feat(llm): attribute and tag OpenRouter requests

[Makisuo]

Why

Every OpenRouter request Maple makes is anonymous today. platform/Llm.ts calls OpenRouter.configure({ apiKey }) with nothing else, and slack-agent calls createOpenRouter({ apiKey }) the same way. So:

• The OpenRouter dashboard is one undifferentiated pile of spend — no way to tell interactive chat from AI triage from the Slack agent, or to attribute cost to an org.
• Maple has no app page on openrouter.ai. OpenRouter only creates one for traffic carrying an HTTP-Referer header, so Maple is invisible on /rankings and gets none of the per-app analytics at /apps.
• docs/openrouter-tracing.md claims both already work and points at apps/chat-agent/src/lib/openrouter.ts, deleted in c3c7cc1a8.

What changed

apps/api/src/platform/Llm.ts — the single seam, covers chat and triage in one edit:

• HTTP-Referer: https://maple.dev + X-Title: Maple on every OpenRouter call.
• New optional LlmCallTags on resolveTriageModel(env, tags), folded into the request body as route defaults: user: <orgId>, session_id, trace: { trace_name }. Because they are route defaults, every generate/stream/generateObject made with that model inherits them — including triage's final structured pass in triage-agent.ts — without each call site threading anything through.
• The Workers AI branch ignores tags entirely. These are OpenRouter's body fields and must never be posted to Cloudflare.

Call sites — turn-runner.ts tags chat + orgId + chat session id; AiTriageWorkflow.run.ts tags ai-triage + orgId + triage_<kind>_<incidentId> (incidentId was already on the input, just unused).

apps/slack-agent/agent/agent.ts — the provider's first-class appUrl/appName (present in the pinned 3.0.0) plus a static extraBody: { trace: { trace_name: "slack" } }. Same referer as apps/api on purpose: the referer is the app's identity, so a second value would mint a second app entry and split the rankings.

docs/openrouter-tracing.md — rewritten against the live docs (verified 2026-08-04).

Reviewer notes

• No lib/llm changes. ModelOptions already extends RouteDefaultsInput, which carries both headers and http; mergeRouteDefaults folds them onto LLMRequest.http; and user/session_id/trace are not in PROTOCOL_BODY_OVERLAY_DENYLIST (that only guards protocol-owned generation fields). So nothing here is at risk from bun run llm:sync, and no cassettes move.
• Where each signal lands is not uniform, which is why all three are sent: user appears on /activity and in exports (OpenRouter folds it into a hashed identity and never forwards it raw upstream); session_id groups a conversation and makes OpenRouter route it stickily, so prompt caches hit better; trace is Broadcast-only and will not show in the OpenRouter dashboard until a Broadcast destination is configured.
• MCP evals stay unattributed (__evals__/model.ts) so CI spend stays out of the product's numbers — only its stale comment was fixed.
• Not fixed here: canReachModel() in AiTriageWorkflow.run.ts gates the OpenRouter path on Cloudflare credentials and never checks OPENROUTER_API_KEY. Real pre-existing bug, unrelated to this change.

Testing

New apps/api/src/platform/Llm.test.ts swaps FetchHttpClient.Fetch for a capture and asserts the actual outgoing request. LLMClient.prepare is no good here — it returns the protocol body, built before the http.body overlay, so it cannot see the tags at all. The fake responds 400 (non-retryable) to keep each case to one request with no backoff.

Covers: attribution headers present; user/session_id/trace present; session_id omitted when there is no session; over-long session id truncated to OpenRouter's 256-char limit; and none of it on the Workers AI path.

• bun run --cwd apps/api vitest run src/platform/Llm.test.ts src/chat → 27 passed
• bun typecheck → clean
• bunx tsc --noEmit in apps/slack-agent → exit 0

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