test(desktop): assert the tracer contract before the timing budget

Blind-review round 15 (Fable xhigh) finding: a clean measure recorded
behind the held chunk — the exact regression under test — clears the
start mark and nulls elapsedSinceClick, so the timing-budget assertion
failed first with a 'rerun, not a tracer bug' message stating the
opposite of the truth. The contract assertion now runs first.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Max Lampert <maxwell@squareup.com>

desktop/tests/e2e/switch-settle-after-paint.spec.ts

@@ -130,14 +130,18 @@ test("settle waits for a delayed lazy channel-pane chunk", async ({ page }) => {
       elapsedSinceClick: start ? performance.now() - start.startTime : null,
     };
   }, SWITCH_MEASURE);
-  expect(
-    early.elapsedSinceClick,
-    "harness overhead consumed the tracer's settle deadline — timing, not a tracer bug",
-  ).toBeLessThan(4_500);
+  // Order matters: a clean measure recorded behind the held chunk — the
+  // regression under test — clears the start mark, nulling elapsedSinceClick.
+  // Asserting the budget first would then fail with a "rerun, not a tracer
+  // bug" message that states the opposite of the truth.
   expect(
     early.cleanMeasures,
     "no clean settle may be recorded while the pane chunk is suspended",
   ).toBe(0);
+  expect(
+    early.elapsedSinceClick,
+    "harness overhead consumed the tracer's settle deadline — timing, not a tracer bug",
+  ).toBeLessThan(4_500);
 
   releaseChunk();