingerprint = ComputeRegistrationFingerprint(request);
+        string derivationSalt = capabilities.CreateDerivationSalt();
+        string leaseToken = capabilities.DeriveCapability(
+            "lease-token",
+            context.Subject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt);
+        string presenceCapability = capabilities.DeriveCapability(
+            "host-presence",
+            context.Subject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt);
+        if (!capabilities.TryFingerprint(leaseToken, out SecretFingerprint leaseFingerprint)
+            || !capabilities.TryFingerprint(presenceCapability, out SecretFingerprint presenceFingerprint))
+        {
+            throw new InvalidOperationException("Derived session capabilities could not be fingerprinted.");
+        }
+
+        SessionListingId listingId = new(capabilities.DeriveGuid(
+            "listing-id",
+            context.Subject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt));
+        LeaseId leaseId = new(capabilities.DeriveGuid(
+            "lease-id",
+            context.Subject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt));
+        MediationHandle presenceHandle = new(capabilities.DeriveGuid(
+            "presence-handle",
+            context.Subject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt));
+        int ownerLimit = context.TrustMode == PublisherTrustMode.AnonymousUnlisted
+            ? context.Policy.MaxAnonymousListingsPerAddress
+            : context.Policy.MaxListingsPerPrincipal;
+        if (ownerLimit <= 0)
+        {
+            return new(RendezvousErrorCode.CapacityExceeded);
+        }
+
+        StoreResult<StoredListing> created = store.CreateListing(new(
+            request.IdempotencyKey,
+            requestFingerprint,
+            new ListingDefinition
+            {
+                ListingId = listingId,
+                LeaseId = leaseId,
+                Scope = new(context.GameId, context.EnvironmentId),
+                OwnerSubject = context.Subject,
+                RegionId = context.RegionId,
+                ProtocolVersion = context.ProtocolVersion,
+                BuildVersion = request.BuildVersion,
+                DisplayName = request.DisplayName,
+                Visibility = context.Visibility,
+                TrustMode = context.TrustMode,
+                CurrentPlayers = request.Capacity.CurrentPlayers,
+                MaximumPlayers = request.Capacity.MaximumPlayers,
+                Metadata = request.Metadata,
+                LeaseFingerprint = leaseFingerprint,
+                HostPresenceHandle = presenceHandle,
+                HostPresenceFingerprint = presenceFingerprint,
+                CapabilityDerivationSalt = derivationSalt,
+            },
+            ownerLimit), cancellationToken);
+        if (!created.Succeeded || created.Value is null)
+        {
+            return new(MapStore(created.Code));
+        }
+
+        ListingDefinition persisted = created.Value.Definition;
+        leaseToken = capabilities.DeriveCapability(
+            "lease-token",
+            context.Subject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            persisted.CapabilityDerivationSalt);
+        presenceCapability = capabilities.DeriveCapability(
+            "host-presence",
+            context.Subject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            persisted.CapabilityDerivationSalt);
+
+        return new(RendezvousErrorCode.None, new RegisterSessionResponse
+        {
+            ListingId = persisted.ListingId,
+            LeaseId = persisted.LeaseId,
+            LeaseToken = leaseToken,
+            HostPresenceHandle = persisted.HostPresenceHandle,
+            HostPresenceCapability = presenceCapability,
+            ExpiresAt = created.Value.LeaseExpiresAt,
+            LeaseRenewAfterSeconds = timing.LeaseRenewAfterSeconds,
+            HostPresenceRefreshAfterSeconds = timing.HostPresenceRefreshAfterSeconds,
+        });
+    }
+
+    public SessionServiceResult<RenewLeaseResponse> Renew(
+        AuthenticatedPrincipal principal,
+        SessionListingId listingId,
+        RenewLeaseRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(principal);
+        ArgumentNullException.ThrowIfNull(request);
+        RendezvousErrorCode validation = ValidateLeaseRequest(request.ContractVersion, request.LeaseToken);
+        if (validation != RendezvousErrorCode.None)
+        {
+            return new(validation);
+        }
+
+        RendezvousErrorCode lookup = GetAuthorizedListing(
+            principal,
+            listingId,
+            request.LeaseToken,
+            cancellationToken,
+            out StoredListing? listing);
+        if (lookup != RendezvousErrorCode.None)
+        {
+            return new(lookup);
+        }
+
+        StoredListing ownedListing = listing!;
+        PublisherAuthorizationResult authorized = AuthorizeExisting(
+            principal,
+            ownedListing,
+            ownedListing.Definition.Metadata);
+        if (!authorized.IsAllowed)
+        {
+            return new(MapAuthorization(authorized.Error));
+        }
+
+        capabilities.TryFingerprint(request.LeaseToken, out SecretFingerprint fingerprint);
+        StoreResult<StoredListing> renewed = store.RenewLease(new(
+            listingId,
+            ownedListing.Definition.LeaseId,
+            fingerprint,
+            ownedListing.Definition.OwnerSubject,
+            ownedListing.Version), cancellationToken);
+        return renewed.Succeeded && renewed.Value is not null
+            ? new(RendezvousErrorCode.None, new RenewLeaseResponse
+            {
+                ExpiresAt = renewed.Value.LeaseExpiresAt,
+                RenewAfterSeconds = timing.LeaseRenewAfterSeconds,
+            })
+            : new(MapStore(renewed.Code));
+    }
+
+    public SessionServiceResult<bool> Update(
+        AuthenticatedPrincipal principal,
+        SessionListingId listingId,
+        UpdateSessionRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(principal);
+        ArgumentNullException.ThrowIfNull(request);
+        RendezvousErrorCode validation = ValidateUpdate(request);
+        if (validation != RendezvousErrorCode.None)
+        {
+            return new(validation);
+        }
+
+        RendezvousErrorCode lookup = GetAuthorizedListing(
+            principal,
+            listingId,
+            request.LeaseToken,
+            cancellationToken,
+            out StoredListing? listing);
+        if (lookup != RendezvousErrorCode.None)
+        {
+            return new(lookup);
+        }
+
+        StoredListing ownedListing = listing!;
+        PublisherAuthorizationResult authorized = AuthorizeExisting(principal, ownedListing, request.Metadata);
+        if (!authorized.IsAllowed)
+        {
+            return new(MapAuthorization(authorized.Error));
+        }
+
+        capabilities.TryFingerprint(request.LeaseToken, out SecretFingerprint fingerprint);
+        StoreResult<StoredListing> updated = store.UpdateListing(new(
+            listingId,
+            ownedListing.Definition.LeaseId,
+            fingerprint,
+            ownedListing.Definition.OwnerSubject,
+            request.BuildVersion,
+            request.DisplayName,
+            request.Capacity.CurrentPlayers,
+            request.Capacity.MaximumPlayers,
+            request.Metadata), cancellationToken);
+        return updated.Succeeded
+            ? new(RendezvousErrorCode.None, true)
+            : new(MapStore(updated.Code));
+    }
+
+    public SessionServiceResult<bool> Delete(
+        AuthenticatedPrincipal principal,
+        SessionListingId listingId,
+        DeleteSessionRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(principal);
+        ArgumentNullException.ThrowIfNull(request);
+        RendezvousErrorCode validation = ValidateLeaseRequest(request.ContractVersion, request.LeaseToken);
+        if (validation != RendezvousErrorCode.None)
+        {
+            return new(validation);
+        }
+
+        if (principal is not IPublisherPrincipal publisher
+            || !capabilities.TryFingerprint(request.LeaseToken, out SecretFingerprint fingerprint))
+        {
+            return new(RendezvousErrorCode.Forbidden);
+        }
+
+        StoreResult<StoredListing> found = store.GetListing(listingId, false, cancellationToken);
+        if (!found.Succeeded || found.Value is null)
+        {
+            return found.Code == StoreResultCode.ServiceUnavailable
+                ? new(RendezvousErrorCode.ServiceUnavailable)
+                : new(RendezvousErrorCode.None, true);
+        }
+
+        StoreResult<bool> deleted = store.DeleteListing(new(
+            listingId,
+            found.Value.Definition.LeaseId,
+            fingerprint,
+            publisher.Subject), cancellationToken);
+        return deleted.Succeeded || deleted.Code == StoreResultCode.NotFound
+            ? new(RendezvousErrorCode.None, true)
+            : new(MapStore(deleted.Code));
+    }
+
+    private RendezvousErrorCode GetAuthorizedListing(
+        AuthenticatedPrincipal principal,
+        SessionListingId listingId,
+        string leaseToken,
+        CancellationToken cancellationToken,
+        out StoredListing? listing)
+    {
+        listing = null;
+        if (principal is not IPublisherPrincipal publisher)
+        {
+            return RendezvousErrorCode.Forbidden;
+        }
+
+        if (!capabilities.TryFingerprint(leaseToken, out SecretFingerprint fingerprint))
+        {
+            return RendezvousErrorCode.NotFound;
+        }
+
+        StoreResult<StoredListing> found = store.GetListing(listingId, false, cancellationToken);
+        if (!found.Succeeded || found.Value is null)
+        {
+            return MapStore(found.Code);
+        }
+
+        if (!string.Equals(found.Value.Definition.OwnerSubject, publisher.Subject, StringComparison.Ordinal)
+            || found.Value.Definition.LeaseFingerprint != fingerprint)
+        {
+            return RendezvousErrorCode.NotFound;
+        }
+
+        listing = found.Value;
+        return RendezvousErrorCode.None;
+    }
+
+    private PublisherAuthorizationResult AuthorizeExisting(
+        AuthenticatedPrincipal principal,
+        StoredListing listing,
+        IReadOnlyDictionary<string, string> metadata) => authorization.Authorize(
+            principal,
+            listing.Definition.Scope.GameId,
+            listing.Definition.Scope.EnvironmentId,
+            listing.Definition.RegionId,
+            listing.Definition.ProtocolVersion,
+            listing.Definition.Visibility,
+            metadata,
+            clock.UtcNow);
+
+    private static RendezvousErrorCode ValidateRegistration(RegisterSessionRequest request)
+    {
+        RendezvousErrorCode version = ContractValidation.ValidateContractVersion(request.ContractVersion);
+        if (version != RendezvousErrorCode.None)
+        {
+            return version;
+        }
+
+        return !ContractValidation.IsIdempotencyKeyValid(request.IdempotencyKey)
+            || string.IsNullOrEmpty(request.GameId.Value)
+            || string.IsNullOrEmpty(request.EnvironmentId.Value)
+            || string.IsNullOrEmpty(request.RegionId.Value)
+            || request.ProtocolVersion == 0
+            || !ContractValidation.IsBuildVersionValid(request.BuildVersion)
+            || !ContractValidation.IsDisplayNameValid(request.DisplayName)
+            || !Enum.IsDefined(request.Visibility)
+            || !ContractValidation.IsCapacityValid(request.Capacity)
+            || !ContractValidation.IsMetadataValid(request.Metadata)
+            ? RendezvousErrorCode.InvalidRequest
+            : RendezvousErrorCode.None;
+    }
+
+    private static RendezvousErrorCode ValidateUpdate(UpdateSessionRequest request)
+    {
+        RendezvousErrorCode lease = ValidateLeaseRequest(request.ContractVersion, request.LeaseToken);
+        if (lease != RendezvousErrorCode.None)
+        {
+            return lease;
+        }
+
+        return !ContractValidation.IsBuildVersionValid(request.BuildVersion)
+            || !ContractValidation.IsDisplayNameValid(request.DisplayName)
+            || !ContractValidation.IsCapacityValid(request.Capacity)
+            || !ContractValidation.IsMetadataValid(request.Metadata)
+            ? RendezvousErrorCode.InvalidRequest
+            : RendezvousErrorCode.None;
+    }
+
+    private static RendezvousErrorCode ValidateLeaseRequest(int contractVersion, string leaseToken)
+    {
+        RendezvousErrorCode version = ContractValidation.ValidateContractVersion(contractVersion);
+        if (version != RendezvousErrorCode.None)
+        {
+            return version;
+        }
+
+        return ContractValidation.IsOpaqueHttpCredentialValid(leaseToken)
+            ? RendezvousErrorCode.None
+            : RendezvousErrorCode.InvalidRequest;
+    }
+
+    private static RendezvousErrorCode MapAuthorization(PublisherAuthorizationError error) => error switch
+    {
+        PublisherAuthorizationError.PrincipalExpired => RendezvousErrorCode.AuthenticationRequired,
+        PublisherAuthorizationError.ProtocolNotAllowed => RendezvousErrorCode.IncompatibleProtocol,
+        PublisherAuthorizationError.RegionNotAllowed
+            or PublisherAuthorizationError.VisibilityNotAllowed
+            or PublisherAuthorizationError.AnonymousMustBeUnlisted
+            or PublisherAuthorizationError.MetadataNotAllowed => RendezvousErrorCode.InvalidRequest,
+        _ => RendezvousErrorCode.Forbidden,
+    };
+
+    private static RendezvousErrorCode MapStore(StoreResultCode code) => code switch
+    {
+        StoreResultCode.NotFound => RendezvousErrorCode.NotFound,
+        StoreResultCode.Expired => RendezvousErrorCode.Expired,
+        StoreResultCode.Revoked => RendezvousErrorCode.Forbidden,
+        StoreResultCode.Conflict => RendezvousErrorCode.Conflict,
+        StoreResultCode.CapacityExceeded => RendezvousErrorCode.CapacityExceeded,
+        StoreResultCode.ReplayRejected => RendezvousErrorCode.ReplayRejected,
+        StoreResultCode.Draining or StoreResultCode.ServiceUnavailable => RendezvousErrorCode.ServiceUnavailable,
+        _ => RendezvousErrorCode.InternalError,
+    };
+
+    private static string ComputeRegistrationFingerprint(RegisterSessionRequest request)
+    {
+        RegisterSessionRequest canonical = new()
+        {
+            ContractVersion = request.ContractVersion,
+            IdempotencyKey = request.IdempotencyKey,
+            GameId = request.GameId,
+            EnvironmentId = request.EnvironmentId,
+            RegionId = request.RegionId,
+            ProtocolVersion = request.ProtocolVersion,
+            BuildVersion = request.BuildVersion,
+            DisplayName = request.DisplayName,
+            Visibility = request.Visibility,
+            Capacity = new SessionCapacity
+            {
+                CurrentPlayers = request.Capacity.CurrentPlayers,
+                MaximumPlayers = request.Capacity.MaximumPlayers,
+            },
+            Metadata = request.Metadata
+                .OrderBy(static item => item.Key, StringComparer.Ordinal)
+                .ToDictionary(static item => item.Key, static item => item.Value, StringComparer.Ordinal),
+        };
+        byte[] encoded = JsonSerializer.SerializeToUtf8Bytes(canonical, ContractJson.Options);
+        byte[] digest = SHA256.HashData(encoded);
+        CryptographicOperations.ZeroMemory(encoded);
+        try
+        {
+            return Convert.ToBase64String(digest).TrimEnd('=').Replace('+', '-').Replace('/', '_');
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(digest);
+        }
+    }
+}

src/FinalFactory.Rendezvous.Server/State/EphemeralStateContracts.cs

@@ -0,0 +1,325 @@
+using System.Collections.Frozen;
+using System.Diagnostics;
+using System.Net;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Server.State;
+
+internal interface IWallClock
+{
+    DateTimeOffset UtcNow { get; }
+}
+
+internal interface IMonotonicClock
+{
+    TimeSpan Elapsed { get; }
+}
+
+internal sealed class SystemRendezvousClock : IWallClock, IMonotonicClock
+{
+    private readonly long _origin = Stopwatch.GetTimestamp();
+
+    public DateTimeOffset UtcNow => DateTimeOffset.UtcNow;
+
+    public TimeSpan Elapsed => Stopwatch.GetElapsedTime(_origin);
+}
+
+internal sealed record EphemeralStoreOptions
+{
+    public int MaxListings { get; init; } = 25_000;
+    public int MaxPresenceBindings { get; init; } = 25_000;
+    public int MaxJoinAttempts { get; init; } = 10_000;
+    public int MaxReplayEntries { get; init; } = 30_000;
+    public int MaxRevocations { get; init; } = 10_000;
+    public int MaxIdempotencyEntries { get; init; } = 35_000;
+    public TimeSpan LeaseLifetime { get; init; } = TimeSpan.FromSeconds(60);
+    public TimeSpan PresenceLifetime { get; init; } = TimeSpan.FromSeconds(20);
+    public TimeSpan JoinAttemptLifetime { get; init; } = TimeSpan.FromSeconds(30);
+    public TimeSpan ReplayLifetime { get; init; } = TimeSpan.FromSeconds(30);
+    public TimeSpan IdempotencyLifetime { get; init; } = TimeSpan.FromMinutes(2);
+    public TimeSpan GracefulDrainLifetime { get; init; } = TimeSpan.FromSeconds(30);
+
+    public void Validate()
+    {
+        RequirePositive(MaxListings, nameof(MaxListings));
+        RequirePositive(MaxPresenceBindings, nameof(MaxPresenceBindings));
+        RequirePositive(MaxJoinAttempts, nameof(MaxJoinAttempts));
+        RequirePositive(MaxReplayEntries, nameof(MaxReplayEntries));
+        RequirePositive(MaxRevocations, nameof(MaxRevocations));
+        RequirePositive(MaxIdempotencyEntries, nameof(MaxIdempotencyEntries));
+        RequireDuration(LeaseLifetime, TimeSpan.FromSeconds(60), nameof(LeaseLifetime));
+        RequireDuration(PresenceLifetime, TimeSpan.FromSeconds(20), nameof(PresenceLifetime));
+        RequireDuration(JoinAttemptLifetime, TimeSpan.FromSeconds(30), nameof(JoinAttemptLifetime));
+        RequireDuration(ReplayLifetime, TimeSpan.FromSeconds(30), nameof(ReplayLifetime));
+        RequireDuration(IdempotencyLifetime, TimeSpan.FromMinutes(10), nameof(IdempotencyLifetime));
+        RequireDuration(GracefulDrainLifetime, TimeSpan.FromSeconds(30), nameof(GracefulDrainLifetime));
+        if (IdempotencyLifetime < LeaseLifetime || IdempotencyLifetime < JoinAttemptLifetime)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(IdempotencyLifetime),
+                "Idempotency retention must cover every idempotent resource lifetime.");
+        }
+    }
+
+    private static void RequirePositive(int value, string name)
+    {
+        if (value <= 0)
+        {
+            throw new ArgumentOutOfRangeException(name, "Store capacity must be positive.");
+        }
+    }
+
+    private static void RequireDuration(TimeSpan value, TimeSpan maximum, string name)
+    {
+        if (value <= TimeSpan.Zero || value > maximum)
+        {
+            throw new ArgumentOutOfRangeException(name, $"Duration must be positive and no greater than {maximum}.");
+        }
+    }
+}
+
+internal readonly record struct TenantScope(GameId GameId, EnvironmentId EnvironmentId);
+
+internal readonly struct SecretFingerprint : IEquatable<SecretFingerprint>
+{
+    private readonly string? _value;
+
+    public SecretFingerprint(string value)
+    {
+        if (string.IsNullOrWhiteSpace(value) || value.Length > 128)
+        {
+            throw new ArgumentException("Secret fingerprints must contain 1-128 characters.", nameof(value));
+        }
+
+        _value = value;
+    }
+
+    public bool IsValid => !string.IsNullOrWhiteSpace(_value) && _value.Length <= 128;
+    public bool Equals(SecretFingerprint other)
+    {
+        ReadOnlySpan<char> left = _value.AsSpan();
+        ReadOnlySpan<char> right = other._value.AsSpan();
+        if (left.Length != right.Length)
+        {
+            return false;
+        }
+
+        int difference = 0;
+        for (int index = 0; index < left.Length; index++)
+        {
+            difference |= left[index] ^ right[index];
+        }
+
+        return difference == 0;
+    }
+
+    public override bool Equals(object? obj) => obj is SecretFingerprint other && Equals(other);
+    public override int GetHashCode() => StringComparer.Ordinal.GetHashCode(_value ?? string.Empty);
+    public override string ToString() => "[REDACTED]";
+    public static bool operator ==(SecretFingerprint left, SecretFingerprint right) => left.Equals(right);
+    public static bool operator !=(SecretFingerprint left, SecretFingerprint right) => !left.Equals(right);
+}
+
+internal readonly record struct ObservedEndpoint
+{
+    public ObservedEndpoint(AddressFamilyKind addressFamily, string address, int port)
+    {
+        if (!IPAddress.TryParse(address, out IPAddress? parsed)
+            || (addressFamily == AddressFamilyKind.Ipv4 && parsed.AddressFamily != System.Net.Sockets.AddressFamily.InterNetwork)
+            || (addressFamily == AddressFamilyKind.Ipv6 && parsed.AddressFamily != System.Net.Sockets.AddressFamily.InterNetworkV6))
+        {
+            throw new ArgumentException("The address must match the declared address family.", nameof(address));
+        }
+
+        if (port is < 1 or > 65_535)
+        {
+            throw new ArgumentOutOfRangeException(nameof(port));
+        }
+
+        AddressFamily = addressFamily;
+        Address = parsed.ToString();
+        Port = port;
+    }
+
+    public AddressFamilyKind AddressFamily { get; }
+    public string Address { get; }
+    public int Port { get; }
+    public bool IsValid => !string.IsNullOrEmpty(Address)
+        && Port is >= 1 and <= 65_535
+        && AddressFamily is AddressFamilyKind.Ipv4 or AddressFamilyKind.Ipv6;
+}
+
+internal sealed record ListingDefinition
+{
+    public required SessionListingId ListingId { get; init; }
+    public required LeaseId LeaseId { get; init; }
+    public required TenantScope Scope { get; init; }
+    public required string OwnerSubject { get; init; }
+    public required RegionId RegionId { get; init; }
+    public required uint ProtocolVersion { get; init; }
+    public required string BuildVersion { get; init; }
+    public required string DisplayName { get; init; }
+    public required ListingVisibility Visibility { get; init; }
+    public required PublisherTrustMode TrustMode { get; init; }
+    public required int CurrentPlayers { get; init; }
+    public required int MaximumPlayers { get; init; }
+    public required IReadOnlyDictionary<string, string> Metadata { get; init; }
+    public required SecretFingerprint LeaseFingerprint { get; init; }
+    public required MediationHandle HostPresenceHandle { get; init; }
+    public required SecretFingerprint HostPresenceFingerprint { get; init; }
+    public required string CapabilityDerivationSalt { get; init; }
+}
+
+internal sealed record StoredListing
+{
+    public required ListingDefinition Definition { get; init; }
+    public required DateTimeOffset LeaseExpiresAt { get; init; }
+    public required long Version { get; init; }
+    public required bool HasFreshPresence { get; init; }
+
+    public static ListingDefinition Freeze(ListingDefinition source) => source with
+    {
+        Metadata = source.Metadata.ToFrozenDictionary(StringComparer.Ordinal),
+    };
+}
+
+internal sealed record CreateListingCommand(
+    string IdempotencyKey,
+    string RequestFingerprint,
+    ListingDefinition Listing,
+    int OwnerListingLimit = int.MaxValue);
+
+internal sealed record RenewLeaseCommand(
+    SessionListingId ListingId,
+    LeaseId LeaseId,
+    SecretFingerprint LeaseFingerprint,
+    string OwnerSubject,
+    long ExpectedVersion);
+
+internal sealed record UpdateListingCommand(
+    SessionListingId ListingId,
+    LeaseId LeaseId,
+    SecretFingerprint LeaseFingerprint,
+    string OwnerSubject,
+    string BuildVersion,
+    string DisplayName,
+    int CurrentPlayers,
+    int MaximumPlayers,
+    IReadOnlyDictionary<string, string> Metadata);
+
+internal sealed record DeleteListingCommand(
+    SessionListingId ListingId,
+    LeaseId LeaseId,
+    SecretFingerprint LeaseFingerprint,
+    string OwnerSubject);
+
+internal sealed record BindHostPresenceCommand(
+    MediationHandle Handle,
+    SecretFingerprint CapabilityFingerprint,
+    ObservedEndpoint PublicEndpoint,
+    ObservedEndpoint? LocalEndpoint);
+
+internal sealed record VisibleListingQuery(
+    TenantScope Scope,
+    uint ProtocolVersion,
+    RegionId? RegionId,
+    int MaximumResults = ContractLimits.BrowserPageMaxItems,
+    SessionListingId? AfterListingId = null,
+    bool ExcludeFull = false);
+
+internal enum AttemptPeerRole
+{
+    Host = 1,
+    Client = 2,
+}
+
+internal sealed record CreateJoinAttemptCommand
+{
+    public required string IdempotencyOwner { get; init; }
+    public required string IdempotencyKey { get; init; }
+    public required string RequestFingerprint { get; init; }
+    public required string ClientSubject { get; init; }
+    public required JoinAttemptId AttemptId { get; init; }
+    public required MediationHandle MediationHandle { get; init; }
+    public required TenantScope Scope { get; init; }
+    public required SessionListingId ListingId { get; init; }
+    public required uint ProtocolVersion { get; init; }
+    public required SecretFingerprint HostCapabilityFingerprint { get; init; }
+    public required SecretFingerprint ClientCapabilityFingerprint { get; init; }
+    public int ScopeAttemptLimit { get; init; } = int.MaxValue;
+}
+
+internal sealed record AttemptEndpointBinding(
+    ObservedEndpoint PublicEndpoint,
+    ObservedEndpoint? LocalEndpoint);
+
+internal sealed record StoredJoinAttempt
+{
+    public required JoinAttemptId AttemptId { get; init; }
+    public required MediationHandle MediationHandle { get; init; }
+    public required TenantScope Scope { get; init; }
+    public required SessionListingId ListingId { get; init; }
+    public required string ClientSubject { get; init; }
+    public required uint ProtocolVersion { get; init; }
+    public required DateTimeOffset ExpiresAt { get; init; }
+    public AttemptEndpointBinding? HostEndpoint { get; init; }
+    public AttemptEndpointBinding? ClientEndpoint { get; init; }
+    public required bool IntroductionConsumed { get; init; }
+}
+
+internal sealed record BindAttemptEndpointCommand(
+    MediationHandle Handle,
+    AttemptPeerRole Role,
+    SecretFingerprint CapabilityFingerprint,
+    ObservedEndpoint PublicEndpoint,
+    ObservedEndpoint? LocalEndpoint);
+
+internal sealed record IntroductionEndpoints(
+    JoinAttemptId AttemptId,
+    AttemptEndpointBinding Host,
+    AttemptEndpointBinding Client);
+
+internal sealed record ReplayConsumption(
+    string Namespace,
+    string Key,
+    TimeSpan? Lifetime = null);
+
+internal enum StoreResultCode
+{
+    Success = 0,
+    NotFound = 1,
+    Expired = 2,
+    Revoked = 3,
+    Conflict = 4,
+    CapacityExceeded = 5,
+    Draining = 6,
+    ReplayRejected = 7,
+    ServiceUnavailable = 8,
+}
+
+internal sealed record StoreResult<T>(StoreResultCode Code, T? Value = default, bool IsIdempotentReplay = false)
+{
+    public bool Succeeded => Code == StoreResultCode.Success;
+}
+
+internal interface IEphemeralRendezvousStore
+{
+    Guid InstanceId { get; }
+    bool IsAvailable { get; }
+    bool IsDraining { get; }
+
+    StoreResult<StoredListing> CreateListing(CreateListingCommand command, CancellationToken cancellationToken = default);
+    StoreResult<StoredListing> RenewLease(RenewLeaseCommand command, CancellationToken cancellationToken = default);
+    StoreResult<StoredListing> UpdateListing(UpdateListingCommand command, CancellationToken cancellationToken = default);
+    StoreResult<bool> DeleteListing(DeleteListingCommand command, CancellationToken cancellationToken = default);
+    StoreResult<StoredListing> GetListing(SessionListingId listingId, bool requireFreshPresence, CancellationToken cancellationToken = default);
+    StoreResult<IReadOnlyList<StoredListing>> BrowseVisibleListings(VisibleListingQuery query, CancellationToken cancellationToken = default);
+    StoreResult<StoredListing> BindHostPresence(BindHostPresenceCommand command, CancellationToken cancellationToken = default);
+    StoreResult<StoredJoinAttempt> CreateJoinAttempt(CreateJoinAttemptCommand command, CancellationToken cancellationToken = default);
+    StoreResult<StoredJoinAttempt> BindAttemptEndpoint(BindAttemptEndpointCommand command, CancellationToken cancellationToken = default);
+    StoreResult<IntroductionEndpoints> ConsumeIntroduction(MediationHandle handle, CancellationToken cancellationToken = default);
+    StoreResult<bool> ConsumeReplay(ReplayConsumption consumption, CancellationToken cancellationToken = default);
+    StoreResult<bool> RevokeListing(SessionListingId listingId, CancellationToken cancellationToken = default);
+    StoreResult<int> RevokePrincipal(string subject, TimeSpan lifetime, CancellationToken cancellationToken = default);
+    void BeginDrain(CancellationToken cancellationToken = default);
+}

src/FinalFactory.Rendezvous.Server/State/InMemoryEphemeralRendezvousStore.cs

@@ -0,0 +1,867 @@
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Server.State;
+
+internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousStore
+{
+    private readonly object _gate = new();
+    private readonly EphemeralStoreOptions _options;
+    private readonly IMonotonicClock _monotonicClock;
+    private readonly DateTimeOffset _wallOrigin;
+    private readonly TimeSpan _monotonicOrigin;
+    private readonly Dictionary<SessionListingId, ListingEntry> _listings = [];
+    private readonly Dictionary<LeaseId, SessionListingId> _leases = [];
+    private readonly Dictionary<MediationHandle, SessionListingId> _presenceHandles = [];
+    private readonly Dictionary<MediationHandle, PresenceEntry> _presence = [];
+    private readonly Dictionary<JoinAttemptId, AttemptEntry> _attempts = [];
+    private readonly Dictionary<MediationHandle, JoinAttemptId> _attemptHandles = [];
+    private readonly Dictionary<string, IdempotencyEntry> _idempotency = new(StringComparer.Ordinal);
+    private readonly Dictionary<string, TimeSpan> _replay = new(StringComparer.Ordinal);
+    private readonly Dictionary<string, TimeSpan> _revocations = new(StringComparer.Ordinal);
+    private TimeSpan? _drainDeadline;
+    private bool _available = true;
+
+    public InMemoryEphemeralRendezvousStore(
+        EphemeralStoreOptions options,
+        IWallClock wallClock,
+        IMonotonicClock monotonicClock)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        ArgumentNullException.ThrowIfNull(wallClock);
+        ArgumentNullException.ThrowIfNull(monotonicClock);
+        options.Validate();
+        _options = options;
+        _monotonicClock = monotonicClock;
+        _wallOrigin = wallClock.UtcNow;
+        _monotonicOrigin = monotonicClock.Elapsed;
+        InstanceId = Guid.NewGuid();
+    }
+
+    public Guid InstanceId { get; }
+
+    public bool IsAvailable
+    {
+        get
+        {
+            lock (_gate)
+            {
+                return _available;
+            }
+        }
+    }
+
+    public bool IsDraining
+    {
+        get
+        {
+            lock (_gate)
+            {
+                return _drainDeadline.HasValue;
+            }
+        }
+    }
+
+    public StoreResult<StoredListing> CreateListing(
+        CreateListingCommand command,
+        CancellationToken cancellationToken = default) => Atomic<StoredListing>(now =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        ValidateListing(command.Listing);
+        if (command.OwnerListingLimit <= 0)
+        {
+            throw new ArgumentOutOfRangeException(nameof(command), "Owner listing limit must be positive.");
+        }
+
+        ValidateIdempotency(command.IdempotencyKey, command.RequestFingerprint);
+
+        StoreResult<StoredListing>? admission = CheckNewWorkAdmission<StoredListing>(command.Listing.OwnerSubject);
+        if (admission is not null)
+        {
+            return admission;
+        }
+
+        string idempotencyKey = $"listing:{command.Listing.Scope.GameId}:{command.Listing.Scope.EnvironmentId}:{command.Listing.OwnerSubject}:{command.IdempotencyKey}";
+        if (_idempotency.TryGetValue(idempotencyKey, out IdempotencyEntry? previous))
+        {
+            if (!string.Equals(previous.RequestFingerprint, command.RequestFingerprint, StringComparison.Ordinal))
+            {
+                return new(StoreResultCode.Conflict);
+            }
+
+            if (previous.ResourceId is SessionListingId listingId
+                && _listings.TryGetValue(listingId, out ListingEntry? existing))
+            {
+                return new(StoreResultCode.Success, Snapshot(existing), true);
+            }
+
+            return new(StoreResultCode.Expired);
+        }
+
+        if (_listings.Count >= _options.MaxListings
+            || _idempotency.Count >= _options.MaxIdempotencyEntries
+            || _listings.Values.Count(entry => string.Equals(
+                entry.Definition.OwnerSubject,
+                command.Listing.OwnerSubject,
+                StringComparison.Ordinal)) >= command.OwnerListingLimit)
+        {
+            return new(StoreResultCode.CapacityExceeded);
+        }
+
+        ListingDefinition frozen = StoredListing.Freeze(command.Listing);
+        if (_listings.ContainsKey(frozen.ListingId)
+            || _leases.ContainsKey(frozen.LeaseId)
+            || HandleExists(frozen.HostPresenceHandle))
+        {
+            return new(StoreResultCode.Conflict);
+        }
+
+        ListingEntry entry = new(
+            frozen,
+            now + _options.LeaseLifetime,
+            WallDeadline(now, _options.LeaseLifetime),
+            version: 1);
+        _listings.Add(frozen.ListingId, entry);
+        _leases.Add(frozen.LeaseId, frozen.ListingId);
+        _presenceHandles.Add(frozen.HostPresenceHandle, frozen.ListingId);
+        _idempotency.Add(idempotencyKey, new(
+            command.RequestFingerprint,
+            frozen.ListingId,
+            now + _options.IdempotencyLifetime));
+        return new(StoreResultCode.Success, Snapshot(entry));
+    }, cancellationToken);
+
+    public StoreResult<StoredListing> RenewLease(
+        RenewLeaseCommand command,
+        CancellationToken cancellationToken = default) => Atomic<StoredListing>(now =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (_drainDeadline.HasValue)
+        {
+            return new(StoreResultCode.Draining);
+        }
+
+        if (!_listings.TryGetValue(command.ListingId, out ListingEntry? entry))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        if (entry.Definition.LeaseId != command.LeaseId
+            || entry.Definition.LeaseFingerprint != command.LeaseFingerprint
+            || !string.Equals(entry.Definition.OwnerSubject, command.OwnerSubject, StringComparison.Ordinal))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        if (entry.Version != command.ExpectedVersion)
+        {
+            return new(StoreResultCode.Conflict, Snapshot(entry));
+        }
+
+        entry.LeaseDeadline = now + _options.LeaseLifetime;
+        entry.WallExpiresAt = WallDeadline(now, _options.LeaseLifetime);
+        entry.Version++;
+        return new(StoreResultCode.Success, Snapshot(entry));
+    }, cancellationToken);
+
+    public StoreResult<StoredListing> UpdateListing(
+        UpdateListingCommand command,
+        CancellationToken cancellationToken = default) => Atomic<StoredListing>(_ =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        ValidateSubject(command.OwnerSubject, nameof(command.OwnerSubject));
+        if (!ContractValidation.IsBuildVersionValid(command.BuildVersion)
+            || !ContractValidation.IsDisplayNameValid(command.DisplayName)
+            || command.MaximumPlayers is <= 0 or > ContractLimits.SessionCapacityMaxPlayers
+            || command.CurrentPlayers < 0
+            || command.CurrentPlayers > command.MaximumPlayers
+            || !ContractValidation.IsMetadataValid(command.Metadata))
+        {
+            throw new ArgumentException("Listing update invariants are invalid.", nameof(command));
+        }
+
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (_drainDeadline.HasValue)
+        {
+            return new(StoreResultCode.Draining);
+        }
+
+        if (!_listings.TryGetValue(command.ListingId, out ListingEntry? entry)
+            || entry.Definition.LeaseId != command.LeaseId
+            || entry.Definition.LeaseFingerprint != command.LeaseFingerprint
+            || !string.Equals(entry.Definition.OwnerSubject, command.OwnerSubject, StringComparison.Ordinal))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        entry.Definition = StoredListing.Freeze(entry.Definition with
+        {
+            BuildVersion = command.BuildVersion,
+            DisplayName = command.DisplayName,
+            CurrentPlayers = command.CurrentPlayers,
+            MaximumPlayers = command.MaximumPlayers,
+            Metadata = command.Metadata,
+        });
+        entry.Version++;
+        return new(StoreResultCode.Success, Snapshot(entry));
+    }, cancellationToken);
+
+    public StoreResult<bool> DeleteListing(
+        DeleteListingCommand command,
+        CancellationToken cancellationToken = default) => Atomic<bool>(_ =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        if (!_listings.TryGetValue(command.ListingId, out ListingEntry? entry)
+            || entry.Definition.LeaseId != command.LeaseId
+            || entry.Definition.LeaseFingerprint != command.LeaseFingerprint
+            || !string.Equals(entry.Definition.OwnerSubject, command.OwnerSubject, StringComparison.Ordinal))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        RemoveListing(command.ListingId);
+        return new(StoreResultCode.Success, true);
+    }, cancellationToken);
+
+    public StoreResult<StoredListing> GetListing(
+        SessionListingId listingId,
+        bool requireFreshPresence,
+        CancellationToken cancellationToken = default) => Atomic<StoredListing>(_ =>
+    {
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (!_listings.TryGetValue(listingId, out ListingEntry? entry))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        bool fresh = _presence.ContainsKey(entry.Definition.HostPresenceHandle);
+        return requireFreshPresence && !fresh
+            ? new(StoreResultCode.NotFound)
+            : new(StoreResultCode.Success, Snapshot(entry));
+    }, cancellationToken);
+
+    public StoreResult<StoredListing> BindHostPresence(
+        BindHostPresenceCommand command,
+        CancellationToken cancellationToken = default) => Atomic<StoredListing>(now =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        if (command.Handle.Value == Guid.Empty || !command.CapabilityFingerprint.IsValid)
+        {
+            throw new ArgumentException("Host presence binding is invalid.", nameof(command));
+        }
+
+        ValidateEndpoint(command.PublicEndpoint, command.LocalEndpoint);
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (!_presenceHandles.TryGetValue(command.Handle, out SessionListingId listingId)
+            || !_listings.TryGetValue(listingId, out ListingEntry? entry)
+            || entry.Definition.HostPresenceFingerprint != command.CapabilityFingerprint)
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        if (!_presence.ContainsKey(command.Handle) && _presence.Count >= _options.MaxPresenceBindings)
+        {
+            return new(StoreResultCode.CapacityExceeded);
+        }
+
+        _presence[command.Handle] = new(
+            command.PublicEndpoint,
+            command.LocalEndpoint,
+            now + _options.PresenceLifetime);
+        return new(StoreResultCode.Success, Snapshot(entry));
+    }, cancellationToken);
+
+    public StoreResult<IReadOnlyList<StoredListing>> BrowseVisibleListings(
+        VisibleListingQuery query,
+        CancellationToken cancellationToken = default) => Atomic<IReadOnlyList<StoredListing>>(_ =>
+    {
+        ArgumentNullException.ThrowIfNull(query);
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (!IsScopeValid(query.Scope)
+            || query.ProtocolVersion == 0
+            || (query.RegionId.HasValue && string.IsNullOrEmpty(query.RegionId.Value.Value))
+            || query.MaximumResults <= 0
+            || query.MaximumResults > ContractLimits.BrowserPageMaxItems + 1)
+        {
+            throw new ArgumentOutOfRangeException(nameof(query));
+        }
+
+        IReadOnlyList<StoredListing> visible = _listings.Values
+            .Where(entry => entry.Definition.Scope == query.Scope
+                && entry.Definition.ProtocolVersion == query.ProtocolVersion
+                && entry.Definition.Visibility == ListingVisibility.Public
+                && (!query.RegionId.HasValue || entry.Definition.RegionId == query.RegionId.Value)
+                && (!query.AfterListingId.HasValue
+                    || entry.Definition.ListingId.Value.CompareTo(query.AfterListingId.Value.Value) > 0)
+                && (!query.ExcludeFull
+                    || entry.Definition.CurrentPlayers < entry.Definition.MaximumPlayers)
+                && _presence.ContainsKey(entry.Definition.HostPresenceHandle))
+            .OrderBy(static entry => entry.Definition.ListingId.Value)
+            .Take(query.MaximumResults)
+            .Select(Snapshot)
+            .ToArray();
+        return new(StoreResultCode.Success, visible);
+    }, cancellationToken);
+
+    public StoreResult<StoredJoinAttempt> CreateJoinAttempt(
+        CreateJoinAttemptCommand command,
+        CancellationToken cancellationToken = default) => Atomic<StoredJoinAttempt>(now =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        ValidateAttempt(command);
+        ValidateIdempotency(command.IdempotencyKey, command.RequestFingerprint);
+        ValidateSubject(command.IdempotencyOwner, nameof(command.IdempotencyOwner));
+        ValidateSubject(command.ClientSubject, nameof(command.ClientSubject));
+
+        StoreResult<StoredJoinAttempt>? admission = CheckNewWorkAdmission<StoredJoinAttempt>(command.ClientSubject);
+        if (admission is not null)
+        {
+            return admission;
+        }
+
+        string idempotencyKey = $"attempt:{command.Scope.GameId}:{command.Scope.EnvironmentId}:{command.IdempotencyOwner}:{command.IdempotencyKey}";
+        if (_idempotency.TryGetValue(idempotencyKey, out IdempotencyEntry? previous))
+        {
+            if (!string.Equals(previous.RequestFingerprint, command.RequestFingerprint, StringComparison.Ordinal))
+            {
+                return new(StoreResultCode.Conflict);
+            }
+
+            if (previous.ResourceId is JoinAttemptId attemptId
+                && _attempts.TryGetValue(attemptId, out AttemptEntry? priorAttempt))
+            {
+                return new(StoreResultCode.Success, Snapshot(priorAttempt), true);
+            }
+
+            return new(StoreResultCode.Expired);
+        }
+
+        if (!_listings.TryGetValue(command.ListingId, out ListingEntry? listing)
+            || listing.Definition.Scope != command.Scope
+            || listing.Definition.ProtocolVersion != command.ProtocolVersion
+            || !_presence.ContainsKey(listing.Definition.HostPresenceHandle))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        if (_attempts.Count >= _options.MaxJoinAttempts
+            || _idempotency.Count >= _options.MaxIdempotencyEntries
+            || _attempts.Values.Count(entry => entry.Command.Scope == command.Scope)
+                >= command.ScopeAttemptLimit)
+        {
+            return new(StoreResultCode.CapacityExceeded);
+        }
+
+        if (_attempts.ContainsKey(command.AttemptId) || HandleExists(command.MediationHandle))
+        {
+            return new(StoreResultCode.Conflict);
+        }
+
+        AttemptEntry attempt = new(
+            command,
+            now + _options.JoinAttemptLifetime,
+            WallDeadline(now, _options.JoinAttemptLifetime));
+        _attempts.Add(command.AttemptId, attempt);
+        _attemptHandles.Add(command.MediationHandle, command.AttemptId);
+        _idempotency.Add(idempotencyKey, new(
+            command.RequestFingerprint,
+            command.AttemptId,
+            now + _options.IdempotencyLifetime));
+        return new(StoreResultCode.Success, Snapshot(attempt));
+    }, cancellationToken);
+
+    public StoreResult<StoredJoinAttempt> BindAttemptEndpoint(
+        BindAttemptEndpointCommand command,
+        CancellationToken cancellationToken = default) => Atomic<StoredJoinAttempt>(_ =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        if (command.Handle.Value == Guid.Empty
+            || command.Role is not (AttemptPeerRole.Host or AttemptPeerRole.Client)
+            || !command.CapabilityFingerprint.IsValid)
+        {
+            throw new ArgumentException("Attempt endpoint binding is invalid.", nameof(command));
+        }
+
+        ValidateEndpoint(command.PublicEndpoint, command.LocalEndpoint);
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (!_attemptHandles.TryGetValue(command.Handle, out JoinAttemptId attemptId)
+            || !_attempts.TryGetValue(attemptId, out AttemptEntry? attempt))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        SecretFingerprint expected = command.Role == AttemptPeerRole.Host
+            ? attempt.HostCapabilityFingerprint
+            : attempt.ClientCapabilityFingerprint;
+        if (expected != command.CapabilityFingerprint)
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        AttemptEndpointBinding binding = new(command.PublicEndpoint, command.LocalEndpoint);
+        AttemptEndpointBinding? current = command.Role == AttemptPeerRole.Host
+            ? attempt.HostEndpoint
+            : attempt.ClientEndpoint;
+        if (current is not null)
+        {
+            return current == binding
+                ? new(StoreResultCode.Success, Snapshot(attempt), true)
+                : new(StoreResultCode.ReplayRejected);
+        }
+
+        if (command.Role == AttemptPeerRole.Host)
+        {
+            attempt.HostEndpoint = binding;
+        }
+        else
+        {
+            attempt.ClientEndpoint = binding;
+        }
+
+        return new(StoreResultCode.Success, Snapshot(attempt));
+    }, cancellationToken);
+
+    public StoreResult<IntroductionEndpoints> ConsumeIntroduction(
+        MediationHandle handle,
+        CancellationToken cancellationToken = default) => Atomic<IntroductionEndpoints>(_ =>
+    {
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (!_attemptHandles.TryGetValue(handle, out JoinAttemptId attemptId)
+            || !_attempts.TryGetValue(attemptId, out AttemptEntry? attempt))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        if (attempt.IntroductionConsumed)
+        {
+            return new(StoreResultCode.ReplayRejected);
+        }
+
+        if (attempt.HostEndpoint is null || attempt.ClientEndpoint is null)
+        {
+            return new(StoreResultCode.Conflict);
+        }
+
+        attempt.IntroductionConsumed = true;
+        return new(StoreResultCode.Success, new(
+            attempt.Command.AttemptId,
+            attempt.HostEndpoint,
+            attempt.ClientEndpoint));
+    }, cancellationToken);
+
+    public StoreResult<bool> ConsumeReplay(
+        ReplayConsumption consumption,
+        CancellationToken cancellationToken = default) => Atomic<bool>(now =>
+    {
+        ArgumentNullException.ThrowIfNull(consumption);
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        ValidateReplay(consumption);
+        string key = $"{consumption.Namespace}:{consumption.Key}";
+        if (_replay.ContainsKey(key))
+        {
+            return new(StoreResultCode.ReplayRejected);
+        }
+
+        if (_replay.Count >= _options.MaxReplayEntries)
+        {
+            return new(StoreResultCode.CapacityExceeded);
+        }
+
+        TimeSpan lifetime = consumption.Lifetime ?? _options.ReplayLifetime;
+        if (lifetime <= TimeSpan.Zero || lifetime > _options.ReplayLifetime)
+        {
+            throw new ArgumentOutOfRangeException(nameof(consumption), "Replay lifetime exceeds the configured ceiling.");
+        }
+
+        _replay.Add(key, now + lifetime);
+        return new(StoreResultCode.Success, true);
+    }, cancellationToken);
+
+    public StoreResult<bool> RevokeListing(
+        SessionListingId listingId,
+        CancellationToken cancellationToken = default) => Atomic<bool>(_ =>
+    {
+        if (!_listings.ContainsKey(listingId))
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        RemoveListing(listingId);
+        return new(StoreResultCode.Success, true);
+    }, cancellationToken);
+
+    public StoreResult<int> RevokePrincipal(
+        string subject,
+        TimeSpan lifetime,
+        CancellationToken cancellationToken = default) => Atomic<int>(now =>
+    {
+        ValidateSubject(subject, nameof(subject));
+        if (lifetime <= TimeSpan.Zero || lifetime > TimeSpan.FromMinutes(10))
+        {
+            throw new ArgumentOutOfRangeException(nameof(lifetime));
+        }
+
+        if (!_revocations.ContainsKey(subject) && _revocations.Count >= _options.MaxRevocations)
+        {
+            return new(StoreResultCode.CapacityExceeded);
+        }
+
+        _revocations[subject] = now + lifetime;
+        SessionListingId[] listings = _listings
+            .Where(item => string.Equals(item.Value.Definition.OwnerSubject, subject, StringComparison.Ordinal))
+            .Select(static item => item.Key)
+            .ToArray();
+        JoinAttemptId[] attempts = _attempts
+            .Where(item => string.Equals(item.Value.Command.ClientSubject, subject, StringComparison.Ordinal))
+            .Select(static item => item.Key)
+            .ToArray();
+        foreach (SessionListingId listingId in listings)
+        {
+            RemoveListing(listingId);
+        }
+
+        foreach (JoinAttemptId attemptId in attempts)
+        {
+            RemoveAttempt(attemptId);
+        }
+
+        return new(StoreResultCode.Success, listings.Length + attempts.Length);
+    }, cancellationToken);
+
+    public void BeginDrain(CancellationToken cancellationToken = default)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+        lock (_gate)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            if (!_drainDeadline.HasValue)
+            {
+                _drainDeadline = _monotonicClock.Elapsed + _options.GracefulDrainLifetime;
+            }
+        }
+    }
+
+    internal void MarkUnavailable()
+    {
+        lock (_gate)
+        {
+            _available = false;
+            ClearActiveState();
+        }
+    }
+
+    private StoreResult<T> Atomic<T>(Func<TimeSpan, StoreResult<T>> operation, CancellationToken cancellationToken)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+        lock (_gate)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            TimeSpan now = _monotonicClock.Elapsed;
+            Cleanup(now);
+            return operation(now);
+        }
+    }
+
+    private StoreResult<T>? CheckNewWorkAdmission<T>(string subject)
+    {
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (_drainDeadline.HasValue)
+        {
+            return new(StoreResultCode.Draining);
+        }
+
+        return _revocations.ContainsKey(subject)
+            ? new(StoreResultCode.Revoked)
+            : null;
+    }
+
+    private void Cleanup(TimeSpan now)
+    {
+        if (_drainDeadline is TimeSpan drainDeadline && now >= drainDeadline)
+        {
+            ClearActiveState();
+        }
+
+        RemoveExpired(_revocations, now);
+        RemoveExpired(_replay, now);
+        foreach (string key in _idempotency
+                     .Where(item => item.Value.Deadline <= now)
+                     .Select(static item => item.Key)
+                     .ToArray())
+        {
+            _idempotency.Remove(key);
+        }
+
+        foreach (MediationHandle handle in _presence
+                     .Where(item => item.Value.Deadline <= now)
+                     .Select(static item => item.Key)
+                     .ToArray())
+        {
+            _presence.Remove(handle);
+        }
+
+        foreach (JoinAttemptId attemptId in _attempts
+                     .Where(item => item.Value.Deadline <= now)
+                     .Select(static item => item.Key)
+                     .ToArray())
+        {
+            RemoveAttempt(attemptId);
+        }
+
+        foreach (SessionListingId listingId in _listings
+                     .Where(item => item.Value.LeaseDeadline <= now)
+                     .Select(static item => item.Key)
+                     .ToArray())
+        {
+            RemoveListing(listingId);
+        }
+    }
+
+    private void ClearActiveState()
+    {
+        _listings.Clear();
+        _leases.Clear();
+        _presenceHandles.Clear();
+        _presence.Clear();
+        _attempts.Clear();
+        _attemptHandles.Clear();
+        _idempotency.Clear();
+        _replay.Clear();
+    }
+
+    private void RemoveListing(SessionListingId listingId)
+    {
+        if (!_listings.Remove(listingId, out ListingEntry? listing))
+        {
+            return;
+        }
+
+        _leases.Remove(listing.Definition.LeaseId);
+        _presenceHandles.Remove(listing.Definition.HostPresenceHandle);
+        _presence.Remove(listing.Definition.HostPresenceHandle);
+        foreach (JoinAttemptId attemptId in _attempts
+                     .Where(item => item.Value.Command.ListingId == listingId)
+                     .Select(static item => item.Key)
+                     .ToArray())
+        {
+            RemoveAttempt(attemptId);
+        }
+    }
+
+    private void RemoveAttempt(JoinAttemptId attemptId)
+    {
+        if (_attempts.Remove(attemptId, out AttemptEntry? attempt))
+        {
+            _attemptHandles.Remove(attempt.Command.MediationHandle);
+        }
+    }
+
+    private bool HandleExists(MediationHandle handle) =>
+        _presenceHandles.ContainsKey(handle) || _attemptHandles.ContainsKey(handle);
+
+    private DateTimeOffset WallDeadline(TimeSpan now, TimeSpan lifetime) =>
+        _wallOrigin + (now - _monotonicOrigin) + lifetime;
+
+    private StoredListing Snapshot(ListingEntry entry) => new()
+    {
+        Definition = entry.Definition,
+        LeaseExpiresAt = entry.WallExpiresAt,
+        Version = entry.Version,
+        HasFreshPresence = _presence.ContainsKey(entry.Definition.HostPresenceHandle),
+    };
+
+    private static StoredJoinAttempt Snapshot(AttemptEntry entry) => new()
+    {
+        AttemptId = entry.Command.AttemptId,
+        MediationHandle = entry.Command.MediationHandle,
+        Scope = entry.Command.Scope,
+        ListingId = entry.Command.ListingId,
+        ClientSubject = entry.Command.ClientSubject,
+        ProtocolVersion = entry.Command.ProtocolVersion,
+        ExpiresAt = entry.WallExpiresAt,
+        HostEndpoint = entry.HostEndpoint,
+        ClientEndpoint = entry.ClientEndpoint,
+        IntroductionConsumed = entry.IntroductionConsumed,
+    };
+
+    private static void RemoveExpired(Dictionary<string, TimeSpan> entries, TimeSpan now)
+    {
+        foreach (string key in entries
+                     .Where(item => item.Value <= now)
+                     .Select(static item => item.Key)
+                     .ToArray())
+        {
+            entries.Remove(key);
+        }
+    }
+
+    private static void ValidateListing(ListingDefinition listing)
+    {
+        ArgumentNullException.ThrowIfNull(listing);
+        ValidateSubject(listing.OwnerSubject, nameof(listing.OwnerSubject));
+        ArgumentNullException.ThrowIfNull(listing.Metadata);
+        if (listing.ListingId.Value == Guid.Empty
+            || listing.LeaseId.Value == Guid.Empty
+            || listing.HostPresenceHandle.Value == Guid.Empty
+            || !IsScopeValid(listing.Scope)
+            || string.IsNullOrEmpty(listing.RegionId.Value)
+            || listing.ProtocolVersion == 0
+            || !ContractValidation.IsBuildVersionValid(listing.BuildVersion)
+            || !ContractValidation.IsDisplayNameValid(listing.DisplayName)
+            || !Enum.IsDefined(listing.Visibility)
+            || !Enum.IsDefined(listing.TrustMode)
+            || listing.MaximumPlayers is <= 0 or > ContractLimits.SessionCapacityMaxPlayers
+            || listing.CurrentPlayers < 0
+            || listing.CurrentPlayers > listing.MaximumPlayers
+            || !ContractValidation.IsMetadataValid(listing.Metadata)
+            || !listing.LeaseFingerprint.IsValid
+            || !listing.HostPresenceFingerprint.IsValid
+            || !IsDerivationSaltValid(listing.CapabilityDerivationSalt))
+        {
+            throw new ArgumentException("Listing invariants are invalid.", nameof(listing));
+        }
+    }
+
+    private static void ValidateIdempotency(string key, string requestFingerprint)
+    {
+        if (string.IsNullOrWhiteSpace(key) || key.Length > 128)
+        {
+            throw new ArgumentException("Idempotency keys must contain 1-128 characters.", nameof(key));
+        }
+
+        if (string.IsNullOrWhiteSpace(requestFingerprint) || requestFingerprint.Length > 128)
+        {
+            throw new ArgumentException("Request fingerprints must contain 1-128 characters.", nameof(requestFingerprint));
+        }
+    }
+
+    private static void ValidateReplay(ReplayConsumption consumption)
+    {
+        if (string.IsNullOrWhiteSpace(consumption.Namespace) || consumption.Namespace.Length > 64
+            || string.IsNullOrWhiteSpace(consumption.Key) || consumption.Key.Length > 128)
+        {
+            throw new ArgumentException("Replay namespace/key is invalid.", nameof(consumption));
+        }
+    }
+
+    private static void ValidateAttempt(CreateJoinAttemptCommand command)
+    {
+        if (command.AttemptId.Value == Guid.Empty
+            || command.MediationHandle.Value == Guid.Empty
+            || command.ListingId.Value == Guid.Empty
+            || !IsScopeValid(command.Scope)
+            || command.ProtocolVersion == 0
+            || !command.HostCapabilityFingerprint.IsValid
+            || !command.ClientCapabilityFingerprint.IsValid
+            || command.ScopeAttemptLimit <= 0)
+        {
+            throw new ArgumentException("Join attempt invariants are invalid.", nameof(command));
+        }
+    }
+
+    private static void ValidateEndpoint(ObservedEndpoint publicEndpoint, ObservedEndpoint? localEndpoint)
+    {
+        if (!publicEndpoint.IsValid || (localEndpoint.HasValue && !localEndpoint.Value.IsValid))
+        {
+            throw new ArgumentException("Observed endpoints must be valid immutable endpoint values.", nameof(publicEndpoint));
+        }
+    }
+
+    private static bool IsScopeValid(TenantScope scope) =>
+        !string.IsNullOrEmpty(scope.GameId.Value) && !string.IsNullOrEmpty(scope.EnvironmentId.Value);
+
+    private static bool IsDerivationSaltValid(string? value) => value is not null
+        && value.Length == 43
+        && value.All(static character =>
+            character is >= 'A' and <= 'Z'
+            or >= 'a' and <= 'z'
+            or >= '0' and <= '9'
+            or '-'
+            or '_');
+
+    private static void ValidateSubject(string subject, string parameterName)
+    {
+        if (string.IsNullOrWhiteSpace(subject) || subject.Length > 256)
+        {
+            throw new ArgumentException("Subjects must contain 1-256 characters.", parameterName);
+        }
+    }
+
+    private sealed class ListingEntry(
+        ListingDefinition definition,
+        TimeSpan leaseDeadline,
+        DateTimeOffset wallExpiresAt,
+        long version)
+    {
+        public ListingDefinition Definition { get; set; } = definition;
+        public TimeSpan LeaseDeadline { get; set; } = leaseDeadline;
+        public DateTimeOffset WallExpiresAt { get; set; } = wallExpiresAt;
+        public long Version { get; set; } = version;
+    }
+
+    private sealed class PresenceEntry(
+        ObservedEndpoint publicEndpoint,
+        ObservedEndpoint? localEndpoint,
+        TimeSpan deadline)
+    {
+        public ObservedEndpoint PublicEndpoint { get; } = publicEndpoint;
+        public ObservedEndpoint? LocalEndpoint { get; } = localEndpoint;
+        public TimeSpan Deadline { get; } = deadline;
+    }
+
+    private sealed class AttemptEntry(
+        CreateJoinAttemptCommand command,
+        TimeSpan deadline,
+        DateTimeOffset wallExpiresAt)
+    {
+        public CreateJoinAttemptCommand Command { get; } = command;
+        public SecretFingerprint HostCapabilityFingerprint { get; } = command.HostCapabilityFingerprint;
+        public SecretFingerprint ClientCapabilityFingerprint { get; } = command.ClientCapabilityFingerprint;
+        public TimeSpan Deadline { get; } = deadline;
+        public DateTimeOffset WallExpiresAt { get; } = wallExpiresAt;
+        public AttemptEndpointBinding? HostEndpoint { get; set; }
+        public AttemptEndpointBinding? ClientEndpoint { get; set; }
+        public bool IntroductionConsumed { get; set; }
+    }
+
+    private sealed record IdempotencyEntry(
+        string RequestFingerprint,
+        object ResourceId,
+        TimeSpan Deadline);
+}

src/FinalFactory.Rendezvous.Server/Transport/UdpMediatorService.cs

@@ -1,5 +1,8 @@
 using System.Net;
 using System.Net.Sockets;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
 using Microsoft.Extensions.Options;
 
 namespace FinalFactory.Rendezvous.Server.Transport;
@@ -7,10 +10,12 @@ namespace FinalFactory.Rendezvous.Server.Transport;
 /// <summary>
 /// Owns the cancellable UDP socket used by the future NAT mediator.
 /// </summary>
-public sealed partial class UdpMediatorService : BackgroundService
+internal sealed partial class UdpMediatorService : BackgroundService
 {
     private readonly ILogger<UdpMediatorService> _logger;
     private readonly UdpMediatorOptions _options;
+    private readonly IEphemeralRendezvousStore _store;
+    private readonly ISessionCapabilityService _capabilities;
     private UdpClient? _udpClient;
 
     /// <summary>
@@ -18,10 +23,14 @@ public sealed partial class UdpMediatorService : BackgroundService
     /// </summary>
     public UdpMediatorService(
         IOptions<UdpMediatorOptions> options,
-        ILogger<UdpMediatorService> logger)
+        ILogger<UdpMediatorService> logger,
+        IEphemeralRendezvousStore store,
+        ISessionCapabilityService capabilities)
     {
         _options = options.Value;
         _logger = logger;
+        _store = store;
+        _capabilities = capabilities;
     }
 
     /// <summary>
@@ -81,7 +90,10 @@ public sealed partial class UdpMediatorService : BackgroundService
         {
             while (!stoppingToken.IsCancellationRequested)
             {
-                _ = await udpClient.ReceiveAsync(stoppingToken).ConfigureAwait(false);
+                UdpReceiveResult received = await udpClient
+                    .ReceiveAsync(stoppingToken)
+                    .ConfigureAwait(false);
+                ProcessDatagram(received.Buffer, received.RemoteEndPoint, stoppingToken);
                 // Bootstrap deliberately emits no UDP response. Protocol handling lands in #11.
             }
         }
@@ -99,6 +111,53 @@ public sealed partial class UdpMediatorService : BackgroundService
         }
     }
 
+    internal UdpPresenceProcessingResult ProcessDatagram(
+        ReadOnlySpan<byte> encoded,
+        IPEndPoint observedSource,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(observedSource);
+        if (!RendezvousUdpCodec.TryDecode(encoded, out PresenceDatagram? datagram, out _)
+            || datagram is null
+            || !_capabilities.TryFingerprint(datagram.Capability, out SecretFingerprint fingerprint))
+        {
+            return UdpPresenceProcessingResult.Dropped;
+        }
+
+        if (datagram.MessageType != UdpPresenceMessageType.HostPresence)
+        {
+            return UdpPresenceProcessingResult.ClientPresenceDeferred;
+        }
+
+        AddressFamilyKind publicFamily = observedSource.AddressFamily switch
+        {
+            AddressFamily.InterNetwork => AddressFamilyKind.Ipv4,
+            AddressFamily.InterNetworkV6 => AddressFamilyKind.Ipv6,
+            _ => 0,
+        };
+        if (publicFamily == 0)
+        {
+            return UdpPresenceProcessingResult.Dropped;
+        }
+
+        ObservedEndpoint publicEndpoint = new(
+            publicFamily,
+            observedSource.Address.ToString(),
+            observedSource.Port);
+        ObservedEndpoint localEndpoint = new(
+            datagram.AddressFamily,
+            datagram.LocalAddress,
+            datagram.LocalPort);
+        StoreResult<StoredListing> bound = _store.BindHostPresence(new(
+            datagram.MediationHandle,
+            fingerprint,
+            publicEndpoint,
+            localEndpoint), cancellationToken);
+        return bound.Succeeded
+            ? UdpPresenceProcessingResult.HostPresenceAccepted
+            : UdpPresenceProcessingResult.HostPresenceRejected;
+    }
+
     [LoggerMessage(
         EventId = 1,
         Level = LogLevel.Information,
@@ -114,3 +173,11 @@ public sealed partial class UdpMediatorService : BackgroundService
         Message = "UDP mediator stopped")]
     private static partial void LogMediatorStopped(ILogger logger);
 }
+
+internal enum UdpPresenceProcessingResult
+{
+    Dropped = 0,
+    HostPresenceAccepted = 1,
+    HostPresenceRejected = 2,
+    ClientPresenceDeferred = 3,
+}

tests/FinalFactory.Rendezvous.Tests/Browser/SessionBrowserServiceTests.cs

@@ -0,0 +1,153 @@
+using System.Text.Json;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Browser;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Tests.Browser;
+
+public sealed class SessionBrowserServiceTests
+{
+    [Fact]
+    public void ListEnforcesTenantProtocolPresenceVisibilityAndAvailabilityFilters()
+    {
+        using SessionBrowserFixture fixture = new();
+        StoredListing eligible = fixture.Add();
+        fixture.Add(scope: new(new("other-game"), fixture.Scope.EnvironmentId));
+        fixture.Add(scope: new(fixture.Scope.GameId, new("other-env")));
+        fixture.Add(protocolVersion: 8);
+        fixture.Add(regionId: new("us-east"));
+        fixture.Add(visibility: ListingVisibility.Unlisted);
+        fixture.Add(fresh: false);
+        fixture.Add(currentPlayers: 8, maximumPlayers: 8);
+        BrowseSessionsRequest request = fixture.Request();
+        request.ExcludeFull = true;
+
+        BrowserServiceResult<BrowseSessionsResponse> result = fixture.Browser.Browse(request);
+
+        Assert.True(result.Succeeded);
+        Assert.Collection(result.Value!.Items, item => Assert.Equal(eligible.Definition.ListingId, item.ListingId));
+    }
+
+    [Fact]
+    public void UnguessableIdRetrievalAllowsFreshUnlistedOnlyWithinExactScope()
+    {
+        using SessionBrowserFixture fixture = new();
+        StoredListing unlisted = fixture.Add(visibility: ListingVisibility.Unlisted);
+
+        Assert.True(fixture.Browser.Get(
+            unlisted.Definition.ListingId,
+            fixture.Scope.GameId,
+            fixture.Scope.EnvironmentId,
+            7).Succeeded);
+        Assert.Equal(RendezvousErrorCode.NotFound, fixture.Browser.Get(
+            unlisted.Definition.ListingId,
+            new("other-game"),
+            fixture.Scope.EnvironmentId,
+            7).Error);
+        Assert.Equal(RendezvousErrorCode.NotFound, fixture.Browser.Get(
+            unlisted.Definition.ListingId,
+            fixture.Scope.GameId,
+            fixture.Scope.EnvironmentId,
+            8).Error);
+        fixture.Clock.Advance(TimeSpan.FromSeconds(20));
+        Assert.Equal(RendezvousErrorCode.NotFound, fixture.Browser.Get(
+            unlisted.Definition.ListingId,
+            fixture.Scope.GameId,
+            fixture.Scope.EnvironmentId,
+            7).Error);
+    }
+
+    [Fact]
+    public void KeysetCursorReturnsStableRecordsOnceAndRejectsTamperingOrRescoping()
+    {
+        using SessionBrowserFixture fixture = new();
+        for (int index = 0; index < 7; index++)
+        {
+            fixture.Add();
+        }
+
+        BrowseSessionsRequest request = fixture.Request(pageSize: 2);
+        List<SessionListingId> seen = [];
+        do
+        {
+            BrowseSessionsResponse page = fixture.Browser.Browse(request).Value!;
+            seen.AddRange(page.Items.Select(static item => item.ListingId));
+            request.Cursor = page.NextCursor;
+        }
+        while (request.Cursor is not null);
+
+        Assert.Equal(7, seen.Count);
+        Assert.Equal(7, seen.Distinct().Count());
+        Assert.Equal(seen.OrderBy(static id => id.Value), seen);
+
+        BrowseSessionsRequest tampered = fixture.Request(pageSize: 2);
+        tampered.Cursor = fixture.Browser.Browse(tampered).Value!.NextCursor + "A";
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, fixture.Browser.Browse(tampered).Error);
+        BrowseSessionsRequest rescoped = fixture.Request(pageSize: 2);
+        rescoped.Cursor = fixture.Browser.Browse(fixture.Request(pageSize: 2)).Value!.NextCursor;
+        rescoped.ExcludeFull = true;
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, fixture.Browser.Browse(rescoped).Error);
+
+        BrowseSessionsRequest expired = fixture.Request(pageSize: 2);
+        expired.Cursor = fixture.Browser.Browse(expired).Value!.NextCursor;
+        fixture.Clock.Advance(TimeSpan.FromMinutes(5));
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, fixture.Browser.Browse(expired).Error);
+    }
+
+    [Fact]
+    public void ResponseByteBudgetTrimsLargePagesAndContinuesWithCursor()
+    {
+        using SessionBrowserFixture fixture = new();
+        Dictionary<string, string> metadata = Enumerable.Range(0, 14).ToDictionary(
+            static index => $"key-{index}",
+            static index => new string((char)('a' + index % 26), 256),
+            EqualityComparer<string>.Default);
+        for (int index = 0; index < 100; index++)
+        {
+            fixture.Add(metadata: metadata);
+        }
+
+        BrowseSessionsResponse response = fixture.Browser.Browse(fixture.Request()).Value!;
+        int encodedBytes = JsonSerializer.SerializeToUtf8Bytes(response, ContractJson.Options).Length;
+
+        Assert.InRange(encodedBytes, 1, ContractLimits.BrowserResponseMaxBytes);
+        Assert.NotEmpty(response.Items);
+        Assert.NotNull(response.NextCursor);
+        Assert.True(response.Items.Count < 100);
+    }
+
+    [Fact]
+    public void PresentationMetadataIsJsonEscapedAndResponseHasNoConnectionSecrets()
+    {
+        using SessionBrowserFixture fixture = new();
+        fixture.Add(metadata: new Dictionary<string, string>(StringComparer.Ordinal)
+        {
+            ["mode"] = "co-op",
+            ["map"] = "<script>alert(1)</script>",
+        });
+
+        BrowseSessionsResponse response = fixture.Browser.Browse(fixture.Request()).Value!;
+        string json = JsonSerializer.Serialize(response, ContractJson.Options);
+
+        Assert.DoesNotContain("<script>", json, StringComparison.OrdinalIgnoreCase);
+        Assert.DoesNotContain("endpoint", json, StringComparison.OrdinalIgnoreCase);
+        Assert.DoesNotContain("token", json, StringComparison.OrdinalIgnoreCase);
+        Assert.DoesNotContain("capability", json, StringComparison.OrdinalIgnoreCase);
+        Assert.Equal("<script>alert(1)</script>", Assert.Single(response.Items).Metadata["map"]);
+    }
+
+    [Fact]
+    public void RevokedListingDisappearsBeforeAnotherReadPathCanObserveIt()
+    {
+        using SessionBrowserFixture fixture = new();
+        StoredListing listing = fixture.Add();
+        fixture.Store.RevokeListing(listing.Definition.ListingId);
+
+        Assert.Empty(fixture.Browser.Browse(fixture.Request()).Value!.Items);
+        Assert.Equal(RendezvousErrorCode.NotFound, fixture.Browser.Get(
+            listing.Definition.ListingId,
+            fixture.Scope.GameId,
+            fixture.Scope.EnvironmentId,
+            7).Error);
+    }
+}

tests/FinalFactory.Rendezvous.Tests/Browser/SessionBrowserTestData.cs

@@ -0,0 +1,71 @@
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Browser;
+using FinalFactory.Rendezvous.Server.State;
+using FinalFactory.Rendezvous.Tests.State;
+
+namespace FinalFactory.Rendezvous.Tests.Browser;
+
+internal sealed class SessionBrowserFixture : IDisposable
+{
+    private readonly EphemeralStateFixture _state = new();
+
+    public SessionBrowserFixture()
+    {
+        Cursors = new();
+        Browser = new(_state.Store, Cursors, _state.Clock);
+    }
+
+    public InMemoryEphemeralRendezvousStore Store => _state.Store;
+    public ManualRendezvousClock Clock => _state.Clock;
+    public SessionBrowserCursorCodec Cursors { get; }
+    public SessionBrowserService Browser { get; }
+    public TenantScope Scope => _state.Scope;
+
+    public StoredListing Add(
+        TenantScope? scope = null,
+        uint protocolVersion = 7,
+        RegionId? regionId = null,
+        ListingVisibility visibility = ListingVisibility.Public,
+        bool fresh = true,
+        int currentPlayers = 1,
+        int maximumPlayers = 8,
+        IReadOnlyDictionary<string, string>? metadata = null)
+    {
+        CreateListingCommand seed = _state.ListingCommand();
+        CreateListingCommand command = seed with
+        {
+            Listing = seed.Listing with
+            {
+                Scope = scope ?? Scope,
+                ProtocolVersion = protocolVersion,
+                RegionId = regionId ?? seed.Listing.RegionId,
+                Visibility = visibility,
+                CurrentPlayers = currentPlayers,
+                MaximumPlayers = maximumPlayers,
+                Metadata = metadata ?? seed.Listing.Metadata,
+            },
+        };
+        StoredListing listing = Store.CreateListing(command).Value!;
+        if (fresh)
+        {
+            listing = Store.BindHostPresence(new(
+                command.Listing.HostPresenceHandle,
+                command.Listing.HostPresenceFingerprint,
+                EphemeralStateFixture.PublicEndpoint(40_000),
+                null)).Value!;
+        }
+
+        return listing;
+    }
+
+    public BrowseSessionsRequest Request(int pageSize = 100) => new()
+    {
+        GameId = Scope.GameId,
+        EnvironmentId = Scope.EnvironmentId,
+        ProtocolVersion = 7,
+        RegionId = new("eu-central"),
+        PageSize = pageSize,
+    };
+
+    public void Dispose() => Cursors.Dispose();
+}

tests/FinalFactory.Rendezvous.Tests/Contracts/ContractLimitTests.cs

@@ -4,6 +4,15 @@ namespace FinalFactory.Rendezvous.Tests.Contracts;
 
 public sealed class ContractLimitTests
 {
+    [Fact]
+    public void RequiredPlayerFacingTextRejectsEmptyOrWhitespaceValues()
+    {
+        Assert.False(ContractValidation.IsBuildVersionValid(string.Empty));
+        Assert.False(ContractValidation.IsBuildVersionValid("   "));
+        Assert.False(ContractValidation.IsDisplayNameValid(string.Empty));
+        Assert.False(ContractValidation.IsDisplayNameValid("   "));
+    }
+
     [Fact]
     public void ByteAndCollectionLimitsAcceptTheBoundaryOnly()
     {

tests/FinalFactory.Rendezvous.Tests/Contracts/ContractSerializationTests.cs

@@ -8,6 +8,7 @@ public sealed class ContractSerializationTests
     public static TheoryData<string, Type> GoldenJsonVectors => new()
     {
         { "register-session.json", typeof(RegisterSessionRequest) },
+        { "register-session-response.json", typeof(RegisterSessionResponse) },
         { "browse-sessions.json", typeof(BrowseSessionsResponse) },
         { "create-join-response.json", typeof(CreateJoinAttemptResponse) },
         { "api-error.json", typeof(ApiError) },

tests/FinalFactory.Rendezvous.Tests/Contracts/OpenApiCompatibilityTests.cs

@@ -64,5 +64,26 @@ public sealed class OpenApiCompatibilityTests
             property.Contains("token", StringComparison.OrdinalIgnoreCase)
             || property.Contains("endpoint", StringComparison.OrdinalIgnoreCase)
             || property.Contains("playerId", StringComparison.OrdinalIgnoreCase));
+
+        JsonElement publisherBearer = root.GetProperty("components")
+            .GetProperty("securitySchemes")
+            .GetProperty("PublisherBearer");
+        Assert.Equal("http", publisherBearer.GetProperty("type").GetString());
+        Assert.Equal("bearer", publisherBearer.GetProperty("scheme").GetString());
+        (string Path, string Method)[] publisherOperations =
+        [
+            ("/v1/sessions", "post"),
+            ("/v1/sessions/{listingId}", "put"),
+            ("/v1/sessions/{listingId}", "delete"),
+            ("/v1/sessions/{listingId}/renew", "post"),
+        ];
+        foreach ((string operationPath, string method) in publisherOperations)
+        {
+            JsonElement security = root.GetProperty("paths")
+                .GetProperty(operationPath)
+                .GetProperty(method)
+                .GetProperty("security");
+            Assert.True(security[0].TryGetProperty("PublisherBearer", out _));
+        }
     }
 }

tests/FinalFactory.Rendezvous.Tests/Server/UdpMediatorServiceTests.cs

@@ -1,5 +1,10 @@
 using System.Net;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
 using FinalFactory.Rendezvous.Server.Transport;
+using FinalFactory.Rendezvous.Tests.Sessions;
+using FinalFactory.Rendezvous.Tests.State;
 using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.Options;
 
@@ -7,6 +12,39 @@ namespace FinalFactory.Rendezvous.Tests.Server;
 
 public sealed class UdpMediatorServiceTests
 {
+    [Fact]
+    public void AuthenticatedHostDatagramGatesVisibilityUsingObservedGameplaySocket()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionResponse registration = fixture.Register();
+        using UdpMediatorService service = new(
+            Options.Create(new UdpMediatorOptions { ListenAddress = "127.0.0.1", Port = 0 }),
+            NullLogger<UdpMediatorService>.Instance,
+            fixture.Store,
+            fixture.Capabilities);
+        PresenceDatagram presence = new()
+        {
+            MessageType = UdpPresenceMessageType.HostPresence,
+            MediationHandle = registration.HostPresenceHandle,
+            AddressFamily = AddressFamilyKind.Ipv4,
+            LocalAddress = "192.168.1.50",
+            LocalPort = 40_000,
+            Capability = registration.HostPresenceCapability,
+        };
+        IPEndPoint observedGameplaySocket = new(IPAddress.Parse("203.0.113.77"), 51_234);
+        presence.Capability = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
+        Assert.Equal(
+            UdpPresenceProcessingResult.HostPresenceRejected,
+            service.ProcessDatagram(RendezvousUdpCodec.Encode(presence), observedGameplaySocket));
+        Assert.Empty(fixture.Browse());
+
+        presence.Capability = registration.HostPresenceCapability;
+        Assert.Equal(
+            UdpPresenceProcessingResult.HostPresenceAccepted,
+            service.ProcessDatagram(RendezvousUdpCodec.Encode(presence), observedGameplaySocket));
+        Assert.Equal(registration.ListingId, Assert.Single(fixture.Browse()).Definition.ListingId);
+    }
+
     [Fact]
     public async Task ServiceBindsAnEphemeralUdpPortAndStopsCleanly()
     {
@@ -16,9 +54,14 @@ public sealed class UdpMediatorServiceTests
             ListenAddress = IPAddress.Loopback.ToString(),
             Port = 0,
         };
+        ManualRendezvousClock clock = new();
+        InMemoryEphemeralRendezvousStore store = new(new EphemeralStoreOptions(), clock, clock);
+        using EphemeralCapabilityIssuer capabilities = new();
         using UdpMediatorService service = new(
             Options.Create(options),
-            NullLogger<UdpMediatorService>.Instance);
+            NullLogger<UdpMediatorService>.Instance,
+            store,
+            capabilities);
 
         await service.StartAsync(timeout.Token);
 

tests/FinalFactory.Rendezvous.Tests/Sessions/SessionHttpEndpointTests.cs

@@ -0,0 +1,165 @@
+using System.Net;
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using System.Text;
+using System.Text.Json;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Browser;
+using FinalFactory.Rendezvous.Server.Http;
+using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
+using FinalFactory.Rendezvous.Tests.Provisioning;
+using FinalFactory.Rendezvous.Tests.State;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Hosting.Server;
+using Microsoft.AspNetCore.Hosting.Server.Features;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace FinalFactory.Rendezvous.Tests.Sessions;
+
+public sealed class SessionHttpEndpointTests
+{
+    [Fact]
+    public async Task AuthenticatedHttpLifecycleReturnsStableContractsAndStatuses()
+    {
+        ManualRendezvousClock clock = new(ProvisioningTestData.Now);
+        EphemeralStoreOptions stateOptions = new();
+        InMemoryEphemeralRendezvousStore store = new(stateOptions, clock, clock);
+        EphemeralCapabilityIssuer capabilities = new();
+        ProvisioningRuntime provisioning = ProvisioningRuntime.Create(
+            ProvisioningTestData.CreateOptions(),
+            ProvisioningTestData.CreateSecrets("secret-1"),
+            clock.UtcNow);
+        DedicatedPublisherPrincipal principal = ProvisioningTestData.CreateDedicatedPublisher();
+        string publisherCredential = provisioning.Credentials.Issue(principal, clock.UtcNow);
+
+        WebApplicationBuilder builder = WebApplication.CreateBuilder();
+        builder.WebHost.UseUrls("http://127.0.0.1:0");
+        builder.Services.ConfigureHttpJsonOptions(static options =>
+            ContractJson.Configure(options.SerializerOptions));
+        builder.Services.Configure<RouteHandlerOptions>(static options =>
+            options.ThrowOnBadRequest = true);
+        builder.Services.AddProblemDetails();
+        builder.Services.AddExceptionHandler<RendezvousExceptionHandler>();
+        builder.Services.AddSingleton(provisioning);
+        builder.Services.AddSingleton(provisioning.Credentials);
+        builder.Services.AddSingleton(provisioning.PublisherAuthorization);
+        builder.Services.AddSingleton<IEphemeralRendezvousStore>(store);
+        builder.Services.AddSingleton<IWallClock>(clock);
+        builder.Services.AddSingleton(capabilities);
+        builder.Services.AddSingleton<ISessionCapabilityService>(capabilities);
+        builder.Services.AddSingleton(SessionLeaseTiming.From(stateOptions));
+        builder.Services.AddSingleton<SessionLeaseService>();
+        builder.Services.AddSingleton<SessionBrowserCursorCodec>();
+        builder.Services.AddSingleton<SessionBrowserService>();
+        await using WebApplication app = builder.Build();
+        app.UseExceptionHandler();
+        app.MapRendezvousContractEndpoints();
+        await app.StartAsync();
+        IServer server = app.Services.GetRequiredService<IServer>();
+        string address = Assert.Single(server.Features.Get<IServerAddressesFeature>()!.Addresses);
+        using HttpClient client = new() { BaseAddress = new Uri(address) };
+        RegisterSessionRequest registration = new()
+        {
+            IdempotencyKey = "http-register-1",
+            GameId = new("space-game"),
+            EnvironmentId = new("production"),
+            RegionId = new("eu-central"),
+            ProtocolVersion = 7,
+            BuildVersion = "1.4.2",
+            DisplayName = "HTTP host",
+            Visibility = ListingVisibility.Public,
+            Capacity = new() { CurrentPlayers = 1, MaximumPlayers = 8 },
+            Metadata = new Dictionary<string, string>(StringComparer.Ordinal)
+            {
+                ["mode"] = "co-op",
+            },
+        };
+
+        HttpResponseMessage unauthenticated = await client.PostAsJsonAsync(
+            "/v1/sessions",
+            registration,
+            ContractJson.Options);
+        Assert.Equal(HttpStatusCode.Unauthorized, unauthenticated.StatusCode);
+        Assert.Equal("Bearer", Assert.Single(unauthenticated.Headers.WwwAuthenticate).Scheme);
+        ApiError? authenticationError = await unauthenticated.Content.ReadFromJsonAsync<ApiError>(
+            ContractJson.Options);
+        Assert.Equal(RendezvousErrorCode.AuthenticationRequired, authenticationError!.Code);
+
+        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
+            "Bearer",
+            publisherCredential);
+        string invalidJson = JsonSerializer.Serialize(registration, ContractJson.Options)
+            .Replace("\"public\"", "\"futureVisibility\"", StringComparison.Ordinal);
+        HttpResponseMessage invalid = await client.PostAsync(
+            "/v1/sessions",
+            new StringContent(invalidJson, Encoding.UTF8, "application/json"));
+        Assert.Equal(HttpStatusCode.BadRequest, invalid.StatusCode);
+        ApiError? invalidError = await invalid.Content.ReadFromJsonAsync<ApiError>(ContractJson.Options);
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, invalidError!.Code);
+
+        HttpResponseMessage created = await client.PostAsJsonAsync(
+            "/v1/sessions",
+            registration,
+            ContractJson.Options);
+        Assert.Equal(HttpStatusCode.Created, created.StatusCode);
+        RegisterSessionResponse? session = await created.Content.ReadFromJsonAsync<RegisterSessionResponse>(
+            ContractJson.Options);
+        Assert.NotNull(session);
+        Assert.Equal($"/v1/sessions/{session.ListingId}", created.Headers.Location!.OriginalString);
+        Assert.True(capabilities.TryFingerprint(
+            session.HostPresenceCapability,
+            out SecretFingerprint presenceFingerprint));
+        store.BindHostPresence(new(
+            session.HostPresenceHandle,
+            presenceFingerprint,
+            new(AddressFamilyKind.Ipv4, "203.0.113.80", 41_000),
+            null));
+
+        BrowseSessionsResponse? browser = await client.GetFromJsonAsync<BrowseSessionsResponse>(
+            "/v1/sessions?contractVersion=1&gameId=space-game&environmentId=production&protocolVersion=7&regionId=eu-central&pageSize=10&excludeFull=true",
+            ContractJson.Options);
+        Assert.Equal(session.ListingId, Assert.Single(browser!.Items).ListingId);
+        GetSessionResponse? direct = await client.GetFromJsonAsync<GetSessionResponse>(
+            $"/v1/sessions/{session.ListingId}?contractVersion=1&gameId=space-game&environmentId=production&protocolVersion=7",
+            ContractJson.Options);
+        Assert.Equal(session.ListingId, direct!.Session.ListingId);
+
+        HttpResponseMessage renewed = await client.PostAsJsonAsync(
+            $"/v1/sessions/{session.ListingId}/renew",
+            new RenewLeaseRequest { LeaseToken = session.LeaseToken },
+            ContractJson.Options);
+        Assert.Equal(HttpStatusCode.OK, renewed.StatusCode);
+        Assert.NotNull(await renewed.Content.ReadFromJsonAsync<RenewLeaseResponse>(ContractJson.Options));
+
+        HttpResponseMessage updated = await client.PutAsJsonAsync(
+            $"/v1/sessions/{session.ListingId}",
+            new UpdateSessionRequest
+            {
+                LeaseToken = session.LeaseToken,
+                BuildVersion = "1.4.3",
+                DisplayName = "HTTP host updated",
+                Capacity = new() { CurrentPlayers = 2, MaximumPlayers = 8 },
+                Metadata = new Dictionary<string, string> { ["mode"] = "co-op" },
+            },
+            ContractJson.Options);
+        Assert.Equal(HttpStatusCode.NoContent, updated.StatusCode);
+
+        using HttpRequestMessage deleteRequest = new(
+            HttpMethod.Delete,
+            $"/v1/sessions/{session.ListingId}")
+        {
+            Content = JsonContent.Create(
+                new DeleteSessionRequest { LeaseToken = session.LeaseToken },
+                options: ContractJson.Options),
+        };
+        HttpResponseMessage deleted = await client.SendAsync(deleteRequest);
+        Assert.Equal(HttpStatusCode.NoContent, deleted.StatusCode);
+        Assert.Equal(StoreResultCode.NotFound, store.GetListing(session.ListingId, false).Code);
+
+        await app.StopAsync();
+    }
+}

tests/FinalFactory.Rendezvous.Tests/Sessions/SessionLeaseServiceTests.cs

@@ -0,0 +1,294 @@
+using System.Text.Json;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Tests.Sessions;
+
+public sealed class SessionLeaseServiceTests
+{
+    [Fact]
+    public void RegistrationReturnsOpaqueCredentialsButRemainsHiddenUntilPresence()
+    {
+        using SessionLeaseFixture fixture = new();
+
+        RegisterSessionResponse response = fixture.Register();
+
+        Assert.Equal(30, response.LeaseRenewAfterSeconds);
+        Assert.Equal(10, response.HostPresenceRefreshAfterSeconds);
+        Assert.Equal(43, response.LeaseToken.Length);
+        Assert.Equal(43, response.HostPresenceCapability.Length);
+        Assert.Empty(fixture.Browse());
+        string json = JsonSerializer.Serialize(response, ContractJson.Options);
+        Assert.DoesNotContain("endpoint", json, StringComparison.OrdinalIgnoreCase);
+        Assert.DoesNotContain("fingerprint", json, StringComparison.OrdinalIgnoreCase);
+        Assert.DoesNotContain("store", json, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void ExactRegistrationRetryReproducesIdsAndCapabilitiesWithoutRetainingPlaintext()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionRequest request = fixture.Request("same-key");
+
+        RegisterSessionResponse first = fixture.Register(request);
+        RegisterSessionRequest reordered = fixture.Request("same-key");
+        reordered.Metadata = new Dictionary<string, string>(StringComparer.Ordinal)
+        {
+            ["map"] = "europa",
+            ["mode"] = "co-op",
+        };
+        RegisterSessionResponse duplicate = fixture.Register(reordered);
+        RegisterSessionRequest changedRequest = fixture.Request("same-key");
+        changedRequest.DisplayName = "Changed";
+        SessionServiceResult<RegisterSessionResponse> changed = fixture.Service.Register(
+            fixture.Principal,
+            changedRequest);
+
+        Assert.Equal(first.ListingId, duplicate.ListingId);
+        Assert.Equal(first.LeaseId, duplicate.LeaseId);
+        Assert.Equal(first.LeaseToken, duplicate.LeaseToken);
+        Assert.Equal(first.HostPresenceHandle, duplicate.HostPresenceHandle);
+        Assert.Equal(first.HostPresenceCapability, duplicate.HostPresenceCapability);
+        Assert.Equal(RendezvousErrorCode.Conflict, changed.Error);
+    }
+
+    [Fact]
+    public void ReRegistrationAfterIdempotencyExpiryRotatesIdsAndCapabilities()
+    {
+        EphemeralStoreOptions options = new()
+        {
+            LeaseLifetime = TimeSpan.FromSeconds(5),
+            JoinAttemptLifetime = TimeSpan.FromSeconds(5),
+            IdempotencyLifetime = TimeSpan.FromSeconds(6),
+        };
+        using SessionLeaseFixture fixture = new(options);
+        RegisterSessionRequest request = fixture.Request("reused-after-expiry");
+        RegisterSessionResponse first = fixture.Register(request);
+
+        fixture.Clock.Advance(options.IdempotencyLifetime);
+        RegisterSessionResponse second = fixture.Register(request);
+
+        Assert.NotEqual(first.ListingId, second.ListingId);
+        Assert.NotEqual(first.LeaseId, second.LeaseId);
+        Assert.NotEqual(first.LeaseToken, second.LeaseToken);
+        Assert.NotEqual(first.HostPresenceCapability, second.HostPresenceCapability);
+    }
+
+    [Fact]
+    public void PresenceTransitionsAwaitingToListedToStaleAndBackWithoutChangingIdentity()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionResponse registration = fixture.Register();
+
+        Assert.Empty(fixture.Browse());
+        Assert.True(fixture.BindPresence(registration).Succeeded);
+        Assert.Equal(registration.ListingId, Assert.Single(fixture.Browse()).Definition.ListingId);
+
+        fixture.Clock.Advance(fixture.StoreOptions.PresenceLifetime);
+        Assert.Empty(fixture.Browse());
+        Assert.True(fixture.BindPresence(registration).Succeeded);
+        Assert.Equal(registration.ListingId, Assert.Single(fixture.Browse()).Definition.ListingId);
+    }
+
+    [Fact]
+    public void RenewUpdateAndDeleteMaintainCanonicalIdentityAndAdvisoryCapacity()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionResponse registration = fixture.Register();
+        fixture.Clock.Advance(TimeSpan.FromSeconds(1));
+
+        SessionServiceResult<RenewLeaseResponse> renewed = fixture.Service.Renew(
+            fixture.Principal,
+            registration.ListingId,
+            new() { LeaseToken = registration.LeaseToken });
+        SessionServiceResult<bool> updated = fixture.Service.Update(
+            fixture.Principal,
+            registration.ListingId,
+            new()
+            {
+                LeaseToken = registration.LeaseToken,
+                BuildVersion = "1.4.3",
+                DisplayName = "Europa Updated",
+                Capacity = new() { CurrentPlayers = 8, MaximumPlayers = 8 },
+                Metadata = new Dictionary<string, string>(StringComparer.Ordinal)
+                {
+                    ["mode"] = "co-op",
+                    ["map"] = "europa",
+                },
+            });
+        StoredListing stored = fixture.Store.GetListing(registration.ListingId, false).Value!;
+
+        Assert.True(renewed.Succeeded);
+        Assert.Equal(fixture.Clock.UtcNow.Add(fixture.StoreOptions.LeaseLifetime), renewed.Value!.ExpiresAt);
+        Assert.True(updated.Succeeded);
+        Assert.Equal(registration.ListingId, stored.Definition.ListingId);
+        Assert.Equal(fixture.Scope, stored.Definition.Scope);
+        Assert.Equal(8, stored.Definition.CurrentPlayers);
+        Assert.Equal(8, stored.Definition.MaximumPlayers);
+        Assert.True(fixture.Service.Delete(
+            fixture.Principal,
+            registration.ListingId,
+            new() { LeaseToken = registration.LeaseToken }).Succeeded);
+        Assert.True(fixture.Service.Delete(
+            fixture.Principal,
+            registration.ListingId,
+            new() { LeaseToken = registration.LeaseToken }).Succeeded);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(registration.ListingId, false).Code);
+    }
+
+    [Fact]
+    public void AnotherPublisherCannotRenewUpdateOrDeleteListing()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionResponse registration = fixture.Register();
+        DedicatedPublisherPrincipal other = fixture.Publisher("publisher-2");
+
+        Assert.Equal(RendezvousErrorCode.NotFound, fixture.Service.Renew(
+            other,
+            registration.ListingId,
+            new() { LeaseToken = registration.LeaseToken }).Error);
+        Assert.Equal(RendezvousErrorCode.NotFound, fixture.Service.Update(
+            other,
+            registration.ListingId,
+            new()
+            {
+                LeaseToken = registration.LeaseToken,
+                BuildVersion = "1.4.3",
+                DisplayName = "Hijacked",
+                Capacity = new() { CurrentPlayers = 1, MaximumPlayers = 2 },
+                Metadata = new Dictionary<string, string> { ["mode"] = "co-op" },
+            }).Error);
+        Assert.True(fixture.Service.Delete(
+            other,
+            registration.ListingId,
+            new() { LeaseToken = registration.LeaseToken }).Succeeded);
+        Assert.True(fixture.Store.GetListing(registration.ListingId, false).Succeeded);
+    }
+
+    [Fact]
+    public async Task ConcurrentRenewDeleteCannotResurrectListing()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionResponse registration = fixture.Register();
+        using ManualResetEventSlim start = new(false);
+        Task<SessionServiceResult<RenewLeaseResponse>> renew = Task.Run(() =>
+        {
+            start.Wait();
+            return fixture.Service.Renew(
+                fixture.Principal,
+                registration.ListingId,
+                new() { LeaseToken = registration.LeaseToken });
+        });
+        Task<SessionServiceResult<bool>> delete = Task.Run(() =>
+        {
+            start.Wait();
+            return fixture.Service.Delete(
+                fixture.Principal,
+                registration.ListingId,
+                new() { LeaseToken = registration.LeaseToken });
+        });
+
+        start.Set();
+        await Task.WhenAll(renew, delete);
+        SessionServiceResult<RenewLeaseResponse> renewResult = await renew;
+        SessionServiceResult<bool> deleteResult = await delete;
+
+        Assert.True(deleteResult.Succeeded);
+        Assert.Contains(renewResult.Error, new[]
+        {
+            RendezvousErrorCode.None,
+            RendezvousErrorCode.NotFound,
+            RendezvousErrorCode.Conflict,
+        });
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(registration.ListingId, false).Code);
+    }
+
+    [Fact]
+    public void AbandonedRegistrationExpiresAndFreesBoundedCapacity()
+    {
+        EphemeralStoreOptions options = new()
+        {
+            MaxListings = 1,
+            LeaseLifetime = TimeSpan.FromSeconds(5),
+        };
+        using SessionLeaseFixture fixture = new(options);
+        fixture.Register(fixture.Request("first"));
+        Assert.Equal(RendezvousErrorCode.CapacityExceeded, fixture.Service.Register(
+            fixture.Principal,
+            fixture.Request("second")).Error);
+
+        fixture.Clock.Advance(options.LeaseLifetime);
+
+        Assert.True(fixture.Service.Register(
+            fixture.Principal,
+            fixture.Request("second")).Succeeded);
+    }
+
+    [Fact]
+    public void LeaseExpiryRemovesMutationAndPresencePaths()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionResponse registration = fixture.Register();
+        fixture.BindPresence(registration);
+
+        fixture.Clock.Advance(fixture.StoreOptions.LeaseLifetime);
+
+        Assert.Empty(fixture.Browse());
+        Assert.Equal(RendezvousErrorCode.NotFound, fixture.Service.Renew(
+            fixture.Principal,
+            registration.ListingId,
+            new() { LeaseToken = registration.LeaseToken }).Error);
+        Assert.Equal(StoreResultCode.NotFound, fixture.BindPresence(registration).Code);
+    }
+
+    [Fact]
+    public void LossOfAtomicStateFailsLeaseMutationClosed()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionResponse registration = fixture.Register();
+        fixture.Store.MarkUnavailable();
+
+        Assert.Equal(RendezvousErrorCode.ServiceUnavailable, fixture.Service.Renew(
+            fixture.Principal,
+            registration.ListingId,
+            new() { LeaseToken = registration.LeaseToken }).Error);
+    }
+
+    [Fact]
+    public void InvalidPolicyBoundInputsReturnStableTypedErrors()
+    {
+        using SessionLeaseFixture fixture = new();
+        RegisterSessionRequest capacity = fixture.Request("bad-capacity");
+        capacity.Capacity = new() { CurrentPlayers = 2, MaximumPlayers = 1 };
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, fixture.Service.Register(
+            fixture.Principal,
+            capacity).Error);
+        RegisterSessionRequest protocol = fixture.Request("bad-protocol");
+        protocol.ProtocolVersion = 8;
+        Assert.Equal(RendezvousErrorCode.IncompatibleProtocol, fixture.Service.Register(
+            fixture.Principal,
+            protocol).Error);
+        RegisterSessionRequest region = fixture.Request("bad-region");
+        region.RegionId = new("us-east");
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, fixture.Service.Register(
+            fixture.Principal,
+            region).Error);
+        RegisterSessionRequest visibility = fixture.Request("bad-visibility");
+        visibility.Visibility = (ListingVisibility)99;
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, fixture.Service.Register(
+            fixture.Principal,
+            visibility).Error);
+        RegisterSessionRequest metadata = fixture.Request("bad-metadata");
+        metadata.Metadata = new Dictionary<string, string> { ["unknown"] = "value" };
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, fixture.Service.Register(
+            fixture.Principal,
+            metadata).Error);
+        RegisterSessionRequest build = fixture.Request("bad-build");
+        build.BuildVersion = " ";
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, fixture.Service.Register(
+            fixture.Principal,
+            build).Error);
+    }
+}

tests/FinalFactory.Rendezvous.Tests/Sessions/SessionLeaseTestData.cs

@@ -0,0 +1,93 @@
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
+using FinalFactory.Rendezvous.Tests.Provisioning;
+using FinalFactory.Rendezvous.Tests.State;
+
+namespace FinalFactory.Rendezvous.Tests.Sessions;
+
+internal sealed class SessionLeaseFixture : IDisposable
+{
+    private int _sequence;
+
+    public SessionLeaseFixture(EphemeralStoreOptions? storeOptions = null)
+    {
+        StoreOptions = storeOptions ?? new EphemeralStoreOptions();
+        Clock = new();
+        Store = new(StoreOptions, Clock, Clock);
+        Capabilities = new();
+        GamePolicyRegistry policies = GamePolicyRegistry.Create([ProvisioningTestData.CreatePolicy()]);
+        Service = new(
+            new PublisherAuthorizationService(policies),
+            Store,
+            Capabilities,
+            SessionLeaseTiming.From(StoreOptions),
+            Clock);
+        Principal = Publisher("publisher-1");
+    }
+
+    public EphemeralStoreOptions StoreOptions { get; }
+    public ManualRendezvousClock Clock { get; }
+    public InMemoryEphemeralRendezvousStore Store { get; }
+    public EphemeralCapabilityIssuer Capabilities { get; }
+    public SessionLeaseService Service { get; }
+    public DedicatedPublisherPrincipal Principal { get; }
+    public TenantScope Scope { get; } = new(new("space-game"), new("production"));
+
+    public DedicatedPublisherPrincipal Publisher(string subject) => new(
+        subject,
+        Clock.UtcNow.AddMinutes(10),
+        Scope.GameId,
+        Scope.EnvironmentId,
+        new HashSet<RegionId> { new("eu-central") });
+
+    public RegisterSessionRequest Request(string? idempotencyKey = null) => new()
+    {
+        IdempotencyKey = idempotencyKey ?? $"register-{Interlocked.Increment(ref _sequence)}",
+        GameId = Scope.GameId,
+        EnvironmentId = Scope.EnvironmentId,
+        RegionId = new("eu-central"),
+        ProtocolVersion = 7,
+        BuildVersion = "1.4.2",
+        DisplayName = "Europa Relay",
+        Visibility = ListingVisibility.Public,
+        Capacity = new() { CurrentPlayers = 2, MaximumPlayers = 8 },
+        Metadata = new Dictionary<string, string>(StringComparer.Ordinal)
+        {
+            ["mode"] = "co-op",
+            ["map"] = "europa",
+        },
+    };
+
+    public RegisterSessionResponse Register(
+        RegisterSessionRequest? request = null,
+        DedicatedPublisherPrincipal? principal = null)
+    {
+        SessionServiceResult<RegisterSessionResponse> result = Service.Register(
+            principal ?? Principal,
+            request ?? Request());
+        Assert.True(result.Succeeded);
+        Assert.NotNull(result.Value);
+        return result.Value;
+    }
+
+    public StoreResult<StoredListing> BindPresence(RegisterSessionResponse registration)
+    {
+        Assert.True(Capabilities.TryFingerprint(
+            registration.HostPresenceCapability,
+            out SecretFingerprint fingerprint));
+        return Store.BindHostPresence(new(
+            registration.HostPresenceHandle,
+            fingerprint,
+            new(AddressFamilyKind.Ipv4, "203.0.113.50", 40_000),
+            new ObservedEndpoint(AddressFamilyKind.Ipv4, "192.168.1.50", 40_000)));
+    }
+
+    public IReadOnlyList<StoredListing> Browse() => Store.BrowseVisibleListings(new(
+        Scope,
+        7,
+        new RegionId("eu-central"))).Value!;
+
+    public void Dispose() => Capabilities.Dispose();
+}

tests/FinalFactory.Rendezvous.Tests/State/EphemeralStateTestData.cs

@@ -0,0 +1,109 @@
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Tests.State;
+
+internal sealed class ManualRendezvousClock : IWallClock, IMonotonicClock
+{
+    public ManualRendezvousClock(DateTimeOffset? utcNow = null) =>
+        UtcNow = utcNow ?? new DateTimeOffset(2026, 7, 16, 0, 0, 0, TimeSpan.Zero);
+
+    public DateTimeOffset UtcNow { get; private set; }
+    public TimeSpan Elapsed { get; private set; }
+
+    public void Advance(TimeSpan duration)
+    {
+        Elapsed += duration;
+        UtcNow += duration;
+    }
+
+    public void MoveWall(TimeSpan duration) => UtcNow += duration;
+}
+
+internal sealed class EphemeralStateFixture
+{
+    private int _sequence;
+
+    public EphemeralStateFixture(EphemeralStoreOptions? options = null)
+    {
+        Clock = new();
+        Store = new(options ?? new EphemeralStoreOptions(), Clock, Clock);
+    }
+
+    public ManualRendezvousClock Clock { get; }
+    public InMemoryEphemeralRendezvousStore Store { get; }
+    public TenantScope Scope { get; } = new(new GameId("space-game"), new EnvironmentId("test"));
+
+    public CreateListingCommand ListingCommand(
+        string owner = "publisher-1",
+        string? idempotencyKey = null,
+        string? requestFingerprint = null)
+    {
+        int sequence = Interlocked.Increment(ref _sequence);
+        return new(
+            idempotencyKey ?? $"register-{sequence}",
+            requestFingerprint ?? $"request-{sequence}",
+            new ListingDefinition
+            {
+                ListingId = NewListingId(),
+                LeaseId = NewLeaseId(),
+                Scope = Scope,
+                OwnerSubject = owner,
+                RegionId = new RegionId("eu-central"),
+                ProtocolVersion = 7,
+                BuildVersion = "1.2.3",
+                DisplayName = "Test host",
+                Visibility = ListingVisibility.Public,
+                TrustMode = PublisherTrustMode.ManagedDedicated,
+                CurrentPlayers = 1,
+                MaximumPlayers = 8,
+                Metadata = new Dictionary<string, string>(StringComparer.Ordinal) { ["mode"] = "coop" },
+                LeaseFingerprint = Fingerprint($"lease-{sequence}"),
+                HostPresenceHandle = NewHandle(),
+                HostPresenceFingerprint = Fingerprint($"presence-{sequence}"),
+                CapabilityDerivationSalt = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
+            });
+    }
+
+    public StoredListing CreateVisibleListing(out CreateListingCommand command)
+    {
+        command = ListingCommand();
+        StoreResult<StoredListing> created = Store.CreateListing(command);
+        Assert.True(created.Succeeded);
+        StoreResult<StoredListing> bound = Store.BindHostPresence(new(
+            command.Listing.HostPresenceHandle,
+            command.Listing.HostPresenceFingerprint,
+            PublicEndpoint(40_000),
+            LocalEndpoint(40_000)));
+        Assert.True(bound.Succeeded);
+        return bound.Value!;
+    }
+
+    public CreateJoinAttemptCommand AttemptCommand(StoredListing listing, string owner = "client-1")
+    {
+        int sequence = Interlocked.Increment(ref _sequence);
+        return new()
+        {
+            IdempotencyOwner = owner,
+            IdempotencyKey = $"join-{sequence}",
+            RequestFingerprint = $"join-request-{sequence}",
+            ClientSubject = owner,
+            AttemptId = NewAttemptId(),
+            MediationHandle = NewHandle(),
+            Scope = listing.Definition.Scope,
+            ListingId = listing.Definition.ListingId,
+            ProtocolVersion = listing.Definition.ProtocolVersion,
+            HostCapabilityFingerprint = Fingerprint($"host-{sequence}"),
+            ClientCapabilityFingerprint = Fingerprint($"client-{sequence}"),
+        };
+    }
+
+    public static SecretFingerprint Fingerprint(string value) => new(value);
+    public static ObservedEndpoint PublicEndpoint(int port) => new(AddressFamilyKind.Ipv4, "203.0.113.10", port);
+    public static ObservedEndpoint OtherPublicEndpoint(int port) => new(AddressFamilyKind.Ipv4, "198.51.100.20", port);
+    public static ObservedEndpoint LocalEndpoint(int port) => new(AddressFamilyKind.Ipv4, "192.168.1.20", port);
+    public static SessionListingId NewListingId() => new(Guid.NewGuid());
+    public static LeaseId NewLeaseId() => new(Guid.NewGuid());
+    public static JoinAttemptId NewAttemptId() => new(Guid.NewGuid());
+    public static MediationHandle NewHandle() => new(Guid.NewGuid());
+}

tests/FinalFactory.Rendezvous.Tests/State/InMemoryEphemeralRendezvousStoreTests.cs

@@ -0,0 +1,461 @@
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Tests.State;
+
+public sealed class InMemoryEphemeralRendezvousStoreTests
+{
+    [Fact]
+    public void IdempotencyRetentionMustCoverResourceLifetimes()
+    {
+        ManualRendezvousClock clock = new();
+        Assert.Throws<ArgumentOutOfRangeException>(() => new InMemoryEphemeralRendezvousStore(
+            new EphemeralStoreOptions { IdempotencyLifetime = TimeSpan.FromSeconds(5) },
+            clock,
+            clock));
+    }
+
+    [Fact]
+    public void DuplicateRegistrationIsIdempotentButChangedRequestConflicts()
+    {
+        EphemeralStateFixture fixture = new();
+        CreateListingCommand command = fixture.ListingCommand();
+
+        StoreResult<StoredListing> first = fixture.Store.CreateListing(command);
+        StoreResult<StoredListing> duplicate = fixture.Store.CreateListing(command);
+        StoreResult<StoredListing> changed = fixture.Store.CreateListing(command with { RequestFingerprint = "different" });
+
+        Assert.True(first.Succeeded);
+        Assert.True(duplicate.Succeeded);
+        Assert.True(duplicate.IsIdempotentReplay);
+        Assert.Equal(first.Value!.Definition.ListingId, duplicate.Value!.Definition.ListingId);
+        Assert.Equal(StoreResultCode.Conflict, changed.Code);
+    }
+
+    [Fact]
+    public void LeaseAndPresenceExpiryUseMonotonicTime()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out _);
+
+        fixture.Clock.Advance(TimeSpan.FromSeconds(20));
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(listing.Definition.ListingId, true).Code);
+        Assert.True(fixture.Store.GetListing(listing.Definition.ListingId, false).Succeeded);
+
+        fixture.Clock.Advance(TimeSpan.FromSeconds(40));
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(listing.Definition.ListingId, false).Code);
+    }
+
+    [Fact]
+    public void WallClockMovementDoesNotExpireOrExtendLease()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out CreateListingCommand command);
+
+        fixture.Clock.MoveWall(TimeSpan.FromDays(30));
+        Assert.True(fixture.Store.GetListing(listing.Definition.ListingId, false).Succeeded);
+        fixture.Clock.Advance(TimeSpan.FromSeconds(1));
+        StoreResult<StoredListing> renewed = fixture.Store.RenewLease(new(
+            listing.Definition.ListingId,
+            listing.Definition.LeaseId,
+            listing.Definition.LeaseFingerprint,
+            listing.Definition.OwnerSubject,
+            listing.Version));
+        Assert.Equal(new DateTimeOffset(2026, 7, 16, 0, 1, 1, TimeSpan.Zero), renewed.Value!.LeaseExpiresAt);
+        fixture.Clock.MoveWall(TimeSpan.FromDays(-60));
+        fixture.Clock.Advance(TimeSpan.FromSeconds(59));
+        Assert.True(fixture.Store.GetListing(listing.Definition.ListingId, false).Succeeded);
+        fixture.Clock.Advance(TimeSpan.FromSeconds(1));
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(command.Listing.ListingId, false).Code);
+    }
+
+    [Fact]
+    public async Task RenewDeleteRaceIsAtomicAndDeleteAlwaysWinsEventually()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out CreateListingCommand command);
+        using ManualResetEventSlim start = new(false);
+
+        Task<StoreResult<StoredListing>> renew = Task.Run(() =>
+        {
+            start.Wait();
+            return fixture.Store.RenewLease(new(
+                listing.Definition.ListingId,
+                listing.Definition.LeaseId,
+                listing.Definition.LeaseFingerprint,
+                listing.Definition.OwnerSubject,
+                listing.Version));
+        });
+        Task<StoreResult<bool>> delete = Task.Run(() =>
+        {
+            start.Wait();
+            return fixture.Store.DeleteListing(new(
+                command.Listing.ListingId,
+                command.Listing.LeaseId,
+                command.Listing.LeaseFingerprint,
+                command.Listing.OwnerSubject));
+        });
+
+        start.Set();
+        await Task.WhenAll(renew, delete);
+        StoreResult<StoredListing> renewResult = await renew;
+        StoreResult<bool> deleteResult = await delete;
+
+        Assert.True(deleteResult.Succeeded);
+        Assert.Contains(renewResult.Code, new[] { StoreResultCode.Success, StoreResultCode.NotFound });
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(command.Listing.ListingId, false).Code);
+    }
+
+    [Fact]
+    public void CompareAndSwapPreventsStaleRenewal()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out _);
+        RenewLeaseCommand command = new(
+            listing.Definition.ListingId,
+            listing.Definition.LeaseId,
+            listing.Definition.LeaseFingerprint,
+            listing.Definition.OwnerSubject,
+            listing.Version);
+
+        StoreResult<StoredListing> first = fixture.Store.RenewLease(command);
+        StoreResult<StoredListing> stale = fixture.Store.RenewLease(command);
+
+        Assert.Equal(2, first.Value!.Version);
+        Assert.Equal(StoreResultCode.Conflict, stale.Code);
+        Assert.Equal(2, stale.Value!.Version);
+    }
+
+    [Fact]
+    public void JoinRequiresExactScopeProtocolAndFreshHostPresence()
+    {
+        EphemeralStateFixture fixture = new();
+        CreateListingCommand listingCommand = fixture.ListingCommand();
+        StoredListing listing = fixture.Store.CreateListing(listingCommand).Value!;
+        CreateJoinAttemptCommand attempt = fixture.AttemptCommand(listing);
+
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.CreateJoinAttempt(attempt).Code);
+        fixture.Store.BindHostPresence(new(
+            listingCommand.Listing.HostPresenceHandle,
+            listingCommand.Listing.HostPresenceFingerprint,
+            EphemeralStateFixture.PublicEndpoint(40_000),
+            null));
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.CreateJoinAttempt(attempt with { ProtocolVersion = 8 }).Code);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.CreateJoinAttempt(attempt with
+        {
+            Scope = new(new("other-game"), new("test")),
+        }).Code);
+        Assert.True(fixture.Store.CreateJoinAttempt(attempt).Succeeded);
+    }
+
+    [Fact]
+    public void DuplicateJoinIsIdempotentAndDoesNotAllocateTwice()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out _);
+        CreateJoinAttemptCommand command = fixture.AttemptCommand(listing);
+
+        StoreResult<StoredJoinAttempt> first = fixture.Store.CreateJoinAttempt(command);
+        StoreResult<StoredJoinAttempt> duplicate = fixture.Store.CreateJoinAttempt(command);
+
+        Assert.True(first.Succeeded);
+        Assert.True(duplicate.Succeeded);
+        Assert.True(duplicate.IsIdempotentReplay);
+        Assert.Equal(first.Value!.AttemptId, duplicate.Value!.AttemptId);
+    }
+
+    [Fact]
+    public void BrowseReturnsOnlyFreshPublicCompatibleListingsInStableOrder()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing visible = fixture.CreateVisibleListing(out _);
+        CreateListingCommand staleCommand = fixture.ListingCommand();
+        fixture.Store.CreateListing(staleCommand);
+        CreateListingCommand unlistedCommand = fixture.ListingCommand();
+        unlistedCommand = unlistedCommand with
+        {
+            Listing = unlistedCommand.Listing with { Visibility = ListingVisibility.Unlisted },
+        };
+        fixture.Store.CreateListing(unlistedCommand);
+        fixture.Store.BindHostPresence(new(
+            unlistedCommand.Listing.HostPresenceHandle,
+            unlistedCommand.Listing.HostPresenceFingerprint,
+            EphemeralStateFixture.PublicEndpoint(40_099),
+            null));
+
+        StoreResult<IReadOnlyList<StoredListing>> result = fixture.Store.BrowseVisibleListings(new(
+            fixture.Scope,
+            visible.Definition.ProtocolVersion,
+            visible.Definition.RegionId));
+
+        Assert.True(result.Succeeded);
+        Assert.Collection(result.Value!, item => Assert.Equal(visible.Definition.ListingId, item.Definition.ListingId));
+    }
+
+    [Fact]
+    public async Task ConcurrentEndpointBindingAcceptsOneCompleteEndpointOnly()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out _);
+        CreateJoinAttemptCommand command = fixture.AttemptCommand(listing);
+        fixture.Store.CreateJoinAttempt(command);
+        BindAttemptEndpointCommand first = new(
+            command.MediationHandle,
+            AttemptPeerRole.Client,
+            command.ClientCapabilityFingerprint,
+            EphemeralStateFixture.PublicEndpoint(40_001),
+            EphemeralStateFixture.LocalEndpoint(40_001));
+        BindAttemptEndpointCommand second = first with
+        {
+            PublicEndpoint = EphemeralStateFixture.OtherPublicEndpoint(50_001),
+            LocalEndpoint = null,
+        };
+        using ManualResetEventSlim start = new(false);
+
+        Task<StoreResult<StoredJoinAttempt>> left = Task.Run(() => { start.Wait(); return fixture.Store.BindAttemptEndpoint(first); });
+        Task<StoreResult<StoredJoinAttempt>> right = Task.Run(() => { start.Wait(); return fixture.Store.BindAttemptEndpoint(second); });
+        start.Set();
+        await Task.WhenAll(left, right);
+        StoreResult<StoredJoinAttempt> leftResult = await left;
+        StoreResult<StoredJoinAttempt> rightResult = await right;
+
+        Assert.Equal(1, new[] { leftResult, rightResult }.Count(static result => result.Succeeded));
+        Assert.Equal(1, new[] { leftResult, rightResult }.Count(static result => result.Code == StoreResultCode.ReplayRejected));
+    }
+
+    [Fact]
+    public void AttemptCapabilitiesAndIntroductionAreOneTime()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out _);
+        CreateJoinAttemptCommand command = fixture.AttemptCommand(listing);
+        fixture.Store.CreateJoinAttempt(command);
+        BindAttemptEndpointCommand host = new(
+            command.MediationHandle,
+            AttemptPeerRole.Host,
+            command.HostCapabilityFingerprint,
+            EphemeralStateFixture.PublicEndpoint(40_010),
+            null);
+        BindAttemptEndpointCommand client = new(
+            command.MediationHandle,
+            AttemptPeerRole.Client,
+            command.ClientCapabilityFingerprint,
+            EphemeralStateFixture.OtherPublicEndpoint(40_020),
+            null);
+
+        Assert.True(fixture.Store.BindAttemptEndpoint(host).Succeeded);
+        Assert.True(fixture.Store.BindAttemptEndpoint(client).Succeeded);
+        Assert.True(fixture.Store.BindAttemptEndpoint(client).IsIdempotentReplay);
+        Assert.True(fixture.Store.ConsumeIntroduction(command.MediationHandle).Succeeded);
+        Assert.Equal(StoreResultCode.ReplayRejected, fixture.Store.ConsumeIntroduction(command.MediationHandle).Code);
+        Assert.Equal(StoreResultCode.ReplayRejected, fixture.Store.BindAttemptEndpoint(client with
+        {
+            PublicEndpoint = EphemeralStateFixture.OtherPublicEndpoint(40_021),
+        }).Code);
+    }
+
+    [Fact]
+    public void ExpiredAttemptCannotBeObservedBoundOrConsumed()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out _);
+        CreateJoinAttemptCommand command = fixture.AttemptCommand(listing);
+        fixture.Store.CreateJoinAttempt(command);
+
+        fixture.Clock.Advance(TimeSpan.FromSeconds(30));
+
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.BindAttemptEndpoint(new(
+            command.MediationHandle,
+            AttemptPeerRole.Client,
+            command.ClientCapabilityFingerprint,
+            EphemeralStateFixture.PublicEndpoint(40_050),
+            null)).Code);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.ConsumeIntroduction(command.MediationHandle).Code);
+    }
+
+    [Fact]
+    public void GenericReplayConsumptionIsBoundedAndExpires()
+    {
+        EphemeralStoreOptions options = new() { MaxReplayEntries = 1 };
+        EphemeralStateFixture fixture = new(options);
+
+        Assert.True(fixture.Store.ConsumeReplay(new("ticket", "one")).Succeeded);
+        Assert.Equal(StoreResultCode.ReplayRejected, fixture.Store.ConsumeReplay(new("ticket", "one")).Code);
+        Assert.Equal(StoreResultCode.CapacityExceeded, fixture.Store.ConsumeReplay(new("ticket", "two")).Code);
+        fixture.Clock.Advance(options.ReplayLifetime);
+        Assert.True(fixture.Store.ConsumeReplay(new("ticket", "two")).Succeeded);
+    }
+
+    [Fact]
+    public void PresenceAttemptAndRevocationPoolsShedWithoutPartialMutation()
+    {
+        EphemeralStoreOptions options = new()
+        {
+            MaxPresenceBindings = 1,
+            MaxJoinAttempts = 1,
+            MaxRevocations = 1,
+        };
+        EphemeralStateFixture fixture = new(options);
+        StoredListing first = fixture.CreateVisibleListing(out CreateListingCommand firstCommand);
+        CreateListingCommand secondCommand = fixture.ListingCommand(owner: "publisher-2");
+        fixture.Store.CreateListing(secondCommand);
+
+        Assert.Equal(StoreResultCode.CapacityExceeded, fixture.Store.BindHostPresence(new(
+            secondCommand.Listing.HostPresenceHandle,
+            secondCommand.Listing.HostPresenceFingerprint,
+            EphemeralStateFixture.OtherPublicEndpoint(42_000),
+            null)).Code);
+        Assert.True(fixture.Store.CreateJoinAttempt(fixture.AttemptCommand(first)).Succeeded);
+        Assert.Equal(StoreResultCode.CapacityExceeded, fixture.Store.CreateJoinAttempt(fixture.AttemptCommand(first, "client-2")).Code);
+        Assert.True(fixture.Store.RevokePrincipal("unrelated", TimeSpan.FromMinutes(1)).Succeeded);
+        Assert.Equal(StoreResultCode.CapacityExceeded, fixture.Store.RevokePrincipal(firstCommand.Listing.OwnerSubject, TimeSpan.FromMinutes(1)).Code);
+        Assert.True(fixture.Store.GetListing(first.Definition.ListingId, true).Succeeded);
+        Assert.True(fixture.Store.GetListing(secondCommand.Listing.ListingId, false).Succeeded);
+    }
+
+    [Fact]
+    public void ExhaustionShedsNewListingWithoutMutatingExistingState()
+    {
+        EphemeralStoreOptions options = new() { MaxListings = 1 };
+        EphemeralStateFixture fixture = new(options);
+        CreateListingCommand first = fixture.ListingCommand();
+        CreateListingCommand second = fixture.ListingCommand();
+
+        Assert.True(fixture.Store.CreateListing(first).Succeeded);
+        Assert.Equal(StoreResultCode.CapacityExceeded, fixture.Store.CreateListing(second).Code);
+        Assert.True(fixture.Store.GetListing(first.Listing.ListingId, false).Succeeded);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(second.Listing.ListingId, false).Code);
+    }
+
+    [Fact]
+    public void IdempotencyPoolExhaustionDoesNotCreateUntrackedResource()
+    {
+        EphemeralStoreOptions options = new() { MaxListings = 2, MaxIdempotencyEntries = 1 };
+        EphemeralStateFixture fixture = new(options);
+        CreateListingCommand first = fixture.ListingCommand();
+        CreateListingCommand second = fixture.ListingCommand();
+
+        Assert.True(fixture.Store.CreateListing(first).Succeeded);
+        Assert.Equal(StoreResultCode.CapacityExceeded, fixture.Store.CreateListing(second).Code);
+        Assert.True(fixture.Store.GetListing(first.Listing.ListingId, false).Succeeded);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(second.Listing.ListingId, false).Code);
+    }
+
+    [Fact]
+    public void PolicyQuotasAreCheckedInsideAtomicCreation()
+    {
+        EphemeralStateFixture fixture = new();
+        CreateListingCommand first = fixture.ListingCommand(owner: "publisher-quota") with { OwnerListingLimit = 1 };
+        CreateListingCommand second = fixture.ListingCommand(owner: "publisher-quota") with { OwnerListingLimit = 1 };
+        Assert.True(fixture.Store.CreateListing(first).Succeeded);
+        Assert.Equal(StoreResultCode.CapacityExceeded, fixture.Store.CreateListing(second).Code);
+
+        fixture.Store.BindHostPresence(new(
+            first.Listing.HostPresenceHandle,
+            first.Listing.HostPresenceFingerprint,
+            EphemeralStateFixture.PublicEndpoint(42_100),
+            null));
+        StoredListing listing = fixture.Store.GetListing(first.Listing.ListingId, true).Value!;
+        CreateJoinAttemptCommand attempt = fixture.AttemptCommand(listing) with { ScopeAttemptLimit = 1 };
+        Assert.True(fixture.Store.CreateJoinAttempt(attempt).Succeeded);
+        Assert.Equal(StoreResultCode.CapacityExceeded, fixture.Store.CreateJoinAttempt(
+            fixture.AttemptCommand(listing, "client-quota-2") with { ScopeAttemptLimit = 1 }).Code);
+    }
+
+    [Fact]
+    public void InvalidDefaultSecurityValuesCannotEnterStore()
+    {
+        EphemeralStateFixture fixture = new();
+        CreateListingCommand command = fixture.ListingCommand();
+
+        Assert.Throws<ArgumentException>(() => fixture.Store.CreateListing(command with
+        {
+            Listing = command.Listing with { LeaseFingerprint = default },
+        }));
+    }
+
+    [Fact]
+    public void RevocationRemovesEveryPathAndBlocksNewWorkAtomically()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out CreateListingCommand command);
+        CreateJoinAttemptCommand attempt = fixture.AttemptCommand(listing, command.Listing.OwnerSubject);
+        fixture.Store.CreateJoinAttempt(attempt);
+
+        StoreResult<int> revoked = fixture.Store.RevokePrincipal(command.Listing.OwnerSubject, TimeSpan.FromMinutes(1));
+
+        Assert.True(revoked.Succeeded);
+        Assert.Equal(2, revoked.Value);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(listing.Definition.ListingId, false).Code);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.BindAttemptEndpoint(new(
+            attempt.MediationHandle,
+            AttemptPeerRole.Client,
+            attempt.ClientCapabilityFingerprint,
+            EphemeralStateFixture.PublicEndpoint(40_030),
+            null)).Code);
+        Assert.Equal(StoreResultCode.Revoked, fixture.Store.CreateListing(fixture.ListingCommand(owner: command.Listing.OwnerSubject)).Code);
+    }
+
+    [Fact]
+    public void RestartHasNewGenerationAndNoEphemeralState()
+    {
+        EphemeralStateFixture before = new();
+        StoredListing listing = before.CreateVisibleListing(out _);
+        EphemeralStateFixture after = new();
+
+        Assert.NotEqual(before.Store.InstanceId, after.Store.InstanceId);
+        Assert.Equal(StoreResultCode.NotFound, after.Store.GetListing(listing.Definition.ListingId, false).Code);
+    }
+
+    [Fact]
+    public void DrainRejectsNewWorkAllowsInflightCompletionThenClearsState()
+    {
+        EphemeralStoreOptions options = new() { GracefulDrainLifetime = TimeSpan.FromSeconds(5) };
+        EphemeralStateFixture fixture = new(options);
+        StoredListing listing = fixture.CreateVisibleListing(out _);
+        CreateJoinAttemptCommand attempt = fixture.AttemptCommand(listing);
+        fixture.Store.CreateJoinAttempt(attempt);
+        fixture.Store.BeginDrain();
+
+        Assert.Equal(StoreResultCode.Draining, fixture.Store.CreateListing(fixture.ListingCommand()).Code);
+        Assert.Equal(StoreResultCode.Draining, fixture.Store.CreateJoinAttempt(fixture.AttemptCommand(listing)).Code);
+        Assert.True(fixture.Store.BindAttemptEndpoint(new(
+            attempt.MediationHandle,
+            AttemptPeerRole.Client,
+            attempt.ClientCapabilityFingerprint,
+            EphemeralStateFixture.PublicEndpoint(41_000),
+            null)).Succeeded);
+
+        fixture.Clock.Advance(options.GracefulDrainLifetime);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(listing.Definition.ListingId, false).Code);
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.BindAttemptEndpoint(new(
+            attempt.MediationHandle,
+            AttemptPeerRole.Host,
+            attempt.HostCapabilityFingerprint,
+            EphemeralStateFixture.PublicEndpoint(41_001),
+            null)).Code);
+    }
+
+    [Fact]
+    public void PrecancelledOperationHasNoPartialEffect()
+    {
+        EphemeralStateFixture fixture = new();
+        CreateListingCommand command = fixture.ListingCommand();
+        using CancellationTokenSource cancellation = new();
+        cancellation.Cancel();
+
+        Assert.Throws<OperationCanceledException>(() => fixture.Store.CreateListing(command, cancellation.Token));
+        Assert.Equal(StoreResultCode.NotFound, fixture.Store.GetListing(command.Listing.ListingId, false).Code);
+    }
+
+    [Fact]
+    public void UnavailableStoreFailsNewAuthorizationClosedAndErasesActiveState()
+    {
+        EphemeralStateFixture fixture = new();
+        StoredListing listing = fixture.CreateVisibleListing(out _);
+        fixture.Store.MarkUnavailable();
+
+        Assert.Equal(StoreResultCode.ServiceUnavailable, fixture.Store.GetListing(listing.Definition.ListingId, false).Code);
+        Assert.Equal(StoreResultCode.ServiceUnavailable, fixture.Store.CreateJoinAttempt(fixture.AttemptCommand(listing)).Code);
+    }
+}

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/contracts-public-api.txt

@@ -18,6 +18,7 @@ TYPE FinalFactory.Rendezvous.Contracts.BrowseSessionsRequest
   PROP System.Int32 ContractVersion {get;set;}
   PROP System.String Cursor {get;set;}
   PROP FinalFactory.Rendezvous.Contracts.EnvironmentId EnvironmentId {get;set;}
+  PROP System.Boolean ExcludeFull {get;set;}
   PROP FinalFactory.Rendezvous.Contracts.GameId GameId {get;set;}
   PROP System.Int32 PageSize {get;set;}
   PROP System.UInt32 ProtocolVersion {get;set;}
@@ -217,7 +218,9 @@ TYPE FinalFactory.Rendezvous.Contracts.RegisterSessionResponse
   PROP System.DateTimeOffset ExpiresAt {get;set;}
   PROP System.String HostPresenceCapability {get;set;}
   PROP FinalFactory.Rendezvous.Contracts.MediationHandle HostPresenceHandle {get;set;}
+  PROP System.Int32 HostPresenceRefreshAfterSeconds {get;set;}
   PROP FinalFactory.Rendezvous.Contracts.LeaseId LeaseId {get;set;}
+  PROP System.Int32 LeaseRenewAfterSeconds {get;set;}
   PROP System.String LeaseToken {get;set;}
   PROP FinalFactory.Rendezvous.Contracts.SessionListingId ListingId {get;set;}
 TYPE FinalFactory.Rendezvous.Contracts.RendezvousErrorCode
@@ -250,6 +253,7 @@ TYPE FinalFactory.Rendezvous.Contracts.RenewLeaseResponse
   CTOR ()
   PROP System.Int32 ContractVersion {get;set;}
   PROP System.DateTimeOffset ExpiresAt {get;set;}
+  PROP System.Int32 RenewAfterSeconds {get;set;}
 TYPE FinalFactory.Rendezvous.Contracts.ReportConnectionOutcomeRequest
   CTOR ()
   PROP System.Int32 ContractVersion {get;set;}

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/register-session-response.json

@@ -0,0 +1 @@
+{"contractVersion":1,"listingId":"00112233-4455-6677-8899-aabbccddeeff","leaseId":"11112233-4455-6677-8899-aabbccddeeff","leaseToken":"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA","hostPresenceHandle":"22222233-4455-6677-8899-aabbccddeeff","hostPresenceCapability":"BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB","expiresAt":"2026-07-16T12:01:00+00:00","leaseRenewAfterSeconds":30,"hostPresenceRefreshAfterSeconds":10}