A doctor that says why a build will not start

Written after an auto-update deleted nine of the twelve builtin plugin directories and left the app on a splash screen for ever, with Windows reporting the process as responding the whole time. Each build is health-checked on every scan, and one that will not start says so on its own card, with the cause found on disk.

An auto-update applied while the old version was running, deleted nine of the twelve directories under resources/builtin-plugins, and left the app starting to a splash screen for ever — with Windows reporting the process as responding the whole time.

Each build is health-checked on every scan, and one that will not start says why on its own card. The symptom is read from the window title and the cause is found on disk.

• Responding and IsHungAppWindow do not catch a boot that stalled. The window pumps messages perfectly; it just never rendered. Measured on the real failure: responding True, 6.5s of CPU across 37 minutes.
• The main window title is the signal that does. A booted Tabby titles its window after the active tab; one still on the splash is called Tabby. No cooperation from the app required, so it works for stock builds too. Past a 30s grace period, that is stuck at boot.
• fs.access lies about app.asar. Electron mounts the archive as a directory, so access() answers ENOENT for a file that is plainly there while stat() calls it a directory. Ask the parent's directory listing instead — this produced a false "bundle is missing" on every packaged build until it was caught in testing.
• A builtin copied into the user plugin directory is reported too: a second tabby-core on the module path loads a second Angular and breaks dependency injection.
• Verified by reproducing the fault — a copy of a slot with tabby-local deleted, launched, and confirmed to be reported as "will not start" with both the cause and the symptom, while every healthy build stayed clean.

• The source catalogue records no separate caveats for this entry. The implementation and evidence above define its scope.