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docs/features/checked/router/router-backpressure.md

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+# Router Backpressure (HTTP 429/503 + Retry-After)
+
+## Module
+Router
+
+## Status
+IMPLEMENTED
+
+## Description
+Rate limiting and backpressure testing with dedicated chaos test suite for the router, including Testcontainers-based fixture for burst testing.
+
+## Implementation Details
+- **Modules**: `src/Router/__Libraries/StellaOps.Router.Gateway/RateLimit/`, `src/Router/__Libraries/StellaOps.Router.Transport.InMemory/`
+- **Key Classes**:
+  - `ValkeyRateLimitStore` (`src/Router/__Libraries/StellaOps.Router.Gateway/RateLimit/ValkeyRateLimitStore.cs`) - Valkey-backed rate limit storage for per-instance throttling
+  - `InMemoryRateLimiter` (`src/Router/__Libraries/StellaOps.Messaging.Transport.InMemory/InMemoryRateLimiter.cs`) - in-memory rate limiter for testing
+- **Source**: Feature matrix scan
+
+## E2E Test Plan
+- [ ] Send requests exceeding the rate limit and verify HTTP 429 responses with Retry-After header
+- [ ] Verify HTTP 503 response when all instances are overloaded
+- [ ] Verify backpressure propagation: confirm the gateway signals backpressure to callers when queues are full
+- [ ] Verify rate limit recovery: after throttling, confirm requests resume when the limit window expires
+- [ ] Verify per-instance rate limiting: confirm each microservice instance has its own rate limit counter