feat(phase7): grow corpus, MCP write-tools+auth, /metrics observability

- content/: +5 real docs (caddy, bullmq, mcp-streamable-http, postgres-fts,
  cloudflare-525 writeup) across docs/writeups/notes. Reindexed: 9 docs, 17
  chunks, 5 revisions (was 4 docs).
- apps/mcp: add write-tools index_document/reindex_all/restore_revision (require
  x-webhook-secret) + queue_status (public). createMcpServer(authSecret?) threads
  the HTTP header; stdio keeps writes open (trusted local).
- apps/api: GET /metrics (Prometheus text: uptime + queue job gauges).
- Caddy: expose /metrics on wiki. domain -> :4020.
Verified live: /metrics 200; MCP tools/list -> 10; index_document unauth -> error,
auth -> enqueues + worker drains; typecheck green.

content/docs/bullmq/workers.md

@@ -0,0 +1,68 @@
+---
+id: bullmq-workers
+title: BullMQ Background Workers
+type: documentation
+tags:
+  - bullmq
+  - redis
+  - jobs
+  - queue
+  - infra
+status: published
+author: asep
+created_at: 2026-08-20
+updated_at: 2026-08-20
+---
+
+# BullMQ Background Workers
+
+BullMQ runs the async indexing/embedding pipeline. Jobs are enqueued by the CLI, the
+git-sync webhook, or an MCP tool, and drained by a long-running worker connected to the
+shared Redis instance.
+
+## Connection requirements
+
+BullMQ requires an **ioredis** connection with `maxRetriesPerRequest: null`. A finite
+retry count causes the cryptic `Connection in key mode` error on blocking commands.
+The shared client in `packages/queue` sets this correctly:
+
+```ts
+const opts: RedisOptions = {
+  maxRetriesPerRequest: null,
+  lazyConnect: true,
+  enableOfflineQueue: true,
+};
+```
+
+## Job model
+
+Three job types flow through the `mcpedia-index` queue (prefix `mcpedia:` on Redis):
+
+| name       | data              | action                          |
+|------------|-------------------|---------------------------------|
+| `index-doc`| `{ relPath, reason }` | index one content file      |
+| `index-all`| `{ reason }`      | full corpus reindex            |
+| `reindex`  | (legacy)          | alias of full                  |
+
+Job IDs use a `__` separator (`doc__<slug>`, `full__<ts>`) — BullMQ reserves `:` for
+repeatable jobs, so a literal `:` in a custom jobId is rejected.
+
+## Worker lifecycle
+
+The worker is a `Worker` with `concurrency: 4`. Each job calls the shared
+`indexContentFile` / `runFullIndex` entry points in `@mcpedia/core` — the same code
+path the CLI uses, so behavior never diverges. On completion it logs; on failure it
+logs the reason and the job is retried per BullMQ defaults.
+
+Graceful shutdown: `worker.close()` on `SIGINT`/`SIGTERM`. systemd sends SIGTERM on
+stop, so the process exits cleanly and in-flight jobs are returned to the queue.
+
+## Inspecting state
+
+```bash
+bun run enqueue --all          # enqueue a full reindex
+curl localhost:4020/trpc/queueStatus   # waiting/active/completed/failed
+```
+
+A stuck queue (waiting > 0, active = 0) means the worker died — check
+`systemctl status mcpedia-worker` and the journal.