Module 5: Game Hosting Architecture (backend)

[MohanEhab]

Summary

• Adds the Module 5 GameHost plugin-contract layer: a typed IGameDefinition<TState,TCommand,TPlayerView> contract, a non-generic host adapter, a TryResolve(slug, engineVersion) registry, an allow-listed System.Text.Json codec with a checksummed byte envelope, a PCG32-v1 deterministic RNG, a size/budget/redaction invoker boundary, and a catalog/engine-compatibility validator.
• Deletes the three orphaned, unimplemented legacy stubs (IGameEngine.cs, GameSession.cs, and the old IGameRegistry.cs contract) they replace.
• Backend-only: no EF entity/migration, no public route, no frontend change. Module 4's game-library UI is untouched.

What changed

• feat: GameHost domain contracts (envelopes, RNG, error codes) + removal of legacy stubs
• feat: GameHost application services (codec, registry, invoker, catalog validator) + DI/Program.cs wiring with startup fail-fast on duplicate/mismatched catalog entries
• test: 177 unit + 12 integration tests (189/189 passing), including a two-process golden-vector determinism proof and a Stopwatch benchmark

Tests

• dotnet test --filter "FullyQualifiedName~GameHost": 189/189 passed (177 unit + 12 integration)
• Full solution: 589/589 unit, 231/231 non-skipped integration passed (52 skipped — pre-existing real-Postgres group, unrelated to this module)
• Two independently launched dotnet test processes produced byte-identical golden-vector SHA-256 hashes (10/10 vectors)
• GameHostBenchmarkTests: p95 = 0.0293 ms (budget < 25 ms), max single command 12.1803 ms (soft budget ≤ 100 ms)
• check-contract-drift.mjs: DRIFT=0 (no new route/frontend surface)

Security/docs

• --security=asvs-lite backend review complete: zero unwaived Critical/High/Medium findings. 3 deferred non-blocking findings (M05-001 Low, M05-002/M05-003 Info) — see SimPle.Project/docs/security/audits/module-05-game-hosting-architecture.md.
• Module docs (api-reference.md, technical-flow.md, testing-report.md) are in the companion SimPle.Project PR.

Risks/deferred

• In-process isolation for hostile plugins is an explicit non-goal (documented residual risk); the soft/hard timing budgets, two-process determinism check, and code review are the only guards.
• Zero product game engines are registered in Phase 1 (Array.Empty<IHostedGameDefinition>() in Program.cs) — intentional, valid state.
• Match lifecycle, persistence, AI, rating/stats, matchmaking, and presence/chat are explicitly out of scope, owned by Modules 6–10.