docs(adopt): document the routes and the overlay, correct stale comments

The two routes are public under /api/v1, so they get an API reference section.
The overlay gets an architecture note and a CLAUDE.md rule: an adopted session
has session.remote and session.docker undefined and a neutral workingDir, so any
new code that reads workingDir as a workspace must also test isAdopted. That is
the class of bug this round fixed a dozen times.

Records a measured limit: while the view exists an owner's kill-session leaves
the window alive under it until the tab closes.

Comments that still called workingDir the foreign pane's cwd now say what is
true since the wrapper got its neutral folder. Also drops a zh-CN key that
duplicated an existing one, and updates the two structure tests pinned on the
lines this round changed.

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

docs/api-reference.md

@@ -1085,6 +1085,71 @@ the caller's case space, a linked case's exact path, or a Claude worktree of eit
 session, the create response carries `tabLayout` as it does for `tabGroupId`. Deleting the
 case forgets the value; existing sessions never move.
 
+## Adopting a foreign tmux session
+
+A tmux session someone started by hand (`tmux new -s work`) lives on its own socket,
+where Codeman does not look for its own sessions. These two routes list such sessions
+and open one as a tab. Admin-only in multi-user mode (403), since the list shows other
+people's processes and adopting a shell is arbitrary execution as the server account.
+
+`GET /api/v1/mux/foreign` lists candidates. Local sessions are always scanned, and
+cached for 5 s. `?docker=1` and `?remote=1` add the containers behind the saved Docker
+cases and the saved ssh hosts, one `docker exec` or ssh connection per target, so the
+browser sends them only on an explicit scan. `?force=1` skips the local cache.
+
+```json
+{
+  "sessions": [
+    {
+      "id": "fa9b76d36",
+      "location": "local",
+      "socketPath": "/tmp/tmux-1000/default",
+      "sessionName": "work",
+      "windows": 1,
+      "attached": false,
+      "createdAt": 1793931275000,
+      "mode": "claude",
+      "command": "claude",
+      "workingDir": "/home/me/project",
+      "adoptedBy": "961d0a82-6888-425d-a3ee-dab38ecbb598"
+    }
+  ],
+  "scannedAt": 1793931277916,
+  "notes": ["remote Build box: unreachable, or no tmux"],
+  "pollIntervalMs": 8000,
+  "canScanWide": true
+}
+```
+
+`hostId`, `hostLabel` and `containerName` appear on a docker or remote candidate.
+`adoptedBy` names the session already wrapping that target. `notes` says why a location
+gave nothing, each opening with where it came from (`local`, `docker <name>`,
+`remote <label>`). A session whose name or socket path holds characters Codeman will not
+pass to a shell is skipped and counted in a note. Sessions on a Codeman socket never
+appear.
+
+`POST /api/v1/sessions/adopt` wraps one, with `{ "id": "...", "docker": true, "remote":
+true }` (the two flags must match the listing the id came from; `name` and
+`parentSessionId` are optional). The body carries only that opaque id: the target is
+re-resolved by a fresh scan, so a candidate that is gone answers `404`, and one on a
+location unreachable this time answers `404` saying so.
+
+The answer is `{ "session": SessionState, "adopted": true }`, or
+`{ "session": SessionState, "alreadyAdopted": true }` when the target already has a
+wrapper. A second adopt of a target whose wrapper is still being created is
+`SESSION_BUSY`. The session has `adopt` set and `pid: null`: start it like any other,
+`POST .../shell` for `mode: "shell"` and `POST .../interactive` for the rest. `mode`
+comes from the pane's process tree.
+
+Closing the session detaches. The foreign session keeps running, and only Codeman's
+wrapper and its grouped `codeman-view-<id>` session go, so `DELETE` removes nothing that
+belongs to someone else. Codeman did not start this agent, so these refuse an adopted
+session: respawn, Ralph, auto-clear, auto-compact, auto-resume, custom model endpoints,
+prompt uploads and the image watcher. `stop` and `blocked` waits are a 400, the git
+routes answer `unsupported` with `reason: "adopted"`, and `last-response` answers empty,
+since Codeman knows no transcript for it. Its `paneExit` stays absent, because the pane
+holds a `tmux attach` and not the agent. Reboot restore does not rebuild one.
+
 ## Approvals Inbox
 
 Cross-session queue of prompts waiting on a human (permission dialogs,