fix(m7): make executed_at override editable in non-UTC timezones

The naive `new Date(executedAt).toISOString().slice(0, 16)` round-trip on
every keystroke silently shifted the hour by the local TZ offset (Europe
input field is local-time but we kept reformatting via UTC), so the user
could only edit the date — the time component snapped back to UTC every
render.

Fix: keep the local state in `YYYY-MM-DDTHH:MM` form (`executedAtLocal`)
and only convert to/from a UTC ISO at the boundaries — initial sync from
server and submit. Two small helpers `isoToLocalInputValue` /
`localInputValueToIso` carry the conversion explicitly.

Also tightened the useEffect on both Red and Blue zones to depend on
`test.id` instead of the whole `test` object, so polling refetches no
longer wipe an in-progress edit (the 15 s activity poll returns a fresh
object reference even when the row's contents are unchanged).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/pages/MissionTestPage.tsx

@@ -74,6 +74,30 @@ function formatRelative(iso: string | null | undefined): string {
   return `${days}d ago`;
 }
 
+/**
+ * Convert a UTC ISO datetime to the wall-clock `YYYY-MM-DDTHH:MM` string that
+ * `<input type="datetime-local">` expects (and displays) in the operator's
+ * timezone. The naive `new Date(iso).toISOString().slice(0, 16)` shortcut
+ * round-trips through UTC and silently shifts the time by the local offset
+ * every time the user types, making the hour un-editable in any non-UTC TZ.
+ */
+function isoToLocalInputValue(iso: string | null | undefined): string {
+  if (!iso) return '';
+  const d = new Date(iso);
+  if (Number.isNaN(d.getTime())) return '';
+  const pad = (n: number) => String(n).padStart(2, '0');
+  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}T${pad(d.getHours())}:${pad(d.getMinutes())}`;
+}
+
+/** Parse a `datetime-local` input value (already in wall-clock local time)
+ * back into a UTC ISO string. Returns null if the input is empty/invalid. */
+function localInputValueToIso(local: string): string | null {
+  if (!local) return null;
+  const d = new Date(local);
+  if (Number.isNaN(d.getTime())) return null;
+  return d.toISOString();
+}
+
 function useMissionTest(missionId: string, testId: string) {
   return useQuery({
     queryKey: missionTestKeys.detail(missionId, testId),
@@ -155,25 +179,35 @@ function RedZone({ test, missionId, canWriteRed }: RedZoneProps) {
   const [output, setOutput] = useState(test.red_output ?? '');
   const [comment, setComment] = useState(test.red_comment_md ?? '');
   const [override, setOverride] = useState(test.executed_at_overridden);
-  const [executedAt, setExecutedAt] = useState(test.executed_at ?? '');
+  // `executedAtLocal` is the raw `YYYY-MM-DDTHH:MM` string the datetime-local
+  // input speaks; we only convert to/from UTC ISO at the boundaries
+  // (initial sync + submit). Doing the round-trip on every keystroke shifted
+  // the hour by the local TZ offset and made the time field uneditable in
+  // any non-UTC zone (cf. tasks/lessons.md M7 fix).
+  const [executedAtLocal, setExecutedAtLocal] = useState(
+    isoToLocalInputValue(test.executed_at),
+  );
   const dirty =
     command !== (test.red_command ?? '') ||
     output !== (test.red_output ?? '') ||
     comment !== (test.red_comment_md ?? '') ||
     override !== test.executed_at_overridden ||
-    (override && executedAt !== (test.executed_at ?? ''));
+    (override &&
+      executedAtLocal !== isoToLocalInputValue(test.executed_at));
 
-  // Sync local state when a refetch lands a newer version of the test
+  // Sync local state only when the *identity* of the test changes (route
-  // (concurrent collaboration: blue's edit shouldn't blow away our local
+  // change). Polling refetches return a new object reference for the same
-  // unsaved changes, but a fresh load should).
+  // test_id; resetting on those would wipe whatever the user is mid-typing.
+  // Successful saves push the new test through `setQueryData`, which is fine
+  // — the saved fields already match local state.
   useEffect(() => {
     setCommand(test.red_command ?? '');
     setOutput(test.red_output ?? '');
     setComment(test.red_comment_md ?? '');
     setOverride(test.executed_at_overridden);
-    setExecutedAt(test.executed_at ?? '');
+    setExecutedAtLocal(isoToLocalInputValue(test.executed_at));
-    // We deliberately reset on every test reload — see comment above.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [test]);
+  }, [test.id]);
 
   const save = useMutation({
     mutationFn: (body: UpdateMissionTestPayload) =>
@@ -197,10 +231,7 @@ function RedZone({ test, missionId, canWriteRed }: RedZoneProps) {
       body.executed_at_overridden = override;
     }
     if (override) {
-      const iso = executedAt
+      body.executed_at = localInputValueToIso(executedAtLocal);
-        ? new Date(executedAt).toISOString()
-        : null;
-      body.executed_at = iso;
     }
     save.mutate(body);
   }
@@ -257,10 +288,8 @@ function RedZone({ test, missionId, canWriteRed }: RedZoneProps) {
         {override && (
           <input
             type="datetime-local"
-            value={
+            value={executedAtLocal}
-              executedAt ? new Date(executedAt).toISOString().slice(0, 16) : ''
+            onChange={(e) => setExecutedAtLocal(e.target.value)}
-            }
-            onChange={(e) => setExecutedAt(e.target.value)}
             disabled={!canOverride}
             className="rounded-md border border-border bg-bg-card px-2 py-1 font-mono text-2xs text-text"
             data-testid="red-executed-at"
@@ -309,10 +338,13 @@ function BlueZone({ test, missionId, canWriteBlue, detectionLevels }: BlueZonePr
     comment !== (test.blue_comment_md ?? '') ||
     levelId !== (test.detection_level_id ?? '');
 
+  // Sync from server only on test-identity change (route nav), not on every
+  // polling refetch — see RedZone for the rationale.
   useEffect(() => {
     setComment(test.blue_comment_md ?? '');
     setLevelId(test.detection_level_id ?? '');
-  }, [test]);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [test.id]);
 
   const save = useMutation({
     mutationFn: (body: UpdateMissionTestPayload) =>