diff --git a/cron/jobs.py b/cron/jobs.py
index e1b775bb4b505..c4d06d30e203b 100644
--- a/cron/jobs.py
+++ b/cron/jobs.py
@@ -370,6 +370,44 @@ def _jobs_lock():
 # into output writes/deletes.
 _IMMUTABLE_JOB_FIELDS = frozenset({"id"})
 
+# Fields a caller may legitimately change via update_job. Everything else —
+# including typos like ``promt`` — is rejected loudly instead of being
+# silently persisted to jobs.json and reported as a successful update
+# (#67625). Mirrors the create_job() parameter set plus schedule_display
+# (which update_job derives itself) and the scheduler-owned lifecycle fields
+# that pause_job/resume_job/trigger_job persist through update_job. Other
+# runtime fields (last_run_at, last_status, run_claim, ...) are owned by
+# the scheduler and never updatable.
+_UPDATEABLE_JOB_FIELDS = frozenset(
+    {
+        "prompt",
+        "schedule",
+        "name",
+        "repeat",
+        "deliver",
+        "origin",
+        "skill",
+        "skills",
+        "model",
+        "provider",
+        "base_url",
+        "script",
+        "context_from",
+        "description",
+        "enabled_toolsets",
+        "workdir",
+        "no_agent",
+        "attach_to_session",
+        "schedule_display",
+        # lifecycle fields written by pause/resume/trigger
+        "enabled",
+        "state",
+        "paused_at",
+        "paused_reason",
+        "next_run_at",
+    }
+)
+
 
 def _job_output_dir(job_id: str) -> Path:
     """Resolve a job's output directory, rejecting any path-escape attempt.
@@ -1515,6 +1553,14 @@ def update_job(job_id: str, updates: Dict[str, Any]) -> Optional[Dict[str, Any]]
             f"Cron job field(s) cannot be updated: {', '.join(sorted(bad_fields))}"
         )
 
+    unknown_fields = (updates or {}).keys() - _UPDATEABLE_JOB_FIELDS
+    if unknown_fields:
+        raise ValueError(
+            "Cron job update contains unknown field(s): "
+            f"{', '.join(sorted(unknown_fields))}. Known updateable fields: "
+            f"{', '.join(sorted(_UPDATEABLE_JOB_FIELDS))}"
+        )
+
     with _jobs_lock():
         jobs = load_jobs()
         for i, job in enumerate(jobs):
diff --git a/tests/cron/test_jobs.py b/tests/cron/test_jobs.py
index 6bfb7edffdf23..d06fdc5a9f57a 100644
--- a/tests/cron/test_jobs.py
+++ b/tests/cron/test_jobs.py
@@ -251,6 +251,32 @@ def test_update_name(self, tmp_cron_dir):
         fetched = get_job(job["id"])
         assert fetched["name"] == "New Name"
 
+    def test_update_rejects_unknown_fields(self, tmp_cron_dir):
+        """#67625: a typo'd field like ``promt`` must be rejected loudly
+        instead of silently persisted as a successful update."""
+        job = create_job(prompt="Check server status", schedule="every 1h", name="Old Name")
+        with pytest.raises(ValueError, match="unknown field.*promt"):
+            update_job(job["id"], {"promt": "some value"})
+        # Nothing was persisted
+        fetched = get_job(job["id"])
+        assert "promt" not in fetched
+        assert fetched["prompt"] == "Check server status"
+
+    def test_update_accepts_all_known_fields(self, tmp_cron_dir):
+        """Every create_job parameter is a legal update key."""
+        job = create_job(prompt="P", schedule="30m")
+        updates = {
+            "prompt": "P2", "schedule": "1h", "name": "n", "repeat": 2,
+            "deliver": "local", "origin": {"platform": "test"},
+            "skill": "s1", "skills": ["s1", "s2"], "model": "m", "provider": "p",
+            "base_url": "http://x", "script": "", "context_from": None,
+            "enabled_toolsets": ["web"], "workdir": None, "no_agent": False,
+            "attach_to_session": None, "schedule_display": "1h",
+        }
+        updated = update_job(job["id"], updates)
+        assert updated is not None
+        assert updated["name"] == "n"
+
 
 class TestPauseResumeJob:
     def test_pause_sets_state(self, tmp_cron_dir):