fix(electron): show the main window once its document has loaded; enforce J1 IPC and mutation counters (#1828)

* fix(electron): show the main window once its document has loaded; enforce J1 IPC and mutation counters

Re-lands #1788, which merged into #1782's branch after #1782 had already
reached master, so none of it is on master.

The hidden main window was shown on ready-to-show only. On Linux under
X11, when the startup scripts run before the window's first frame, the
next frame comes about a second later: nothing is on screen and the
splash's requestAnimationFrame waits, so J1's first card came ~940 ms
after load instead of ~480 ms in most runner launches (18 bridge calls /
1,031-1,033 DOM mutations instead of 15 / 558).

The window is now shown at ready-to-show or the main frame's
did-finish-load, whichever comes first, with the splash colour as its
background so showing before the first paint does not flash. The journey
gate keeps the app's did-finish-load listeners away from its about:blank
detour, as it already does for ready-to-show.

Three dispatched runs on this branch (37192092882, 37192097790,
37192103151) read 15 calls and 558 mutations in all 18 iterations,
stable: true. Both become baselines (slack 0), and the Performance
journeys job checks them with check-journey-ratchet.mjs --only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* chore(perf): record the evidence PR of the J1 runtime baselines

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: 4gray <fourgray@proton.me>

.github/workflows/ci.yml

@@ -324,8 +324,23 @@ jobs:
             # Electron dependency check, the xvfb run, the summary lookup and
             # the job-summary report; shared with performance-ratchet.yml.
             - name: Run the performance journeys
+              id: journeys
               uses: ./.github/actions/performance-journeys
 
+            # Only the J1 counters shown deterministic on this runner; the
+            # other journey measurements stay evidence (see Ratchet in
+            # docs/architecture/performance-journeys.md). Here and not in
+            # the composite action, so the weekly tightening still measures
+            # a run that would fail it.
+            - name: Check the J1 runtime counters against the baselines
+              env:
+                  SUMMARY: ${{ steps.journeys.outputs.summary }}
+              run: >-
+                  node tools/performance/check-journey-ratchet.mjs
+                  --summary "$SUMMARY"
+                  --only launch/renderer.ipcCallsToFirstCard
+                  --only launch/renderer.domMutationsToFirstCard
+
             - name: Upload journey summaries
               if: always()
               uses: actions/upload-artifact@v7