test: warm cold dynamic imports before the timed cases

Under a full coverage run on every core, a test file's first cold import
(0.6-0.8 s alone) outran the 5 s case timeout and the half-done import
failed every later case in the file: the vitest lane went red in 2 of 5
runs with no defect. A beforeAll warm-up in the 4 files of that pattern;
5 of 5 full runs green after.

frontend/src/lib/diagnostics.dom.test.ts

@@ -3,7 +3,7 @@
 // E22 S5: the consented level applied to the tab, and the stream it opens. The module keeps its state
 // at module level (what is applied, the queue), so every test imports a fresh copy — and the log
 // from that same copy, or it would be reading a different ring.
-import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
 
 const sent: unknown[][] = [];
 const unloaded: unknown[][] = [];
@@ -24,6 +24,15 @@ vi.mock("./api", async () => {
   };
 });
 
+// Warm the transform cache once (see verifyEntry.dom.test.tsx): the first cold import costs ~0.8 s
+// alone and outran the 5 s case timeout under a full coverage run. Transformed code outlives
+// vi.resetModules, so each case still gets fresh module instances, only faster.
+beforeAll(async () => {
+  await import("./diagnostics");
+  await import("./log");
+  await import("./api");
+}, 60_000);
+
 beforeEach(() => {
   vi.useFakeTimers();
   vi.resetModules();