[Linux][26.924] SIGCHLD handler overwritten during startup; preserving libuv handler restores thread loading #48618

Environment

• ChatGPT Desktop: 26.924.22138-1
• Build: 11645, commit 2e782921399a788a842b74ee1944a2e1e6e003a1
• Bundled app-server: 0.158.0-alpha.2.1
• OS: CachyOS, x86_64
• Kernel: 7.2.8-1-cachyos
• Desktop: KDE Wayland; application running through XWayland

Related reports: #48419, #48413, #48397. This report adds process-level tracing and a controlled diagnostic intervention. A shared root cause across those reports has not been independently verified.

Symptoms

After updating to 26.924.x, existing local conversations remain loading. Reinstalling 26.924.22138-1 does not resolve it.

The local app-server initializes successfully and answers thread/read, but conversation loading does not complete.

Additional symptoms:

Failed to load shell env ... Timed out after 5000ms.
Git is unavailable

The desktop process retains terminated zsh, git, ps, and gh children as zombies. Inspected zsh and git children exited successfully with status 0.

Startup tracing

Tracing rt_sigaction, wait4, waitid, and SIGCHLD showed this sequence in the desktop main process:

12:49:56.548989  SIGCHLD handler registered: libuv handler, SA_RESTART
12:49:56.611927  SIGCHLD handler replaced: no-op handler, flags=0
12:50:00.037904  SIGCHLD delivered: child exited with status 0

Disassembly of the replacement handler showed that it returns without doing work.

The registration pattern matches the no-op handler installed by ChromeBrowserMainPartsPosix::PreEarlyInitialization. The precise caller identification is inferred from the disassembly and upstream source; full application debug symbols were unavailable.

Controlled comparison

A baseline run under GDB reproduced the failure.

In a second run, GDB intercepted only the identified no-op SIGCHLD registration and changed its act argument to NULL, preserving the previously installed handler. Installed application files were not modified.

Both runs used the same application version, user profile, configuration, and existing conversation.

Successful-run log excerpts, with identifiers omitted:

method=thread/resume durationMs=467 errorCode=null
maybe_resume_success
name=thread_navigation outcome=success
marksMs={"hydration_started":444.3,"history_ready":1246.8,
         "hydration_finished":1287.4,"content_visible":1512}

Additional checks

• Reproduced with Qt excluded and GTK used instead.
• Both local SQLite databases passed read-only PRAGMA quick_check.
• Running Git through login zsh succeeds in approximately 0.6 seconds.
• Running Git through the separately bundled Node runtime succeeds in approximately 6 ms.
• Existing conversation data loaded successfully without resetting the profile.

Expected behavior / suggested investigation

Desktop initialization should preserve libuv's child-exit handling.

Please investigate initialization ordering between Chromium's placeholder SIGCHLD registration and libuv. Preserving the existing handler, or ensuring libuv registers after Chromium initialization, appears to address the observed failure.

The debugger intervention was diagnostic only, not a proposed production patch. It used a build-specific handler identification; no permanent workaround was installed.