## Summary
Expands the `/.well-known/healthcheck.json` endpoint with runtime statistics, giving operators visibility into server load and usage patterns.
closes#74
## New healthcheck fields
| Field | Source | Description |
|-------|--------|-------------|
| `sessions` | DB | Current active session count |
| `clients` | DB | Current connected client count |
| `queuedLines` | DB | Total entries in client output queues |
| `channels` | DB | Current channel count |
| `connectionsSinceBoot` | Memory | Total client connections since server start |
| `sessionsSinceBoot` | Memory | Total sessions created since server start |
| `messagesSinceBoot` | Memory | Total PRIVMSG/NOTICE messages since server start |
## Implementation
- **New `internal/stats` package** — atomic counters for boot-scoped metrics (`connectionsSinceBoot`, `sessionsSinceBoot`, `messagesSinceBoot`). Thread-safe via `sync/atomic`.
- **New DB queries** — `GetClientCount()` and `GetQueueEntryCount()` for current snapshot counts.
- **Healthcheck changes** — `Healthcheck()` now accepts `context.Context` to query the database. Response struct extended with all 7 new fields. DB-derived stats populated with graceful error handling (logged, not fatal).
- **Counter instrumentation** — Increments added at:
- `handleCreateSession` → `IncrSessions` + `IncrConnections`
- `handleRegister` → `IncrSessions` + `IncrConnections`
- `handleLogin` → `IncrConnections` (new client for existing session)
- `handlePrivmsg` → `IncrMessages` (covers both PRIVMSG and NOTICE)
- **Wired via fx** — `stats.Tracker` provided through Uber fx DI in both production and test setups.
## Tests
- `internal/stats/stats_test.go` — 5 tests covering all counter operations (100% coverage)
- `TestHealthcheckRuntimeStatsFields` — verifies all 7 new fields are present in the response
- `TestHealthcheckRuntimeStatsValues` — end-to-end: creates a session, joins a channel, sends a message, then verifies counts are nonzero
## README
Updated healthcheck documentation with full response shape, field descriptions, and project structure listing for `internal/stats/`.
Co-authored-by: user <user@Mac.lan guest wan>
Reviewed-on: sneak/chat#80
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
