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>

apps/electron-backend-e2e/src/journeys/journey-renderer-gate-client.ts

@@ -12,6 +12,8 @@ export interface JourneyRendererGateState {
     readonly gatedEpochMs: number | null;
     readonly gatedMethod: string | null;
     readonly passThroughLoads: number;
+    /** `did-finish-load` events kept from the app's listeners on about:blank. */
+    readonly didFinishLoadHeldOnBlank: number;
     /** `ready-to-show` events dropped while the window was on about:blank. */
     readonly readyToShowHeldOnBlank: number;
     readonly releasedEpochMs: number | null;

apps/electron-backend-e2e/src/performance/journey-renderer-gate-client.spec.ts

@@ -14,6 +14,7 @@ function gate(
         blankLoadedEpochMs: 1_050,
         errors: [],
         gatedEpochMs: 1_020,
+        didFinishLoadHeldOnBlank: 1,
         gatedMethod: 'loadFile',
         passThroughLoads: 0,
         readyToShowHeldOnBlank: 1,

apps/electron-backend-e2e/src/performance/journey-renderer-gate.cjs

@@ -22,6 +22,11 @@
  * therefore drops `ready-to-show` while the window is on `about:blank`;
  * Electron emits it again for the real document's first paint, because the
  * window is still hidden, which is the moment production sees.
+ * The app also shows its window at the main frame's `did-finish-load`
+ * when that comes first, so the gate keeps the app's `did-finish-load`
+ * listeners (those registered before the gated load) away from the
+ * about:blank load too. Electron's own listener that resolves
+ * `loadURL(about:blank)` is registered later and still runs.
  *
  * With `ipcMain` passed in, the gate also keeps the listeners registered
  * with `ipcMain.handle` for `TAPPED_IPC_CHANNELS`, so the test can call a
@@ -53,6 +58,38 @@ function holdReadyToShowWhileBlank(window, state) {
     };
 }
 
+function holdDidFinishLoadWhileBlank(window, state) {
+    const contents = window.webContents;
+    if (
+        !contents ||
+        typeof contents.emit !== 'function' ||
+        typeof contents.rawListeners !== 'function'
+    ) {
+        return;
+    }
+    const appListeners = contents.rawListeners('did-finish-load');
+    const originalEmit = contents.emit;
+    contents.emit = function gatedContentsEmit(eventName, ...args) {
+        if (eventName !== 'did-finish-load' || !isShowingBlank(window)) {
+            return originalEmit.call(this, eventName, ...args);
+        }
+        state.didFinishLoadHeldOnBlank += 1;
+        const attached = this.rawListeners(eventName);
+        const held = appListeners.filter((listener) =>
+            attached.includes(listener)
+        );
+        for (const listener of held) this.removeListener(eventName, listener);
+        try {
+            return originalEmit.call(this, eventName, ...args);
+        } finally {
+            // Raw listeners keep their `once` wrappers, so a re-added once
+            // listener still fires once for the real document.
+            for (const listener of held)
+                this.prependListener(eventName, listener);
+        }
+    };
+}
+
 function tapIpcHandlers(ipcMain, channels) {
     const handlers = new Map();
     const originalHandle = ipcMain.handle;
@@ -78,6 +115,7 @@ function installJourneyRendererGate(BrowserWindow, target, options = {}) {
         errors: [],
         gatedEpochMs: null,
         gatedMethod: null,
+        didFinishLoadHeldOnBlank: 0,
         passThroughLoads: 0,
         readyToShowHeldOnBlank: 0,
         releasedEpochMs: null,
@@ -128,6 +166,7 @@ function installJourneyRendererGate(BrowserWindow, target, options = {}) {
             state.gatedEpochMs = now();
             state.gatedMethod = method;
             holdReadyToShowWhileBlank(this, state);
+            holdDidFinishLoadWhileBlank(this, state);
             try {
                 await this.webContents.loadURL(BLANK_URL);
                 state.blankLoadedEpochMs = now();

apps/electron-backend-e2e/src/performance/journey-renderer-gate.spec.ts

@@ -4,6 +4,7 @@ import test from 'node:test';
 
 interface GateState {
     blankLoadedEpochMs: number | null;
+    didFinishLoadHeldOnBlank: number;
     errors: string[];
     gatedEpochMs: number | null;
     gatedMethod: string | null;
@@ -155,13 +156,13 @@ test('records a failed about:blank navigation and still loads after release', as
 function createEmittingBrowserWindow(log: string[]) {
     class EmittingBrowserWindow extends EventEmitter {
         url = '';
-        webContents = {
+        webContents = Object.assign(new EventEmitter(), {
             getURL: () => this.url,
             loadURL: async (url: string) => {
                 this.url = url;
                 log.push(`webContents.loadURL:${url}`);
             },
-        };
+        });
         async loadFile(file: string): Promise<void> {
             this.url = `file:///${file}`;
             log.push(`loadFile:${file}`);
@@ -201,6 +202,47 @@ test('holds ready-to-show while the window shows about:blank, then lets the real
     assert.equal(api.state.readyToShowHeldOnBlank, 1);
 });
 
+test('keeps did-finish-load of about:blank from the app listeners, not from later ones', async () => {
+    const log: string[] = [];
+    const EmittingBrowserWindow = createEmittingBrowserWindow(log);
+    const api = gateModule.installJourneyRendererGate(
+        EmittingBrowserWindow as unknown as {
+            prototype: Record<string, unknown>;
+        },
+        {},
+        { timeoutMs: 60_000 }
+    );
+    const window = new EmittingBrowserWindow();
+    // The app shows its window at the first did-finish-load.
+    window.webContents.once('did-finish-load', () =>
+        log.push('app:did-finish-load')
+    );
+    const load = window.loadFile('index.html');
+    await settle();
+    // Registered after the gated load, like Electron's own listener that
+    // resolves loadURL(about:blank).
+    window.webContents.on('did-finish-load', () =>
+        log.push('electron:did-finish-load')
+    );
+    window.webContents.emit('did-finish-load');
+    assert.equal(api.state.didFinishLoadHeldOnBlank, 1);
+
+    api.release();
+    await load;
+    window.webContents.emit('did-finish-load');
+    window.webContents.emit('did-finish-load');
+
+    assert.deepEqual(log, [
+        'webContents.loadURL:about:blank',
+        'electron:did-finish-load',
+        'loadFile:index.html',
+        'app:did-finish-load',
+        'electron:did-finish-load',
+        'electron:did-finish-load',
+    ]);
+    assert.equal(api.state.didFinishLoadHeldOnBlank, 1);
+});
+
 test('taps ipcMain.handle for the counters channel and passes registrations through', async () => {
     const registered: string[] = [];
     const ipcMain: FakeIpcMain = {

apps/electron-backend-e2e/src/performance/launch-journey-record.spec.ts

@@ -112,6 +112,7 @@ function measurement(
             blankLoadedEpochMs: 1_050,
             errors: [],
             gatedEpochMs: 1_020,
+            didFinishLoadHeldOnBlank: 1,
             gatedMethod: 'loadFile',
             passThroughLoads: 0,
             readyToShowHeldOnBlank: 1,
@@ -185,6 +186,7 @@ test('maps the probe, IPC capture and main counters to exact counters and spawn-
         'main.startupPhases': 9,
     });
     assert.equal(record.evidence['rendererGateReadyToShowHeldOnBlank'], 1);
+    assert.equal(record.evidence['rendererGateDidFinishLoadHeldOnBlank'], 1);
     assert.deepEqual(record.evidence['epochs'], {
         firstCard: 2_600.04,
         firstCardPaint: 2_650,

apps/electron-backend-e2e/src/performance/launch-journey-record.ts

@@ -185,6 +185,8 @@ export function toLaunchIterationRecord(
             mainCountersAtRead: mainCounters.counters,
             rendererGateReadyToShowHeldOnBlank:
                 measurement.gate.readyToShowHeldOnBlank,
+            rendererGateDidFinishLoadHeldOnBlank:
+                measurement.gate.didFinishLoadHeldOnBlank,
             ipcCallsByMethod: ipc.callsByMethod,
             ipcSerialDepth: serialDepth,
             ipcTimelineAmbiguousCompletions: ipc.ambiguousTimelineCompletions,

apps/electron-backend-e2e/src/window-visibility.e2e.ts

@@ -27,8 +27,9 @@ const setWindowState = (
     );
 
 /**
- * The app creates its window with `show: false` and shows it on
- * `ready-to-show`; a `hide()` sent earlier would be undone by that `show()`.
+ * The app creates its window with `show: false` and shows it at
+ * `ready-to-show` or `did-finish-load`, whichever comes first; a `hide()`
+ * sent earlier would be undone by that `show()`.
  */
 async function waitUntilShown(app: UnautomatedElectronApp): Promise<void> {
     await expect