fix(spawn): capture worktree lease by repo-identity, not treehouse root

[maximebrmd]

What Changed

• Replaced the spawn worktree-capture check in bin/fm-spawn.sh: instead of accepting the first pane cwd that merely differs from the project dir (which could latch onto shell-init noise like a transient ~/.oh-my-zsh cwd), it now accepts a path only when it is a genuine worktree of the same repository, comparing canonical git common dirs and resolving every path with pwd -P so a symlinked $HOME or a non-default treehouse pool root no longer breaks the match.
• Made the worktree wait window configurable via FM_SPAWN_WORKTREE_WAIT (default 60s), threaded through the loop and the timeout error message, and documented it in docs/configuration.md.
• Guarded the bash 3.2 empty-array expansion in bin/fm-pr-merge.sh and updated tests/fm-tangle-guard.test.sh for the new repo-identity worktree check.

Risk Assessment

✅ Low: A well-bounded 46-line change to a single spawn helper that faithfully replaces a brittle treehouse-root containment check with a symlink-safe repository-identity check, keeps the existing isolation guard as a backstop, and leaves no orphaned code.

Testing

Completed 1 recorded test check.

• Outcome: 🔧 1 issue found → auto-fixed ✅ across 2 runs (25m25s)

Pipeline

Updates from git push no-mistakes

⏭️ **intent** - skipped

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

🔧 **Review** - 2 issues found → auto-fixed ✅

• ⚠️ bin/fm-spawn.sh:655 - is_treehouse_worktree gates lease capture on containment under TH_ROOT=${FM_TREEHOUSE_ROOT:-$HOME/.treehouse}, but treehouse's pool root is configurable via treehouse.toml (root key: worktrees are placed under {root}/.treehouse/, e.g. root = "./" puts them under <repo>/.treehouse/). For any repo with a non-default treehouse root, the captured pane cwd will never be under $HOME/.treehouse, so the loop never selects, and spawn fails with the confusing 'treehouse get did not enter a worktree within 60s' timeout unless the operator knows to set the undocumented FM_TREEHOUSE_ROOT env var. Since this repo is a shared template for every user, consider deriving the root from treehouse.toml (or relaxing to 'is a git worktree distinct from PROJ_ABS' and relying on the existing isolation guard) rather than assuming $HOME/.treehouse.
• ℹ️ bin/fm-spawn.sh:429 - The containment check uses raw string-prefix matching (path_is_ancestor_of) between the tmux pane_current_path (a resolved physical path on macOS/Linux) and the unresolved TH_ROOT ($HOME/.treehouse). If $HOME contains a symlinked component (common on some Linux hosts where /home is symlinked), the physical pane path won't be prefixed by the logical $HOME and the match silently fails, causing the same 60s timeout. The later isolation guard resolves both sides with pwd -P; this new pre-check does not.

🔧 Fix: replace treehouse-root check with repo-identity worktree check
✅ Re-checked - no issues remain.

🔧 **Test** - 1 issue found → auto-fixed ✅

• 🚨 tests failed with exit code 1
• command -v tmux >/dev/null || { echo "tmux is required for e2e tests" >&2; exit 1; }; tmux -V; rc=0; for t in tests/*.test.sh; do echo "== $t =="; bash "$t" || rc=1; done; exit "$rc"

🔧 Fix: guard bash 3.2 empty array in pr-merge; fix stale spawn worktree test
✅ Re-checked - no issues remain.

• command -v tmux >/dev/null || { echo "tmux is required for e2e tests" >&2; exit 1; }; tmux -V; rc=0; for t in tests/*.test.sh; do echo "== $t =="; bash "$t" || rc=1; done; exit "$rc"

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.