fix(spell-check): stop service views crashing while typing

[manusa]

Problem

Since v0.0.123, typing in a service (a Slack or Telegram DM, for example) eventually kills the service view and leaves a blank screen. It only happens with the non-native spell checker (the nodehun dictionaries).

The renderer segfaults with EXC_BAD_ACCESS at 0x18 on its main thread, from a resolved promise calling back into Electron.

Root cause

• Electron's SpellCheckClient tracks a single pending request. OnSpellCheckDone dereferences it without a null check: pending_request_param_->wordlist(), which sits at offset 0x18.
• Chromium 152, which came with the Electron 39 → 44 bump, added user-dictionary-leak mitigations to IdleSpellCheckController. A selection change in an element that wasn't focused by a user gesture, or a content change without transient user activation, now calls Deactivate(). That cancels Blink's in-flight check. Slack and Telegram focus their composers by script.
• Blink then issues a new request on the next keystroke. The late answer to the cancelled request completes the new one and clears the pending pointer. The new request's own answer then finds nothing pending, and the renderer crashes.
• Chromium 142 only deactivated when spell checking was disabled or the document was destroyed, which is why this never showed up before.

Fix

preload.spell-check.js now only answers the most recent spellCheck request, exactly once, and delivers the answer from a requestIdleCallback.

The idle hop covers the case where Blink has issued a request that hasn't reached the preload yet. Electron hands requests over from a normal-priority task it posts, and that task always runs before an idle callback, so the stale answer finds itself superseded.

A dictionary failure still answers with nothing misspelled, so Blink never stalls on an unanswered request.

Testing

• preload.spell-check.test.js now covers a request superseded while its dictionary lookup is in flight, and one superseded while its answer waits for the renderer to be idle. Removing only the superseded-request guard makes exactly those two tests fail.
• npm run pretest and npm test pass (60 suites, 1181 tests).
• A standalone Electron app with scripted typing into a script-focused contenteditable reproduces the crash deterministically:

Setup	Result
Electron 44.3.0, previous provider	crashed 3/3 at the first overlapping request
Electron 39.1.2, previous provider	survived 3/3, no overlapping requests
Electron 44.3.0 with UnrestrictSpellingAndGrammarForTesting	survived 3/3, no overlapping requests
Electron 44.3.0, this fix	survived 3/3 (21 overlapping requests, 20 stale answers dropped)

Enabling the native spell checker is a workaround until this ships.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud