test(#4850): read freshness under the fixture git timeout in derivationIsNotMemoizedAcrossRenders (#4870)

The row asserts that deriveStateFreshness is not memoized across renders,
and it did so through the hook's real git spawn bounded by the 1500 ms
production timeout. On a loaded Windows runner the second spawn can exceed
that bound, and readStateHeadCommits returns its designed null, which the
exact-count assertion reads as a failure (null !== 10).

Wrap the two freshness reads in the block's existing withSpawnSpy, forwarding
to the real execFileSync with the fixture-scoped GIT_FIXTURE_TIMEOUT_MS in
place of the production bound. The spawn stays real, so a genuine memoization
regression (second read returning 5) still fails the row. No production file
changes; STATE_FRESHNESS_GIT_TIMEOUT_MS stays 1500.

Closes #4850

Co-authored-by: Tom Boucher <trekkie@nomorestars.com>

tests/gsd-statusline.test.cjs

@@ -3236,16 +3236,25 @@ describe('evaluateUpdateCache lineage guard', () => {
       test('derivationIsNotMemoizedAcrossRenders', (t) => {
         const dir = createTempGitProject('gsd-freshness-no-memo-');
         t.after(() => cleanup(dir));
+        // This row asserts non-memoization, not the timeout degrade: keep the
+        // real git spawn, lift only the hook's 1500 ms production bound so
+        // runner load cannot turn its designed `null` into a red (#4850).
+        const realExec = childProcess.execFileSync;
+        const unbounded = (file, args, opts) => realExec(file, args, { ...opts, timeout: GIT_FIXTURE_TIMEOUT_MS });
+        const read = () => {
+          let state;
+          withSpawnSpy(unbounded, () => { state = readGsdState(dir, { stateFreshness: true }); });
+          return state;
+        };
+
         const stampA = commitN(dir, 5);
         writeStateHead(dir, stampA);
-
+        const first = read();
-        const first = readGsdState(dir, { stateFreshness: true });
         assert.equal(first.freshness.commits_behind, 5);
 
         const stampB = commitN(dir, 10);
         writeStateHead(dir, stampB);
-
+        const second = read();
-        const second = readGsdState(dir, { stateFreshness: true });
         assert.equal(second.freshness.commits_behind, 10);
         assert.notEqual(first.freshness.commits_behind, second.freshness.commits_behind);
       });