feat(wails): move the e2e harness and headless launch onto v3

make e2e is green on chromium: 92 passed. The harness is rebuilt on
what v3 actually offers, and three of the four things it replaced turn
out to be better than what they replaced.

The headless launch is v3's own server mode. scripts/dev-headless.sh
ran a `-tags dev` binary whose app_dev.go parsed -devserver/-assetdir
out of os.Args; that file went with v2, so the harness had no server at
all. `-tags dev,server` is a first-class mode and needs no display, so
Xvfb is gone from the script and from CI.

The bridge hooks two places, neither of them EventsOn. Inbound is
window._wails.dispatchWailsEvent, wrapped by pre-creating the object
the runtime keeps and putting an accessor on the one property.
Outbound is fetch: v3 routes every runtime call through one POST, so
the bridge sees binding calls and event emits from any module, needs no
walk of an object graph, and cannot miss a call made before it looked.

__yjEvents.call posts to that endpoint by method name, so it depends on
nothing in the app's bundle and works on a page with no init script.
That is what lets seed-sandbox.sh drop playwright-cli entirely — it
drove AddLibrary through a browser only because window.go was v2's one
way in — and with it a global npm install and a second Chromium in CI.

measure.mjs and one spec lose their window.go walks and read the
bridge's log instead; e2e/support/method-ids.mjs derives id -> name
from frontend/bindings/ (phase 6b option 1, so it cannot go stale
silently). Plain .mjs because measure.mjs runs under bare node and one
derivation beats two that can disagree.

Four bugs surfaced, and the migration is how.

The cross-service wiring never ran headless. It hung off
Common.ApplicationStarted, which server mode never emits —
setupCommonEvents is an explicit no-op there — so the queue had no
TrackLoader and playing a track changed the queue and then silently did
nothing. It is a service registered last now (backend/startup.go):
services start in registration order, which is the ordering the wiring
needs, in every mode.

Six specs called SetQueue with 3 of its 4 arguments. v2 accepted that
and filled the gap; v3 answers "expects 4 arguments, got 3".

requested-badge's cleanup read window.go and returned early on
`if (!svc)` — the silent cleanup its own comment was written to
prevent, one migration later. It posts to the runtime endpoint now,
which any page can do.

SearchIndex.Search trusted a startup latch, so rows a spec staged
afterwards were unsearchable and three specs passed only when an
earlier one happened to flip it. shelves.go fixed exactly this and left
hasCatalogRows behind; the search path now uses it as the fallback,
with the latch still the fast path.

Two spec edits are deletions of assertions about v2. harness.spec
checked Object.keys(window.go) and that a bad call *hung*; it now
checks the real runtime is loaded and that the backend rejects with a
TypeError naming the argument. album-actions asserted a tracklist
legend that dcc40b1 deleted on main — that spec has been failing since,
and what replaced it is covered in frontend/test/components.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UDCbcCZQepnpSQYJ6SxxZm

.pi/skills/yellowjacket-dev/SKILL.md

@@ -21,12 +21,21 @@ here has disappeared.
 Fifteen things cost a cycle each the first time. They are here, not in a
 reference, because you need them *before* the failure, not after.
 
-- **Time out every binding call.** A bound Go method called with wrong
-  argument types makes the backend log `error parsing arguments` and
-  **never fire the callback**, so the promise hangs forever. Use
-  `window.__yjEvents.call(path, args, ms)` (browser) or `callBinding`
-  (specs), never a bare `window.go.…`. When one hangs anyway,
-  `make dev-logs` — `.dev/app.log` is the only place the reason appears.
+- **Call a binding through the bridge.** `window.go` does not exist
+  under Wails v3 — the bindings are bundled modules, not a global — so
+  use `window.__yjEvents.call(path, args, ms)` (browser) or
+  `callBinding` (specs). Both post to the runtime's own endpoint by
+  method name, so they work on any page, including one with no init
+  script.
+
+  A bad call now *rejects*, and says why: a wrong type comes back as a
+  TypeError naming the argument, a wrong count as
+  `expects 4 arguments, got 3`, an unknown method as a ReferenceError.
+  Under v2 the backend logged `error parsing arguments` and never fired
+  the callback, so `.dev/app.log` was the only place the reason
+  appeared and the timeout was the only thing that made the mistake
+  visible. The timeout is still there, but now it means a genuinely
+  hung request.
 - **Nothing is clickable on a fresh `YJ_HOME`.** `<first-run-wizard>`
   intercepts all pointer events until a library exists, and the click
   fails with a Playwright interception error that reads like a selector

.pi/skills/yellowjacket-dev/references/harness.md

@@ -74,9 +74,14 @@ behind `YJ_TESTCTL=1`, which `scripts/dev-headless.sh` sets and
 - **`snapshot` writes a file, it does not print the tree.** The
   command prints a path under `outputDir`; read that. Only the tail
   is echoed.
-- **Three separate browser caches.** `playwright-cli`, `@playwright/test`
+- **Two separate browser caches.** `@playwright/test`
   (`make e2e-setup`) and the Vitest provider (`make ui-setup`) each
-  download their own Chromium. One working is no guarantee for the next.
+  download their own Chromium. One working is no guarantee for the
+  other. There used to be a third: `playwright-cli` was a *required*
+  dependency because `scripts/seed-sandbox.sh` drove `AddLibrary`
+  through a real page, `window.go` being v2's only way in. v3 answers
+  the same call over HTTP, so the seed is `curl` now and the CLI is
+  only an exploratory convenience.
 - **`getByRole('button', { name })` matches substrings.** "Play" also
   matches "Add queue to playlist"; transport controls need
   `exact: true`.