feat(statehub): add offline write buffer relay

api/main.py

@@ -11,6 +11,7 @@ from starlette.responses import Response as StarletteResponse
 
 from api.database import engine
 from api.events import shutdown_publisher
+from api.services.write_idempotency import WriteIdempotencyMiddleware
 from api.routers import decisions, extension_points, progress, state, tasks, technical_debt, topics, workstreams, workstream_dependencies
 from api.routers import domains, repos, contributions, sbom, policy, domain_goals, repo_goals, messages, capability_requests, tpsc, services
 from api.routers import token_events
@@ -91,13 +92,14 @@ _default_dashboard_origins = [
 _cors_env = os.getenv("CORS_ORIGINS", ",".join(_default_dashboard_origins))
 _cors_origins = [o.strip() for o in _cors_env.split(",") if o.strip()]
 
+app.add_middleware(WriteIdempotencyMiddleware)
 app.add_middleware(ETagMiddleware)
 app.add_middleware(
     CORSMiddleware,
     allow_origins=_cors_origins,
     allow_methods=["GET", "POST", "PATCH", "DELETE", "PUT"],
-    allow_headers=["Content-Type", "If-None-Match"],
-    expose_headers=["ETag", "X-StateHub-Elapsed-Ms", "X-StateHub-Response-Bytes", "X-StateHub-Cache"],
+    allow_headers=["Content-Type", "If-None-Match", "Idempotency-Key", "X-StateHub-Source-Agent", "X-StateHub-Source-Host"],
+    expose_headers=["ETag", "X-StateHub-Elapsed-Ms", "X-StateHub-Response-Bytes", "X-StateHub-Cache", "X-StateHub-Idempotency-Replay"],
 )
 
 app.include_router(domains.router)