hermes desktop failed on Linux with an ENOENT renaming
release/linux-unpacked/electron -> Hermes. Root cause is a corrupt
cached Electron zip (~/.cache/electron/electron-*.zip): app-builder
unpack-electron extracts a partial tree from the bad zip that is
missing the electron binary, so electron-builder dies on the final
rename. Re-running repeats the broken extraction, leaving the desktop
app permanently unlaunchable until the cache is manually purged.
- Add _electron_download_cache_dirs() + _purge_corrupt_electron_cache()
to hermes_cli/main.py: validate every electron-*.zip via
zipfile.testzip() and delete corrupt ones; honor electron_config_cache
/ ELECTRON_CACHE overrides with per-OS defaults.
- Wire purge + single retry into cmd_gui packaged-build failure path so
a poisoned download self-heals (electron re-downloads clean).
- Add beforePack hook (apps/desktop/scripts/before-pack.cjs) to wipe the
target unpacked dir before staging, making packaging idempotent across
interrupted runs. Cross-platform, best-effort.
- Tests: corrupt-zip detector, cmd_gui purge/retry/launch path,
no-retry-when-clean path, and node --test for the cleanup helper.
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