feat: freeze v1 transport contracts (#4)

Closes #4

.editorconfig

@@ -0,0 +1,26 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{cs,csproj,props,targets}]
+indent_style = space
+indent_size = 4
+
+[*.cs]
+dotnet_sort_system_directives_first = true
+csharp_new_line_before_open_brace = all
+csharp_style_namespace_declarations = file_scoped:warning
+csharp_style_var_for_built_in_types = false:suggestion
+csharp_style_var_when_type_is_apparent = true:suggestion
+csharp_style_var_elsewhere = false:suggestion
+
+[*.{json,yml,yaml}]
+indent_style = space
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false

.gitea/workflows/ci.yml

@@ -0,0 +1,37 @@
+name: quality-gate
+
+on:
+  push:
+    branches:
+      - main
+      - codex/**
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  quality:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Install .NET SDK
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: 10.0.301
+
+      - name: Restore locked dependencies
+        run: dotnet restore Rendezvous.slnx --locked-mode
+
+      - name: Verify formatting and analyzers
+        run: dotnet format Rendezvous.slnx --verify-no-changes --no-restore
+
+      - name: Build
+        run: dotnet build Rendezvous.slnx --configuration Release --no-restore
+
+      - name: Verify generated API contract
+        run: git diff --exit-code -- docs/api
+
+      - name: Test
+        run: dotnet test Rendezvous.slnx --configuration Release --no-build

.gitignore

@@ -0,0 +1,8 @@
+**/bin/
+**/obj/
+TestResults/
+.idea/
+.vs/
+*.suo
+*.user
+*.userosscache

Directory.Build.props

@@ -0,0 +1,15 @@
+<Project>
+  <PropertyGroup>
+    <AnalysisLevel>latest-recommended</AnalysisLevel>
+    <ContinuousIntegrationBuild Condition="'$(CI)' == 'true'">true</ContinuousIntegrationBuild>
+    <Deterministic>true</Deterministic>
+    <EnableNETAnalyzers>true</EnableNETAnalyzers>
+    <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <LangVersion>latest</LangVersion>
+    <Nullable>enable</Nullable>
+    <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
+    <RestoreLockedMode Condition="'$(CI)' == 'true'">true</RestoreLockedMode>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+</Project>

Directory.Packages.props

@@ -0,0 +1,16 @@
+<Project>
+  <PropertyGroup>
+    <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
+    <CentralPackageTransitivePinningEnabled>true</CentralPackageTransitivePinningEnabled>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageVersion Include="LiteNetLib" Version="2.1.4" />
+    <PackageVersion Include="Microsoft.AspNetCore.OpenApi" Version="10.0.9" />
+    <PackageVersion Include="Microsoft.Extensions.ApiDescription.Server" Version="10.0.9" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
+    <PackageVersion Include="Microsoft.OpenApi" Version="2.7.5" />
+    <PackageVersion Include="System.Text.Json" Version="10.0.10" />
+    <PackageVersion Include="xunit" Version="2.9.3" />
+    <PackageVersion Include="xunit.runner.visualstudio" Version="3.1.5" />
+  </ItemGroup>
+</Project>

NuGet.config

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+  </packageSources>
+  <packageSourceMapping>
+    <packageSource key="nuget.org">
+      <package pattern="*" />
+    </packageSource>
+  </packageSourceMapping>
+</configuration>

README.md

@@ -79,3 +79,23 @@ Rendezvous is currently in its initial design and bootstrap stage. The first imp
 
 The ratified v1 boundaries, trust decisions, privacy rules, safety budgets, and
 threat model are indexed in [the architecture documentation](docs/architecture/README.md).
+The frozen v1 wire surface is documented in the
+[HTTP, UDP, and generated OpenAPI contracts](docs/contracts/README.md).
+
+## Development
+
+The repository pins .NET SDK 10.0.301. From a clean clone, run the same gates as
+CI from the repository root:
+
+```bash
+dotnet restore Rendezvous.slnx --locked-mode
+dotnet format Rendezvous.slnx --verify-no-changes --no-restore
+dotnet build Rendezvous.slnx --configuration Release --no-restore
+dotnet test Rendezvous.slnx --configuration Release --no-build
+```
+
+Run the bootstrap server with
+`dotnet run --project src/FinalFactory.Rendezvous.Server`. It serves HTTP health endpoints and binds
+the configured UDP mediator port; both stop through normal host cancellation.
+The project dependency rules and supported runtime choices are documented in
+[project and dependency boundaries](docs/architecture/project-boundaries.md).

Rendezvous.slnx

@@ -0,0 +1,11 @@
+<Solution>
+  <Folder Name="/src/">
+    <Project Path="src/FinalFactory.Rendezvous.Client/FinalFactory.Rendezvous.Client.csproj" />
+    <Project Path="src/FinalFactory.Rendezvous.Contracts/FinalFactory.Rendezvous.Contracts.csproj" />
+    <Project Path="src/FinalFactory.Rendezvous.Server/FinalFactory.Rendezvous.Server.csproj" />
+    <Project Path="src/FinalFactory.Rendezvous.TestClient/FinalFactory.Rendezvous.TestClient.csproj" />
+  </Folder>
+  <Folder Name="/tests/">
+    <Project Path="tests/FinalFactory.Rendezvous.Tests/FinalFactory.Rendezvous.Tests.csproj" />
+  </Folder>
+</Solution>

docs/architecture/README.md

@@ -8,6 +8,7 @@ decision requires a superseding ADR and corresponding contract/test updates.
 - [ADR 0003: state, privacy, availability, and safety budgets](0003-state-privacy-availability-and-budgets.md)
 - [Threat model](../security/threat-model.md)
 - [Security promise and test matrix](../security/control-matrix.md)
+- [Versioned HTTP and UDP contracts](../contracts/README.md)
 
 These decisions intentionally leave gameplay authority, player identity,
 simulation, persistence, social features, skill matchmaking, and gameplay

docs/architecture/project-boundaries.md

@@ -0,0 +1,51 @@
+# Project and dependency boundaries
+
+Tracking: #3
+
+```text
+FinalFactory.Rendezvous.Contracts  <-  FinalFactory.Rendezvous.Client
+                ^                               ^
+                |                               |
+FinalFactory.Rendezvous.Server     FinalFactory.Rendezvous.TestClient
+```
+
+- `Contracts` targets `netstandard2.1` and contains only versioned,
+  transport-neutral IDs and wire contracts. It cannot reference Server,
+  LiteNetLib, or Godot. Its only package is `System.Text.Json`, used for the
+  canonical cross-runtime JSON contract.
+- `Client` targets `netstandard2.1`, references Contracts and the pinned
+  LiteNetLib package, and contains no Godot or Server dependency.
+- `Server` targets .NET 10 LTS, references Contracts, LiteNetLib, and the
+  first-party ASP.NET Core OpenAPI generator, and owns HTTP hosting, UDP
+  mediation, application policy, and ephemeral state.
+- `TestClient` targets .NET 8, references only the public Client/Contracts seams
+  and LiteNetLib, and must never reach into Server internals.
+- `Tests` target .NET 10 and may reference every project solely to verify public
+  behavior and architecture boundaries.
+
+The dependency-boundary tests inspect compiled assembly references. A forbidden
+engine, transport, or server dependency therefore fails the normal test gate.
+
+## Supported toolchain
+
+- Build SDK: .NET SDK 10.0.301, pinned by `global.json`.
+- Server runtime: .NET 10 LTS.
+- Client/contracts compatibility target: .NET Standard 2.1, consumable by the
+  .NET 8-or-later runtime used by current Godot 4 C# projects.
+- TestClient runtime: .NET 8.
+- LiteNetLib: 2.1.4, pinned centrally and restored from the lock files.
+- Microsoft.OpenApi: patched 2.7.5 line, centrally pinned because the version
+  originally pulled by the .NET 10 generator is affected by CVE-2026-49451.
+
+The repository uses central package versions, per-project lock files,
+deterministic compilation, nullable reference types, warnings as errors, current
+.NET analyzers, and formatting verification. CI restores in locked mode so a
+package graph change must be deliberate and committed.
+
+Primary compatibility references:
+
+- [.NET support policy](https://dotnet.microsoft.com/en-us/platform/support/policy)
+- [Godot stable C# prerequisites](https://docs.godotengine.org/en/stable/tutorials/scripting/c_sharp/c_sharp_basics.html)
+- [LiteNetLib 2.1.4 on NuGet](https://www.nuget.org/packages/LiteNetLib/2.1.4)
+- [ASP.NET Core OpenAPI generation](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/openapi/overview?view=aspnetcore-10.0)
+- [Microsoft.OpenApi security advisory](https://github.com/advisories/GHSA-v5pm-xwqc-g5wc)

docs/contracts/README.md

@@ -0,0 +1,18 @@
+# Versioned contracts
+
+Tracking: #4
+
+The v1 contract is defined by three artifacts that are reviewed and versioned
+together:
+
+- [HTTP v1 semantics](http-v1.md)
+- [UDP v1 wire format](udp-v1.md)
+- [Generated OpenAPI 3.1 document](../api/rendezvous-v1.json)
+
+The public .NET types live in `FinalFactory.Rendezvous.Contracts`, target
+`netstandard2.1`, and contain no Server, Godot, or LiteNetLib dependency. Golden
+vectors and a public-API snapshot make accidental wire or source compatibility
+changes fail the normal test gate.
+
+Any incompatible change requires a new contract version. Additive JSON fields
+may be introduced within v1 because v1 readers ignore unknown object members.

docs/contracts/http-v1.md

@@ -0,0 +1,105 @@
+# HTTP contract v1
+
+Tracking: #4
+
+All production endpoints require HTTPS. JSON uses UTF-8, camel-case property
+names, compact output, string-valued camel-case enums, and ISO 8601 timestamps.
+Every request that contains a body carries `contractVersion: 1`; browse carries
+the same value as a required query parameter.
+
+## Compatibility and parsing
+
+- Contract version matching is exact. Any value other than `1` fails with
+  `unsupportedContractVersion`; it is never guessed or downgraded.
+- Gameplay protocol matching is exact. `buildVersion` is display and diagnostic
+  text only and never decides compatibility.
+- Unknown JSON object properties are ignored so additive v1 responses remain
+  readable. Unknown enum names, numeric enum values, comments, trailing commas,
+  invalid identifier strings, and excessive nesting are rejected.
+- Game, environment, and region IDs are lowercase URL-safe slugs. Listing,
+  lease, join-attempt, and mediation IDs are non-empty UUIDs serialized as JSON
+  strings.
+- Clients must honor request cancellation. A disconnected or cancelled request
+  does not promise a response body; the server should stop work where safe.
+
+## Endpoints
+
+| Method | Path | Purpose |
+| --- | --- | --- |
+| `POST` | `/v1/sessions` | Register a session and create its renewable lease. |
+| `POST` | `/v1/sessions/{listingId}/renew` | Renew the listing lease. |
+| `PUT` | `/v1/sessions/{listingId}` | Replace mutable browser fields and capacity. |
+| `DELETE` | `/v1/sessions/{listingId}` | Withdraw a listing. |
+| `GET` | `/v1/sessions` | Browse compatible public sessions. |
+| `GET` | `/v1/sessions/{listingId}` | Resolve a public or explicitly shared unlisted listing. |
+| `POST` | `/v1/join-attempts` | Authorize and create a short-lived join attempt. |
+| `GET` | `/v1/sessions/{listingId}/join-attempts` | Let an authenticated host poll pending attempts. |
+| `POST` | `/v1/join-attempts/{attemptId}/outcome` | Report a bounded connection outcome. |
+| `GET` | `/health/live` | Report that the HTTP process is alive. |
+| `GET` | `/health/ready` | Report whether the UDP mediator is bound and ready. |
+
+The generated [OpenAPI document](../api/rendezvous-v1.json) is the normative
+shape reference for parameters, bodies, and responses. Contract-only endpoints
+return `501` until their behavior is implemented by the subsequent directory,
+lease, and join-orchestration issues.
+
+Host polling sends its reusable lease credential in
+`X-Rendezvous-Lease-Token`; it must never be placed in a URL. Lease credentials
+for mutation operations are carried in their request bodies. Public browser
+responses contain no IP endpoints, lease tokens, punch capabilities, connection
+tickets, player identifiers, or gameplay state.
+
+## Idempotency, cursors, and retries
+
+Registration and join creation require a caller-generated visible-ASCII
+`idempotencyKey`. A repeat in the same authorization scope returns the original
+result while the key is retained; reusing a key with a different payload fails
+with `conflict`. Keys are opaque and must not contain credentials.
+
+Cursors are opaque, endpoint-specific, short-lived values. A client may echo a
+cursor only to the endpoint and filters that produced it. Invalid or expired
+cursors fail with `invalidRequest`; clients restart browsing from the first page.
+Renew, update, delete, and outcome reporting are safe to retry with the same
+lease/attempt identity after a transport-level failure.
+
+## Limits
+
+Limits are measured after UTF-8 encoding where stated. Servers reject the
+entire request rather than truncate values.
+
+| Item | v1 limit |
+| --- | ---: |
+| HTTP request body | 16 KiB |
+| Browser response body | 256 KiB |
+| Browser page | 100 listings |
+| Metadata document | 4 KiB, 32 keys |
+| Metadata key / value | 64 / 256 UTF-8 bytes |
+| Game / environment / region ID | 64 / 32 / 32 characters |
+| Display name / build version | 128 / 64 UTF-8 bytes |
+| Idempotency key | 64 visible ASCII characters |
+| Cursor | 512 visible ASCII characters |
+| Diagnostic code | 64 visible ASCII characters |
+| Error message | 256 UTF-8 bytes |
+| Reusable HTTP credential | 1,024 characters |
+| Session capacity | 1–10,000 players |
+
+## Error mapping
+
+Errors use `ApiError` with a stable `code`, bounded safe `message`, optional
+`correlationId`, and optional `retryAfterSeconds`. Messages are diagnostic and
+must not be parsed. Secrets and raw credentials are never echoed.
+
+| HTTP | Codes |
+| ---: | --- |
+| 400 | `invalidRequest`, `unsupportedContractVersion` |
+| 401 | `authenticationRequired` |
+| 403 | `forbidden` |
+| 404 | `notFound` |
+| 409 | `conflict`, `incompatibleProtocol`, `replayRejected`, `capacityExceeded` |
+| 410 | `expired`, `staleHost` |
+| 429 | `rateLimited` (with retry guidance when known) |
+| 503 | `serviceUnavailable` (with retry guidance when known) |
+| 500 | `internalError` |
+
+Malformed input must receive the same bounded error family regardless of which
+parser or validation stage rejected it.

docs/contracts/udp-v1.md

@@ -0,0 +1,53 @@
+# UDP presence contract v1
+
+Tracking: #4
+
+The UDP mediator accepts a single bounded presence envelope from a host or
+client. It associates the authenticated mediation handle with the packet's
+observed public source endpoint and the sender's reported local endpoint. It
+does not carry gameplay packets.
+
+All multi-byte integers use network byte order. UUID bytes use the canonical
+RFC 4122 textual order (the byte pairs from the 32 hexadecimal digits), not the
+mixed-endian layout returned by `Guid.ToByteArray()`.
+
+## Datagram layout
+
+| Offset | Size | Field |
+| ---: | ---: | --- |
+| 0 | 2 | Magic bytes `52 56` (`RV`). |
+| 2 | 1 | Contract version, exactly `01`. |
+| 3 | 1 | Message type: host presence `01`, client presence `02`. |
+| 4 | 1 | Flags, exactly `00` in v1. |
+| 5 | 16 | Non-empty mediation-handle UUID. |
+| 21 | 1 | Address family: IPv4 `04`, IPv6 `06`. |
+| 22 | 1 | Address length: `04` for IPv4, `10` for IPv6. |
+| 23 | 4 or 16 | Raw local IP address bytes. |
+| next | 2 | Local UDP port, 1–65535. |
+| next | 1 | Capability length, 1–192. |
+| next | variable | ASCII base64url capability, without padding. |
+
+No trailing bytes are permitted. The whole datagram is limited to 1,200 bytes,
+well below common Internet path MTUs. The v1 capability limit is 192 characters,
+which also keeps any value passed through LiteNetLib's 256-character NAT token
+surface safely below that library boundary.
+
+## Validation and failure behavior
+
+Decoders return one stable failure category: oversized, truncated, invalid
+magic, unsupported version, unknown message type, non-zero flags, invalid
+handle, invalid address family, invalid address, invalid port, invalid
+capability, or trailing data. Unknown versions and message types are rejected;
+they are never interpreted as v1.
+
+The address-family byte, encoded address length, and parsed address must agree.
+The service derives the public endpoint from the UDP packet source and never
+trusts a client-supplied public address. Reported local endpoints are candidates
+only and grant no authority.
+
+Capabilities are short-lived, single-purpose, scoped to one mediation handle,
+and compared without exposing them in logs. A valid-looking packet does not
+prove authorization until the capability is checked. Invalid packets receive
+no UDP response, preventing the mediator from becoming an amplification oracle.
+Replay, expiry, pairing, and rate-limit policy are defined by later mediator
+issues; the v1 envelope deliberately leaves no unbounded or reflected payload.

global.json

@@ -0,0 +1,7 @@
+{
+  "sdk": {
+    "version": "10.0.301",
+    "rollForward": "disable",
+    "allowPrerelease": false
+  }
+}

src/FinalFactory.Rendezvous.Client/FinalFactory.Rendezvous.Client.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>netstandard2.1</TargetFramework>
+    <AssemblyName>FinalFactory.Rendezvous.Client</AssemblyName>
+    <RootNamespace>FinalFactory.Rendezvous.Client</RootNamespace>
+    <IsPackable>true</IsPackable>
+    <PackageId>FinalFactory.Rendezvous.Client</PackageId>
+    <Description>Godot-independent client SDK for Final Factory Rendezvous.</Description>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="../FinalFactory.Rendezvous.Contracts/FinalFactory.Rendezvous.Contracts.csproj" />
+    <PackageReference Include="LiteNetLib" />
+  </ItemGroup>
+</Project>

src/FinalFactory.Rendezvous.Client/packages.lock.json

@@ -0,0 +1,79 @@
+{
+  "version": 2,
+  "dependencies": {
+    ".NETStandard,Version=v2.1": {
+      "LiteNetLib": {
+        "type": "Direct",
+        "requested": "[2.1.4, )",
+        "resolved": "2.1.4",
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+      },
+      "Microsoft.Bcl.AsyncInterfaces": {
+        "type": "Transitive",
+        "resolved": "10.0.10",
+        "contentHash": "TFI6OKYE1XZz4SGuTSH70c6SBdPpFktXsoa1gCxTr3mKrhmXirnvaS0tKz+J3ZWICEAmMpEGn59nO4ICtUpQXA=="
+      },
+      "System.Buffers": {
+        "type": "Transitive",
+        "resolved": "4.6.1",
+        "contentHash": "N8GXpmiLMtljq7gwvyS+1QvKT/W2J8sNAvx+HVg4NGmsG/H+2k/y9QI23auLJRterrzCiDH+IWAw4V/GPwsMlw=="
+      },
+      "System.IO.Pipelines": {
+        "type": "Transitive",
+        "resolved": "10.0.10",
+        "contentHash": "7WX0W96y3dpQdYG4sEGdh38g3/0lOD4/dKbn2rRVOVzKhzoZUn2gKNIKaFeKWs8RCbpFfmmEWsRhSy95hMpvqA==",
+        "dependencies": {
+          "System.Buffers": "4.6.1",
+          "System.Memory": "4.6.3",
+          "System.Threading.Tasks.Extensions": "4.6.3"
+        }
+      },
+      "System.Memory": {
+        "type": "Transitive",
+        "resolved": "4.6.3",
+        "contentHash": "qdcDOgnFZY40+Q9876JUHnlHu7bosOHX8XISRoH94fwk6hgaeQGSgfZd8srWRZNt5bV9ZW2TljcegDNxsf+96A=="
+      },
+      "System.Runtime.CompilerServices.Unsafe": {
+        "type": "Transitive",
+        "resolved": "6.1.2",
+        "contentHash": "2hBr6zdbIBTDE3EhK7NSVNdX58uTK6iHW/P/Axmm9sl1xoGSLqDvMtpecn226TNwHByFokYwJmt/aQQNlO5CRw=="
+      },
+      "System.Text.Encodings.Web": {
+        "type": "Transitive",
+        "resolved": "10.0.10",
+        "contentHash": "o16m2YpDN/pjHsnxf9pTGwkpcuvjW8v1/wGUwJtM1c3QZUKm7ZEO/eYRJg7iIx6GxS2Zv9lAMHpiQwHDdgqauA==",
+        "dependencies": {
+          "System.Buffers": "4.6.1",
+          "System.Memory": "4.6.3",
+          "System.Runtime.CompilerServices.Unsafe": "6.1.2"
+        }
+      },
+      "System.Threading.Tasks.Extensions": {
+        "type": "Transitive",
+        "resolved": "4.6.3",
+        "contentHash": "7sCiwilJLYbTZELaKnc7RecBBXWXA+xMLQWZKWawBxYjp6DBlSE3v9/UcvKBvr1vv2tTOhipiogM8rRmxlhrVA=="
+      },
+      "finalfactory.rendezvous.contracts": {
+        "type": "Project",
+        "dependencies": {
+          "System.Text.Json": "[10.0.10, )"
+        }
+      },
+      "System.Text.Json": {
+        "type": "CentralTransitive",
+        "requested": "[10.0.10, )",
+        "resolved": "10.0.10",
+        "contentHash": "bmsO6UdYtBdtn32zYXfsh7KlyTIzV/3V9hdT9RIb4pXKgYOsNxXR+VbWigNwBtNFVGYGm6Hwmqw5a+/IWFd36Q==",
+        "dependencies": {
+          "Microsoft.Bcl.AsyncInterfaces": "10.0.10",
+          "System.Buffers": "4.6.1",
+          "System.IO.Pipelines": "10.0.10",
+          "System.Memory": "4.6.3",
+          "System.Runtime.CompilerServices.Unsafe": "6.1.2",
+          "System.Text.Encodings.Web": "10.0.10",
+          "System.Threading.Tasks.Extensions": "4.6.3"
+        }
+      }
+    }
+  }
+}

src/FinalFactory.Rendezvous.Contracts/ContractEnums.cs

@@ -0,0 +1,75 @@
+namespace FinalFactory.Rendezvous.Contracts;
+
+public enum RendezvousErrorCode
+{
+    None = 0,
+    InvalidRequest = 1,
+    UnsupportedContractVersion = 2,
+    IncompatibleProtocol = 3,
+    AuthenticationRequired = 4,
+    Forbidden = 5,
+    NotFound = 6,
+    Conflict = 7,
+    RateLimited = 8,
+    StaleHost = 9,
+    Expired = 10,
+    ReplayRejected = 11,
+    CapacityExceeded = 12,
+    ServiceUnavailable = 13,
+    InternalError = 14,
+}
+
+public enum ListingVisibility
+{
+    Public = 1,
+    Unlisted = 2,
+}
+
+public enum PublisherTrustMode
+{
+    ManagedDedicated = 1,
+    PlayerGrant = 2,
+    AnonymousUnlisted = 3,
+}
+
+public enum AddressFamilyKind
+{
+    Ipv4 = 4,
+    Ipv6 = 6,
+}
+
+public enum ConnectionOutcomeKind
+{
+    Connected = 1,
+    Cancelled = 2,
+    TimedOut = 3,
+    IncompatibleProtocol = 4,
+    StaleHost = 5,
+    ServiceRejected = 6,
+    HostRejected = 7,
+    TransportFailed = 8,
+    FallbackOffered = 9,
+}
+
+public enum UdpPresenceMessageType : byte
+{
+    HostPresence = 1,
+    ClientPresence = 2,
+}
+
+public enum UdpDecodeError
+{
+    None = 0,
+    DatagramTooLarge = 1,
+    Truncated = 2,
+    InvalidMagic = 3,
+    UnsupportedVersion = 4,
+    UnknownMessageType = 5,
+    InvalidFlags = 6,
+    InvalidHandle = 7,
+    InvalidAddressFamily = 8,
+    InvalidAddress = 9,
+    InvalidPort = 10,
+    InvalidCapability = 11,
+    TrailingData = 12,
+}

src/FinalFactory.Rendezvous.Contracts/ContractLimits.cs

@@ -0,0 +1,28 @@
+namespace FinalFactory.Rendezvous.Contracts;
+
+public static class ContractLimits
+{
+    public const int ContractVersion = 1;
+    public const int HttpRequestMaxBytes = 16 * 1024;
+    public const int BrowserResponseMaxBytes = 256 * 1024;
+    public const int UdpDatagramMaxBytes = 1_200;
+    public const int MetadataMaxBytes = 4 * 1024;
+    public const int MetadataMaxKeys = 32;
+    public const int MetadataKeyMaxBytes = 64;
+    public const int MetadataValueMaxBytes = 256;
+    public const int BrowserPageMaxItems = 100;
+    public const int GameIdMaxCharacters = 64;
+    public const int EnvironmentIdMaxCharacters = 32;
+    public const int RegionIdMaxCharacters = 32;
+    public const int DisplayNameMaxBytes = 128;
+    public const int BuildVersionMaxBytes = 64;
+    public const int IdempotencyKeyMaxCharacters = 64;
+    public const int CursorMaxCharacters = 512;
+    public const int DiagnosticCodeMaxCharacters = 64;
+    public const int ErrorMessageMaxBytes = 256;
+    public const int OpaqueHttpCredentialMaxCharacters = 1_024;
+    public const int UdpCapabilityMaxCharacters = 192;
+    public const int ConnectionTicketMaxCharacters = 192;
+    public const int LiteNetLibNatTokenMaxCharacters = 256;
+    public const int SessionCapacityMaxPlayers = 10_000;
+}

src/FinalFactory.Rendezvous.Contracts/ContractModels.cs

@@ -0,0 +1,47 @@
+using System.Text.Json.Serialization;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+public sealed class SessionCapacity
+{
+    [JsonRequired]
+    public int CurrentPlayers { get; set; }
+
+    [JsonRequired]
+    public int MaximumPlayers { get; set; }
+}
+
+public sealed class NetworkEndpoint
+{
+    [JsonRequired]
+    public AddressFamilyKind AddressFamily { get; set; }
+
+    [JsonRequired]
+    public string Address { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public int Port { get; set; }
+}
+
+public sealed class ApiError
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public RendezvousErrorCode Code { get; set; }
+
+    [JsonRequired]
+    public string Message { get; set; } = string.Empty;
+    public string? CorrelationId { get; set; }
+    public int? RetryAfterSeconds { get; set; }
+}
+
+public sealed class HealthResponse
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public string Status { get; set; } = string.Empty;
+}

src/FinalFactory.Rendezvous.Contracts/ContractValidation.cs

@@ -0,0 +1,134 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using System.Text.Json;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+public static class ContractValidation
+{
+    private const string CapabilityAlphabet =
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+    public static RendezvousErrorCode ValidateContractVersion(int contractVersion) =>
+        contractVersion == ContractLimits.ContractVersion
+            ? RendezvousErrorCode.None
+            : RendezvousErrorCode.UnsupportedContractVersion;
+
+    public static bool AreProtocolsCompatible(uint requested, uint offered) => requested == offered;
+
+    public static bool IsHttpRequestSizeValid(int byteCount) =>
+        byteCount is >= 0 and <= ContractLimits.HttpRequestMaxBytes;
+
+    public static bool IsBrowserResponseSizeValid(int byteCount) =>
+        byteCount is >= 0 and <= ContractLimits.BrowserResponseMaxBytes;
+
+    public static bool IsUtf8LengthWithin(string? value, int maximumBytes)
+    {
+        if (maximumBytes < 0)
+        {
+            throw new ArgumentOutOfRangeException(nameof(maximumBytes));
+        }
+
+        return value is not null && Encoding.UTF8.GetByteCount(value) <= maximumBytes;
+    }
+
+    public static bool IsPageSizeValid(int pageSize) =>
+        pageSize is >= 1 and <= ContractLimits.BrowserPageMaxItems;
+
+    public static bool IsIdempotencyKeyValid(string? value) =>
+        IsVisibleAsciiWithin(value, ContractLimits.IdempotencyKeyMaxCharacters);
+
+    public static bool IsCursorValid(string? value) =>
+        value is null || IsVisibleAsciiWithin(value, ContractLimits.CursorMaxCharacters);
+
+    public static bool IsDiagnosticCodeValid(string? value) =>
+        value is null || IsVisibleAsciiWithin(value, ContractLimits.DiagnosticCodeMaxCharacters);
+
+    public static bool IsBuildVersionValid(string? value) =>
+        IsUtf8LengthWithin(value, ContractLimits.BuildVersionMaxBytes);
+
+    public static bool IsDisplayNameValid(string? value) =>
+        IsUtf8LengthWithin(value, ContractLimits.DisplayNameMaxBytes);
+
+    public static bool IsOpaqueHttpCredentialValid(string? value) =>
+        value is not null
+        && value.Length is > 0 and <= ContractLimits.OpaqueHttpCredentialMaxCharacters;
+
+    public static bool IsCapacityValid(SessionCapacity? capacity) =>
+        capacity is not null
+        && capacity.MaximumPlayers is >= 1 and <= ContractLimits.SessionCapacityMaxPlayers
+        && capacity.CurrentPlayers >= 0
+        && capacity.CurrentPlayers <= capacity.MaximumPlayers;
+
+    public static bool IsCapabilityValid(string? capability) =>
+        IsBase64UrlValueValid(capability, ContractLimits.UdpCapabilityMaxCharacters);
+
+    public static bool IsConnectionTicketValid(string? ticket) =>
+        IsBase64UrlValueValid(ticket, ContractLimits.ConnectionTicketMaxCharacters);
+
+    public static bool IsNetworkEndpointValid(NetworkEndpoint? endpoint)
+    {
+        if (endpoint is null
+            || endpoint.Port is < 1 or > ushort.MaxValue
+            || !IPAddress.TryParse(endpoint.Address, out IPAddress? address))
+        {
+            return false;
+        }
+
+        return endpoint.AddressFamily switch
+        {
+            AddressFamilyKind.Ipv4 => address.AddressFamily == AddressFamily.InterNetwork,
+            AddressFamilyKind.Ipv6 => address.AddressFamily == AddressFamily.InterNetworkV6,
+            _ => false,
+        };
+    }
+
+    public static bool IsMetadataValid(IReadOnlyDictionary<string, string>? metadata)
+    {
+        if (metadata is null || metadata.Count > ContractLimits.MetadataMaxKeys)
+        {
+            return false;
+        }
+
+        foreach (KeyValuePair<string, string> item in metadata)
+        {
+            if (string.IsNullOrWhiteSpace(item.Key)
+                || !IsUtf8LengthWithin(item.Key, ContractLimits.MetadataKeyMaxBytes)
+                || !IsUtf8LengthWithin(item.Value, ContractLimits.MetadataValueMaxBytes))
+            {
+                return false;
+            }
+        }
+
+        byte[] encoded = JsonSerializer.SerializeToUtf8Bytes(metadata, ContractJson.Options);
+        return encoded.Length <= ContractLimits.MetadataMaxBytes;
+    }
+
+    internal static bool IsSlug(string? value, int maximumCharacters)
+    {
+        if (string.IsNullOrEmpty(value)
+            || value.Length > maximumCharacters
+            || value[0] is < 'a' or > 'z')
+        {
+            return false;
+        }
+
+        return value.All(static character =>
+            character is >= 'a' and <= 'z'
+            or >= '0' and <= '9'
+            or '-');
+    }
+
+    private static bool IsBase64UrlValueValid(string? value, int maximumCharacters) =>
+        value is not null
+        && value.Length is > 0
+        && value.Length <= maximumCharacters
+        && value.All(static character => CapabilityAlphabet.Contains(character));
+
+    private static bool IsVisibleAsciiWithin(string? value, int maximumCharacters) =>
+        value is not null
+        && value.Length is > 0
+        && value.Length <= maximumCharacters
+        && value.All(static character => character is >= '!' and <= '~');
+}

src/FinalFactory.Rendezvous.Contracts/FinalFactory.Rendezvous.Contracts.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>netstandard2.1</TargetFramework>
+    <AssemblyName>FinalFactory.Rendezvous.Contracts</AssemblyName>
+    <RootNamespace>FinalFactory.Rendezvous.Contracts</RootNamespace>
+    <IsPackable>true</IsPackable>
+    <PackageId>FinalFactory.Rendezvous.Contracts</PackageId>
+    <Description>Versioned transport-neutral contracts for Final Factory Rendezvous.</Description>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="System.Text.Json" />
+  </ItemGroup>
+</Project>

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

@@ -0,0 +1,92 @@
+using System.Text.Json.Serialization;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+public sealed class CreateJoinAttemptRequest
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public string IdempotencyKey { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public GameId GameId { get; set; }
+
+    [JsonRequired]
+    public EnvironmentId EnvironmentId { get; set; }
+
+    [JsonRequired]
+    public SessionListingId ListingId { get; set; }
+
+    [JsonRequired]
+    public uint ProtocolVersion { get; set; }
+}
+
+public sealed class CreateJoinAttemptResponse
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public JoinAttemptId AttemptId { get; set; }
+
+    [JsonRequired]
+    public MediationHandle MediationHandle { get; set; }
+
+    [JsonRequired]
+    public string ClientPunchCapability { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public DateTimeOffset ExpiresAt { get; set; }
+    public NetworkEndpoint? DedicatedFallback { get; set; }
+}
+
+public sealed class HostJoinAttempt
+{
+    [JsonRequired]
+    public JoinAttemptId AttemptId { get; set; }
+
+    [JsonRequired]
+    public MediationHandle MediationHandle { get; set; }
+
+    [JsonRequired]
+    public string HostPunchCapability { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public DateTimeOffset ExpiresAt { get; set; }
+}
+
+public sealed class BrowseHostJoinAttemptsResponse
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public List<HostJoinAttempt> Items { get; set; } = [];
+
+    public string? NextCursor { get; set; }
+}
+
+public sealed class ReportConnectionOutcomeRequest
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public ConnectionOutcomeKind Outcome { get; set; }
+
+    [JsonRequired]
+    public int ElapsedMilliseconds { get; set; }
+
+    public string? DiagnosticCode { get; set; }
+}
+
+public sealed class ReportConnectionOutcomeResponse
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public bool Accepted { get; set; }
+}

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

@@ -0,0 +1,189 @@
+using System.Text.Json.Serialization;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+public sealed class SessionListing
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public SessionListingId ListingId { get; set; }
+
+    [JsonRequired]
+    public GameId GameId { get; set; }
+
+    [JsonRequired]
+    public EnvironmentId EnvironmentId { get; set; }
+
+    [JsonRequired]
+    public RegionId RegionId { get; set; }
+
+    [JsonRequired]
+    public uint ProtocolVersion { get; set; }
+
+    [JsonRequired]
+    public string BuildVersion { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public string DisplayName { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public ListingVisibility Visibility { get; set; }
+
+    [JsonRequired]
+    public PublisherTrustMode PublisherTrustMode { get; set; }
+
+    [JsonRequired]
+    public SessionCapacity Capacity { get; set; } = new();
+
+    [JsonRequired]
+    public Dictionary<string, string> Metadata { get; set; } = new(StringComparer.Ordinal);
+}
+
+public sealed class RegisterSessionRequest
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public string IdempotencyKey { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public GameId GameId { get; set; }
+
+    [JsonRequired]
+    public EnvironmentId EnvironmentId { get; set; }
+
+    [JsonRequired]
+    public RegionId RegionId { get; set; }
+
+    [JsonRequired]
+    public uint ProtocolVersion { get; set; }
+
+    [JsonRequired]
+    public string BuildVersion { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public string DisplayName { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public ListingVisibility Visibility { get; set; }
+
+    [JsonRequired]
+    public SessionCapacity Capacity { get; set; } = new();
+
+    [JsonRequired]
+    public Dictionary<string, string> Metadata { get; set; } = new(StringComparer.Ordinal);
+}
+
+public sealed class RegisterSessionResponse
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public SessionListingId ListingId { get; set; }
+
+    [JsonRequired]
+    public LeaseId LeaseId { get; set; }
+
+    [JsonRequired]
+    public string LeaseToken { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public MediationHandle HostPresenceHandle { get; set; }
+
+    [JsonRequired]
+    public string HostPresenceCapability { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public DateTimeOffset ExpiresAt { get; set; }
+}
+
+public sealed class RenewLeaseRequest
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public string LeaseToken { get; set; } = string.Empty;
+}
+
+public sealed class RenewLeaseResponse
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public DateTimeOffset ExpiresAt { get; set; }
+}
+
+public sealed class UpdateSessionRequest
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public string LeaseToken { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public string BuildVersion { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public string DisplayName { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public SessionCapacity Capacity { get; set; } = new();
+
+    [JsonRequired]
+    public Dictionary<string, string> Metadata { get; set; } = new(StringComparer.Ordinal);
+}
+
+public sealed class DeleteSessionRequest
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public string LeaseToken { get; set; } = string.Empty;
+}
+
+public sealed class BrowseSessionsRequest
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public GameId GameId { get; set; }
+
+    [JsonRequired]
+    public EnvironmentId EnvironmentId { get; set; }
+
+    [JsonRequired]
+    public uint ProtocolVersion { get; set; }
+    public RegionId? RegionId { get; set; }
+    public int PageSize { get; set; } = ContractLimits.BrowserPageMaxItems;
+
+    public string? Cursor { get; set; }
+}
+
+public sealed class BrowseSessionsResponse
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public List<SessionListing> Items { get; set; } = [];
+
+    public string? NextCursor { get; set; }
+}
+
+public sealed class GetSessionResponse
+{
+    [JsonRequired]
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+
+    [JsonRequired]
+    public SessionListing Session { get; set; } = new();
+}

src/FinalFactory.Rendezvous.Contracts/Identifiers/OpaqueIdentifiers.cs

@@ -0,0 +1,112 @@
+using System.Text.Json.Serialization;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+[JsonConverter(typeof(SessionListingIdJsonConverter))]
+public readonly struct SessionListingId : IEquatable<SessionListingId>
+{
+    public SessionListingId(Guid value) => Value = GuidIdentifier.RequireNonEmpty(value, nameof(value));
+    public Guid Value { get; }
+    public static bool TryParse(string? value, out SessionListingId id) =>
+        GuidIdentifier.TryParse(value, static guid => new SessionListingId(guid), out id);
+    public bool Equals(SessionListingId other) => Value.Equals(other.Value);
+    public override bool Equals(object? obj) => obj is SessionListingId other && Equals(other);
+    public override int GetHashCode() => Value.GetHashCode();
+    public override string ToString() => Value.ToString("D");
+    public static bool operator ==(SessionListingId left, SessionListingId right) => left.Equals(right);
+    public static bool operator !=(SessionListingId left, SessionListingId right) => !left.Equals(right);
+}
+
+[JsonConverter(typeof(LeaseIdJsonConverter))]
+public readonly struct LeaseId : IEquatable<LeaseId>
+{
+    public LeaseId(Guid value) => Value = GuidIdentifier.RequireNonEmpty(value, nameof(value));
+    public Guid Value { get; }
+    public static bool TryParse(string? value, out LeaseId id) =>
+        GuidIdentifier.TryParse(value, static guid => new LeaseId(guid), out id);
+    public bool Equals(LeaseId other) => Value.Equals(other.Value);
+    public override bool Equals(object? obj) => obj is LeaseId other && Equals(other);
+    public override int GetHashCode() => Value.GetHashCode();
+    public override string ToString() => Value.ToString("D");
+    public static bool operator ==(LeaseId left, LeaseId right) => left.Equals(right);
+    public static bool operator !=(LeaseId left, LeaseId right) => !left.Equals(right);
+}
+
+[JsonConverter(typeof(JoinAttemptIdJsonConverter))]
+public readonly struct JoinAttemptId : IEquatable<JoinAttemptId>
+{
+    public JoinAttemptId(Guid value) => Value = GuidIdentifier.RequireNonEmpty(value, nameof(value));
+    public Guid Value { get; }
+    public static bool TryParse(string? value, out JoinAttemptId id) =>
+        GuidIdentifier.TryParse(value, static guid => new JoinAttemptId(guid), out id);
+    public bool Equals(JoinAttemptId other) => Value.Equals(other.Value);
+    public override bool Equals(object? obj) => obj is JoinAttemptId other && Equals(other);
+    public override int GetHashCode() => Value.GetHashCode();
+    public override string ToString() => Value.ToString("D");
+    public static bool operator ==(JoinAttemptId left, JoinAttemptId right) => left.Equals(right);
+    public static bool operator !=(JoinAttemptId left, JoinAttemptId right) => !left.Equals(right);
+}
+
+[JsonConverter(typeof(MediationHandleJsonConverter))]
+public readonly struct MediationHandle : IEquatable<MediationHandle>
+{
+    public MediationHandle(Guid value) => Value = GuidIdentifier.RequireNonEmpty(value, nameof(value));
+    public Guid Value { get; }
+    public static bool TryParse(string? value, out MediationHandle id) =>
+        GuidIdentifier.TryParse(value, static guid => new MediationHandle(guid), out id);
+    public bool Equals(MediationHandle other) => Value.Equals(other.Value);
+    public override bool Equals(object? obj) => obj is MediationHandle other && Equals(other);
+    public override int GetHashCode() => Value.GetHashCode();
+    public override string ToString() => Value.ToString("D");
+    public static bool operator ==(MediationHandle left, MediationHandle right) => left.Equals(right);
+    public static bool operator !=(MediationHandle left, MediationHandle right) => !left.Equals(right);
+}
+
+internal static class GuidIdentifier
+{
+    public static Guid RequireNonEmpty(Guid value, string parameterName) =>
+        value != Guid.Empty
+            ? value
+            : throw new ArgumentException("Opaque identifiers cannot be empty.", parameterName);
+
+    public static bool TryParse<TIdentifier>(
+        string? value,
+        Func<Guid, TIdentifier> factory,
+        out TIdentifier identifier)
+    {
+        if (Guid.TryParseExact(value, "D", out Guid guid) && guid != Guid.Empty)
+        {
+            identifier = factory(guid);
+            return true;
+        }
+
+        identifier = default!;
+        return false;
+    }
+}
+
+internal abstract class GuidIdentifierJsonConverter<TIdentifier> :
+    StringIdentifierJsonConverter<TIdentifier>
+{
+    protected sealed override string Format(TIdentifier value) => value?.ToString() ?? string.Empty;
+}
+
+internal sealed class SessionListingIdJsonConverter : GuidIdentifierJsonConverter<SessionListingId>
+{
+    protected override SessionListingId Parse(string value) => new(Guid.ParseExact(value, "D"));
+}
+
+internal sealed class LeaseIdJsonConverter : GuidIdentifierJsonConverter<LeaseId>
+{
+    protected override LeaseId Parse(string value) => new(Guid.ParseExact(value, "D"));
+}
+
+internal sealed class JoinAttemptIdJsonConverter : GuidIdentifierJsonConverter<JoinAttemptId>
+{
+    protected override JoinAttemptId Parse(string value) => new(Guid.ParseExact(value, "D"));
+}
+
+internal sealed class MediationHandleJsonConverter : GuidIdentifierJsonConverter<MediationHandle>
+{
+    protected override MediationHandle Parse(string value) => new(Guid.ParseExact(value, "D"));
+}

src/FinalFactory.Rendezvous.Contracts/Identifiers/ScopeIdentifiers.cs

@@ -0,0 +1,126 @@
+using System.Text.Json.Serialization;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+[JsonConverter(typeof(GameIdJsonConverter))]
+public readonly struct GameId : IEquatable<GameId>
+{
+    public GameId(string value)
+    {
+        if (!ContractValidation.IsSlug(value, ContractLimits.GameIdMaxCharacters))
+        {
+            throw new ArgumentException("Game IDs must be lowercase URL-safe slugs.", nameof(value));
+        }
+
+        Value = value;
+    }
+
+    public string Value { get; }
+
+    public static bool TryParse(string? value, out GameId gameId)
+    {
+        if (ContractValidation.IsSlug(value, ContractLimits.GameIdMaxCharacters))
+        {
+            gameId = new GameId(value!);
+            return true;
+        }
+
+        gameId = default;
+        return false;
+    }
+
+    public bool Equals(GameId other) => string.Equals(Value, other.Value, StringComparison.Ordinal);
+    public override bool Equals(object? obj) => obj is GameId other && Equals(other);
+    public override int GetHashCode() => StringComparer.Ordinal.GetHashCode(Value ?? string.Empty);
+    public override string ToString() => Value ?? string.Empty;
+    public static bool operator ==(GameId left, GameId right) => left.Equals(right);
+    public static bool operator !=(GameId left, GameId right) => !left.Equals(right);
+}
+
+[JsonConverter(typeof(EnvironmentIdJsonConverter))]
+public readonly struct EnvironmentId : IEquatable<EnvironmentId>
+{
+    public EnvironmentId(string value)
+    {
+        if (!ContractValidation.IsSlug(value, ContractLimits.EnvironmentIdMaxCharacters))
+        {
+            throw new ArgumentException("Environment IDs must be lowercase URL-safe slugs.", nameof(value));
+        }
+
+        Value = value;
+    }
+
+    public string Value { get; }
+
+    public static bool TryParse(string? value, out EnvironmentId environmentId)
+    {
+        if (ContractValidation.IsSlug(value, ContractLimits.EnvironmentIdMaxCharacters))
+        {
+            environmentId = new EnvironmentId(value!);
+            return true;
+        }
+
+        environmentId = default;
+        return false;
+    }
+
+    public bool Equals(EnvironmentId other) => string.Equals(Value, other.Value, StringComparison.Ordinal);
+    public override bool Equals(object? obj) => obj is EnvironmentId other && Equals(other);
+    public override int GetHashCode() => StringComparer.Ordinal.GetHashCode(Value ?? string.Empty);
+    public override string ToString() => Value ?? string.Empty;
+    public static bool operator ==(EnvironmentId left, EnvironmentId right) => left.Equals(right);
+    public static bool operator !=(EnvironmentId left, EnvironmentId right) => !left.Equals(right);
+}
+
+[JsonConverter(typeof(RegionIdJsonConverter))]
+public readonly struct RegionId : IEquatable<RegionId>
+{
+    public RegionId(string value)
+    {
+        if (!ContractValidation.IsSlug(value, ContractLimits.RegionIdMaxCharacters))
+        {
+            throw new ArgumentException("Region IDs must be lowercase URL-safe slugs.", nameof(value));
+        }
+
+        Value = value;
+    }
+
+    public string Value { get; }
+
+    public static bool TryParse(string? value, out RegionId regionId)
+    {
+        if (ContractValidation.IsSlug(value, ContractLimits.RegionIdMaxCharacters))
+        {
+            regionId = new RegionId(value!);
+            return true;
+        }
+
+        regionId = default;
+        return false;
+    }
+
+    public bool Equals(RegionId other) => string.Equals(Value, other.Value, StringComparison.Ordinal);
+    public override bool Equals(object? obj) => obj is RegionId other && Equals(other);
+    public override int GetHashCode() => StringComparer.Ordinal.GetHashCode(Value ?? string.Empty);
+    public override string ToString() => Value ?? string.Empty;
+    public static bool operator ==(RegionId left, RegionId right) => left.Equals(right);
+    public static bool operator !=(RegionId left, RegionId right) => !left.Equals(right);
+}
+
+internal sealed class GameIdJsonConverter : StringIdentifierJsonConverter<GameId>
+{
+    protected override GameId Parse(string value) => new(value);
+    protected override string Format(GameId value) => value.Value;
+}
+
+internal sealed class EnvironmentIdJsonConverter : StringIdentifierJsonConverter<EnvironmentId>
+{
+    protected override EnvironmentId Parse(string value) => new(value);
+    protected override string Format(EnvironmentId value) => value.Value;
+}
+
+internal sealed class RegionIdJsonConverter : StringIdentifierJsonConverter<RegionId>
+{
+    protected override RegionId Parse(string value) => new(value);
+    protected override string Format(RegionId value) => value.Value;
+}

src/FinalFactory.Rendezvous.Contracts/Identifiers/StringIdentifierJsonConverter.cs

@@ -0,0 +1,37 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+internal abstract class StringIdentifierJsonConverter<TIdentifier> : JsonConverter<TIdentifier>
+{
+    public sealed override TIdentifier Read(
+        ref Utf8JsonReader reader,
+        Type typeToConvert,
+        JsonSerializerOptions options)
+    {
+        if (reader.TokenType != JsonTokenType.String)
+        {
+            throw new JsonException($"{typeof(TIdentifier).Name} must be a JSON string.");
+        }
+
+        string value = reader.GetString() ?? string.Empty;
+
+        try
+        {
+            return Parse(value);
+        }
+        catch (Exception exception) when (exception is ArgumentException or FormatException)
+        {
+            throw new JsonException($"Invalid {typeof(TIdentifier).Name}.", exception);
+        }
+    }
+
+    public sealed override void Write(
+        Utf8JsonWriter writer,
+        TIdentifier value,
+        JsonSerializerOptions options) => writer.WriteStringValue(Format(value));
+
+    protected abstract TIdentifier Parse(string value);
+    protected abstract string Format(TIdentifier value);
+}

src/FinalFactory.Rendezvous.Contracts/Serialization/ContractJson.cs

@@ -0,0 +1,49 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+public static class ContractJson
+{
+    private static readonly JsonSerializerOptions SharedOptions = CreateReadOnlyOptions();
+
+    public static JsonSerializerOptions Options => SharedOptions;
+
+    public static JsonSerializerOptions CreateOptions()
+    {
+        JsonSerializerOptions options = new(JsonSerializerDefaults.Web);
+        Configure(options);
+        return options;
+    }
+
+    public static void Configure(JsonSerializerOptions options)
+    {
+        if (options is null)
+        {
+            throw new ArgumentNullException(nameof(options));
+        }
+
+        options.AllowTrailingCommas = false;
+        options.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;
+        options.MaxDepth = 8;
+        options.NumberHandling = JsonNumberHandling.Strict;
+        options.PropertyNameCaseInsensitive = false;
+        options.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
+        options.ReadCommentHandling = JsonCommentHandling.Disallow;
+        options.UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip;
+        options.WriteIndented = false;
+
+        if (!options.Converters.OfType<JsonStringEnumConverter>().Any())
+        {
+            options.Converters.Add(
+                new JsonStringEnumConverter(JsonNamingPolicy.CamelCase, allowIntegerValues: false));
+        }
+    }
+
+    private static JsonSerializerOptions CreateReadOnlyOptions()
+    {
+        JsonSerializerOptions options = CreateOptions();
+        options.MakeReadOnly(populateMissingResolver: true);
+        return options;
+    }
+}

src/FinalFactory.Rendezvous.Contracts/Udp/PresenceDatagram.cs

@@ -0,0 +1,12 @@
+namespace FinalFactory.Rendezvous.Contracts;
+
+public sealed class PresenceDatagram
+{
+    public int ContractVersion { get; set; } = ContractLimits.ContractVersion;
+    public UdpPresenceMessageType MessageType { get; set; }
+    public MediationHandle MediationHandle { get; set; }
+    public AddressFamilyKind AddressFamily { get; set; }
+    public string LocalAddress { get; set; } = string.Empty;
+    public int LocalPort { get; set; }
+    public string Capability { get; set; } = string.Empty;
+}

src/FinalFactory.Rendezvous.Contracts/Udp/RendezvousUdpCodec.cs

@@ -0,0 +1,281 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+public static class RendezvousUdpCodec
+{
+    public const byte MagicFirst = 0x52;
+    public const byte MagicSecond = 0x56;
+    public const byte FlagsNone = 0;
+
+    private const int FixedPrefixLength = 23;
+    private const int FixedSuffixLength = 3;
+
+    public static byte[] Encode(PresenceDatagram datagram)
+    {
+        if (datagram is null)
+        {
+            throw new ArgumentNullException(nameof(datagram));
+        }
+
+        if (ContractValidation.ValidateContractVersion(datagram.ContractVersion)
+            != RendezvousErrorCode.None)
+        {
+            throw new ArgumentException("The UDP contract version is unsupported.", nameof(datagram));
+        }
+
+        if (datagram.MessageType is not UdpPresenceMessageType.HostPresence
+            and not UdpPresenceMessageType.ClientPresence)
+        {
+            throw new ArgumentException("The UDP presence message type is unknown.", nameof(datagram));
+        }
+
+        if (datagram.MediationHandle.Value == Guid.Empty)
+        {
+            throw new ArgumentException("The mediation handle cannot be empty.", nameof(datagram));
+        }
+
+        if (!TryGetAddressBytes(datagram.LocalAddress, datagram.AddressFamily, out byte[] addressBytes))
+        {
+            throw new ArgumentException("The local address does not match its address family.", nameof(datagram));
+        }
+
+        if (datagram.LocalPort is < 1 or > ushort.MaxValue)
+        {
+            throw new ArgumentOutOfRangeException(nameof(datagram), "The local port must be between 1 and 65535.");
+        }
+
+        if (!ContractValidation.IsCapabilityValid(datagram.Capability))
+        {
+            throw new ArgumentException("The UDP capability is invalid.", nameof(datagram));
+        }
+
+        byte[] capabilityBytes = Encoding.ASCII.GetBytes(datagram.Capability);
+        int encodedLength = FixedPrefixLength + addressBytes.Length + FixedSuffixLength
+            + capabilityBytes.Length;
+        if (encodedLength > ContractLimits.UdpDatagramMaxBytes)
+        {
+            throw new ArgumentException("The encoded UDP datagram exceeds its size limit.", nameof(datagram));
+        }
+
+        byte[] encoded = new byte[encodedLength];
+        int offset = 0;
+        encoded[offset++] = MagicFirst;
+        encoded[offset++] = MagicSecond;
+        encoded[offset++] = checked((byte)datagram.ContractVersion);
+        encoded[offset++] = (byte)datagram.MessageType;
+        encoded[offset++] = FlagsNone;
+        WriteGuid(datagram.MediationHandle.Value, encoded, offset);
+        offset += 16;
+        encoded[offset++] = (byte)datagram.AddressFamily;
+        encoded[offset++] = checked((byte)addressBytes.Length);
+        addressBytes.CopyTo(encoded, offset);
+        offset += addressBytes.Length;
+        encoded[offset++] = checked((byte)(datagram.LocalPort >> 8));
+        encoded[offset++] = checked((byte)(datagram.LocalPort & 0xff));
+        encoded[offset++] = checked((byte)capabilityBytes.Length);
+        capabilityBytes.CopyTo(encoded, offset);
+        return encoded;
+    }
+
+    public static bool TryDecode(
+        ReadOnlySpan<byte> encoded,
+        out PresenceDatagram? datagram,
+        out UdpDecodeError error)
+    {
+        datagram = null;
+        error = UdpDecodeError.None;
+
+        if (encoded.Length > ContractLimits.UdpDatagramMaxBytes)
+        {
+            error = UdpDecodeError.DatagramTooLarge;
+            return false;
+        }
+
+        if (encoded.Length < FixedPrefixLength)
+        {
+            error = UdpDecodeError.Truncated;
+            return false;
+        }
+
+        int offset = 0;
+        if (encoded[offset++] != MagicFirst || encoded[offset++] != MagicSecond)
+        {
+            error = UdpDecodeError.InvalidMagic;
+            return false;
+        }
+
+        int version = encoded[offset++];
+        if (ContractValidation.ValidateContractVersion(version) != RendezvousErrorCode.None)
+        {
+            error = UdpDecodeError.UnsupportedVersion;
+            return false;
+        }
+
+        UdpPresenceMessageType messageType = (UdpPresenceMessageType)encoded[offset++];
+        if (messageType is not UdpPresenceMessageType.HostPresence
+            and not UdpPresenceMessageType.ClientPresence)
+        {
+            error = UdpDecodeError.UnknownMessageType;
+            return false;
+        }
+
+        if (encoded[offset++] != FlagsNone)
+        {
+            error = UdpDecodeError.InvalidFlags;
+            return false;
+        }
+
+        if (!TryReadGuid(encoded.Slice(offset, 16), out Guid handle)
+            || handle == Guid.Empty)
+        {
+            error = UdpDecodeError.InvalidHandle;
+            return false;
+        }
+
+        offset += 16;
+        AddressFamilyKind addressFamily = (AddressFamilyKind)encoded[offset++];
+        int expectedAddressLength = addressFamily switch
+        {
+            AddressFamilyKind.Ipv4 => 4,
+            AddressFamilyKind.Ipv6 => 16,
+            _ => 0,
+        };
+        if (expectedAddressLength == 0)
+        {
+            error = UdpDecodeError.InvalidAddressFamily;
+            return false;
+        }
+
+        int addressLength = encoded[offset++];
+        if (addressLength != expectedAddressLength)
+        {
+            error = UdpDecodeError.InvalidAddress;
+            return false;
+        }
+
+        if (encoded.Length < offset + addressLength + FixedSuffixLength)
+        {
+            error = UdpDecodeError.Truncated;
+            return false;
+        }
+
+        string address;
+        try
+        {
+            address = new IPAddress(encoded.Slice(offset, addressLength).ToArray()).ToString();
+        }
+        catch (ArgumentException)
+        {
+            error = UdpDecodeError.InvalidAddress;
+            return false;
+        }
+
+        offset += addressLength;
+        int port = (encoded[offset++] << 8) | encoded[offset++];
+        if (port == 0)
+        {
+            error = UdpDecodeError.InvalidPort;
+            return false;
+        }
+
+        int capabilityLength = encoded[offset++];
+        if (capabilityLength == 0 || capabilityLength > ContractLimits.UdpCapabilityMaxCharacters)
+        {
+            error = UdpDecodeError.InvalidCapability;
+            return false;
+        }
+
+        if (encoded.Length < offset + capabilityLength)
+        {
+            error = UdpDecodeError.Truncated;
+            return false;
+        }
+
+        if (encoded.Length > offset + capabilityLength)
+        {
+            error = UdpDecodeError.TrailingData;
+            return false;
+        }
+
+        string capability = Encoding.ASCII.GetString(encoded.Slice(offset, capabilityLength).ToArray());
+        if (!ContractValidation.IsCapabilityValid(capability))
+        {
+            error = UdpDecodeError.InvalidCapability;
+            return false;
+        }
+
+        datagram = new PresenceDatagram
+        {
+            ContractVersion = version,
+            MessageType = messageType,
+            MediationHandle = new MediationHandle(handle),
+            AddressFamily = addressFamily,
+            LocalAddress = address,
+            LocalPort = port,
+            Capability = capability,
+        };
+        return true;
+    }
+
+    private static bool TryGetAddressBytes(
+        string value,
+        AddressFamilyKind addressFamily,
+        out byte[] addressBytes)
+    {
+        addressBytes = [];
+        if (!IPAddress.TryParse(value, out IPAddress? address))
+        {
+            return false;
+        }
+
+        bool familyMatches = addressFamily switch
+        {
+            AddressFamilyKind.Ipv4 => address.AddressFamily == AddressFamily.InterNetwork,
+            AddressFamilyKind.Ipv6 => address.AddressFamily == AddressFamily.InterNetworkV6,
+            _ => false,
+        };
+        if (!familyMatches)
+        {
+            return false;
+        }
+
+        addressBytes = address.GetAddressBytes();
+        return true;
+    }
+
+    private static void WriteGuid(Guid value, byte[] destination, int offset)
+    {
+        string hexadecimal = value.ToString("N");
+        for (int index = 0; index < 16; index++)
+        {
+            int high = ParseHexadecimal(hexadecimal[index * 2]);
+            int low = ParseHexadecimal(hexadecimal[(index * 2) + 1]);
+            destination[offset + index] = checked((byte)((high << 4) | low));
+        }
+    }
+
+    private static bool TryReadGuid(ReadOnlySpan<byte> encoded, out Guid value)
+    {
+        char[] hexadecimal = new char[32];
+        for (int index = 0; index < encoded.Length; index++)
+        {
+            hexadecimal[index * 2] = FormatHexadecimal(encoded[index] >> 4);
+            hexadecimal[(index * 2) + 1] = FormatHexadecimal(encoded[index] & 0x0f);
+        }
+
+        return Guid.TryParseExact(new string(hexadecimal), "N", out value);
+    }
+
+    private static int ParseHexadecimal(char value) => value switch
+    {
+        >= '0' and <= '9' => value - '0',
+        >= 'a' and <= 'f' => value - 'a' + 10,
+        _ => throw new FormatException("A GUID contained a non-hexadecimal character."),
+    };
+
+    private static char FormatHexadecimal(int value) =>
+        (char)(value < 10 ? '0' + value : 'a' + value - 10);
+}

src/FinalFactory.Rendezvous.Contracts/packages.lock.json

@@ -0,0 +1,67 @@
+{
+  "version": 2,
+  "dependencies": {
+    ".NETStandard,Version=v2.1": {
+      "System.Text.Json": {
+        "type": "Direct",
+        "requested": "[10.0.10, )",
+        "resolved": "10.0.10",
+        "contentHash": "bmsO6UdYtBdtn32zYXfsh7KlyTIzV/3V9hdT9RIb4pXKgYOsNxXR+VbWigNwBtNFVGYGm6Hwmqw5a+/IWFd36Q==",
+        "dependencies": {
+          "Microsoft.Bcl.AsyncInterfaces": "10.0.10",
+          "System.Buffers": "4.6.1",
+          "System.IO.Pipelines": "10.0.10",
+          "System.Memory": "4.6.3",
+          "System.Runtime.CompilerServices.Unsafe": "6.1.2",
+          "System.Text.Encodings.Web": "10.0.10",
+          "System.Threading.Tasks.Extensions": "4.6.3"
+        }
+      },
+      "Microsoft.Bcl.AsyncInterfaces": {
+        "type": "Transitive",
+        "resolved": "10.0.10",
+        "contentHash": "TFI6OKYE1XZz4SGuTSH70c6SBdPpFktXsoa1gCxTr3mKrhmXirnvaS0tKz+J3ZWICEAmMpEGn59nO4ICtUpQXA=="
+      },
+      "System.Buffers": {
+        "type": "Transitive",
+        "resolved": "4.6.1",
+        "contentHash": "N8GXpmiLMtljq7gwvyS+1QvKT/W2J8sNAvx+HVg4NGmsG/H+2k/y9QI23auLJRterrzCiDH+IWAw4V/GPwsMlw=="
+      },
+      "System.IO.Pipelines": {
+        "type": "Transitive",
+        "resolved": "10.0.10",
+        "contentHash": "7WX0W96y3dpQdYG4sEGdh38g3/0lOD4/dKbn2rRVOVzKhzoZUn2gKNIKaFeKWs8RCbpFfmmEWsRhSy95hMpvqA==",
+        "dependencies": {
+          "System.Buffers": "4.6.1",
+          "System.Memory": "4.6.3",
+          "System.Threading.Tasks.Extensions": "4.6.3"
+        }
+      },
+      "System.Memory": {
+        "type": "Transitive",
+        "resolved": "4.6.3",
+        "contentHash": "qdcDOgnFZY40+Q9876JUHnlHu7bosOHX8XISRoH94fwk6hgaeQGSgfZd8srWRZNt5bV9ZW2TljcegDNxsf+96A=="
+      },
+      "System.Runtime.CompilerServices.Unsafe": {
+        "type": "Transitive",
+        "resolved": "6.1.2",
+        "contentHash": "2hBr6zdbIBTDE3EhK7NSVNdX58uTK6iHW/P/Axmm9sl1xoGSLqDvMtpecn226TNwHByFokYwJmt/aQQNlO5CRw=="
+      },
+      "System.Text.Encodings.Web": {
+        "type": "Transitive",
+        "resolved": "10.0.10",
+        "contentHash": "o16m2YpDN/pjHsnxf9pTGwkpcuvjW8v1/wGUwJtM1c3QZUKm7ZEO/eYRJg7iIx6GxS2Zv9lAMHpiQwHDdgqauA==",
+        "dependencies": {
+          "System.Buffers": "4.6.1",
+          "System.Memory": "4.6.3",
+          "System.Runtime.CompilerServices.Unsafe": "6.1.2"
+        }
+      },
+      "System.Threading.Tasks.Extensions": {
+        "type": "Transitive",
+        "resolved": "4.6.3",
+        "contentHash": "7sCiwilJLYbTZELaKnc7RecBBXWXA+xMLQWZKWawBxYjp6DBlSE3v9/UcvKBvr1vv2tTOhipiogM8rRmxlhrVA=="
+      }
+    }
+  }
+}

src/FinalFactory.Rendezvous.Server/FinalFactory.Rendezvous.Server.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <AssemblyName>FinalFactory.Rendezvous.Server</AssemblyName>
+    <RootNamespace>FinalFactory.Rendezvous.Server</RootNamespace>
+    <IsPackable>false</IsPackable>
+    <OpenApiGenerateDocuments>true</OpenApiGenerateDocuments>
+    <OpenApiDocumentsDirectory>$(MSBuildProjectDirectory)/../../docs/api</OpenApiDocumentsDirectory>
+    <OpenApiGenerateDocumentsOptions>--document-name v1 --file-name rendezvous-v1 --openapi-version OpenApi3_1</OpenApiGenerateDocumentsOptions>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="../FinalFactory.Rendezvous.Contracts/FinalFactory.Rendezvous.Contracts.csproj" />
+    <PackageReference Include="LiteNetLib" />
+    <PackageReference Include="Microsoft.AspNetCore.OpenApi" />
+    <PackageReference Include="Microsoft.Extensions.ApiDescription.Server" PrivateAssets="all" />
+  </ItemGroup>
+</Project>

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

@@ -0,0 +1,112 @@
+using FinalFactory.Rendezvous.Contracts;
+using Microsoft.AspNetCore.Mvc;
+
+namespace FinalFactory.Rendezvous.Server.Http;
+
+internal static class ContractEndpoints
+{
+    private const int NotImplementedStatus = StatusCodes.Status501NotImplemented;
+
+    public static IEndpointRouteBuilder MapRendezvousContractEndpoints(
+        this IEndpointRouteBuilder endpoints)
+    {
+        RouteGroupBuilder sessions = endpoints.MapGroup("/v1/sessions").WithTags("Sessions");
+        sessions.MapPost("/", RegisterSession)
+            .Accepts<RegisterSessionRequest>("application/json")
+            .Produces<RegisterSessionResponse>(StatusCodes.Status201Created)
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("RegisterSession");
+        sessions.MapPost("/{listingId}/renew", RenewLease)
+            .Accepts<RenewLeaseRequest>("application/json")
+            .Produces<RenewLeaseResponse>()
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("RenewSessionLease");
+        sessions.MapPut("/{listingId}", UpdateSession)
+            .Accepts<UpdateSessionRequest>("application/json")
+            .Produces(StatusCodes.Status204NoContent)
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("UpdateSession");
+        sessions.MapDelete("/{listingId}", DeleteSession)
+            .Accepts<DeleteSessionRequest>("application/json")
+            .Produces(StatusCodes.Status204NoContent)
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("DeleteSession");
+        sessions.MapGet("/", BrowseSessions)
+            .Produces<BrowseSessionsResponse>()
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("BrowseSessions");
+        sessions.MapGet("/{listingId}", GetSession)
+            .Produces<GetSessionResponse>()
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("GetSession");
+        sessions.MapGet("/{listingId}/join-attempts", BrowseHostJoinAttempts)
+            .Produces<BrowseHostJoinAttemptsResponse>()
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("BrowseHostJoinAttempts");
+
+        RouteGroupBuilder attempts = endpoints
+            .MapGroup("/v1/join-attempts")
+            .WithTags("Join attempts");
+        attempts.MapPost("/", CreateJoinAttempt)
+            .Accepts<CreateJoinAttemptRequest>("application/json")
+            .Produces<CreateJoinAttemptResponse>(StatusCodes.Status201Created)
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("CreateJoinAttempt");
+        attempts.MapPost("/{attemptId}/outcome", ReportConnectionOutcome)
+            .Accepts<ReportConnectionOutcomeRequest>("application/json")
+            .Produces<ReportConnectionOutcomeResponse>()
+            .Produces<ApiError>(NotImplementedStatus)
+            .WithName("ReportConnectionOutcome");
+
+        return endpoints;
+    }
+
+    private static IResult RegisterSession([FromBody] RegisterSessionRequest request) =>
+        NotImplemented();
+
+    private static IResult RenewLease(
+        SessionListingId listingId,
+        [FromBody] RenewLeaseRequest request) => NotImplemented();
+
+    private static IResult UpdateSession(
+        SessionListingId listingId,
+        [FromBody] UpdateSessionRequest request) => NotImplemented();
+
+    private static IResult DeleteSession(
+        SessionListingId listingId,
+        [FromBody] DeleteSessionRequest request) => NotImplemented();
+
+    private static IResult BrowseSessions(
+        [FromQuery] int contractVersion,
+        [FromQuery] string gameId,
+        [FromQuery] string environmentId,
+        [FromQuery] uint protocolVersion,
+        [FromQuery] string? regionId,
+        [FromQuery] int? pageSize,
+        [FromQuery] string? cursor) => NotImplemented();
+
+    private static IResult GetSession(SessionListingId listingId) => NotImplemented();
+
+    private static IResult BrowseHostJoinAttempts(
+        SessionListingId listingId,
+        [FromQuery] int contractVersion,
+        [FromHeader(Name = "X-Rendezvous-Lease-Token")] string leaseToken,
+        [FromQuery] int? pageSize,
+        [FromQuery] string? cursor) => NotImplemented();
+
+    private static IResult CreateJoinAttempt([FromBody] CreateJoinAttemptRequest request) =>
+        NotImplemented();
+
+    private static IResult ReportConnectionOutcome(
+        JoinAttemptId attemptId,
+        [FromBody] ReportConnectionOutcomeRequest request) => NotImplemented();
+
+    private static IResult NotImplemented() => Results.Json(
+        new ApiError
+        {
+            Code = RendezvousErrorCode.ServiceUnavailable,
+            Message = "The v1 contract is reserved; implementation is tracked by subsequent issues.",
+        },
+        ContractJson.Options,
+        statusCode: NotImplementedStatus);
+}

src/FinalFactory.Rendezvous.Server/Program.cs

@@ -0,0 +1,77 @@
+using System.Net;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Http;
+using FinalFactory.Rendezvous.Server.Transport;
+using Microsoft.OpenApi;
+
+WebApplicationBuilder builder = WebApplication.CreateBuilder(args);
+bool isOpenApiGeneration = Environment.GetCommandLineArgs().Any(static argument =>
+    string.Equals(
+        Path.GetFileName(argument),
+        "dotnet-getdocument.dll",
+        StringComparison.OrdinalIgnoreCase));
+
+builder.Services.AddOpenApi("v1", static options =>
+    options.AddSchemaTransformer(static (schema, context, cancellationToken) =>
+    {
+        Type type = context.JsonTypeInfo.Type;
+        if (type == typeof(GameId)
+            || type == typeof(EnvironmentId)
+            || type == typeof(RegionId))
+        {
+            schema.Type = JsonSchemaType.String;
+        }
+        else if (type == typeof(SessionListingId)
+                 || type == typeof(LeaseId)
+                 || type == typeof(JoinAttemptId)
+                 || type == typeof(MediationHandle))
+        {
+            schema.Type = JsonSchemaType.String;
+            schema.Format = "uuid";
+        }
+
+        return Task.CompletedTask;
+    }));
+builder.Services.ConfigureHttpJsonOptions(static options =>
+    ContractJson.Configure(options.SerializerOptions));
+builder.Services
+    .AddOptions<UdpMediatorOptions>()
+    .BindConfiguration(UdpMediatorOptions.SectionName)
+    .ValidateDataAnnotations()
+    .Validate(
+        options => IPAddress.TryParse(options.ListenAddress, out _),
+        $"{UdpMediatorOptions.SectionName}:ListenAddress must be an IP address.")
+    .ValidateOnStart();
+builder.Services.AddSingleton<UdpMediatorService>();
+if (!isOpenApiGeneration)
+{
+    builder.Services.AddHostedService(static services =>
+        services.GetRequiredService<UdpMediatorService>());
+}
+
+WebApplication app = builder.Build();
+
+app.MapOpenApi();
+app.MapRendezvousContractEndpoints();
+app.MapGet(
+        "/health/live",
+        static () => Results.Ok(new HealthResponse { Status = "live" }))
+    .Produces<HealthResponse>()
+    .WithName("GetLiveness")
+    .WithTags("Health");
+app.MapGet(
+    "/health/ready",
+    static (UdpMediatorService mediator) => mediator.LocalEndpoint is null
+        ? Results.StatusCode(StatusCodes.Status503ServiceUnavailable)
+        : Results.Ok(new HealthResponse { Status = "ready" }))
+    .Produces<HealthResponse>()
+    .Produces(StatusCodes.Status503ServiceUnavailable)
+    .WithName("GetReadiness")
+    .WithTags("Health");
+
+await app.RunAsync();
+
+/// <summary>
+/// Entry point marker used by integration-test hosts.
+/// </summary>
+public partial class Program;

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

@@ -0,0 +1,26 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace FinalFactory.Rendezvous.Server.Transport;
+
+/// <summary>
+/// Configures the UDP endpoint reserved for the Rendezvous mediator.
+/// </summary>
+public sealed class UdpMediatorOptions
+{
+    /// <summary>
+    /// Configuration section containing UDP mediator settings.
+    /// </summary>
+    public const string SectionName = "Rendezvous:Udp";
+
+    /// <summary>
+    /// Gets or sets the numeric IP address to bind.
+    /// </summary>
+    [Required]
+    public string ListenAddress { get; set; } = "0.0.0.0";
+
+    /// <summary>
+    /// Gets or sets the UDP port. Zero requests an ephemeral port for tests.
+    /// </summary>
+    [Range(0, 65_535)]
+    public int Port { get; set; } = 9050;
+}

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

@@ -0,0 +1,116 @@
+using System.Net;
+using System.Net.Sockets;
+using Microsoft.Extensions.Options;
+
+namespace FinalFactory.Rendezvous.Server.Transport;
+
+/// <summary>
+/// Owns the cancellable UDP socket used by the future NAT mediator.
+/// </summary>
+public sealed partial class UdpMediatorService : BackgroundService
+{
+    private readonly ILogger<UdpMediatorService> _logger;
+    private readonly UdpMediatorOptions _options;
+    private UdpClient? _udpClient;
+
+    /// <summary>
+    /// Initializes a new UDP mediator service.
+    /// </summary>
+    public UdpMediatorService(
+        IOptions<UdpMediatorOptions> options,
+        ILogger<UdpMediatorService> logger)
+    {
+        _options = options.Value;
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Gets the bound endpoint after startup completes.
+    /// </summary>
+    public IPEndPoint? LocalEndpoint { get; private set; }
+
+    /// <inheritdoc />
+    public override Task StartAsync(CancellationToken cancellationToken)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+
+        if (_udpClient is not null)
+        {
+            throw new InvalidOperationException("The UDP mediator is already running.");
+        }
+
+        IPAddress listenAddress = IPAddress.Parse(_options.ListenAddress);
+        UdpClient udpClient = new(new IPEndPoint(listenAddress, _options.Port));
+        _udpClient = udpClient;
+        IPEndPoint localEndpoint =
+            (IPEndPoint?)udpClient.Client.LocalEndPoint
+            ?? throw new InvalidOperationException("The UDP socket did not expose its bound endpoint.");
+        LocalEndpoint = localEndpoint;
+
+        LogMediatorListening(_logger, localEndpoint.Address, localEndpoint.Port);
+
+        return base.StartAsync(cancellationToken);
+    }
+
+    /// <inheritdoc />
+    public override async Task StopAsync(CancellationToken cancellationToken)
+    {
+        await base.StopAsync(cancellationToken).ConfigureAwait(false);
+        _udpClient?.Dispose();
+        _udpClient = null;
+        LocalEndpoint = null;
+        LogMediatorStopped(_logger);
+    }
+
+    /// <inheritdoc />
+    public override void Dispose()
+    {
+        _udpClient?.Dispose();
+        _udpClient = null;
+        LocalEndpoint = null;
+        base.Dispose();
+    }
+
+    /// <inheritdoc />
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        UdpClient udpClient = _udpClient
+            ?? throw new InvalidOperationException("The UDP mediator socket was not initialized.");
+
+        try
+        {
+            while (!stoppingToken.IsCancellationRequested)
+            {
+                _ = await udpClient.ReceiveAsync(stoppingToken).ConfigureAwait(false);
+                // Bootstrap deliberately emits no UDP response. Protocol handling lands in #11.
+            }
+        }
+        catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+        {
+            // Expected during normal shutdown.
+        }
+        catch (ObjectDisposedException) when (stoppingToken.IsCancellationRequested)
+        {
+            // Disposing the socket is the fallback that releases a blocked receive.
+        }
+        finally
+        {
+            LocalEndpoint = null;
+        }
+    }
+
+    [LoggerMessage(
+        EventId = 1,
+        Level = LogLevel.Information,
+        Message = "UDP mediator listening on {ListenAddress}:{ListenPort}")]
+    private static partial void LogMediatorListening(
+        ILogger logger,
+        IPAddress listenAddress,
+        int listenPort);
+
+    [LoggerMessage(
+        EventId = 2,
+        Level = LogLevel.Information,
+        Message = "UDP mediator stopped")]
+    private static partial void LogMediatorStopped(ILogger logger);
+}

src/FinalFactory.Rendezvous.Server/appsettings.json

@@ -0,0 +1,15 @@
+{
+  "Rendezvous": {
+    "Udp": {
+      "ListenAddress": "0.0.0.0",
+      "Port": 9050
+    }
+  },
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*"
+}

src/FinalFactory.Rendezvous.Server/packages.lock.json

@@ -0,0 +1,37 @@
+{
+  "version": 2,
+  "dependencies": {
+    "net10.0": {
+      "LiteNetLib": {
+        "type": "Direct",
+        "requested": "[2.1.4, )",
+        "resolved": "2.1.4",
+        "contentHash": "KWlxvMw3Urpqj9joD96LRiK+LC62pQNs/zkXRJc+rHnxgkGp+vV703xzDrxRmv+V1YhCFfIGzs5nrVWtREIlyA=="
+      },
+      "Microsoft.AspNetCore.OpenApi": {
+        "type": "Direct",
+        "requested": "[10.0.9, )",
+        "resolved": "10.0.9",
+        "contentHash": "1ihb8FO9cGgEK1/m3CTtT/SfnynwmiZib0W2pcDVj3KSWk/Sca4VOXEtaptKQc582zpFrzTFiwkGRCglt6H+WQ==",
+        "dependencies": {
+          "Microsoft.OpenApi": "2.0.0"
+        }
+      },
+      "Microsoft.Extensions.ApiDescription.Server": {
+        "type": "Direct",
+        "requested": "[10.0.9, )",
+        "resolved": "10.0.9",
+        "contentHash": "n1m7EAbCbHMGiTy++F+mLSan4MrZe0t00XEpJrkai6BFpB6lwEcirflI9FiMm4G4u55h/2RnWToYBDwS+MnN6g=="
+      },
+      "finalfactory.rendezvous.contracts": {
+        "type": "Project"
+      },
+      "Microsoft.OpenApi": {
+        "type": "CentralTransitive",
+        "requested": "[2.7.5, )",
+        "resolved": "2.7.5",
+        "contentHash": "0FA67RSnRM4tcBKqiqVu/HPdZ9+QOKbmeRjxRUGTCjPU4C0bmUhd97Dso7Yild5P7nOV6GxJ2xrK0Kv/O9xp0w=="
+      }
+    }
+  }
+}

src/FinalFactory.Rendezvous.TestClient/FinalFactory.Rendezvous.TestClient.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <AssemblyName>FinalFactory.Rendezvous.TestClient</AssemblyName>
+    <RootNamespace>FinalFactory.Rendezvous.TestClient</RootNamespace>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="../FinalFactory.Rendezvous.Client/FinalFactory.Rendezvous.Client.csproj" />
+    <ProjectReference Include="../FinalFactory.Rendezvous.Contracts/FinalFactory.Rendezvous.Contracts.csproj" />
+    <PackageReference Include="LiteNetLib" />
+  </ItemGroup>
+</Project>

src/FinalFactory.Rendezvous.TestClient/Program.cs

@@ -0,0 +1,16 @@
+namespace FinalFactory.Rendezvous.TestClient;
+
+/// <summary>
+/// Bootstrap entry point for the public-SDK-only diagnostic client.
+/// </summary>
+public static class Program
+{
+    /// <summary>
+    /// Runs the bootstrap diagnostic.
+    /// </summary>
+    public static int Main()
+    {
+        Console.WriteLine("Rendezvous TestClient bootstrap is ready.");
+        return 0;
+    }
+}

src/FinalFactory.Rendezvous.TestClient/packages.lock.json

@@ -0,0 +1,46 @@
+{
+  "version": 2,
+  "dependencies": {
+    "net8.0": {
+      "LiteNetLib": {
+        "type": "Direct",
+        "requested": "[2.1.4, )",
+        "resolved": "2.1.4",
+        "contentHash": "KWlxvMw3Urpqj9joD96LRiK+LC62pQNs/zkXRJc+rHnxgkGp+vV703xzDrxRmv+V1YhCFfIGzs5nrVWtREIlyA=="
+      },
+      "System.IO.Pipelines": {
+        "type": "Transitive",
+        "resolved": "10.0.10",
+        "contentHash": "7WX0W96y3dpQdYG4sEGdh38g3/0lOD4/dKbn2rRVOVzKhzoZUn2gKNIKaFeKWs8RCbpFfmmEWsRhSy95hMpvqA=="
+      },
+      "System.Text.Encodings.Web": {
+        "type": "Transitive",
+        "resolved": "10.0.10",
+        "contentHash": "o16m2YpDN/pjHsnxf9pTGwkpcuvjW8v1/wGUwJtM1c3QZUKm7ZEO/eYRJg7iIx6GxS2Zv9lAMHpiQwHDdgqauA=="
+      },
+      "finalfactory.rendezvous.client": {
+        "type": "Project",
+        "dependencies": {
+          "FinalFactory.Rendezvous.Contracts": "[1.0.0, )",
+          "LiteNetLib": "[2.1.4, )"
+        }
+      },
+      "finalfactory.rendezvous.contracts": {
+        "type": "Project",
+        "dependencies": {
+          "System.Text.Json": "[10.0.10, )"
+        }
+      },
+      "System.Text.Json": {
+        "type": "CentralTransitive",
+        "requested": "[10.0.10, )",
+        "resolved": "10.0.10",
+        "contentHash": "bmsO6UdYtBdtn32zYXfsh7KlyTIzV/3V9hdT9RIb4pXKgYOsNxXR+VbWigNwBtNFVGYGm6Hwmqw5a+/IWFd36Q==",
+        "dependencies": {
+          "System.IO.Pipelines": "10.0.10",
+          "System.Text.Encodings.Web": "10.0.10"
+        }
+      }
+    }
+  }
+}

tests/FinalFactory.Rendezvous.Tests/Architecture/DependencyBoundaryTests.cs

@@ -0,0 +1,117 @@
+using System.Reflection;
+using System.Xml.Linq;
+
+namespace FinalFactory.Rendezvous.Tests.Architecture;
+
+public sealed class DependencyBoundaryTests
+{
+    [Fact]
+    public void ContractsAreTransportAndEngineIndependent()
+    {
+        string[] references = GetReferences("FinalFactory.Rendezvous.Contracts");
+
+        Assert.DoesNotContain(references, IsGodotAssembly);
+        Assert.DoesNotContain(references, IsServerAssembly);
+        Assert.DoesNotContain(references, IsLiteNetLibAssembly);
+    }
+
+    [Fact]
+    public void ClientIsGodotAndServerIndependent()
+    {
+        string[] references = GetReferences("FinalFactory.Rendezvous.Client");
+
+        Assert.DoesNotContain(references, IsGodotAssembly);
+        Assert.DoesNotContain(references, IsServerAssembly);
+    }
+
+    [Fact]
+    public void TestClientUsesOnlyPublicRendezvousDependencies()
+    {
+        string[] references = GetReferences("FinalFactory.Rendezvous.TestClient");
+
+        Assert.DoesNotContain(references, IsGodotAssembly);
+        Assert.DoesNotContain(references, IsServerAssembly);
+    }
+
+    [Fact]
+    public void DeclaredDependencyGraphMatchesTheArchitecture()
+    {
+        AssertDeclaredDependencies(
+            "src/FinalFactory.Rendezvous.Contracts/FinalFactory.Rendezvous.Contracts.csproj",
+            [],
+            ["System.Text.Json"]);
+        AssertDeclaredDependencies(
+            "src/FinalFactory.Rendezvous.Client/FinalFactory.Rendezvous.Client.csproj",
+            ["FinalFactory.Rendezvous.Contracts"],
+            ["LiteNetLib"]);
+        AssertDeclaredDependencies(
+            "src/FinalFactory.Rendezvous.Server/FinalFactory.Rendezvous.Server.csproj",
+            ["FinalFactory.Rendezvous.Contracts"],
+            [
+                "LiteNetLib",
+                "Microsoft.AspNetCore.OpenApi",
+                "Microsoft.Extensions.ApiDescription.Server",
+            ]);
+        AssertDeclaredDependencies(
+            "src/FinalFactory.Rendezvous.TestClient/FinalFactory.Rendezvous.TestClient.csproj",
+            ["FinalFactory.Rendezvous.Client", "FinalFactory.Rendezvous.Contracts"],
+            ["LiteNetLib"]);
+    }
+
+    private static void AssertDeclaredDependencies(
+        string projectPath,
+        string[] expectedProjects,
+        string[] expectedPackages)
+    {
+        XDocument project = XDocument.Load(Path.Combine(FindRepositoryRoot(), projectPath));
+        string[] projects = project
+            .Descendants("ProjectReference")
+            .Select(static element =>
+                Path.GetFileNameWithoutExtension(element.Attribute("Include")?.Value) ?? string.Empty)
+            .Order(StringComparer.Ordinal)
+            .ToArray();
+        string[] packages = project
+            .Descendants("PackageReference")
+            .Select(static element => element.Attribute("Include")?.Value ?? string.Empty)
+            .Order(StringComparer.Ordinal)
+            .ToArray();
+
+        Assert.Equal(expectedProjects.Order(StringComparer.Ordinal), projects);
+        Assert.Equal(expectedPackages.Order(StringComparer.Ordinal), packages);
+    }
+
+    private static string FindRepositoryRoot()
+    {
+        DirectoryInfo? directory = new(AppContext.BaseDirectory);
+
+        while (directory is not null)
+        {
+            if (File.Exists(Path.Combine(directory.FullName, "Rendezvous.slnx")))
+            {
+                return directory.FullName;
+            }
+
+            directory = directory.Parent;
+        }
+
+        throw new DirectoryNotFoundException("Could not locate the Rendezvous repository root.");
+    }
+
+    private static string[] GetReferences(string assemblyName) => Assembly
+        .Load(assemblyName)
+        .GetReferencedAssemblies()
+        .Select(static reference => reference.Name ?? string.Empty)
+        .ToArray();
+
+    private static bool IsGodotAssembly(string assemblyName) =>
+        assemblyName.StartsWith("Godot", StringComparison.OrdinalIgnoreCase);
+
+    private static bool IsLiteNetLibAssembly(string assemblyName) =>
+        string.Equals(assemblyName, "LiteNetLib", StringComparison.Ordinal);
+
+    private static bool IsServerAssembly(string assemblyName) =>
+        string.Equals(
+            assemblyName,
+            "FinalFactory.Rendezvous.Server",
+            StringComparison.Ordinal);
+}

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

@@ -0,0 +1,140 @@
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Tests.Contracts;
+
+public sealed class ContractLimitTests
+{
+    [Fact]
+    public void ByteAndCollectionLimitsAcceptTheBoundaryOnly()
+    {
+        Assert.True(ContractValidation.IsHttpRequestSizeValid(ContractLimits.HttpRequestMaxBytes));
+        Assert.False(ContractValidation.IsHttpRequestSizeValid(ContractLimits.HttpRequestMaxBytes + 1));
+        Assert.True(ContractValidation.IsBrowserResponseSizeValid(ContractLimits.BrowserResponseMaxBytes));
+        Assert.False(ContractValidation.IsBrowserResponseSizeValid(ContractLimits.BrowserResponseMaxBytes + 1));
+        Assert.True(ContractValidation.IsPageSizeValid(ContractLimits.BrowserPageMaxItems));
+        Assert.False(ContractValidation.IsPageSizeValid(ContractLimits.BrowserPageMaxItems + 1));
+        Assert.False(ContractValidation.IsPageSizeValid(0));
+    }
+
+    [Fact]
+    public void Utf8LimitsCountBytesInsteadOfCharacters()
+    {
+        string atLimit = new('é', ContractLimits.DisplayNameMaxBytes / 2);
+        string overLimit = atLimit + "é";
+
+        Assert.True(ContractValidation.IsDisplayNameValid(atLimit));
+        Assert.False(ContractValidation.IsDisplayNameValid(overLimit));
+        Assert.True(ContractValidation.IsBuildVersionValid(
+            new string('a', ContractLimits.BuildVersionMaxBytes)));
+        Assert.False(ContractValidation.IsBuildVersionValid(
+            new string('a', ContractLimits.BuildVersionMaxBytes + 1)));
+    }
+
+    [Fact]
+    public void CapabilityLimitStaysBelowLiteNetLibTokenLimit()
+    {
+        Assert.True(ContractValidation.IsCapabilityValid(
+            new string('a', ContractLimits.UdpCapabilityMaxCharacters - 1)));
+        Assert.True(ContractValidation.IsCapabilityValid(
+            new string('a', ContractLimits.UdpCapabilityMaxCharacters)));
+        Assert.False(ContractValidation.IsCapabilityValid(
+            new string('a', ContractLimits.UdpCapabilityMaxCharacters + 1)));
+        Assert.False(ContractValidation.IsCapabilityValid("not+base64url"));
+        Assert.True(
+            ContractLimits.UdpCapabilityMaxCharacters
+            < ContractLimits.LiteNetLibNatTokenMaxCharacters);
+    }
+
+    [Fact]
+    public void CapacityAndMetadataLimitsAreBounded()
+    {
+        Assert.True(ContractValidation.IsCapacityValid(new SessionCapacity
+        {
+            CurrentPlayers = ContractLimits.SessionCapacityMaxPlayers,
+            MaximumPlayers = ContractLimits.SessionCapacityMaxPlayers,
+        }));
+        Assert.False(ContractValidation.IsCapacityValid(new SessionCapacity
+        {
+            CurrentPlayers = 0,
+            MaximumPlayers = ContractLimits.SessionCapacityMaxPlayers + 1,
+        }));
+
+        Dictionary<string, string> maximumKeys = Enumerable
+            .Range(0, ContractLimits.MetadataMaxKeys)
+            .ToDictionary(index => $"key-{index}", _ => "value", StringComparer.Ordinal);
+        Dictionary<string, string> tooManyKeys = new(maximumKeys, StringComparer.Ordinal)
+        {
+            ["overflow"] = "value",
+        };
+
+        Assert.True(ContractValidation.IsMetadataValid(maximumKeys));
+        Assert.False(ContractValidation.IsMetadataValid(tooManyKeys));
+        Assert.False(ContractValidation.IsMetadataValid(new Dictionary<string, string>
+        {
+            [new string('k', ContractLimits.MetadataKeyMaxBytes + 1)] = "value",
+        }));
+        Assert.False(ContractValidation.IsMetadataValid(new Dictionary<string, string>
+        {
+            ["key"] = new string('v', ContractLimits.MetadataValueMaxBytes + 1),
+        }));
+    }
+
+    [Fact]
+    public void MetadataDocumentLimitAcceptsExactlyFourKibibytes()
+    {
+        Dictionary<string, string> atLimit = Enumerable
+            .Range(0, ContractLimits.MetadataMaxKeys)
+            .ToDictionary(index => $"k{index:00}", _ => string.Empty, StringComparer.Ordinal);
+        for (int index = 0; index < 14; index++)
+        {
+            atLimit[$"k{index:00}"] = new string('v', ContractLimits.MetadataValueMaxBytes);
+        }
+
+        atLimit["k14"] = new string('v', 223);
+        Dictionary<string, string> overLimit = new(atLimit, StringComparer.Ordinal)
+        {
+            ["k14"] = new string('v', 224),
+        };
+
+        Assert.True(ContractValidation.IsMetadataValid(atLimit));
+        Assert.False(ContractValidation.IsMetadataValid(overLimit));
+    }
+
+    [Fact]
+    public void EndpointValidationIsAddressFamilyAware()
+    {
+        Assert.True(ContractValidation.IsNetworkEndpointValid(new NetworkEndpoint
+        {
+            AddressFamily = AddressFamilyKind.Ipv4,
+            Address = "192.0.2.10",
+            Port = 9050,
+        }));
+        Assert.True(ContractValidation.IsNetworkEndpointValid(new NetworkEndpoint
+        {
+            AddressFamily = AddressFamilyKind.Ipv6,
+            Address = "2001:db8::10",
+            Port = 9050,
+        }));
+        Assert.False(ContractValidation.IsNetworkEndpointValid(new NetworkEndpoint
+        {
+            AddressFamily = AddressFamilyKind.Ipv4,
+            Address = "2001:db8::10",
+            Port = 9050,
+        }));
+    }
+
+    [Fact]
+    public void ScopeAndOpaqueTextBoundariesAreEnforced()
+    {
+        Assert.True(GameId.TryParse(new string('a', ContractLimits.GameIdMaxCharacters), out _));
+        Assert.False(GameId.TryParse(
+            new string('a', ContractLimits.GameIdMaxCharacters + 1),
+            out _));
+        Assert.True(ContractValidation.IsIdempotencyKeyValid(
+            new string('i', ContractLimits.IdempotencyKeyMaxCharacters)));
+        Assert.False(ContractValidation.IsIdempotencyKeyValid(
+            new string('i', ContractLimits.IdempotencyKeyMaxCharacters + 1)));
+        Assert.True(ContractValidation.IsCursorValid(null));
+        Assert.False(ContractValidation.IsCursorValid("contains whitespace"));
+    }
+}

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

@@ -0,0 +1,104 @@
+using System.Text.Json;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Tests.Contracts;
+
+public sealed class ContractSerializationTests
+{
+    public static TheoryData<string, Type> GoldenJsonVectors => new()
+    {
+        { "register-session.json", typeof(RegisterSessionRequest) },
+        { "browse-sessions.json", typeof(BrowseSessionsResponse) },
+        { "create-join-response.json", typeof(CreateJoinAttemptResponse) },
+        { "api-error.json", typeof(ApiError) },
+    };
+
+    [Theory]
+    [MemberData(nameof(GoldenJsonVectors))]
+    public void CanonicalJsonRoundtripsGoldenVectors(string fileName, Type contractType)
+    {
+        string expected = ContractTestFiles.Read(fileName);
+        object? value = JsonSerializer.Deserialize(expected, contractType, ContractJson.Options);
+
+        Assert.NotNull(value);
+        Assert.Equal(expected, JsonSerializer.Serialize(value, contractType, ContractJson.Options));
+    }
+
+    [Fact]
+    public void IdentifiersAreSerializedAsStrings()
+    {
+        SessionListingId id = new(new Guid("00112233-4455-6677-8899-aabbccddeeff"));
+
+        Assert.Equal(
+            "\"00112233-4455-6677-8899-aabbccddeeff\"",
+            JsonSerializer.Serialize(id, ContractJson.Options));
+        Assert.Equal(id, JsonSerializer.Deserialize<SessionListingId>(
+            "\"00112233-4455-6677-8899-aabbccddeeff\"",
+            ContractJson.Options));
+    }
+
+    [Fact]
+    public void UnknownObjectFieldsAreIgnoredForAdditiveV1Changes()
+    {
+        const string json = """
+            {"contractVersion":1,"idempotencyKey":"join-001","gameId":"space-game","environmentId":"production","listingId":"00112233-4455-6677-8899-aabbccddeeff","protocolVersion":7,"futureField":{"nested":true}}
+            """;
+
+        CreateJoinAttemptRequest? request = JsonSerializer.Deserialize<CreateJoinAttemptRequest>(
+            json,
+            ContractJson.Options);
+
+        Assert.NotNull(request);
+        Assert.Equal(new GameId("space-game"), request.GameId);
+        Assert.Equal(7u, request.ProtocolVersion);
+    }
+
+    [Fact]
+    public void MissingNormativeFieldsAreRejectedInsteadOfDefaulted()
+    {
+        const string missingVersion = """
+            {"idempotencyKey":"join-001","gameId":"space-game","environmentId":"production","listingId":"00112233-4455-6677-8899-aabbccddeeff","protocolVersion":7}
+            """;
+
+        Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<CreateJoinAttemptRequest>(
+            missingVersion,
+            ContractJson.Options));
+    }
+
+    [Fact]
+    public void UnknownEnumNamesAndNumericValuesAreRejected()
+    {
+        Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ReportConnectionOutcomeRequest>(
+            "{\"contractVersion\":1,\"outcome\":\"futureOutcome\",\"elapsedMilliseconds\":1}",
+            ContractJson.Options));
+        Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<ReportConnectionOutcomeRequest>(
+            "{\"contractVersion\":1,\"outcome\":99,\"elapsedMilliseconds\":1}",
+            ContractJson.Options));
+    }
+
+    [Theory]
+    [InlineData(0)]
+    [InlineData(2)]
+    [InlineData(int.MaxValue)]
+    public void UnknownContractVersionsFailPredictably(int version)
+    {
+        Assert.Equal(
+            RendezvousErrorCode.UnsupportedContractVersion,
+            ContractValidation.ValidateContractVersion(version));
+    }
+
+    [Fact]
+    public void GameplayProtocolCompatibilityIsExactAndBuildIndependent()
+    {
+        Assert.True(ContractValidation.AreProtocolsCompatible(7, 7));
+        Assert.False(ContractValidation.AreProtocolsCompatible(7, 8));
+    }
+
+    [Fact]
+    public void SharedCanonicalOptionsCannotBeMutatedByConsumers()
+    {
+        Assert.True(ContractJson.Options.IsReadOnly);
+        Assert.Throws<InvalidOperationException>(() =>
+            ContractJson.Options.WriteIndented = true);
+    }
+}

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

@@ -0,0 +1,30 @@
+namespace FinalFactory.Rendezvous.Tests.Contracts;
+
+internal static class ContractTestFiles
+{
+    public static string Read(string fileName) => File
+        .ReadAllText(Path.Combine(Directory, fileName))
+        .TrimEnd('\r', '\n');
+
+    public static string Directory
+    {
+        get
+        {
+            DirectoryInfo? directory = new(AppContext.BaseDirectory);
+            while (directory is not null)
+            {
+                string solution = Path.Combine(directory.FullName, "Rendezvous.slnx");
+                if (File.Exists(solution))
+                {
+                    return Path.Combine(
+                        directory.FullName,
+                        "tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1");
+                }
+
+                directory = directory.Parent;
+            }
+
+            throw new DirectoryNotFoundException("Could not locate contract test data.");
+        }
+    }
+}

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

@@ -0,0 +1,68 @@
+using System.Text.Json;
+
+namespace FinalFactory.Rendezvous.Tests.Contracts;
+
+public sealed class OpenApiCompatibilityTests
+{
+    private static readonly string[] ExpectedPaths =
+    [
+        "/health/live",
+        "/health/ready",
+        "/v1/join-attempts",
+        "/v1/join-attempts/{attemptId}/outcome",
+        "/v1/sessions",
+        "/v1/sessions/{listingId}",
+        "/v1/sessions/{listingId}/join-attempts",
+        "/v1/sessions/{listingId}/renew",
+    ];
+
+    private static readonly string[] ExpectedListingProperties =
+    [
+        "buildVersion",
+        "capacity",
+        "contractVersion",
+        "displayName",
+        "environmentId",
+        "gameId",
+        "listingId",
+        "metadata",
+        "protocolVersion",
+        "publisherTrustMode",
+        "regionId",
+        "visibility",
+    ];
+
+    [Fact]
+    public void GeneratedOpenApiContainsTheFrozenV1Surface()
+    {
+        string path = Path.Combine(
+            ContractTestFiles.Directory,
+            "../../../../../docs/api/rendezvous-v1.json");
+        using JsonDocument document = JsonDocument.Parse(File.ReadAllText(Path.GetFullPath(path)));
+        JsonElement root = document.RootElement;
+
+        Assert.Equal("3.1.1", root.GetProperty("openapi").GetString());
+        string[] paths = root.GetProperty("paths")
+            .EnumerateObject()
+            .Select(static item => item.Name)
+            .Order(StringComparer.Ordinal)
+            .ToArray();
+        Assert.Equal(ExpectedPaths, paths);
+
+        JsonElement schemas = root.GetProperty("components").GetProperty("schemas");
+        Assert.Equal("string", schemas.GetProperty("GameId").GetProperty("type").GetString());
+        Assert.Equal("uuid", schemas.GetProperty("SessionListingId").GetProperty("format").GetString());
+
+        string[] listingProperties = schemas.GetProperty("SessionListing")
+            .GetProperty("properties")
+            .EnumerateObject()
+            .Select(static item => item.Name)
+            .Order(StringComparer.Ordinal)
+            .ToArray();
+        Assert.Equal(ExpectedListingProperties, listingProperties);
+        Assert.DoesNotContain(listingProperties, static property =>
+            property.Contains("token", StringComparison.OrdinalIgnoreCase)
+            || property.Contains("endpoint", StringComparison.OrdinalIgnoreCase)
+            || property.Contains("playerId", StringComparison.OrdinalIgnoreCase));
+    }
+}

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

@@ -0,0 +1,103 @@
+using System.Reflection;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Tests.Contracts;
+
+public sealed class PublicApiCompatibilityTests
+{
+    [Fact]
+    public void ContractsPublicApiMatchesTheV1Snapshot()
+    {
+        string snapshot = CreateSnapshot(typeof(ContractLimits).Assembly);
+        string expected = ContractTestFiles.Read("contracts-public-api.txt");
+        if (expected == "SNAPSHOT_PENDING"
+            && Environment.GetEnvironmentVariable("RENDEZVOUS_UPDATE_CONTRACT_SNAPSHOT") == "1")
+        {
+            string snapshotPath = Path.Combine(
+                ContractTestFiles.Directory,
+                "contracts-public-api.txt");
+            File.WriteAllText(snapshotPath, snapshot + Environment.NewLine);
+            expected = snapshot;
+        }
+
+        Assert.Equal(expected, snapshot);
+    }
+
+    private static string CreateSnapshot(Assembly assembly)
+    {
+        List<string> lines = [];
+        foreach (Type type in assembly.GetExportedTypes().OrderBy(static type => type.FullName, StringComparer.Ordinal))
+        {
+            lines.Add($"TYPE {FormatType(type)}");
+            if (type.IsEnum)
+            {
+                foreach (string name in Enum.GetNames(type))
+                {
+                    object value = Enum.Parse(type, name);
+                    lines.Add($"  ENUM {name}={Convert.ToInt64(value, System.Globalization.CultureInfo.InvariantCulture)}");
+                }
+
+                continue;
+            }
+
+            foreach (FieldInfo field in type.GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.DeclaredOnly)
+                         .OrderBy(static field => field.Name, StringComparer.Ordinal))
+            {
+                string value = field.IsLiteral
+                    ? Convert.ToString(field.GetRawConstantValue(), System.Globalization.CultureInfo.InvariantCulture) ?? "null"
+                    : "non-literal";
+                lines.Add($"  FIELD {FormatType(field.FieldType)} {field.Name}={value}");
+            }
+
+            foreach (ConstructorInfo constructor in type.GetConstructors(BindingFlags.Public | BindingFlags.Instance)
+                         .OrderBy(static constructor => FormatParameters(constructor.GetParameters()), StringComparer.Ordinal))
+            {
+                lines.Add($"  CTOR ({FormatParameters(constructor.GetParameters())})");
+            }
+
+            foreach (PropertyInfo property in type.GetProperties(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly)
+                         .OrderBy(static property => property.Name, StringComparer.Ordinal))
+            {
+                string accessors = $"{(property.CanRead ? "get;" : string.Empty)}{(property.CanWrite ? "set;" : string.Empty)}";
+                lines.Add($"  PROP {FormatType(property.PropertyType)} {property.Name} {{{accessors}}}");
+            }
+
+            foreach (MethodInfo method in type.GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly)
+                         .Where(static method => !method.IsSpecialName || method.Name.StartsWith("op_", StringComparison.Ordinal))
+                         .OrderBy(static method => method.Name, StringComparer.Ordinal)
+                         .ThenBy(static method => FormatParameters(method.GetParameters()), StringComparer.Ordinal))
+            {
+                lines.Add($"  METHOD {FormatType(method.ReturnType)} {method.Name}({FormatParameters(method.GetParameters())})");
+            }
+        }
+
+        return string.Join('\n', lines);
+    }
+
+    private static string FormatParameters(ParameterInfo[] parameters) => string.Join(
+        ", ",
+        parameters.Select(static parameter =>
+            $"{FormatType(parameter.ParameterType)} {parameter.Name}"));
+
+    private static string FormatType(Type type)
+    {
+        if (type.IsByRef)
+        {
+            return $"{FormatType(type.GetElementType()!)}&";
+        }
+
+        if (type.IsArray)
+        {
+            return $"{FormatType(type.GetElementType()!)}[]";
+        }
+
+        if (type.IsGenericType)
+        {
+            string name = type.GetGenericTypeDefinition().FullName!;
+            name = name[..name.IndexOf('`')];
+            return $"{name}<{string.Join(",", type.GetGenericArguments().Select(FormatType))}>";
+        }
+
+        return type.FullName ?? type.Name;
+    }
+}

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

@@ -0,0 +1,101 @@
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Tests.Contracts;
+
+public sealed class UdpCodecTests
+{
+    private static readonly Guid Handle = new("00112233-4455-6677-8899-aabbccddeeff");
+
+    [Fact]
+    public void HostPresenceMatchesTheV1GoldenVector()
+    {
+        byte[] encoded = RendezvousUdpCodec.Encode(CreateDatagram());
+
+        Assert.Equal(ContractTestFiles.Read("udp-host-ipv4.hex"), Convert.ToHexString(encoded).ToLowerInvariant());
+        Assert.True(RendezvousUdpCodec.TryDecode(encoded, out PresenceDatagram? decoded, out UdpDecodeError error));
+        Assert.Equal(UdpDecodeError.None, error);
+        Assert.NotNull(decoded);
+        Assert.Equal(Handle, decoded.MediationHandle.Value);
+        Assert.Equal("192.0.2.10", decoded.LocalAddress);
+        Assert.Equal(9050, decoded.LocalPort);
+        Assert.Equal("Abc_123-xYz", decoded.Capability);
+    }
+
+    [Fact]
+    public void Ipv6RoundtripsWithoutLosingItsAddressFamily()
+    {
+        PresenceDatagram original = CreateDatagram();
+        original.MessageType = UdpPresenceMessageType.ClientPresence;
+        original.AddressFamily = AddressFamilyKind.Ipv6;
+        original.LocalAddress = "2001:db8::10";
+
+        byte[] encoded = RendezvousUdpCodec.Encode(original);
+
+        Assert.True(RendezvousUdpCodec.TryDecode(encoded, out PresenceDatagram? decoded, out _));
+        Assert.NotNull(decoded);
+        Assert.Equal(AddressFamilyKind.Ipv6, decoded.AddressFamily);
+        Assert.Equal("2001:db8::10", decoded.LocalAddress);
+    }
+
+    [Fact]
+    public void EncoderRejectsAnAddressFamilyMismatch()
+    {
+        PresenceDatagram datagram = CreateDatagram();
+        datagram.AddressFamily = AddressFamilyKind.Ipv4;
+        datagram.LocalAddress = "2001:db8::10";
+
+        Assert.Throws<ArgumentException>(() => RendezvousUdpCodec.Encode(datagram));
+    }
+
+    [Theory]
+    [InlineData(2, 2, UdpDecodeError.UnsupportedVersion)]
+    [InlineData(3, 3, UdpDecodeError.UnknownMessageType)]
+    [InlineData(4, 1, UdpDecodeError.InvalidFlags)]
+    [InlineData(21, 5, UdpDecodeError.InvalidAddressFamily)]
+    public void DecoderReturnsStableErrorsForUnknownHeaderValues(
+        int offset,
+        byte replacement,
+        UdpDecodeError expected)
+    {
+        byte[] encoded = RendezvousUdpCodec.Encode(CreateDatagram());
+        encoded[offset] = replacement;
+
+        Assert.False(RendezvousUdpCodec.TryDecode(encoded, out _, out UdpDecodeError actual));
+        Assert.Equal(expected, actual);
+    }
+
+    [Fact]
+    public void DecoderRejectsTruncationTrailingDataAndOversizedPackets()
+    {
+        byte[] encoded = RendezvousUdpCodec.Encode(CreateDatagram());
+        byte[] trailing = [.. encoded, 0];
+        byte[] oversized = new byte[ContractLimits.UdpDatagramMaxBytes + 1];
+
+        Assert.False(RendezvousUdpCodec.TryDecode(encoded.AsSpan(0, encoded.Length - 1), out _, out UdpDecodeError truncated));
+        Assert.Equal(UdpDecodeError.Truncated, truncated);
+        Assert.False(RendezvousUdpCodec.TryDecode(trailing, out _, out UdpDecodeError trailingError));
+        Assert.Equal(UdpDecodeError.TrailingData, trailingError);
+        Assert.False(RendezvousUdpCodec.TryDecode(oversized, out _, out UdpDecodeError oversizedError));
+        Assert.Equal(UdpDecodeError.DatagramTooLarge, oversizedError);
+    }
+
+    [Fact]
+    public void DecoderRejectsNonBase64UrlCapabilities()
+    {
+        byte[] encoded = RendezvousUdpCodec.Encode(CreateDatagram());
+        encoded[^1] = (byte)'+';
+
+        Assert.False(RendezvousUdpCodec.TryDecode(encoded, out _, out UdpDecodeError error));
+        Assert.Equal(UdpDecodeError.InvalidCapability, error);
+    }
+
+    private static PresenceDatagram CreateDatagram() => new()
+    {
+        MessageType = UdpPresenceMessageType.HostPresence,
+        MediationHandle = new MediationHandle(Handle),
+        AddressFamily = AddressFamilyKind.Ipv4,
+        LocalAddress = "192.0.2.10",
+        LocalPort = 9050,
+        Capability = "Abc_123-xYz",
+    };
+}

tests/FinalFactory.Rendezvous.Tests/FinalFactory.Rendezvous.Tests.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <AssemblyName>FinalFactory.Rendezvous.Tests</AssemblyName>
+    <RootNamespace>FinalFactory.Rendezvous.Tests</RootNamespace>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" />
+    <PackageReference Include="xunit" />
+    <PackageReference Include="xunit.runner.visualstudio">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="../../src/FinalFactory.Rendezvous.Client/FinalFactory.Rendezvous.Client.csproj" />
+    <ProjectReference Include="../../src/FinalFactory.Rendezvous.Contracts/FinalFactory.Rendezvous.Contracts.csproj" />
+    <ProjectReference Include="../../src/FinalFactory.Rendezvous.Server/FinalFactory.Rendezvous.Server.csproj" />
+    <ProjectReference Include="../../src/FinalFactory.Rendezvous.TestClient/FinalFactory.Rendezvous.TestClient.csproj" />
+  </ItemGroup>
+</Project>

tests/FinalFactory.Rendezvous.Tests/GlobalUsings.cs

@@ -0,0 +1 @@
+global using Xunit;

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

@@ -0,0 +1,34 @@
+using System.Net;
+using FinalFactory.Rendezvous.Server.Transport;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+
+namespace FinalFactory.Rendezvous.Tests.Server;
+
+public sealed class UdpMediatorServiceTests
+{
+    [Fact]
+    public async Task ServiceBindsAnEphemeralUdpPortAndStopsCleanly()
+    {
+        using CancellationTokenSource timeout = new(TimeSpan.FromSeconds(5));
+        UdpMediatorOptions options = new()
+        {
+            ListenAddress = IPAddress.Loopback.ToString(),
+            Port = 0,
+        };
+        using UdpMediatorService service = new(
+            Options.Create(options),
+            NullLogger<UdpMediatorService>.Instance);
+
+        await service.StartAsync(timeout.Token);
+
+        IPEndPoint? boundEndpoint = service.LocalEndpoint;
+        Assert.NotNull(boundEndpoint);
+        Assert.Equal(IPAddress.Loopback, boundEndpoint.Address);
+        Assert.InRange(boundEndpoint.Port, 1, 65_535);
+
+        await service.StopAsync(timeout.Token);
+
+        Assert.Null(service.LocalEndpoint);
+    }
+}

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/api-error.json

@@ -0,0 +1 @@
+{"contractVersion":1,"code":"rateLimited","message":"Try again later.","correlationId":"request-001","retryAfterSeconds":3}

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/browse-sessions.json

@@ -0,0 +1 @@
+{"contractVersion":1,"items":[{"contractVersion":1,"listingId":"00112233-4455-6677-8899-aabbccddeeff","gameId":"space-game","environmentId":"production","regionId":"eu-central","protocolVersion":7,"buildVersion":"1.4.2","displayName":"Europa Relay","visibility":"public","publisherTrustMode":"managedDedicated","capacity":{"currentPlayers":2,"maximumPlayers":8},"metadata":{"mode":"co-op","map":"europa"}}],"nextCursor":"cursor-002"}

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

@@ -0,0 +1,315 @@
+TYPE FinalFactory.Rendezvous.Contracts.AddressFamilyKind
+  ENUM Ipv4=4
+  ENUM Ipv6=6
+TYPE FinalFactory.Rendezvous.Contracts.ApiError
+  CTOR ()
+  PROP FinalFactory.Rendezvous.Contracts.RendezvousErrorCode Code {get;set;}
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String CorrelationId {get;set;}
+  PROP System.String Message {get;set;}
+  PROP System.Nullable<System.Int32> RetryAfterSeconds {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.BrowseHostJoinAttemptsResponse
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.Collections.Generic.List<FinalFactory.Rendezvous.Contracts.HostJoinAttempt> Items {get;set;}
+  PROP System.String NextCursor {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.BrowseSessionsRequest
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String Cursor {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.EnvironmentId EnvironmentId {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.GameId GameId {get;set;}
+  PROP System.Int32 PageSize {get;set;}
+  PROP System.UInt32 ProtocolVersion {get;set;}
+  PROP System.Nullable<FinalFactory.Rendezvous.Contracts.RegionId> RegionId {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.BrowseSessionsResponse
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.Collections.Generic.List<FinalFactory.Rendezvous.Contracts.SessionListing> Items {get;set;}
+  PROP System.String NextCursor {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.ConnectionOutcomeKind
+  ENUM Connected=1
+  ENUM Cancelled=2
+  ENUM TimedOut=3
+  ENUM IncompatibleProtocol=4
+  ENUM StaleHost=5
+  ENUM ServiceRejected=6
+  ENUM HostRejected=7
+  ENUM TransportFailed=8
+  ENUM FallbackOffered=9
+TYPE FinalFactory.Rendezvous.Contracts.ContractJson
+  PROP System.Text.Json.JsonSerializerOptions Options {get;}
+  METHOD System.Void Configure(System.Text.Json.JsonSerializerOptions options)
+  METHOD System.Text.Json.JsonSerializerOptions CreateOptions()
+TYPE FinalFactory.Rendezvous.Contracts.ContractLimits
+  FIELD System.Int32 BrowserPageMaxItems=100
+  FIELD System.Int32 BrowserResponseMaxBytes=262144
+  FIELD System.Int32 BuildVersionMaxBytes=64
+  FIELD System.Int32 ConnectionTicketMaxCharacters=192
+  FIELD System.Int32 ContractVersion=1
+  FIELD System.Int32 CursorMaxCharacters=512
+  FIELD System.Int32 DiagnosticCodeMaxCharacters=64
+  FIELD System.Int32 DisplayNameMaxBytes=128
+  FIELD System.Int32 EnvironmentIdMaxCharacters=32
+  FIELD System.Int32 ErrorMessageMaxBytes=256
+  FIELD System.Int32 GameIdMaxCharacters=64
+  FIELD System.Int32 HttpRequestMaxBytes=16384
+  FIELD System.Int32 IdempotencyKeyMaxCharacters=64
+  FIELD System.Int32 LiteNetLibNatTokenMaxCharacters=256
+  FIELD System.Int32 MetadataKeyMaxBytes=64
+  FIELD System.Int32 MetadataMaxBytes=4096
+  FIELD System.Int32 MetadataMaxKeys=32
+  FIELD System.Int32 MetadataValueMaxBytes=256
+  FIELD System.Int32 OpaqueHttpCredentialMaxCharacters=1024
+  FIELD System.Int32 RegionIdMaxCharacters=32
+  FIELD System.Int32 SessionCapacityMaxPlayers=10000
+  FIELD System.Int32 UdpCapabilityMaxCharacters=192
+  FIELD System.Int32 UdpDatagramMaxBytes=1200
+TYPE FinalFactory.Rendezvous.Contracts.ContractValidation
+  METHOD System.Boolean AreProtocolsCompatible(System.UInt32 requested, System.UInt32 offered)
+  METHOD System.Boolean IsBrowserResponseSizeValid(System.Int32 byteCount)
+  METHOD System.Boolean IsBuildVersionValid(System.String value)
+  METHOD System.Boolean IsCapabilityValid(System.String capability)
+  METHOD System.Boolean IsCapacityValid(FinalFactory.Rendezvous.Contracts.SessionCapacity capacity)
+  METHOD System.Boolean IsConnectionTicketValid(System.String ticket)
+  METHOD System.Boolean IsCursorValid(System.String value)
+  METHOD System.Boolean IsDiagnosticCodeValid(System.String value)
+  METHOD System.Boolean IsDisplayNameValid(System.String value)
+  METHOD System.Boolean IsHttpRequestSizeValid(System.Int32 byteCount)
+  METHOD System.Boolean IsIdempotencyKeyValid(System.String value)
+  METHOD System.Boolean IsMetadataValid(System.Collections.Generic.IReadOnlyDictionary<System.String,System.String> metadata)
+  METHOD System.Boolean IsNetworkEndpointValid(FinalFactory.Rendezvous.Contracts.NetworkEndpoint endpoint)
+  METHOD System.Boolean IsOpaqueHttpCredentialValid(System.String value)
+  METHOD System.Boolean IsPageSizeValid(System.Int32 pageSize)
+  METHOD System.Boolean IsUtf8LengthWithin(System.String value, System.Int32 maximumBytes)
+  METHOD FinalFactory.Rendezvous.Contracts.RendezvousErrorCode ValidateContractVersion(System.Int32 contractVersion)
+TYPE FinalFactory.Rendezvous.Contracts.CreateJoinAttemptRequest
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.EnvironmentId EnvironmentId {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.GameId GameId {get;set;}
+  PROP System.String IdempotencyKey {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.SessionListingId ListingId {get;set;}
+  PROP System.UInt32 ProtocolVersion {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.CreateJoinAttemptResponse
+  CTOR ()
+  PROP FinalFactory.Rendezvous.Contracts.JoinAttemptId AttemptId {get;set;}
+  PROP System.String ClientPunchCapability {get;set;}
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.NetworkEndpoint DedicatedFallback {get;set;}
+  PROP System.DateTimeOffset ExpiresAt {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.MediationHandle MediationHandle {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.DeleteSessionRequest
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String LeaseToken {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.EnvironmentId
+  CTOR (System.String value)
+  PROP System.String Value {get;}
+  METHOD System.Boolean Equals(FinalFactory.Rendezvous.Contracts.EnvironmentId other)
+  METHOD System.Boolean Equals(System.Object obj)
+  METHOD System.Int32 GetHashCode()
+  METHOD System.String ToString()
+  METHOD System.Boolean TryParse(System.String value, FinalFactory.Rendezvous.Contracts.EnvironmentId& environmentId)
+  METHOD System.Boolean op_Equality(FinalFactory.Rendezvous.Contracts.EnvironmentId left, FinalFactory.Rendezvous.Contracts.EnvironmentId right)
+  METHOD System.Boolean op_Inequality(FinalFactory.Rendezvous.Contracts.EnvironmentId left, FinalFactory.Rendezvous.Contracts.EnvironmentId right)
+TYPE FinalFactory.Rendezvous.Contracts.GameId
+  CTOR (System.String value)
+  PROP System.String Value {get;}
+  METHOD System.Boolean Equals(FinalFactory.Rendezvous.Contracts.GameId other)
+  METHOD System.Boolean Equals(System.Object obj)
+  METHOD System.Int32 GetHashCode()
+  METHOD System.String ToString()
+  METHOD System.Boolean TryParse(System.String value, FinalFactory.Rendezvous.Contracts.GameId& gameId)
+  METHOD System.Boolean op_Equality(FinalFactory.Rendezvous.Contracts.GameId left, FinalFactory.Rendezvous.Contracts.GameId right)
+  METHOD System.Boolean op_Inequality(FinalFactory.Rendezvous.Contracts.GameId left, FinalFactory.Rendezvous.Contracts.GameId right)
+TYPE FinalFactory.Rendezvous.Contracts.GetSessionResponse
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.SessionListing Session {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.HealthResponse
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String Status {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.HostJoinAttempt
+  CTOR ()
+  PROP FinalFactory.Rendezvous.Contracts.JoinAttemptId AttemptId {get;set;}
+  PROP System.DateTimeOffset ExpiresAt {get;set;}
+  PROP System.String HostPunchCapability {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.MediationHandle MediationHandle {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.JoinAttemptId
+  CTOR (System.Guid value)
+  PROP System.Guid Value {get;}
+  METHOD System.Boolean Equals(FinalFactory.Rendezvous.Contracts.JoinAttemptId other)
+  METHOD System.Boolean Equals(System.Object obj)
+  METHOD System.Int32 GetHashCode()
+  METHOD System.String ToString()
+  METHOD System.Boolean TryParse(System.String value, FinalFactory.Rendezvous.Contracts.JoinAttemptId& id)
+  METHOD System.Boolean op_Equality(FinalFactory.Rendezvous.Contracts.JoinAttemptId left, FinalFactory.Rendezvous.Contracts.JoinAttemptId right)
+  METHOD System.Boolean op_Inequality(FinalFactory.Rendezvous.Contracts.JoinAttemptId left, FinalFactory.Rendezvous.Contracts.JoinAttemptId right)
+TYPE FinalFactory.Rendezvous.Contracts.LeaseId
+  CTOR (System.Guid value)
+  PROP System.Guid Value {get;}
+  METHOD System.Boolean Equals(FinalFactory.Rendezvous.Contracts.LeaseId other)
+  METHOD System.Boolean Equals(System.Object obj)
+  METHOD System.Int32 GetHashCode()
+  METHOD System.String ToString()
+  METHOD System.Boolean TryParse(System.String value, FinalFactory.Rendezvous.Contracts.LeaseId& id)
+  METHOD System.Boolean op_Equality(FinalFactory.Rendezvous.Contracts.LeaseId left, FinalFactory.Rendezvous.Contracts.LeaseId right)
+  METHOD System.Boolean op_Inequality(FinalFactory.Rendezvous.Contracts.LeaseId left, FinalFactory.Rendezvous.Contracts.LeaseId right)
+TYPE FinalFactory.Rendezvous.Contracts.ListingVisibility
+  ENUM Public=1
+  ENUM Unlisted=2
+TYPE FinalFactory.Rendezvous.Contracts.MediationHandle
+  CTOR (System.Guid value)
+  PROP System.Guid Value {get;}
+  METHOD System.Boolean Equals(FinalFactory.Rendezvous.Contracts.MediationHandle other)
+  METHOD System.Boolean Equals(System.Object obj)
+  METHOD System.Int32 GetHashCode()
+  METHOD System.String ToString()
+  METHOD System.Boolean TryParse(System.String value, FinalFactory.Rendezvous.Contracts.MediationHandle& id)
+  METHOD System.Boolean op_Equality(FinalFactory.Rendezvous.Contracts.MediationHandle left, FinalFactory.Rendezvous.Contracts.MediationHandle right)
+  METHOD System.Boolean op_Inequality(FinalFactory.Rendezvous.Contracts.MediationHandle left, FinalFactory.Rendezvous.Contracts.MediationHandle right)
+TYPE FinalFactory.Rendezvous.Contracts.NetworkEndpoint
+  CTOR ()
+  PROP System.String Address {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.AddressFamilyKind AddressFamily {get;set;}
+  PROP System.Int32 Port {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.PresenceDatagram
+  CTOR ()
+  PROP FinalFactory.Rendezvous.Contracts.AddressFamilyKind AddressFamily {get;set;}
+  PROP System.String Capability {get;set;}
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String LocalAddress {get;set;}
+  PROP System.Int32 LocalPort {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.MediationHandle MediationHandle {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.UdpPresenceMessageType MessageType {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.PublisherTrustMode
+  ENUM ManagedDedicated=1
+  ENUM PlayerGrant=2
+  ENUM AnonymousUnlisted=3
+TYPE FinalFactory.Rendezvous.Contracts.RegionId
+  CTOR (System.String value)
+  PROP System.String Value {get;}
+  METHOD System.Boolean Equals(FinalFactory.Rendezvous.Contracts.RegionId other)
+  METHOD System.Boolean Equals(System.Object obj)
+  METHOD System.Int32 GetHashCode()
+  METHOD System.String ToString()
+  METHOD System.Boolean TryParse(System.String value, FinalFactory.Rendezvous.Contracts.RegionId& regionId)
+  METHOD System.Boolean op_Equality(FinalFactory.Rendezvous.Contracts.RegionId left, FinalFactory.Rendezvous.Contracts.RegionId right)
+  METHOD System.Boolean op_Inequality(FinalFactory.Rendezvous.Contracts.RegionId left, FinalFactory.Rendezvous.Contracts.RegionId right)
+TYPE FinalFactory.Rendezvous.Contracts.RegisterSessionRequest
+  CTOR ()
+  PROP System.String BuildVersion {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.SessionCapacity Capacity {get;set;}
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String DisplayName {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.EnvironmentId EnvironmentId {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.GameId GameId {get;set;}
+  PROP System.String IdempotencyKey {get;set;}
+  PROP System.Collections.Generic.Dictionary<System.String,System.String> Metadata {get;set;}
+  PROP System.UInt32 ProtocolVersion {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.RegionId RegionId {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.ListingVisibility Visibility {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.RegisterSessionResponse
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.DateTimeOffset ExpiresAt {get;set;}
+  PROP System.String HostPresenceCapability {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.MediationHandle HostPresenceHandle {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.LeaseId LeaseId {get;set;}
+  PROP System.String LeaseToken {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.SessionListingId ListingId {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.RendezvousErrorCode
+  ENUM None=0
+  ENUM InvalidRequest=1
+  ENUM UnsupportedContractVersion=2
+  ENUM IncompatibleProtocol=3
+  ENUM AuthenticationRequired=4
+  ENUM Forbidden=5
+  ENUM NotFound=6
+  ENUM Conflict=7
+  ENUM RateLimited=8
+  ENUM StaleHost=9
+  ENUM Expired=10
+  ENUM ReplayRejected=11
+  ENUM CapacityExceeded=12
+  ENUM ServiceUnavailable=13
+  ENUM InternalError=14
+TYPE FinalFactory.Rendezvous.Contracts.RendezvousUdpCodec
+  FIELD System.Byte FlagsNone=0
+  FIELD System.Byte MagicFirst=82
+  FIELD System.Byte MagicSecond=86
+  METHOD System.Byte[] Encode(FinalFactory.Rendezvous.Contracts.PresenceDatagram datagram)
+  METHOD System.Boolean TryDecode(System.ReadOnlySpan<System.Byte> encoded, FinalFactory.Rendezvous.Contracts.PresenceDatagram& datagram, FinalFactory.Rendezvous.Contracts.UdpDecodeError& error)
+TYPE FinalFactory.Rendezvous.Contracts.RenewLeaseRequest
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String LeaseToken {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.RenewLeaseResponse
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.DateTimeOffset ExpiresAt {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.ReportConnectionOutcomeRequest
+  CTOR ()
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String DiagnosticCode {get;set;}
+  PROP System.Int32 ElapsedMilliseconds {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.ConnectionOutcomeKind Outcome {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.ReportConnectionOutcomeResponse
+  CTOR ()
+  PROP System.Boolean Accepted {get;set;}
+  PROP System.Int32 ContractVersion {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.SessionCapacity
+  CTOR ()
+  PROP System.Int32 CurrentPlayers {get;set;}
+  PROP System.Int32 MaximumPlayers {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.SessionListing
+  CTOR ()
+  PROP System.String BuildVersion {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.SessionCapacity Capacity {get;set;}
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String DisplayName {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.EnvironmentId EnvironmentId {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.GameId GameId {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.SessionListingId ListingId {get;set;}
+  PROP System.Collections.Generic.Dictionary<System.String,System.String> Metadata {get;set;}
+  PROP System.UInt32 ProtocolVersion {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.PublisherTrustMode PublisherTrustMode {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.RegionId RegionId {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.ListingVisibility Visibility {get;set;}
+TYPE FinalFactory.Rendezvous.Contracts.SessionListingId
+  CTOR (System.Guid value)
+  PROP System.Guid Value {get;}
+  METHOD System.Boolean Equals(FinalFactory.Rendezvous.Contracts.SessionListingId other)
+  METHOD System.Boolean Equals(System.Object obj)
+  METHOD System.Int32 GetHashCode()
+  METHOD System.String ToString()
+  METHOD System.Boolean TryParse(System.String value, FinalFactory.Rendezvous.Contracts.SessionListingId& id)
+  METHOD System.Boolean op_Equality(FinalFactory.Rendezvous.Contracts.SessionListingId left, FinalFactory.Rendezvous.Contracts.SessionListingId right)
+  METHOD System.Boolean op_Inequality(FinalFactory.Rendezvous.Contracts.SessionListingId left, FinalFactory.Rendezvous.Contracts.SessionListingId right)
+TYPE FinalFactory.Rendezvous.Contracts.UdpDecodeError
+  ENUM None=0
+  ENUM DatagramTooLarge=1
+  ENUM Truncated=2
+  ENUM InvalidMagic=3
+  ENUM UnsupportedVersion=4
+  ENUM UnknownMessageType=5
+  ENUM InvalidFlags=6
+  ENUM InvalidHandle=7
+  ENUM InvalidAddressFamily=8
+  ENUM InvalidAddress=9
+  ENUM InvalidPort=10
+  ENUM InvalidCapability=11
+  ENUM TrailingData=12
+TYPE FinalFactory.Rendezvous.Contracts.UdpPresenceMessageType
+  ENUM HostPresence=1
+  ENUM ClientPresence=2
+TYPE FinalFactory.Rendezvous.Contracts.UpdateSessionRequest
+  CTOR ()
+  PROP System.String BuildVersion {get;set;}
+  PROP FinalFactory.Rendezvous.Contracts.SessionCapacity Capacity {get;set;}
+  PROP System.Int32 ContractVersion {get;set;}
+  PROP System.String DisplayName {get;set;}
+  PROP System.String LeaseToken {get;set;}
+  PROP System.Collections.Generic.Dictionary<System.String,System.String> Metadata {get;set;}

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/create-join-response.json

@@ -0,0 +1 @@
+{"contractVersion":1,"attemptId":"11112233-4455-6677-8899-aabbccddeeff","mediationHandle":"22222233-4455-6677-8899-aabbccddeeff","clientPunchCapability":"Abc_123-xYz","expiresAt":"2026-07-16T12:00:00+00:00","dedicatedFallback":{"addressFamily":"ipv6","address":"2001:db8::10","port":9050}}

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

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+{"contractVersion":1,"idempotencyKey":"register-001","gameId":"space-game","environmentId":"production","regionId":"eu-central","protocolVersion":7,"buildVersion":"1.4.2","displayName":"Europa Relay","visibility":"public","capacity":{"currentPlayers":2,"maximumPlayers":8},"metadata":{"mode":"co-op","map":"europa"}}

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/udp-host-ipv4.hex

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+525601010000112233445566778899aabbccddeeff0404c000020a235a0b4162635f3132332d78597a

tests/FinalFactory.Rendezvous.Tests/packages.lock.json

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