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+---
+id: DL-515
+decision: "Agent OTLP rides the agent socket (Matt, RIG-5237): agents export OTLP/HTTP to the Runner gateway's `/v1/traces`, `/v1/metrics` and `/v1/logs`, which stamp the bound `compass.session.id`, `compass.telemetry.origin=agent` and `service.name=compass-agent` and relay to a collector on each runner host; the socket stays the agent's only channel, with no OTLP egress. The stamp attributes per session except on the host tier, which is one trust domain. Lifts the effect-otel ruling that agent OTLP never uses the socket/vsock gateway and the agent deployer contracts' env-file endpoint, and moves loop-otel's SDK session id to `compass.agent.sdk_session.id`"
+status: "Active (Matt, 2026-10-12)"
+record: ../../observability/compass-agent-collector-routing/design.md#rulings
+---
diff --git a/docs/designs/observability/compass-agent-collector-routing/design.md b/docs/designs/observability/compass-agent-collector-routing/design.md
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+# Agent OTLP rides the agent socket to a host collector
+
+Tracker: RIG-4611
+
+Amendment record of the observability-architecture design
+([`../compass-observability-architecture/design.md`](../compass-observability-architecture/design.md),
+§D3 and §T4). The parent stays frozen.
+
+Ledger-impact: DL-515.
+
+## Problem / Intent
+
+Matt ruled (RIG-5144) that agents ship OTLP through a collector to an
+operator upstream. Parent T4 picks no route. This record decides the
+collector's upstream export (C-a), the agent route (C-b) and dev wiring (C-c).
+
+## Rulings
+
+Matt, RIG-5237 (2026-10-11 and 2026-10-12):
+
+1. **OQ1 B: a collector on each runner host** forwards upstream.
+2. **OQ2 B, transport A: agents export OTLP/HTTP over the agent socket.** The
+   Runner gateway serves `/v1/traces` and `/v1/metrics` (`/v1/logs`: Resolved
+   2) and relays to the host collector. No pasta, no OTLP egress entry.
+3. **The socket stays the agent's only channel to its Runner.**
+
+Amended frozen texts:
+
+- `docs/designs/repo/compass-agent-effect-otel/design.md` Open Questions item
+  1 and Decision 3: lifted for agent telemetry.
+- `docs/designs/observability/compass-agent-loop-otel/design.md` Decision 3a:
+  the join key is the gateway-stamped `compass.session.id`; the SDK id moves
+  to `compass.agent.sdk_session.id`.
+- Both agent deployer contracts
+  (`compass-agent-effect-otel/otel-endpoint-deployer-contract.md`,
+  `compass-agent-loop-otel/deployer-contract.md`): env-file endpoints are
+  ignored; the gateway sets `service.name`.
+- Parent D3 "agent-side emission stays exactly as shipped": superseded for the
+  route. Off by default holds.
+
+## Global Constraints
+
+- D3 holds: no export endpoint keeps today's `nop` config bytes; only config
+  and headers files touch disk.
+- No secret in argv or the 0644 config. Upstream credentials live in the 0600
+  headers file and server or runner env, never in agents.
+- Host-tier exception: agents share the Runner's uid
+  (`go/internal/runtime/host_backend.go`), so they can read its env and reach
+  any session's socket. Host-tier telemetry is one trust domain, not
+  per-session evidence.
+- Only the gateway sets `compass.session.id`, `compass.telemetry.origin` and
+  the agent's `service.name` on relayed telemetry.
+- Every endpoint passes `otlpenv.ParseEndpoint` (CA1): plaintext only to
+  loopback.
+- Server and runner emit or relay only with an endpoint, and drop inherited
+  `OTEL_*`. `DefaultCollectorImage` stays 0.140.0.
+- Breaking (`!`): `--otel-external` takes a URL; env-file agent endpoints are
+  ignored; compass-runner refuses per-signal and TLS `OTEL_EXPORTER_OTLP_*`
+  keys.
+
+## Approach
+
+**C-a: the collector exports (CA1).** `collectorConfigYAML`
+(`go/internal/stack/collector_container.go`) hard-codes `nop: {}`. With
+`--otel-export-endpoint` (fallback `COMPASS_OTEL_EXPORT_ENDPOINT`) it renders
+`otlphttp` behind `memory_limiter` (`check_interval: 1s`, 256 MiB, 64 MiB
+spike) and an 8 MiB receiver cap. `--otel-export-headers-file` is copied 0600
+to `/run/compass/otlp-headers.yaml` on every `Start`.
+
+**C-b, host collector (CB2).** The Runner relays agent OTLP to the endpoint its
+own SDK reads, `OTEL_EXPORTER_OTLP_ENDPOINT` plus `_HEADERS` (`setupOtel`,
+`go/cmd/compass-runner/main.go`). `compass-stack` sets it on server and runner;
+any two of these flags is a usage error:
+
+- `--otel-export-endpoint`: the bundled collector,
+  `http://127.0.0.1:<CollectorHTTPPort>`. Without it nothing is set (D3).
+- `--otel-external <URL>`: the operator's host collector, which owns batching,
+  retry and upstream (ruling 1); `--otel-export-headers-file` rides it in `Env`.
+- `--otel-off`: nothing set, overriding `COMPASS_OTEL_EXPORT_ENDPOINT`.
+
+A remote runner host's operator runs the collector (e.g. Grafana Alloy).
+compass-runner refuses a bad endpoint and per-signal or TLS keys. The relay
+appends `/v1/<signal>` by `path.Join`, as the Go SDK's `otlpconfig` does.
+
+**C-b, gateway handlers (CB1).** `gateway.Serve`
+(`go/internal/runner/gateway/gateway.go`) mounts `POST /v1/traces`,
+`/v1/metrics` and `/v1/logs` only when `Deps.OTLPRelay` is set. Each handler:
+
+1. Resolves `g.sessions.Session(g.containerName)`. Unbound is 503 with
+   `Retry-After: 1`: `agentHost.Start` starts the agent before recording its
+   session.
+2. Answers 415 unless `application/x-protobuf` with identity encoding.
+3. Takes one of 8 per-Gateway slots (a flush exports five signals) and 4 MiB
+   of a Runner-wide 128 MiB budget, else 503 with `Retry-After: 1`, unread.
+   One 8 s deadline (as `withBodyReadDeadline`, `go/server/network_door.go`)
+   covers read and upstream.
+4. Reads at most 4 MiB (413). An allocation-free `protowire` pre-scan counts
+   messages and repeated-scalar elements, packed or unpacked; over 65,536
+   messages or depth 32 is 413. It reserves 416 B per message, 16 B per
+   element (append doubling) and twice the body, else 503, then decodes with
+   `go.opentelemetry.io/proto/otlp` (direct; 400 if malformed). 4 MiB of empty
+   attributes measured 244 MiB decoded.
+5. Deletes `compass.session.id` from every scope, span, event, link, data
+   point, exemplar and log record. On each resource it sets
+   `compass.session.id` to the bound id, `compass.telemetry.origin=agent` and
+   `service.name=compass-agent`.
+6. Re-encodes (over 8 MiB is 413) and POSTs under `r.Context()`. Upstream 2xx
+   is 200; 429, 502, 503 or 504 is 503 with its `Retry-After`; 413 stays;
+   another 4xx is 400; else 502.
+
+**C-b, agent (CB3).** When relaying, the Runner sets the reserved
+`COMPASS_AGENT_OTLP=1`. After the env-file merge the agent deletes and logs
+every `OTEL_EXPORTER_OTLP_*` key, and records the SDK session id as
+`compass.agent.sdk_session.id`.
+
+- `makeOtelLayer` (`packages/compass-agent/src/transport/otel-layer.ts`) builds
+  exporters with `url: "http://compass-agent/v1/<signal>"` and
+  `httpAgentOptions: { socketPath }`.
+- The SDK loop's exporters (`registerProviders`, `@oh-my-pi/pi-coding-agent`)
+  read env at construction. A `Bun.serve` proxy on `127.0.0.1:0` checks a
+  per-process token header, caps bodies at 4 MiB and forwards with
+  `fetch(…, { unix, signal: req.signal })`. Endpoint and token are set only
+  across `await telemetryHooks.init()`; a subprocess spawned during its
+  dynamic import gains only what its socket already gives. Egress accepts
+  `oif lo` (`NftScript`).
+
+| Tier | Socket reaches the agent by | OTLP |
+| --- | --- | --- |
+| podman | bind mount at `/run/compass/agent.sock` | covered hermetically |
+| microVM | guestd `gatewayProxy` splice to vsock | covered |
+| host | `COMPASS_AGENT_SOCKET_PATH` | covered; one trust domain |
+| apple-container | `--volume` over virtiofs | none: DL-338's slow-roll holds the agent channel |
+
+**C-c: dev wiring (CC1).** devenv runs the same collector config.
+
+## Alternatives considered
+
+- **Pasta forward** (earlier draft): podman only, agent-asserted attribution;
+  RIG-5249 becomes moot.
+- **Direct export through the egress allowlist**: credentials in every agent,
+  forgeable attribution.
+
+## Plan
+
+### CA1: collector upstream export
+
+Files: `go/internal/stack/{collector_container,config}.go`,
+`go/internal/stack/adapters/collector_container.go`,
+`go/cmd/compass-stack/main.go`, new `go/internal/otel/otlpenv`.
+
+Interfaces:
+
+- `Config.CollectorExportEndpoint`, `Config.CollectorExportHeadersFile string`.
+- `CollectorConfigYAML(p CollectorYAMLParams) string`, with
+  `CollectorYAMLParams{GRPC, HTTP, Health, Export, HeadersPath string}`.
+- `CollectorContainerSpec.ExportHeadersFile string`;
+  `const CollectorHeadersMountPath = "/run/compass/otlp-headers.yaml"`.
+- `otlpenv.ParseEndpoint(raw string) (*url.URL, error)`;
+  `otlpenv.SignalURL(base *url.URL, signal string) *url.URL`.
+
+Red→green:
+
+- `TestCollectorConfigYAMLExportsUpstream` (red today): `otlphttp` and
+  `memory_limiter` with `check_interval` in all three pipelines, an 8388608
+  body cap, no `nop`.
+- `TestCollectorConfigYAMLRealizesD3Posture`: container ports, empty `Export`
+  and `HeadersPath`, today's bytes.
+- `TestParseEndpoint`: `http` only to `127.0.0.1` or `localhost`, `https`
+  anywhere; refuses bare `host:port`, `127.0.0.2`, `[::1]`, `0.0.0.0`,
+  userinfo, query, fragment.
+- `TestSignalURL`: `https://h/otlp` gives `/otlp/v1/traces`.
+- `TestCollectorStartReplacesHeadersCopy`; `TestCollectorRunArgsExportContract`
+  (no header value in argv or config).
+- Smoke: `otelcol validate` on the pinned image; `compass-stack up` delivers a
+  span and the header to a local receiver.
+
+### CB1: gateway OTLP relay
+
+Files: `go/internal/runner/gateway/{gateway,otlp}.go`,
+`go/internal/otel/{otlprelay,otlpscan}`, `go/go.mod`.
+
+Interfaces:
+
+- `type OTLPRelay interface { Export(ctx context.Context, path string, body []byte) error }`;
+  `Deps.OTLPRelay` (nil leaves the paths unmounted);
+  `Deps.OTLPBudget *semaphore.Weighted` (`golang.org/x/sync`).
+- `otlprelay.New(endpoint *url.URL, headers map[string]string) *Relay`; a
+  non-2xx upstream returns `*otlprelay.StatusError{Code int, RetryAfter string}`.
+- `otlpscan.Bound(body []byte, signal string) (uint64, error)`.
+- `const maxOTLPBodyBytes = 4 << 20`, `maxOTLPInFlight = 8`,
+  `maxOTLPMessages = 1 << 16`, `otlpRequestDeadline = 8 * time.Second`.
+- Counter `compass.runner.otlp_relay.requests{signal,outcome}`, nil-guarded,
+  no session label.
+
+Red→green (hermetic, fake relay):
+
+- `TestOTLPStampOverridesAgentSession`: forged ids on a resource, span, data
+  point and log record, and `service.name=compass-server`, arrive as the bound
+  id and `compass-agent`.
+- `TestOTLPUnboundContainerRetryable` (503); `TestOTLPBodyCap` (413);
+  `TestOTLPRejectsCompressedBody` (415).
+- `TestOTLPSaturationShedsWith503`: a ninth request or empty budget, unread.
+- `TestOTLPDecodeBound`: 70,000 empty attributes is 413; `otlpscan.Bound`
+  covers measured allocation, including two million unpacked `BucketCounts`.
+- `TestOTLPRelayFailure`: 400 stays 400, 503 keeps `Retry-After`, transport
+  error is 502.
+- `TestOTLPUnmountedWhenRelayNil` (404); `TestRelayPostsWithHeaders`.
+- microVM e2e `TestVsockGateway_InGuestOTLPStamped` against a fake
+  `AgentHostConfig.OTLPRelay`.
+
+### CB2: runner and stack wiring
+
+Files: `go/cmd/compass-runner/main.go`, `go/internal/runner/{host,agent_exec}.go`,
+`go/internal/runtime/host_backend.go`, `go/internal/stack/{config,spec}.go`,
+`go/internal/stack/adapters/process.go`, `go/cmd/compass-stack/main.go`.
+
+Interfaces:
+
+- `AgentHostConfig.OTLPRelay gateway.OTLPRelay`; `(*agentHost).gatewayDeps()
+  gateway.Deps` replaces both `host.go` literals, sharing one budget.
+- `AgentEnv.Telemetry bool` sets `COMPASS_AGENT_OTLP=1`.
+- `otlpenv.HeadersValue(map[string]string) (string, error)`;
+  `otlpenv.RunnerConfig(environ []string) (*url.URL, map[string]string, error)`.
+- `Config.OTLPOff bool`; `ExternalOTLPEndpoint` becomes a URL;
+  `childEnv(inherited, overlay []string) []string` and `envSlice` drop
+  inherited `OTEL_*`.
+
+Red→green:
+
+- `TestServerAndRunnerSpecOTLPEndpoint`: each mode; headers in `Env`, never
+  `Args`.
+- `TestStartDropsInheritedOTELKeys`, `TestEnvSliceDropsInheritedOTELKeys`,
+  `TestExecSpecTelemetryFlag`.
+- `TestResolveConfigOTelModes`: two OTel flags are refused; `--otel-off` beats
+  the env fallback.
+- `TestRunnerConfig`: refuses a bad endpoint and per-signal or certificate keys.
+- Migration to `--otel-off`: `go/e2e/fixture.go`, `TestContainerPostgresUpDown`,
+  `TestExternalDatabaseUpDown`, `TestNatsUpDown`, `TestExternalNatsUpDown`. To
+  a URL: `TestExternalOTLPUpDown`, `TestResolveConfigCollectorFlags`,
+  `TestConfigValidate`, `TestExternalOTLPSkipsCollector`.
+
+### CB3: agent exporters over the socket
+
+Files: `packages/compass-agent/src/transport/{index,otel-layer,otlp-proxy}.ts`,
+`packages/compass-agent/src/cli.ts`.
+
+Interfaces:
+
+- `makeOtelLayer(socketPath: string): Layer.Layer<never>` (`Layer.empty`
+  without the flag), called by `createUnixSocketTransport`.
+- `startOtlpProxy(socketPath: string): Promise<{ endpoint: string; headers: string; close(): Promise<void> }>`.
+- `scrubOtlpEnv(env: NodeJS.ProcessEnv): string[]` returns the dropped keys;
+  `isTelemetryEndpointConfigured` keys on the flag.
+
+Red→green (bun:test, a Unix-socket server in a temp dir):
+
+- A transport span reaches `/v1/traces` only with the flag.
+- A no-argument `OTLPTraceExporter` reaches the socket through the proxy; a
+  tokenless request is refused; a client abort cancels the forward.
+- A child spawned after init sees no `OTEL_EXPORTER_OTLP_*`.
+- `scrubOtlpEnv` drops and logs an env-file endpoint.
+- Migration to the flag: `cli.test.ts`'s env-file endpoint, "all four
+  loop-OTel env keys…", "endpoint set ⇒ env defaults…" and "deployer-set
+  OTEL_SERVICE_NAME…"; `otel-layer.test.ts`'s three endpoint tests.
+
+### CC1: devenv runs the collector
+
+Interfaces: `compass-stack collector-config --grpc --http --health
+[--otel-export-endpoint] [--otel-export-headers-file]` prints
+`CollectorConfigYAML`; `usageError` names five subcommands.
+
+devenv `processes.otel-collector` runs `otelcol-contrib` when the gitignored
+`devenv.local.nix` sets `env.COMPASS_OTEL_EXPORT_ENDPOINT`.
+
+Red→green: `TestRunCollectorConfig`; `devenv up` with an endpoint delivers an
+agent span upstream.
+
+### CD1: operator docs
+
+Interfaces: none. `docs/self-host.md` gains an observability section (flags,
+remote-runner `OTEL_EXPORTER_OTLP_*`); each deployer contract points there.
+
+Red→green: none; rumdl and the ledger gate pass.
+
+## Tasks
+
+- [ ] CA1: collector export
+- [ ] CB1: gateway relay
+- [ ] CB2: runner and stack wiring
+- [ ] CB3: agent socket exporters
+- [ ] CC1: devenv collector
+- [ ] CD1: operator docs
+
+## Resolved decisions
+
+1. **SDK-loop exporters use the token proxy, not an SDK patch:** no fork.
+   Agent-owned providers would miss the SDK's metric and log hooks, which
+   only its dynamically imported, unexported `telemetry-export-otlp` registers.
+2. **`/v1/logs` is mounted with the same stamp:** env-file endpoints enable SDK
+   logs (`resolveSignalConfig`).
+3. **The remote host collector is operator-run;** a runner-only mode is additive.