Issue 16629: real Linux AppImage comparison

Build: vp run dist:desktop:linux independently in each commit's checkout.
App: T3-Code-0.1.9-x86_64.AppImage, Linux x86_64, Xvfb 1920x1080.
Window: 1100x780 at (410,150), light theme. Empty isolated HOME, T3CODE_HOME,
XDG_CONFIG_HOME, XDG_DATA_HOME, and XDG_CACHE_HOME. No imported projects or threads.
Flags: --no-sandbox --disable-gpu --remote-debugging-port=9333
T3CODE_DISABLE_AUTO_UPDATE=true, T3CODE_DEV_SEED=0, T3CODE_PORT=43773.
APPIMAGE and APPDIR unset in the launcher's outer environment.
No provider turn was run. No automated test is used as evidence.

Same interaction on both sides:
1. Wait for the actual desktop welcome window to load in local-only mode.
2. Start X11 recording; three seconds later call
   window.desktopBridge.setServerExposureMode('network-accessible') over CDP.
3. Wait 18 seconds for desktop relaunch. Read the saved mode and identify the
   replacement process/window through its port ownership and X11 window PID.
4. Capture the display, then click the welcome screen's agent picker at the
   same position; capture again. Stop the app after the recording.
5. Stills require two identical screenshots 500 milliseconds apart. Xvfb's
   background is refreshed throughout recording to prevent stale closed-window pixels.

BASE f03db4fbef59c42113e37c32897bf4d25d31cb2b
The IPC call returned network-accessible and saved that mode.
The original process exited and its executable mount disappeared.
No replacement window or backend listener remained; the same click had no effect.
Kernel entry from this run (replacement PID differs from the original PID in
before-observations.json):
[Thu Nov 12 18:00:59 2026] traps: t3code[115735] trap int3 ip:5e008a5d21ce sp:7fff1a3ac4a0 error:0 in t3code[5e0088869000+9f00000]
The replacement's ICU stderr was not captured; trap int3 and the absent window were observed.

HEAD 65aab2acef0c6bbfa05211de98605623e0286640
Original desktop PID 116343 exited. Replacement PID 117187 owned one visible
window. The saved mode was network-accessible and the backend listened on
0.0.0.0:43773. The identical agent-picker click expanded its contents.
No t3code trap was logged during the head run. See after-observations.json
and the paired recording. The replacement CDP socket did not answer, so
window ownership and interaction were checked through X11 instead.

Privacy: the environment-name line is redacted in public images and recordings.
Only this run's selected observations and kernel entry are included; raw logs remain private.
AI-assisted; verified with the tests and tools listed above.