Implement Monlet MVP stack and UI updates

agent/README.md

@@ -14,19 +14,36 @@ Do not use `go install` or `go env -w`. Module cache, build cache, and tool bina
 
 ## Configuration
 
-See `config.example.toml`. Required sections: top-level `state_dir`, `[server]` (`url`, `token`), at least one `[[checks]]` (`id`, `command`, `interval`, `timeout`). `agent_id` is optional — if empty, the agent generates and persists a UUID under `state_dir/agent_id`.
+See `config.example.toml`. Required fields: top-level `state_dir`, at least one `[[checks]]` (`id`, `command`, `interval`, `timeout`), and at least one output enabled: `server.enabled = true` or `metrics.enabled = true`. `agent_id` is optional; if omitted, it defaults to `hostname`.
 
 | Key | Default | Notes |
 |---|---|---|
-| `mode` | `hybrid` | `prometheus_only` (only `/metrics`), `push_only` (only heartbeat+events), `hybrid` (both). `prometheus_only` does not require `server.url`/`server.token`. |
+| `server.enabled` | `false` | Enables heartbeat/event push. Requires `server.url` and `server.token` when true. |
+| `metrics.enabled` | `false` | Enables `/metrics`. |
+| `labels` | `{}` | Optional heartbeat labels. Max 31 custom labels because `monlet_agent_version` is generated by the agent. Secret-like keys are rejected. |
 | `server.heartbeat_interval` | `30s` | ADR-0005 |
 | `server.batch_interval` | `10s` | events flush cadence |
 | `metrics.listen` | `127.0.0.1:9465` | low-cardinality only |
-| `checks[].notification_owner` | `server` | `server`, `prometheus`, `none` |
+| `checks[].command` | required | Shell string executed as `/bin/sh -c`; TOML multi-line strings are supported. |
+| `checks[].notifications_enabled` | `true` | Set `false` for checks that must not create server notifications. |
+
+Example:
+
+```toml
+[[checks]]
+id = "disk_root"
+command = '''
+set -eu
+/usr/local/lib/monlet/check_disk_root.sh
+'''
+interval = "60s"
+timeout = "10s"
+```
 
 ## Behaviour
 
 - Per-check scheduler with no-overlap: a tick is skipped if the previous run is still in flight (`monlet_agent_check_skipped_total`).
+- Check commands run through `/bin/sh -c`; the old argv-array form is intentionally unsupported.
 - Timeout via `exec.CommandContext` with `Setpgid` so the process group is killed on expiry; timeout → `unknown`.
 - Exit code mapping: 0=ok, 1=warning, 2=critical, 3+=unknown (ADR-0005).
 - `output` (stdout+stderr) is truncated by **UTF-8 byte length** to 8 KiB with marker `...[truncated N bytes]`.
@@ -34,6 +51,8 @@ See `config.example.toml`. Required sections: top-level `state_dir`, `[server]`
 - Spool: per-event JSON files in `state_dir/spool/`, FIFO, limits 10 000 events / 50 MiB, drop oldest on overflow (ADR-0005).
 - Retry backoff for heartbeat and events: 1s → 30s, exp ×2, jitter ±20%. 4xx are dropped (not retried) to avoid hot loop.
 - Bearer auth header on both endpoints (ADR-0007).
+- Heartbeats include configured labels plus reserved `monlet_agent_version=<binary version>`.
+- Heartbeats include explicit feature flags: `push` from `server.enabled`, `metrics` from `metrics.enabled`.
 
 ## Prometheus metrics
 
@@ -52,7 +71,7 @@ Exposed on `metrics.listen` at `/metrics`. Labels are static (`check_id`, `statu
 - `monlet_agent_send_attempts_total{kind}`, `monlet_agent_send_failures_total{kind}` (`kind` ∈ `heartbeat`, `events`)
 - `monlet_agent_events_accepted_total`, `monlet_agent_events_deduplicated_total`
 - `monlet_agent_last_heartbeat_timestamp_seconds`
-- `monlet_agent_build_info{version,mode}` (constant 1)
+- `monlet_agent_build_info{version,push,metrics}` (constant 1)
 
 ## systemd