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backend/examples/plugin/request-lifecycle/README.md

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+# Request Lifecycle Plugin
+
+This Go dynamic-library plugin demonstrates request admission, active termination, and exactly-once terminal lifecycle handling. It requires a host that supports plugin RPC schema version 2 or newer.
+
+It declares two optional capabilities:
+
+- `request_interceptor`: acquires a concurrency slot in `request.intercept_before` and can terminate the request before any upstream executor runs.
+- `request_lifecycle_plugin`: releases the slot in `request.complete` for successful, failed, rejected, and canceled requests.
+
+The host passes the same `RequestID` to request interception, response interception, stream interception, and the terminal `RequestCompletion` event.
+
+## Behavior
+
+- Allows at most `max_concurrency` requests in flight.
+- Returns a custom `429` JSON response with `Retry-After: 1` when the limit is reached.
+- Returns a custom `403` JSON response when the raw request body contains `reject_keyword`.
+- Does not send terminated requests to an upstream model.
+- Releases only request IDs that were previously admitted, so rejected requests and duplicate terminal events do not underflow the counter.
+
+## Configuration
+
+```yaml
+plugins:
+  enabled: true
+  configs:
+    request-lifecycle:
+      enabled: true
+      priority: 100
+      max_concurrency: 2
+      reject_keyword: "blocked"
+```
+
+Set `reject_keyword` to an empty string to disable keyword rejection.
+
+## Build
+
+From the repository root on macOS:
+
+```bash
+mkdir -p plugins/darwin/$(go env GOARCH)
+go build -buildmode=c-shared \
+  -o plugins/darwin/$(go env GOARCH)/request-lifecycle.dylib \
+  ./examples/plugin/request-lifecycle/go
+rm -f plugins/darwin/$(go env GOARCH)/request-lifecycle.h
+```
+
+Use `.so` on Linux or FreeBSD and `.dll` on Windows.
+
+The output filename is the plugin ID, so the example artifact must be named `request-lifecycle` for the configuration above.
+
+## Relevant RPC Methods
+
+```text
+plugin.register
+plugin.reconfigure
+request.intercept_before
+request.intercept_after
+request.complete
+```
+
+`request.complete` is an observational callback. The host schedules it asynchronously so a blocked plugin cannot delay response delivery, logs callback errors, and uses a context detached from downstream cancellation so a canceled request can still release its slot.