feat(broker): production hardening — caps, limits, metrics, logging

Adds the minimum ops surface area for a production broker without
over-engineering. All new config knobs are env-var driven with sane
defaults.

New modules:
- logger.ts: structured JSON logs (one line, stderr, ready for
  Loki/Datadog ingestion without preprocessing)
- metrics.ts: in-process Prometheus counters + gauges, exposed at
  GET /metrics. Tracks connections, messages, queue depth, TTL
  sweeps, hook requests, DB health.
- rate-limit.ts: token-bucket rate limiter keyed by (pid, cwd).
  Applied to POST /hook/set-status at 30/min default.
- db-health.ts: Postgres ping loop with exponential-backoff retry.
  GET /health returns 503 while DB is down.
- build-info.ts: version + gitSha (from GIT_SHA env or `git rev-parse`
  fallback) + uptime, surfaced on /health.

Behavior changes:
- Connection caps: MAX_CONNECTIONS_PER_MESH (default 100). Exceed →
  close(1008, "capacity") + metric increment.
- Message size: MAX_MESSAGE_BYTES (default 65536). WS applies it via
  `ws.maxPayload`. Hook POST bodies cap out with 413.
- Structured logs everywhere replacing the old `log()` helper.
- Env validation stricter: DATABASE_URL required + regex-checked for
  postgres:// prefix.

New endpoints:
- GET /health → {status, db, version, gitSha, uptime}. 503 if DB down.
- GET /metrics → Prometheus text format.

Verified: 21/21 tests still pass. Hit /health + /metrics live —
gitSha resolves correctly via `git rev-parse --short HEAD` in dev.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/broker/src/env.ts

@@ -4,18 +4,26 @@ import { z } from "zod";
  * Broker environment config.
  *
  * Validated at startup with Zod. Fails fast with a useful error if any
- * required var is missing or malformed. Defaults mirror the values
- * proven out in the claude-intercom prototype so local dev works
- * without a .env file.
+ * required var is missing or malformed.
  */
 const envSchema = z.object({
   BROKER_PORT: z.coerce.number().int().positive().default(7900),
-  DATABASE_URL: z.string().min(1, "DATABASE_URL is required"),
+  DATABASE_URL: z
+    .string()
+    .min(1, "DATABASE_URL is required")
+    .refine(
+      (u) => /^postgres(ql)?:\/\//.test(u),
+      "DATABASE_URL must be a postgres:// or postgresql:// connection string",
+    ),
   STATUS_TTL_SECONDS: z.coerce.number().int().positive().default(60),
   HOOK_FRESH_WINDOW_SECONDS: z.coerce.number().int().positive().default(30),
+  MAX_CONNECTIONS_PER_MESH: z.coerce.number().int().positive().default(100),
+  MAX_MESSAGE_BYTES: z.coerce.number().int().positive().default(65_536),
+  HOOK_RATE_LIMIT_PER_MIN: z.coerce.number().int().positive().default(30),
   NODE_ENV: z
     .enum(["development", "production", "test"])
     .default("development"),
+  GIT_SHA: z.string().optional(),
 });
 
 export type BrokerEnv = z.infer<typeof envSchema>;