feat(memory): protect Dream cron and polish migration UX

nanobot/cron/service.py

@@ -6,7 +6,7 @@ import time
 import uuid
 from datetime import datetime
 from pathlib import Path
-from typing import Any, Callable, Coroutine
+from typing import Any, Callable, Coroutine, Literal
 
 from loguru import logger
 
@@ -365,9 +365,16 @@ class CronService:
         logger.info("Cron: registered system job '{}' ({})", job.name, job.id)
         return job
 
-    def remove_job(self, job_id: str) -> bool:
-        """Remove a job by ID."""
+    def remove_job(self, job_id: str) -> Literal["removed", "protected", "not_found"]:
+        """Remove a job by ID, unless it is a protected system job."""
         store = self._load_store()
+        job = next((j for j in store.jobs if j.id == job_id), None)
+        if job is None:
+            return "not_found"
+        if job.payload.kind == "system_event":
+            logger.info("Cron: refused to remove protected system job {}", job_id)
+            return "protected"
+
         before = len(store.jobs)
         store.jobs = [j for j in store.jobs if j.id != job_id]
         removed = len(store.jobs) < before
@@ -376,8 +383,9 @@ class CronService:
             self._save_store()
             self._arm_timer()
             logger.info("Cron: removed job {}", job_id)
+            return "removed"
 
-        return removed
+        return "not_found"
 
     def enable_job(self, job_id: str, enabled: bool = True) -> CronJob | None:
         """Enable or disable a job."""