Correct a Task 4 expectation that contradicted its own rule

The "ancient anchor" test expected three occurrences and omitted 31 August.
With a daily rule anchored at 09:00 and no stated end, the 31st runs to
09:00 on the 1st — inside a window that opens at midnight on the 1st. The
brief's own rule is that an occurrence overlapping either edge is included,
so four is right and three was the plan disagreeing with itself.

Found by the Task 4 implementer, which corrected the test and left the
implementation alone. Verified by running occurrencesOf directly.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/superpowers/plans/2026-08-27-recurring-custom-events.md

@@ -850,6 +850,10 @@ describe("occurrencesOf", () => {
       day("2026-09-04T00:00:00"),
     );
     expect(got.map((o) => o.id)).toEqual([
+      // The 31st opens at 09:00 and, having no stated end, runs to 09:00 on the
+      // 1st — which is inside a window that opens at midnight. Half off the
+      // left edge is still on the board, so it counts.
+      "myevent:k3f9qa2m01#2026-08-31",
       "myevent:k3f9qa2m01#2026-09-01",
       "myevent:k3f9qa2m01#2026-09-02",
       "myevent:k3f9qa2m01#2026-09-03",
@@ -1035,7 +1039,7 @@ export function nextOccurrences(
 - [ ] **Step 4: Run tests and typecheck**
 
 Run: `bun test test/recurrence.test.ts`
-Expected: PASS, 35 tests.
+Expected: PASS, 34 tests.
 
 Run: `bun run typecheck`
 Expected: exit 0.