refactor(desktop): funnel zoom apply+notify so restore can't desync

alelpoan's fix (emit hermes:zoom:changed after restore) is correct, but the
bug's root is duplication: setAndPersistZoomLevel and restorePersistedZoomLevel
each independently did setZoomLevel + send, and restore forgot the send.

Collapse both (and the lifecycle re-assert) into a single applyZoomLevel()
helper in zoom.ts that always applies-then-notifies — the regression can't
recur by omitting a send. Replace the source-grep test (which broke on main:
the sibling source-assertion pet test it copied was refactored to a behavioral
one, dropping the fs/path imports it relied on) with behavioral coverage of the
funnel, matching zoom.ts's "unit-testable without booting a BrowserWindow"
convention.

Co-authored-by: alelpoan <alelpoan@proton.me>

apps/desktop/electron/main.ts

@@ -4705,7 +4705,7 @@ function installPreviewShortcut(window) {
 // process owns setZoomLevel, so we mirror each change into localStorage and
 // read it back on did-finish-load to re-apply after reloads or crash recovery.
 import {
-  clampZoomLevel,
+  applyZoomLevel,
   installZoomReassertOnWindowEvents,
   percentToZoomLevel,
   ZOOM_STORAGE_KEY,
@@ -4718,11 +4718,9 @@ function setAndPersistZoomLevel(window, zoomLevel) {
     return
   }
 
-  const next = clampZoomLevel(zoomLevel)
-  window.webContents.setZoomLevel(next)
-  // Keep any open settings UI in sync, including changes made via the
-  // keyboard shortcuts or the View menu.
-  window.webContents.send('hermes:zoom:changed', { level: next, percent: zoomLevelToPercent(next) })
+  // Apply + notify in one funnel so the settings UI stays in sync, including
+  // changes made via the keyboard shortcuts or the View menu.
+  const next = applyZoomLevel(window.webContents, zoomLevel)
   window.webContents
     .executeJavaScript(
       `try { localStorage.setItem(${JSON.stringify(ZOOM_STORAGE_KEY)}, ${JSON.stringify(String(next))}) } catch {}`
@@ -4744,9 +4742,9 @@ function restorePersistedZoomLevel(window) {
         return
       }
 
-      const level = clampZoomLevel(Number(stored))
-      window.webContents.setZoomLevel(level)
-	  window.webContents.send('hermes:zoom:changed', { level, percent: zoomLevelToPercent(level) })
+      // Notify the renderer too — otherwise the Appearance UI Scale control
+      // can stay stuck at 100% even though the window zoom was restored.
+      applyZoomLevel(window.webContents, Number(stored))
     })
     .catch(error => rememberLog(`[zoom] restore failed: ${error?.message || error}`))
 }

apps/desktop/electron/zoom.test.ts

@@ -9,6 +9,7 @@ import assert from 'node:assert/strict'
 import { test } from 'vitest'
 
 import {
+  applyZoomLevel,
   clampZoomLevel,
   installZoomReassertOnWindowEvents,
   percentToZoomLevel,
@@ -118,31 +119,42 @@ test('unknown window kinds default to chat (zoom enabled)', () => {
   assert.deepEqual(zoomWiringForWindowKind('unknown'), { zoom: true })
   assert.deepEqual(zoomWiringForWindowKind(undefined), { zoom: true })
 })
-// Source assertion, same pattern as the pet-overlay test above: verifies the
-// fix for the UI Scale settings control drifting out of sync after a restart.
-// restorePersistedZoomLevel correctly re-applies the persisted zoom level to
-// the window, but must also notify the renderer — otherwise the renderer's
-// $zoomPercent store (see store/zoom.ts), which only updates from zoom.get()
-// (called once on load) and 'hermes:zoom:changed' events, can be left with a
-// stale value if zoom.get() resolves before the restore finishes, leaving the
-// Appearance settings UI Scale control showing the wrong preset even though
-// the window's actual zoom level was correctly restored.
-test('restorePersistedZoomLevel notifies the renderer, same as setAndPersistZoomLevel', () => {
-  const electronDir = path.dirname(fileURLToPath(import.meta.url))
-  const source = fs.readFileSync(path.join(electronDir, 'main.ts'), 'utf8').replace(/\r\n/g, '\n')
 
-  const restoreStart = source.indexOf('function restorePersistedZoomLevel(window)')
-  assert.notEqual(restoreStart, -1, 'missing restorePersistedZoomLevel')
+// The UI Scale settings control drifts out of sync after a restart when zoom
+// is applied to the window but the renderer is never told: its $zoomPercent
+// store (see store/zoom.ts) only updates from zoom.get() (once, on load) and
+// 'hermes:zoom:changed' events. applyZoomLevel is the single funnel every zoom
+// path (user set, restore-on-load, lifecycle re-assert) shares, so applying a
+// level always notifies — the regression can't come back by forgetting a send.
+function fakeWebContents() {
+  const calls: Array<[string, ...unknown[]]> = []
 
-  const snippet = source.slice(restoreStart, restoreStart + 600)
-  const setZoomIndex = snippet.indexOf('window.webContents.setZoomLevel(level)')
-  const sendIndex = snippet.indexOf("window.webContents.send('hermes:zoom:changed'")
+  return {
+    calls,
+    setZoomLevel: (level: number) => calls.push(['setZoomLevel', level]),
+    send: (channel: string, payload: unknown) => calls.push(['send', channel, payload])
+  }
+}
 
-  assert.notEqual(setZoomIndex, -1, 'restorePersistedZoomLevel must apply the restored zoom level')
-  assert.notEqual(
-    sendIndex,
-    -1,
-    'restorePersistedZoomLevel must notify the renderer after restoring zoom, or the UI Scale control can show a stale preset'
-  )
-  assert.ok(sendIndex > setZoomIndex, 'the renderer notification must happen after the zoom level is applied')
+test('applyZoomLevel applies the level then notifies the renderer', () => {
+  const wc = fakeWebContents()
+  const applied = applyZoomLevel(wc, 3)
+
+  assert.equal(applied, 3)
+  assert.deepEqual(wc.calls, [
+    ['setZoomLevel', 3],
+    ['send', 'hermes:zoom:changed', { level: 3, percent: zoomLevelToPercent(3) }]
+  ])
+})
+
+test('applyZoomLevel clamps garbage before applying and notifying', () => {
+  const wc = fakeWebContents()
+  const applied = applyZoomLevel(wc, 999)
+  const clamped = clampZoomLevel(999)
+
+  assert.equal(applied, clamped)
+  assert.deepEqual(wc.calls, [
+    ['setZoomLevel', clamped],
+    ['send', 'hermes:zoom:changed', { level: clamped, percent: zoomLevelToPercent(clamped) }]
+  ])
 })

apps/desktop/electron/zoom.ts

@@ -32,6 +32,22 @@ export function percentToZoomLevel(percent) {
   return clampZoomLevel(Math.log(percent / 100) / Math.log(ZOOM_FACTOR_BASE))
 }
 
+/**
+ * Apply a clamped zoom level to a webContents AND notify the renderer, in that
+ * order. Every path that changes zoom (user action, restore-on-load, lifecycle
+ * re-assert) funnels through here so the settings UI Scale control can never
+ * drift from the actually-applied level — the bug where restore set the level
+ * but forgot to emit 'hermes:zoom:changed', leaving the control stuck at 100%.
+ * Returns the clamped level so callers can persist it.
+ */
+export function applyZoomLevel(webContents, level) {
+  const clamped = clampZoomLevel(level)
+  webContents.setZoomLevel(clamped)
+  webContents.send('hermes:zoom:changed', { level: clamped, percent: zoomLevelToPercent(clamped) })
+
+  return clamped
+}
+
 // Chromium on Windows can drop webContents zoom when a BrowserWindow is minimized
 // and restored. Re-apply the persisted level on these lifecycle transitions.
 export const ZOOM_REASSERT_WINDOW_EVENTS = ['show', 'restore']