Problem

When the OpenClaw gateway goes down (e.g. due to a config error or model routing failure), cron jobs configured with sessionTarget: "main" continue to fire on schedule and record status: "ok" in the run log. The runs complete in 1–8 ms (durationMs: 1) because executeMainSessionCronJob returns immediately after calling enqueueSystemEvent + requestHeartbeatNow — no actual agent turn is awaited.

There is no alerting, no health check failure, and no indication in the log that the jobs are not actually executing. The cron scheduler marks runs as successful even though no agent turn occurred and no script was run.

Reproduction:

1. Configure a cron job with sessionTarget: "main", payload.kind: "systemEvent", wakeMode: "next-heartbeat"
2. Bring the gateway into a state where the main session cannot process requests (e.g. invalid model config, provider auth error)
3. Observe run log: status: "ok", durationMs: 1

Root Cause

In src/cron/service/timer.ts, executeMainSessionCronJob enqueues a system event and returns { status: "ok" } without waiting for the agent to actually process the heartbeat. If the gateway or agent session is unhealthy, the event is silently dropped and the cron run is still recorded as ok.

The wakeMode: "now" path (runHeartbeatOnce) at least checks the heartbeat result, but wakeMode: "next-heartbeat" (the default for main-session jobs) has no health check at all.

Proposed Fix

Add a ghost-run detector in the onEvent handler in src/gateway/server-cron.ts: when a finished event has status: "ok" and durationMs < GHOST_RUN_THRESHOLD_MS (e.g. 50 ms) for a job where sessionTarget !== "none" and payload.kind === "systemEvent", log a warning and/or record the run with an additional warn flag or summary note so operators can identify silent failures.

At a minimum, the ghost-run check should:

• Apply only to sessionTarget: "main" + payload.kind: "systemEvent" + wakeMode: "next-heartbeat" jobs (the fast-return code path)
• Not treat legitimately fast jobs (e.g. no-op system events) as errors — use a configurable threshold (default 50 ms)
• Emit a structured log warning that can be surfaced in openclaw doctor or cron logs

See src/cron/service/timer.ts → executeMainSessionCronJob and src/gateway/server-cron.ts → onEvent handler.

Acceptance Criteria

• When a main-session cron job completes in < 50 ms, a warning is logged (cron: possible ghost run detected)
• The warning includes jobId, durationMs, sessionTarget, and payloadKind
• The behavior is gated behind a threshold that can be adjusted via cron config
• Existing tests for executeMainSessionCronJob are not broken