fix(sw): the service worker had never installed, and updates raced the reload

Two defects behind "the new version is ready" not going away.

1. THE WORKER NEVER INSTALLED — in any environment, ever.

   install did `cache.addAll([...PRECACHE, SHELL])`. PRECACHE is derived from
   the build's own outputs, which already contain index.html, and SHELL is
   index.html again. addAll() rejects the ENTIRE install on a duplicate
   request:

     InvalidStateError: Cache.addAll(): duplicate requests (.../index.html)

   So install failed on every load, the worker went redundant, and nothing
   ever activated. Registration itself succeeds and the failure is inside the
   install event, so nothing surfaced it — which is why offline behaviour was
   listed as "never verified" rather than "broken". All 11 precached URLs
   return 200; the list was the only fault. Deduping now lives in
   src/swPrecache.ts, at the point of use, so no future addition to either
   list can reintroduce it.

   Verified in a real browser for the first time: the worker installs,
   activates, claims the page, and caches 11 entries. A rebuild is then
   detected, the prompt appears, clicking Reload applies it, stale caches are
   dropped and the prompt does not return.

2. THE DEV WORKER IGNORED THE LIFECYCLE — my own regression, from 53707b1.

   That commit made the dev server serve an inert sw.js to silence a MIME
   error. Inert included the lifecycle: no skipWaiting, no clients.claim, no
   message handler. A worker like that can sit in `waiting` forever and can
   never be applied, so the prompt returns on every load and the Reload button
   cannot possibly clear it. This is the likeliest cause of the reported
   symptom, since with defect 1 a production build could never have shown that
   prompt at all. The dev worker still caches nothing — that would fight HMR —
   but now honours install, activate and SKIP_WAITING.

3. applyUpdate RACED ITS OWN RELOAD — real, measured, but not reproducible on
   demand, so it is hardening rather than a proven fix.

   It posted SKIP_WAITING and called window.location.reload() on the next
   line. Measured in Chrome: at that instant the new worker was still
   `installed` and the controller had NOT changed — it changed 2 ms later. The
   window is wider in practice because activate deletes every stale cache
   before claiming clients. When the reload wins, the reloaded page still finds
   registration.waiting and shows the prompt again. It now waits for
   controllerchange, with a timeout backstop so a worker that ignores
   SKIP_WAITING cannot leave the button dead. The sequencing is pure and
   tested (src/ui/swUpdate.ts): listener attached before the message, reload
   exactly once, unsubscribed after.

Tooling: scripts/screenshot.ts gains --profile (a fresh Chrome profile has no
registered worker, so nothing stateful across loads could be reproduced at all)
and --eval-after-file (observe a flow that ends in a navigation from the other
side of it).

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

scripts/screenshot.ts

@@ -5,6 +5,7 @@
  *   bun scripts/screenshot.ts <url> <out.png> [--w=1280] [--h=900]
  *                             [--wait=1500] [--full] [--click=<selector>]
  *                             [--eval=<js>|--eval-file=<path>] [--dark] [--reload]
+ *                             [--profile=<dir>] [--eval-after-file=<path>]
  *
  * Why this exists: ARCHITECTURE.md and TODO.md both say nothing here can run a
  * browser, so appearance has never been verified. Chrome IS available, but its
@@ -40,6 +41,10 @@ const chrome = Bun.spawn(
     "--hide-scrollbars",
     "--force-device-scale-factor=1",
     "--remote-debugging-port=0",
+    // A fresh profile each run means empty IndexedDB, empty caches and NO
+    // registered service worker — which makes anything stateful across loads
+    // (an update prompt, a migration, an install) impossible to reproduce.
+    ...(flag("profile") ? [`--user-data-dir=${flag("profile")}`] : []),
     `--window-size=${width},${height}`,
     ...(has("dark") ? ["--force-dark-mode", "--enable-features=WebContentsForceDark"] : []),
     "about:blank",
@@ -171,6 +176,21 @@ if (clickSelector) {
   await Bun.sleep(700);
 }
 
+// Runs after the reload, so a flow that ends in a navigation can be observed
+// on the other side of it — an update prompt applying itself, a migration.
+const evalAfterFile = flag("eval-after-file");
+if (evalAfterFile) {
+  const source = await Bun.file(evalAfterFile).text();
+  const result = await send("Runtime.evaluate", {
+    expression: source,
+    awaitPromise: true,
+  });
+  console.log(
+    "eval-after:",
+    JSON.stringify(result?.result?.value ?? result?.result?.description ?? null),
+  );
+}
+
 const shot = await send("Page.captureScreenshot", {
   format: "png",
   captureBeyondViewport: has("full"),