fix(#4768): degrade GET /api/crons gracefully when the cron module is absent

In split-container / minimal Docker deployments the WebUI image may not ship the
agent's cron package on its import path, so the Tasks tab's GET /api/crons did
'from cron.jobs import list_jobs' and 500'd with ModuleNotFoundError — breaking the
whole tab. Now the import is guarded and returns {jobs: [], cron_unavailable: true}
instead, so the Tasks tab loads (empty) instead of erroring. Happy path unchanged.
Co-authored-by: reporter

api/routes.py

@@ -10188,7 +10188,13 @@ def handle_get(handler, parsed) -> bool:
     # os.environ (process-global) at call time. Wrap in cron_profile_context
     # so the TLS-active profile's jobs.json is read, not the process default.
     if parsed.path == "/api/crons":
-        from cron.jobs import list_jobs
+        # #4768: in split-container / minimal Docker deployments the WebUI image may
+        # not ship the agent's `cron` package on its import path. Degrade gracefully
+        # (empty list + cron_unavailable flag) instead of 500ing the whole Task tab.
+        try:
+            from cron.jobs import list_jobs
+        except ModuleNotFoundError:
+            return j(handler, {"jobs": [], "cron_unavailable": True})
         from api.profiles import cron_profile_context
 
         with cron_profile_context():

tests/test_issue4768_cron_module_missing.py

@@ -0,0 +1,49 @@
+"""Regression test for #4768.
+
+In split-container / minimal Docker deployments the WebUI image may not ship the
+agent's ``cron`` package on its import path. Before the fix, ``GET /api/crons``
+(the Tasks tab's initial load) did ``from cron.jobs import list_jobs`` with no
+guard, so a ``ModuleNotFoundError`` bubbled up as a 500 and broke the whole tab.
+
+The fix degrades gracefully: an empty job list with a ``cron_unavailable`` flag.
+"""
+import pathlib
+import re
+
+REPO = pathlib.Path(__file__).resolve().parent.parent
+ROUTES = (REPO / "api" / "routes.py").read_text(encoding="utf-8")
+
+
+def _api_crons_branch() -> str:
+    """Return the source of the `if parsed.path == "/api/crons":` GET branch."""
+    marker = ROUTES.index('if parsed.path == "/api/crons":')
+    # Stop at the next sibling branch so we only inspect this handler.
+    nxt = ROUTES.index('if parsed.path == "/api/crons/output":', marker)
+    return ROUTES[marker:nxt]
+
+
+def test_api_crons_guards_missing_cron_module():
+    """The /api/crons GET branch must wrap the cron.jobs import in a guard that
+    returns a graceful payload instead of letting ModuleNotFoundError 500."""
+    branch = _api_crons_branch()
+    assert "from cron.jobs import list_jobs" in branch
+    assert "except ModuleNotFoundError" in branch, (
+        "GET /api/crons must catch ModuleNotFoundError so the Tasks tab does not "
+        "500 when the cron package is absent (#4768)."
+    )
+    # The except path returns an empty list + an unavailable flag (not a re-raise).
+    assert "cron_unavailable" in branch
+    # The try guards the import specifically (not some unrelated block).
+    try_idx = branch.index("try:")
+    import_idx = branch.index("from cron.jobs import list_jobs")
+    except_idx = branch.index("except ModuleNotFoundError")
+    assert try_idx < import_idx < except_idx
+
+
+def test_api_crons_still_lists_jobs_on_happy_path():
+    """The guard must not remove the normal behavior: when cron imports fine, the
+    branch still calls list_jobs(include_disabled=True) under cron_profile_context."""
+    branch = _api_crons_branch()
+    assert "list_jobs(include_disabled=True)" in branch
+    assert "cron_profile_context()" in branch
+    assert "_cron_jobs_for_api(" in branch