fix: let go of an adopted tab whose tmux session ended (release review)

When a foreign session ended, remain-on-exit kept Codeman's own tmux client
on the wrapper's dead pane, so the tab kept its pid and busy, input went
nowhere, both attach routes refused it, and a new session of that name only
led back to the dead tab. paneExit stays out of it by design.

The reconnect watcher's tick now detaches a client from a dead wrapper. That
is an ordinary PTY exit with status 0, so the pid goes null and selecting the
tab runs the attach again: it joins the target if it is back and otherwise
prints the existing guard text. Checked on an isolated instance and in a
headless browser: boot recovery, target gone, target back, view detached, tab
closed, and no restart loop while the tab sits unselected.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -111,7 +111,7 @@ Input arriving during a wake is buffered: a chunk over 4 KB is dropped whole, ne
 
 **No workspace.** ⚠️ An adopted session keeps its connection on `adopt.remote`/`adopt.docker`, so `session.remote` and `session.docker` are undefined, and its `workingDir` is the neutral `/tmp`. Code that branches on those two reads an in-container or over-ssh adoption as a local session working in `/tmp`. So anything that treats `workingDir` as the session's workspace must also test `session.isAdopted` (`adopt` on a pure view): uploads, the upload GC, git status, git fetch and its scheduler, the image watcher, Read My Mind's git signals, the Discord folder, `last-response`, guarded input and Ralph's `@fix_plan.md` and `@ralph_prompt.md` routes all do. The file surfaces (Files panel, File Viewer and its edit mode) still treat `/tmp` as the workspace, which is harmless: it is world-writable anyway, and adoption is admin-only in multi-user mode. A wrapper reports `statusLineExporter: 'remote'`, which is also what keeps keep-warm off it.
 
-**Lifecycle.** `paneExitApplies` is false for a wrapper, so an attach that ended is never `paneExit` and the sweep never closes the tab. Boot recovery re-attaches a dead wrapper, which prints that the session is gone and exits. Reboot restore refuses one, since all Codeman ever had was an attach command. ⚠️ A wrapper that cannot start fails the start, and selecting the tab tries it again (`_failAdoptedStart()`). It never takes the direct-PTY fallback, which would run a new local `claude --dangerously-skip-permissions` or a server-account shell in `/tmp` under the foreign session's name, and `runPrompt()` refuses it for the same reason.
+**Lifecycle.** `paneExitApplies` is false for a wrapper, so an attach that ended is never `paneExit` and the sweep never closes the tab. ⚠️ `remain-on-exit` still keeps Codeman's own tmux client on the dead pane, where a pid and `busy` hid it and both attach routes refused it, so `detachEndedAdoptedAttaches()` detaches that client on the reconnect watcher's tick: the tab closes nothing, its pid goes null, and selecting it (or "Go to tab" once a session of that name is back) runs the guard again. Boot recovery re-attaches a dead wrapper, which prints that the session is gone and exits. Reboot restore refuses one, since all Codeman ever had was an attach command. ⚠️ A wrapper that cannot start fails the start, and selecting the tab tries it again (`_failAdoptedStart()`). It never takes the direct-PTY fallback, which would run a new local `claude --dangerously-skip-permissions` or a server-account shell in `/tmp` under the foreign session's name, and `runPrompt()` refuses it for the same reason.
 
 ### Docker cases