fm-spawn: crewmate tmux window loses its fm-<id> name to shell precmd renames, breaking name-based targeting

[tkt028]

Summary

A crewmate's tmux window is named fm-<id> at spawn, and the task's
state/<id>.meta records window=<session>:fm-<id> (a session:window-NAME target). But on
setups where the shell prompt renames the window every command (e.g. a Starship/zsh precmd
that calls tmux rename-window to show the repo + git status), the fm-<id> name is
clobbered — the window becomes e.g. tkt-env#tkt-env. After that:

• fm-peek / fm-send / fm-watch can no longer resolve the window by the meta name
  (can't find window: fm-<id>), so stale-pane detection silently breaks (status-file and
  turn-end wakes still work, so it's not total, but pane peeking/steering is lost).
• FirstMate-managed worktrees become visually indistinguishable from the user's own
  worktree windows.

allow-rename off and automatic-rename off do not prevent this — they only block
escape-sequence (OSC) renames, not an explicit tmux rename-window issued by a shell hook.

Reproduction

1. Spawn a crewmate (tmux backend) on a machine whose shell prompt renames the window in a
   precmd hook.
2. After the crewmate's shell runs its prompt once, tmux list-windows shows the window
   renamed away from fm-<id>.
3. bin/fm-peek.sh fm-<id> → error: no window named ....

Root cause

Meta targets the window by its mutable name. Names are not a stable handle when anything
else can rename the window.

Suggested fix

Record the stable tmux window-ID in meta instead of (or in addition to) the name — e.g.
window=<session>:@<window-id> (verified: <session>:@NN resolves through
fm_backend_resolve_selector, while a bare @NN does not). Window-IDs never change for the
life of the window, so every supervision path stays resolvable regardless of renames.

Optionally, also keep a short distinguishing name convention (e.g. fm.<repo>#<issue>) so
FirstMate worktrees are visually separable from the user's own — but that is cosmetic; the
ID-based target is the correctness fix.

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🤖 Claude Code · claude-opus-4-8 · 2026-07-15