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core plans firefox-on-ac-native.md
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at codex/xbox-api-layer

Firefox on AC Native OS — Debug Status #

Goal #

Pop a Firefox browser window on the AC Native OS device for Claude Code OAuth login.

Architecture #

ac-native (PID 1) — owns DRM/KMS display
  └── PTY child: /bin/claude (Claude Code native binary)
        └── Bun.spawn(["xdg-open", url]) — our shim script
              └── cage (Wayland kiosk compositor) + firefox

What Works #

  • DRM handoff: SIGUSR1/SIGUSR2 between xdg-open and ac-native. Confirmed in logs — release and reclaim both fire.
  • xdg-open is called: Claude Code's Bun.spawn(["xdg-open", url]) executes our /bin/xdg-open script (proven by DRM signals firing).
  • cage starts: Screen goes black (cage takes DRM). Confirmed in earlier builds.
  • Trap EXIT: SIGUSR2 always fires on script exit, DRM always reclaimed. No more permanent black screens.
  • 120s timeout: cage killed after 2 min if it hangs.

What Doesn't Work #

  • Firefox crashes immediately inside cage. cage+firefox exits so fast the screen barely flashes black.
  • No log files are created by the xdg-open script — not in /tmp, not in /mnt. Even exec 1>/tmp/xdg-open.log and /bin/sh -c "echo ... > /tmp/xdg-open.log" produce nothing.

Known Firefox Crash History #

  1. EGL init failed (build ~#105) — EGL_EXT_platform_base not supported. Fixed by setting WLR_RENDERER=pixman.
  2. libseat failed (build ~#103) — No backend was able to open a seat. Fixed by WLR_SESSION=direct LIBSEAT_BACKEND=noop.
  3. Wayland socket failed (build ~#107) — Unable to open Wayland socket: Invalid argument. Fixed by per-PID XDG_RUNTIME_DIR.
  4. Firefox segfault (build ~#108) — ExceptionHandler::GenerateDump minidump generation. Missing fontconfig, xkb, font. Partially fixed by bundling those.
  5. Firefox segfault (build ~#110+) — Still crashing. Missing GLib schemas, GTK modules bundled. Still crashes.
  6. "Couldn't find application directory" — Firefox's wrapper reads /proc/self/exe which fails in chroot tests. On device it should work since /proc is mounted.

Bundled Components (current build ~198MB kernel) #

  • Firefox 148 (stripped): 274MB uncompressed, cached at /tmp/ac-firefox-cache
  • cage (Wayland kiosk): 64KB
  • Claude Code native binary: 225MB
  • 94 shared libs (GTK3, Pango, Cairo, Harfbuzz, etc): 81MB
  • fontconfig (/etc/fonts): 188KB
  • xkb keyboard data: 3.9MB
  • DroidSans.ttf font: 188KB
  • GLib schemas: 56KB
  • GTK-3.0 modules: 192KB
  • zstd compressed initramfs: 186MB

Environment Variables Set in xdg-open #

HOME=/tmp
XDG_RUNTIME_DIR=/tmp/xdg-$$  # per-invocation, 0700 perms
WLR_BACKENDS=drm
WLR_SESSION=direct
WLR_RENDERER=pixman
LIBSEAT_BACKEND=noop
LD_LIBRARY_PATH=/lib64:/opt/firefox
LIBGL_ALWAYS_SOFTWARE=1
MOZ_ENABLE_WAYLAND=1
GDK_BACKEND=wayland
MOZ_APP_LAUNCHER=/opt/firefox/firefox
GRE_HOME=/opt/firefox

PTY Environment (set in pty.c) #

TERM=xterm-256color
HOME=/tmp
LANG=en_US.UTF-8
PATH=/bin:/sbin:/usr/bin:/usr/sbin
BROWSER=/bin/xdg-open
DISPLAY=:0              // fake — tricks Claude into calling xdg-open
WAYLAND_DISPLAY=wayland-0  // fake — same

Key Mystery #

The xdg-open script runs (SIGUSR1 proves it) but produces ZERO log output. Multiple approaches tried:

  • echo "..." > /tmp/xdg-open.log
  • exec 1>/tmp/xdg-open.log 2>&1
  • /bin/sh -c "echo ... > /tmp/xdg-open.log"
  • All produce empty or nonexistent files.

Hypothesis: Bun.spawn may close/redirect all file descriptors, or the process exits so fast (cage fails, trap fires) that the kernel never flushes the write.

Possible Next Steps #

  1. Have ac-native run cage+firefox directly via system() from C (not through xdg-open script) — bypasses Bun.spawn fd issues
  2. Run a Wayland session from the start — cage as the compositor, ac-native as a Wayland client. Browser is just another client window.
  3. Use a simpler browser — lynx/links2 for text-mode OAuth (but Claude's React SPA won't work)
  4. Debug Firefox crash by running it standalone from the PTY shell: type cd /opt/firefox && ./firefox --version at the sh prompt to see the exact error
  5. Strace — add strace to initramfs and trace the xdg-open/cage/firefox process

File Locations #

  • xdg-open script: bundled via fedac/native/ac-os (HEREDOC at ~line 129)
  • DRM handoff: fedac/native/src/ac-native.c (SIGUSR1/SIGUSR2 handlers ~line 124, main loop ~line 1644)
  • PTY env setup: fedac/native/src/pty.c (~line 533)
  • Browser open C function: fedac/native/src/js-bindings.c (js_open_browser ~line 2995)
  • Cage/Firefox bundling: fedac/native/ac-os (build_initramfs function)
  • Kernel config: fedac/native/kernel/config-minimal (ZRAM=y, ZSTD initramfs)