feat(cron): add wakeAgent gate — scripts can skip the agent entirely

Extends the existing cron script hook with a wake gate ported from
nanoclaw #1232. When a cron job's pre-check Python script (already
sandboxed to HERMES_HOME/scripts/) writes a JSON line like
```json
{"wakeAgent": false}
```
on its last stdout line, `run_job()` returns the SILENT marker and
skips the agent entirely — no LLM call, no delivery, no tokens spent.
Useful for frequent polls (every 1-5 min) that only need to wake the
agent when something has genuinely changed.

Any other script output (non-JSON, missing key, non-dict, `wakeAgent: true`,
truthy/falsy non-False values) behaves as before: stdout is injected
as context and the agent runs normally. Strict `False` is required
to skip — avoids accidental gating from arbitrary JSON.

Refactor:
- New pure helper `_parse_wake_gate(script_output)` in cron/scheduler.py
- `_build_job_prompt` accepts optional `prerun_script` tuple so the
  script runs exactly once per job (run_job runs it for the gate check,
  reuses the output for prompt injection)
- `run_job` short-circuits with SILENT_MARKER when gate fires

Script failures (success=False) still cannot trigger the gate — the
failure is reported as context to the agent as before.

This replaces the approach in closed PR #3837, which inlined bash
scripts via tempfile and lost the path-traversal/scripts-dir sandbox
that main's impl has. The wake-gate idea (the one net-new capability)
is ported on top of the existing sandboxed Python-script model.

Tests:
- 11 pure unit tests for _parse_wake_gate (empty, whitespace, non-JSON,
  non-dict JSON, missing key, truthy/falsy non-False, multi-line,
  trailing blanks, non-last-line JSON)
- 5 integration tests for run_job wake-gate (skip returns SILENT,
  wake-true passes through, script-runs-only-once, script failure
  doesn't gate, no-script regression)
- Full tests/cron/ suite: 194/194 pass

cron/scheduler.py

@@ -564,15 +564,53 @@ def _run_job_script(script_path: str) -> tuple[bool, str]:
         return False, f"Script execution failed: {exc}"
 
 
-def _build_job_prompt(job: dict) -> str:
-    """Build the effective prompt for a cron job, optionally loading one or more skills first."""
+def _parse_wake_gate(script_output: str) -> bool:
+    """Parse the last non-empty stdout line of a cron job's pre-check script
+    as a wake gate.
+
+    The convention (ported from nanoclaw #1232): if the last stdout line is
+    JSON like ``{"wakeAgent": false}``, the agent is skipped entirely — no
+    LLM run, no delivery. Any other output (non-JSON, missing flag, gate
+    absent, or ``wakeAgent: true``) means wake the agent normally.
+
+    Returns True if the agent should wake, False to skip.
+    """
+    if not script_output:
+        return True
+    stripped_lines = [line for line in script_output.splitlines() if line.strip()]
+    if not stripped_lines:
+        return True
+    last_line = stripped_lines[-1].strip()
+    try:
+        gate = json.loads(last_line)
+    except (json.JSONDecodeError, ValueError):
+        return True
+    if not isinstance(gate, dict):
+        return True
+    return gate.get("wakeAgent", True) is not False
+
+
+def _build_job_prompt(job: dict, prerun_script: Optional[tuple] = None) -> str:
+    """Build the effective prompt for a cron job, optionally loading one or more skills first.
+
+    Args:
+        job: The cron job dict.
+        prerun_script: Optional ``(success, stdout)`` from a script that has
+            already been executed by the caller (e.g. for a wake-gate check).
+            When provided, the script is not re-executed and the cached
+            result is used for prompt injection. When omitted, the script
+            (if any) runs inline as before.
+    """
     prompt = job.get("prompt", "")
     skills = job.get("skills")
 
     # Run data-collection script if configured, inject output as context.
     script_path = job.get("script")
     if script_path:
-        success, script_output = _run_job_script(script_path)
+        if prerun_script is not None:
+            success, script_output = prerun_script
+        else:
+            success, script_output = _run_job_script(script_path)
         if success:
             if script_output:
                 prompt = (
@@ -674,7 +712,30 @@ def run_job(job: dict) -> tuple[bool, str, str, Optional[str]]:
     
     job_id = job["id"]
     job_name = job["name"]
-    prompt = _build_job_prompt(job)
+
+    # Wake-gate: if this job has a pre-check script, run it BEFORE building
+    # the prompt so a ``{"wakeAgent": false}`` response can short-circuit
+    # the whole agent run. We pass the result into _build_job_prompt so
+    # the script is only executed once.
+    prerun_script = None
+    script_path = job.get("script")
+    if script_path:
+        prerun_script = _run_job_script(script_path)
+        _ran_ok, _script_output = prerun_script
+        if _ran_ok and not _parse_wake_gate(_script_output):
+            logger.info(
+                "Job '%s' (ID: %s): wakeAgent=false, skipping agent run",
+                job_name, job_id,
+            )
+            silent_doc = (
+                f"# Cron Job: {job_name}\n\n"
+                f"**Job ID:** {job_id}\n"
+                f"**Run Time:** {_hermes_now().strftime('%Y-%m-%d %H:%M:%S')}\n\n"
+                "Script gate returned `wakeAgent=false` — agent skipped.\n"
+            )
+            return True, silent_doc, SILENT_MARKER, None
+
+    prompt = _build_job_prompt(job, prerun_script=prerun_script)
     origin = _resolve_origin(job)
     _cron_session_id = f"cron_{job_id}_{_hermes_now().strftime('%Y%m%d_%H%M%S')}"