test(e2e): give the job specs their own state back

Both specs stage a job through `/__test/emit` and neither cleared it.
Nothing resets those stores, so the spec that staged it is the one that
should put it back, and `JobsChanged` with `[]` is the whole cleanup --
`JobStore` replaces its list from every snapshot, so `testctl` needs no
special case.

**The leak as reported did not reproduce, and that is worth recording
rather than quietly fixing.**  Measured with a temporary probe: a
positive control confirmed a staged job really does move the shell at a
phone width (`job-band` renders a row, `.main-panel`'s top goes 0 to
55), and the very next page had no job at all.  The reason is that
every test gets a fresh page and `JobStore.init()` refetches `GetJobs()`
from a backend registry `/__test/emit` never writes to -- it calls
`events.Deliver`, which touches frontends and no state.  So the state
cannot cross a spec boundary as described, and the 55px offset the
draft assertion saw in that suite run has another cause that is not in
evidence.

The cleanup stays, because it costs a line and the leak would need only
one spec that keeps a page alive, and the comments say what was
measured rather than asserting the mechanism.

The durable half is the rule, now in the harness reference: measure
against the element next to you, not an absolute coordinate.  An
absolute number in a shell measurement is also a claim about everything
above it -- `contentTop === 0` asserts "and no background job is
running", which that spec could not arrange.

Closes #168

e2e/specs/top-bar-fit.spec.ts

@@ -102,6 +102,22 @@ const collapsed = (page: Page) =>
   }));
 
 test.describe('the top bar fits the window', () => {
+  /**
+   * **State a spec stages is the spec's to clear** (#168). `/__test/emit`
+   * writes to a store nothing resets, and this file stages the widest job
+   * in the app, so it puts it back — with the same event, since the store
+   * replaces its whole list from every snapshot.
+   *
+   * **Measured: it does not currently outlive the page.** Every test gets
+   * a fresh page and `JobStore.init()` refetches `GetJobs()` from a
+   * backend registry `/__test/emit` never writes to, so nothing is being
+   * repaired here; the rule is stated because it costs one line and the
+   * leak would need only one spec that keeps a page alive.
+   */
+  test.afterEach(async ({ testctl }) => {
+    await testctl.emit('JobsChanged', []);
+  });
+
   /**
    * The phone's answer, which is not "it fits" (#57).
    *