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docs/networking/network/network-plugin-circuit-breaker/README.md

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+# @suaveplan/network-plugin-circuit-breaker - Circuit-breaker plugin for mesh relay paths: per-path state machine, registry, half-open probes, and relay middleware integration
+
+## Summary
+
+Mesh-level circuit breakers: per-path state machine (`CLOSED → OPEN → HALF_OPEN`), registry, half-open probe loop, and relay middleware integration. Fast-fails dead relay paths so retries don't cascade.
+
+<!-- begin:auto-docs -->
+## Documentation tree
+
+- [breaker](./src/breaker/mesh-circuit-breaker.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+  - [mesh-circuit-breaker](./src/breaker/mesh-circuit-breaker.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+- [middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+  - [circuit-breaker-middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+- [probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+  - [half-open-probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+- [registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+  - [circuit-breaker-registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+- [error-codes](./src/error-codes.md) — Frozen error-code registry for the mesh circuit-breaker plugin. Two codes cover the full surface: `PATH_OPEN` when a re…
+<!-- end:auto-docs -->  - [mesh-circuit-breaker](./src/breaker/mesh-circuit-breaker.md) — <!-- begin:auto-docs --> _(no submodules)_- [middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_- [circuit-breaker-middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_- [probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_- [half-open-probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_- [registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_- [circuit-breaker-registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_- [error-codes](./src/error-codes.md) — Frozen error-code registry for the mesh circuit-breaker plugin. Two codes cover the full surface: `PATH_OPEN` when a re…
+- [mesh-circuit-breaker](./src/breaker/mesh-circuit-breaker.md) — <!-- begin:auto-docs --> _(no submodules)_- [middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_- [circuit-breaker-middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_- [probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_- [half-open-probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_- [registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_- [circuit-breaker-registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_- [error-codes](./src/error-codes.md) — Frozen error-code registry for the mesh circuit-breaker plugin. Two codes cover the full surface: `PATH_OPEN` when a re…
+- [mesh-circuit-breaker](./src/breaker/mesh-circuit-breaker.md) — <!-- begin:auto-docs --> _(no submodules)_- [middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_- [circuit-breaker-middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_- [probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_- [half-open-probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_- [registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_- [circuit-breaker-registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_- [error-codes](./src/error-codes.md) — Frozen error-code registry for the mesh circuit-breaker plugin. Two codes cover the full surface: `PATH_OPEN` when a re…
+- [mesh-circuit-breaker](./src/breaker/mesh-circuit-breaker.md) — <!-- begin:auto-docs --> _(no submodules)_- [middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_  - [circuit-breaker-middleware](./src/middleware/circuit-breaker-middleware.md) — <!-- begin:auto-docs --> _(no submodules)_- [probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_  - [half-open-probe](./src/probe/half-open-probe.md) — <!-- begin:auto-docs --> _(no submodules)_- [registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_  - [circuit-breaker-registry](./src/registry/circuit-breaker-registry.md) — <!-- begin:auto-docs --> _(no submodules)_- [error-codes](./src/error-codes.md) — Frozen error-code registry for the mesh circuit-breaker plugin. Two codes cover the full surface: `PATH_OPEN` when a re…

docs/networking/network/network-plugin-circuit-breaker/src/breaker/mesh-circuit-breaker.md

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+# MeshCircuitBreaker
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+## Purpose
+
+Per-path circuit-breaker FSM that walks `CLOSED → OPEN → HALF_OPEN → CLOSED`. Stops repeated wire-level retries against a known-dead path so retries don't cascade into healthy paths. Each `(localHostId, nextHopHostId)` pair gets its own breaker instance, identified by `pathId`.
+
+## Features
+
+- Three-state FSM with deterministic transitions.
+- Configurable `failureThreshold` (default 5), `successThreshold` (default 3), `openDurationMs` (default 30 s), `halfOpenMaxCalls` (default 3).
+- Auto-transition `OPEN → HALF_OPEN` after the cooldown elapses (lazy-evaluated on `getState`/`canExecute`).
+- Throws `INVALID_TRANSITION` on `recordSuccess()` from `OPEN` to surface programmer errors loudly.
+- Bus-free: state-change listeners installed via `on(handler)` for downstream observability without coupling to a specific bus.
+- Injectable `clock` for deterministic tests.
+
+## Usage: Basic Example
+
+```ts
+import { MeshCircuitBreaker } from "@suaveplan/network-plugin-circuit-breaker";
+
+const cb = new MeshCircuitBreaker({ pathId: "meshA:host1→meshB:host2" });
+
+if (cb.canExecute()) {
+    try {
+        await sendThroughPath();
+        cb.recordSuccess();
+    } catch (err) {
+        cb.recordFailure();
+        throw err;
+    }
+}
+```
+
+## Usage: Advanced Example
+
+```ts
+import { MeshCircuitBreaker } from "@suaveplan/network-plugin-circuit-breaker";
+
+let now = 0;
+const cb = new MeshCircuitBreaker({
+    pathId: "p",
+    failureThreshold: 2,
+    successThreshold: 1,
+    openDurationMs: 100,
+    halfOpenMaxCalls: 1,
+    clock: () => now,
+});
+
+cb.on((state) => {
+    console.log("breaker", cb.pathId, "→", state);
+});
+
+cb.recordFailure();
+cb.recordFailure(); // OPEN
+now += 200;
+// canExecute lazily transitions to HALF_OPEN
+if (cb.canExecute()) {
+    cb.recordSuccess(); // CLOSED
+}
+```
+
+## API Reference
+
+- `type CircuitBreakerState = "CLOSED" | "OPEN" | "HALF_OPEN"`.
+- `interface MeshCircuitBreakerOptions { pathId, failureThreshold?, successThreshold?, openDurationMs?, halfOpenMaxCalls?, clock? }`.
+- `getState(): CircuitBreakerState` — lazy `OPEN → HALF_OPEN` if cooled down.
+- `canExecute(): boolean` — gating check.
+- `recordSuccess()` / `recordFailure()` — feedback hooks.
+- `on(handler) → () => void` — state-change subscription.
+- `pathId: string` — read-only public path identifier.
+
+## Implementation Notes
+
+The auto-transition from `OPEN → HALF_OPEN` is lazy because we don't run a clock-driven timer inside the breaker — every `getState`/`canExecute` call is the moment we recompute the state if cooldown has elapsed. This avoids leaking timers and keeps the breaker fully synchronous from the caller's perspective. `recordSuccess()` from `OPEN` is a programmer error (the FSM should be `HALF_OPEN` first), so the breaker throws `INVALID_TRANSITION` to surface the bug rather than silently accepting it. In `HALF_OPEN`, `halfOpenMaxCalls` is the cap on trial executions; once exceeded, `canExecute` returns false until the next successful close.

docs/networking/network/network-plugin-circuit-breaker/src/error-codes.md

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+# CB_CODES
+
+## Purpose
+
+Frozen error-code registry for the mesh circuit-breaker plugin. Two codes cover the full surface: `PATH_OPEN` when a request is rejected by an open breaker, and `INVALID_TRANSITION` when the FSM is asked to do something unrepresentable (e.g. `recordSuccess()` while still in `OPEN`). The `CircuitBreakerError` class extends the cross-package `SuaveplanError` so consumers can pattern-match on `code` without parsing message strings.
+
+## Features
+
+- Two frozen codes registered under the `CB` namespace.
+- `CircuitBreakerError extends SuaveplanError<CbErrorCode>`.
+- `name: "CircuitBreakerError"` on every instance for log filtering and dashboard alerting.
+- `cause` and `context` propagation via `SuaveplanErrorOptions`.
+- Codes are stable across versions — once registered they never disappear, only new codes are appended.
+
+## Usage: Basic Example
+
+```ts
+import {
+    CB_CODES,
+    CircuitBreakerError,
+} from "@suaveplan/network-plugin-circuit-breaker";
+
+throw new CircuitBreakerError(CB_CODES.PATH_OPEN, "breaker.path-open", {
+    context: { pathId: "meshA:host1→meshB:host2" },
+});
+```
+
+## Usage: Advanced Example
+
+```ts
+import {
+    CB_CODES,
+    CircuitBreakerError,
+} from "@suaveplan/network-plugin-circuit-breaker";
+
+try {
+    sendThroughRelay(envelope);
+} catch (err) {
+    if (
+        err instanceof CircuitBreakerError &&
+        err.code === CB_CODES.PATH_OPEN
+    ) {
+        return sendThroughBackup(envelope);
+    }
+    throw err;
+}
+```
+
+## API Reference
+
+- `CB_CODES` — frozen `{ PATH_OPEN, INVALID_TRANSITION }`.
+- `type CbErrorCode` — union of the registered code values.
+- `class CircuitBreakerError extends SuaveplanError<CbErrorCode>` — typed throwable for every failure mode the plugin surfaces.
+
+## Implementation Notes
+
+The registry is intentionally tight — two codes are enough because every other failure mode bubbles up as the underlying transport error (the breaker just wraps the wire-level error in `recordFailure`). `INVALID_TRANSITION` is the only "programmer-error" code; it should never appear in production unless someone calls `recordSuccess()` from `OPEN` state, which the FSM forbids. The package barrel side-effect-imports `./error-codes.js` so subpath consumers register the codes too — relying on a tree-shaken root import is unsafe when consumers may import deeper paths only.

docs/networking/network/network-plugin-circuit-breaker/src/middleware/circuit-breaker-middleware.md

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+# createCircuitBreakerMiddleware
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+## Purpose
+
+Factory that produces the relay-middleware glue between a `CircuitBreakerRegistry` and any next-hop send pipeline. The middleware fast-fails with `PATH_OPEN` when the relevant breaker is open and otherwise records the outcome of `next()` so the breaker accumulates the right success/failure counts.
+
+## Features
+
+- `buildPathId` is injectable; default is `${local}→${next}`.
+- Throws `CircuitBreakerError(CB.PATH_OPEN)` on the open path, with `context: { pathId }`.
+- Records success on `next()` resolve, failure on `next()` reject (and re-throws so callers see the original error).
+- Pure function: returns a middleware closure that holds no mutable state of its own — all state lives in the `registry`.
+
+## Usage: Basic Example
+
+```ts
+import {
+    CircuitBreakerRegistry,
+    createCircuitBreakerMiddleware,
+} from "@suaveplan/network-plugin-circuit-breaker";
+
+const registry = new CircuitBreakerRegistry();
+const middleware = createCircuitBreakerMiddleware({
+    registry,
+    localHostId: "host1",
+});
+
+await middleware(envelope, "host2", async () => {
+    await rawSend(envelope);
+});
+```
+
+## Usage: Advanced Example
+
+```ts
+import {
+    CB_CODES,
+    CircuitBreakerError,
+    CircuitBreakerRegistry,
+    createCircuitBreakerMiddleware,
+} from "@suaveplan/network-plugin-circuit-breaker";
+
+const middleware = createCircuitBreakerMiddleware({
+    registry,
+    localHostId: "host1",
+    buildPathId: (local, next) => `mesh:${local}::${next}`,
+});
+
+try {
+    await middleware(envelope, "host2", () => realSend(envelope));
+} catch (err) {
+    if (
+        err instanceof CircuitBreakerError &&
+        err.code === CB_CODES.PATH_OPEN
+    ) {
+        await sendThroughBackup(envelope);
+        return;
+    }
+    throw err;
+}
+```
+
+## API Reference
+
+- `type PathIdBuilder = (localHostId, nextHopHostId) => string`.
+- `interface CircuitBreakerMiddlewareOptions { registry, localHostId, buildPathId? }`.
+- `type RelayNext = () => Promise<void>`.
+- `createCircuitBreakerMiddleware(options): (envelope, nextHopHostId, next) => Promise<void>`.
+
+## Implementation Notes
+
+The middleware is a free function (rather than a class) because it has no internal state — the registry owns all the breaker state and the closure only needs `localHostId` + `buildPathId`. This makes the middleware trivially safe to share across many concurrent sends. The thrown `CircuitBreakerError` always carries `pathId` in its context so log filters and dashboards can group breaker rejections by path. Callers MUST treat the thrown error as a hard fast-fail signal — retrying immediately defeats the entire point of the breaker.

docs/networking/network/network-plugin-circuit-breaker/src/probe/half-open-probe.md

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+# HalfOpenProbe
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+## Purpose
+
+Periodically issues lightweight probe envelopes against every relay path the registry reports as `HALF_OPEN`, then records success/failure into the corresponding breaker. Decoupling the probe from real traffic means a flaky path can be re-tested without risking application payload — if the probe fails the path stays open and real callers continue to fast-fail.
+
+## Features
+
+- Configurable `probeIntervalMs` (default 5 s).
+- Pluggable `probeMessageFactory` so callers can attach signing/auth metadata.
+- Injectable `send`, `setIntervalFn`, `clearIntervalFn` for deterministic tests.
+- Idempotent `start()` and `stop()`; no leaked timers.
+- `tick()` is exposed publicly so test harnesses can step the loop manually.
+
+## Usage: Basic Example
+
+```ts
+import {
+    CircuitBreakerRegistry,
+    HalfOpenProbe,
+} from "@suaveplan/network-plugin-circuit-breaker";
+
+const registry = new CircuitBreakerRegistry();
+const probe = new HalfOpenProbe({
+    registry,
+    probeMessageFactory: (pathId) => ({
+        id: crypto.randomUUID(),
+        type: "relay:probe",
+        senderId: "self",
+        payload: null,
+        timestamp: Date.now(),
+        headers: { pathId },
+        ttl: 16,
+        visitedNodes: [],
+    }),
+    send: async (pathId, envelope) => {
+        await sendThroughRelay(pathId, envelope);
+    },
+});
+probe.start();
+```
+
+## Usage: Advanced Example
+
+```ts
+import {
+    CircuitBreakerRegistry,
+    HalfOpenProbe,
+} from "@suaveplan/network-plugin-circuit-breaker";
+
+const registry = new CircuitBreakerRegistry();
+const probe = new HalfOpenProbe({
+    registry,
+    probeIntervalMs: 1_000,
+    probeMessageFactory: () => makeProbeEnvelope(),
+    send: realSend,
+    setIntervalFn: testHarness.setInterval,
+    clearIntervalFn: testHarness.clearInterval,
+});
+
+probe.start();
+testHarness.advance(1_000);
+await probe.tick(); // explicit tick if the harness doesn't auto-fire
+probe.stop();
+```
+
+## API Reference
+
+- `type ProbeSender = (pathId, envelope) => Promise<void>`.
+- `interface HalfOpenProbeOptions { registry, probeIntervalMs?, probeMessageFactory, send, setIntervalFn?, clearIntervalFn? }`.
+- `start()` — idempotent.
+- `stop()` — idempotent; cancels the timer.
+- `tick()` — runs one probe pass; resolves once every half-open path has a result.
+
+## Implementation Notes
+
+`tick()` lists `OPEN` paths from the registry and then re-queries `getState(pathId)` to filter for `HALF_OPEN` — this catches the lazy `OPEN → HALF_OPEN` transition without forcing the registry to expose a separate "ready to probe" query. A failed probe trips the breaker back to `OPEN` via `recordFailure`; a successful probe accumulates toward `successThreshold` and eventually closes the breaker. The probe never throws — every send error is swallowed into `recordFailure` so a transient probe rejection doesn't crash the periodic loop.

docs/networking/network/network-plugin-circuit-breaker/src/registry/circuit-breaker-registry.md

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+# CircuitBreakerRegistry
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+## Purpose
+
+Owns one `MeshCircuitBreaker` per relay path and exposes a thin facade for cross-path queries (`listOpenPaths`, `getState(pathId)`). Centralising the breakers means there's exactly one place that decides "is this path healthy?" and middleware/probes can both consult it without state-sharing.
+
+## Features
+
+- Lazy construction: `getOrCreate` makes a breaker on first reference, returns the existing instance on subsequent calls.
+- Per-call config overrides on `getOrCreate` so different paths can have different thresholds.
+- Shared `defaults` config applied to every breaker that doesn't override.
+- `listOpenPaths()` for observability dashboards / health endpoints.
+- `remove(pathId)` for explicit teardown when a peer leaves the mesh.
+
+## Usage: Basic Example
+
+```ts
+import { CircuitBreakerRegistry } from "@suaveplan/network-plugin-circuit-breaker";
+
+const registry = new CircuitBreakerRegistry();
+const cb = registry.getOrCreate("meshA:host1→meshB:host2");
+if (cb.canExecute()) {
+    /* ... */
+}
+```
+
+## Usage: Advanced Example
+
+```ts
+import { CircuitBreakerRegistry } from "@suaveplan/network-plugin-circuit-breaker";
+
+const registry = new CircuitBreakerRegistry({
+    defaults: {
+        failureThreshold: 3,
+        successThreshold: 2,
+        openDurationMs: 10_000,
+        halfOpenMaxCalls: 2,
+    },
+});
+
+// per-path override for a known-flaky link
+registry.getOrCreate("meshA:host1→meshC:host5", {
+    failureThreshold: 10,
+});
+
+const open = registry.listOpenPaths();
+if (open.length > 0) {
+    metrics.gauge("mesh.open_breakers", open.length);
+}
+```
+
+## API Reference
+
+- `interface CircuitBreakerRegistryOptions { defaults? }`.
+- `getOrCreate(pathId, options?): MeshCircuitBreaker`.
+- `getState(pathId): CircuitBreakerState | undefined`.
+- `remove(pathId): boolean`.
+- `listOpenPaths(): readonly string[]`.
+- `paths(): readonly string[]` — every known path id, regardless of state.
+- `size(): number`.
+- `clear()`.
+
+## Implementation Notes
+
+`getOrCreate` is the canonical constructor — the registry never returns a raw `new` breaker, so observers don't have to wonder whether they're looking at a registry-owned or one-off instance. Per-call options shallow-merge over `defaults`, with caller options winning. `listOpenPaths` consults `getState()` (not the cached state) so paths that have lazy-transitioned to `HALF_OPEN` are excluded from the open list — matching what callers expect from "which paths are dead right now?". The companion `paths()` accessor returns every known path so probe loops can re-query each one's live state without missing entries that have already moved to `HALF_OPEN`. This split keeps health-dashboard semantics ("just the dead ones") separate from probe-driver semantics ("everything we might want to retry").