Live failure on the first real use of #82328 (2026-08-09): clicking
Update closed the Desktop with "an updater will happen", then nothing.
desktop.log showed `launched repo hand-off script`, but
desktop-update-handoff.log was never created - PowerShell exited 0
without executing a single line.
Root cause, isolated by spawning the exact production shape against a
sandbox HERMES_HOME: `spawn('powershell', [..., '-File', script],
{ detached: true, stdio: 'ignore', windowsHide: true })` kills
powershell.exe during console-subsystem init, before -File processing.
Variant matrix: plain pipes -> runs; hide only -> runs; detached only ->
runs; detached+hide -> exits 0, script never starts. Unit tests and
foreground invocations can't see this class of bug.
Fix: wrapHandoffForDetachedConsole() routes the invocation through
`cmd /d /s /c start "" /min powershell ...` - `start` allocates the
script its own minimized console and fully detaches it; the cmd wrapper
exits immediately. Verified the wrapped form survives the full
detached+hidden production spawn.
Knock-on: child.pid is now the short-lived wrapper, not the script, so
the Electron-side marker pre-write can't represent the script. The
script now claims the update marker itself as step 0 (its own $PID,
byte-exact "<pid>\n<ts>\n" via WriteAllText - Set-Content emits CRLF
and would break the three readers' framing). The Electron pre-write is
kept as a bridge for the spawn window: the script overwrites it, and if
the script never starts the wrapper's dead pid reads as stale and
self-deletes (no wedge). `hermes update` adopts the script's claim via
update_lock.py's process-ancestry rule, unchanged.
E2E in exact production shape (cmd start wrapper, detached, hidden,
parent exits 1.5s after spawn) against a sandbox HERMES_HOME with a
compiled fake hermes.exe: script ran, claimed marker with its own pid
(fake observed "<script-pid>|<ts>|" LF-framed DURING the update),
desktop-pid wait worked, update invoked with correct argv, marker
removed on completion. vitest 13/13 (new wrapper-shape test), 3-project
typecheck clean, eslint clean, PS 5.1 parse + windows-footguns clean.
Teknium
3b08a0f9b5