Add coverage gap tests for command functionalities

- Implement tests for disk alert JSON output to include a message field when below threshold.
- Add tests for runner status when Gitea is online but no webhook URL is provided.
- Introduce tests for job report details to ensure no error line appears when there are no failure events.
- Add tests to skip empty JSONL files in job report listing.

tests/python/test_commands_monitor.py

@@ -659,3 +659,49 @@ def test_runner_pruned_old_entries(
         cli, ["monitor", "runner", "--state-dir", str(tmp_path)]
     )
     assert result.exit_code == 0
+
+
+# ── NEW: coverage gap tests ──────────────────────────────────────────────────
+
+
+def test_disk_alert_json_includes_message_field(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Lines 186-187: disk below threshold + --json → JSON has 'message' key, exit 1."""
+    monkeypatch.setattr(mon.shutil, "disk_usage", lambda _p: _fake_usage(free_gb=5))
+    result = CliRunner().invoke(
+        cli, ["monitor", "disk", "--min-free-gb", "50", "--json"]
+    )
+    assert result.exit_code == 1
+    payload = json.loads(result.output.strip())
+    assert payload["status"] == "alert"
+    assert "message" in payload
+    assert "below" in payload["message"]
+
+
+def test_runner_running_gitea_online_no_webhook(
+    monkeypatch: pytest.MonkeyPatch, tmp_path: Path
+) -> None:
+    """Lines 398->402: online==0 but no webhook_url → branch skips _post_webhook,
+    continues to return (line 402). Covers the 398->402 branch (webhook_url falsy)."""
+    monkeypatch.setattr(mon, "_service_status", lambda _s: "Running")
+    monkeypatch.setattr(mon, "_gitea_runners_online", lambda *_a, **_kw: 0)
+
+    class _Store:
+        def get(self, _target: str) -> Any:
+            from ci_orchestrator.credentials import Credential
+            return Credential("u", "tok")
+
+    import ci_orchestrator.credentials as creds
+    monkeypatch.setattr(creds, "KeyringCredentialStore", _Store)
+
+    result = CliRunner().invoke(
+        cli,
+        [
+            "monitor", "runner",
+            "--state-dir", str(tmp_path),
+            "--gitea-url", "https://g/",
+            "--gitea-credential-target", "tgt",
+            # no --webhook-url → webhook_url is ""
+        ],
+    )
+    assert result.exit_code == 0
+    assert "0 online runners" in result.output