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

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

@@ -57,6 +57,21 @@ behind `YJ_TESTCTL=1`, which `scripts/dev-headless.sh` sets and
   staging the work that would produce it — job progress, download
   progress, scan progress. It calls `events.Deliver`, which *errors*
   when the event reaches nobody, so a `200` means it really arrived.
+- **State you stage, you own** (#168). Nothing resets those stores, so
+  clear yours in `test.afterEach` with the same event that staged it
+  (`emit('JobsChanged', [])`) — the store replaces its list from every
+  snapshot, so `testctl` needs no special case. **Measured: this does
+  not currently cross a spec boundary**, because every test gets a fresh
+  page and `JobStore.init()` refetches `GetJobs()` from a backend
+  registry that `/__test/emit` never writes to. Stated anyway, because
+  it costs one line and the leak needs only one spec that keeps a page
+  alive — but do not cite #168 for a symptom you have not reproduced.
+- **Measure against the thing next to you, not an absolute
+  coordinate.** An absolute number in a shell measurement is also a
+  claim about everything above it — `contentTop === 0` quietly asserts
+  "and no background job is running", which is not what that spec was
+  about or could arrange, while `contentTop === jobBandBottom` is true
+  either way. This is the half of #168 that stands on its own.
 - **`restore` is slow** (~40 s in the suite) because it copies every
   table. Prefer snapshotting once and restoring only when a spec
   genuinely mutates state.