feat(harness): agent-drivable dev harness and CI that gates

A coding agent could develop this repo's Go packages and could not
develop the application: every path to running YellowJacket ended in a
blocking GTK window, so 265 bound methods, 46 events, 33 component
directories and 13 stores had exactly one form of verification
available — `tsc --noEmit`.

The unlock is that `wails dev`'s dev server on :34115 serves the real
frontend with the real generated bindings against the same Go backend a
desktop window attaches to, so a plain Chromium under Xvfb gets a fully
functional app. Four test tiers now exist, cheapest first:

- `make ui-test` — 313 Vitest tests in a real browser in ~2 s, no app,
  no backend, no display. Works because `frontend/wailsjs/` is a pure
  passthrough to `window.go`/`window.runtime`, so faking just those two
  globals runs the real bindings and the real store code.
- `make test` — services in-process, asserting on the payload the
  frontend would receive, via a new `events.Emit` wrapper.
- `make dev-headless` + `playwright-cli` — the real app, driven
  interactively, with an event bridge on `window.__yjEvents` and a
  dev-only control surface at `/__test/`.
- `make e2e` — 19 of those flows frozen as Playwright specs.

`events.Emit(ctx, …)` replaces all 35 direct `runtime.EventsEmit` call
sites: wails' `getEvents` `log.Fatalf`s on any context without its
runtime, so those paths could not run under test and a background
worker could take the app down. Four packages had each hand-rolled the
same guard; nine more guarded on `ctx != nil`, which does not help.
`TestNoDirectRuntimeEmits` fails the build on a new one.

Fixtures are generated, not committed (`make testdata`), and seeds are
built by *running the app* — never by hand-writing config and DB rows,
which would be a second description of a valid YJ_HOME.

`.gitea/workflows/ci.yml` is the first workflow here that tests
anything; the other three only package, so `gitea_ci` reported only
packaging jobs and misled anyone asking whether a push was healthy.
Both jobs were prototyped to green in a bare ubuntu:24.04 container
before the YAML was written, which immediately caught `make lint`
linting three configurations that nothing builds: all three passes
omitted `webkit2_41`, so wails resolved webkit2gtk-4.0 — which Arch
still ships and Ubuntu 24.04 dropped.

Operational instructions live in `.pi/skills/yellowjacket-dev/`,
measured discoveries in `.planning/NOTES.md`, and architecture in
`CLAUDE.md` — split by tense, not by topic, because a topical split
gives every new fact two plausible homes. `make skill-check` fails a
commit if the skill cites a make target that does not exist.

frontend/test/harness.test.ts

@@ -0,0 +1,96 @@
+/**
+ * Self-tests for the component tier, in the spirit of e2e/specs/
+ * harness.spec.ts: prove the rig is what it claims before trusting a
+ * single assertion built on it.
+ */
+import { describe, expect, it } from 'vitest';
+
+import { Events } from '../src/events';
+import { emit, calls, wails, flush } from '@test/support/harness';
+// Importing a store must be enough to make it start listening.
+import { queueStore } from '@store/queue-store';
+
+describe('component-tier harness', () => {
+  it('runs in a real browser with a real shadow DOM', () => {
+    const host = document.createElement('div');
+
+    host.attachShadow({ mode: 'open' }).innerHTML = '<b>x</b>';
+
+    expect(host.shadowRoot?.querySelector('b')?.textContent).toBe('x');
+  });
+
+  it('routes generated bindings through the fake, not a module mock', async () => {
+    // The import path under test is the real generated stub, which does
+    // window['go']['queue']['Queue']['GetState']().
+    const Queue = await import('@go/queue/Queue');
+
+    wails.stub('queue.Queue.GetState', { currentIndex: 4 });
+
+    await expect(Queue.GetState()).resolves.toEqual({ currentIndex: 4 });
+    expect(calls('queue.Queue.GetState')).toHaveLength(1);
+  });
+
+  it('resolves an unstubbed binding instead of hanging', async () => {
+    const Queue = await import('@go/queue/Queue');
+
+    // The real trap this pays for is the reverse: a *real* binding
+    // called with wrong argument types never settles. Here, silence is
+    // an immediate undefined so a test fails on the assertion rather
+    // than on a timeout.
+    await expect(Queue.Play()).resolves.toBeUndefined();
+  });
+
+  it('registers listeners merely by importing a store', () => {
+    expect(wails.listenerNames()).toContain(Events.QueueChanged);
+  });
+
+  it('delivers events to store listeners with their payload', () => {
+    emit(Events.QueueIndexChanged, { currentIndex: 11 });
+
+    expect(queueStore.getState().currentIndex).toBe(11);
+  });
+
+  it('expires a once-listener after a single delivery', () => {
+    let fired = 0;
+
+    wails.on('SyntheticEvent', () => {
+      fired += 1;
+    }, 1);
+
+    wails.notify('SyntheticEvent', []);
+    wails.notify('SyntheticEvent', []);
+
+    expect(fired).toBe(1);
+  });
+
+  it('notifies local listeners on a frontend-side EventsEmit', async () => {
+    // Wails' own runtime notifies JS listeners before it notifies Go
+    // (desktop/events.js), so a frontend emit is observable in-page.
+    const { EventsEmit } = await import('@runtime/runtime');
+    let seen: unknown;
+
+    wails.on('SyntheticEmit', (data) => {
+      seen = data;
+    }, -1);
+
+    EventsEmit('SyntheticEmit', 42);
+
+    expect(seen).toBe(42);
+  });
+
+  it('flushes the microtask queue stores notify on', async () => {
+    let notified = false;
+
+    const off = queueStore.subscribe(() => {
+      notified = true;
+    });
+
+    emit(Events.QueueIndexChanged, { currentIndex: 1 });
+    const beforeFlush = notified;
+
+    await flush();
+    off();
+
+    expect([beforeFlush, notified]).toEqual([false, true]);
+  });
+});