fix(spawn): stop clobbering a project's tracked .claude/settings.local.json

[CodeAhmedJamil]

Problem

bin/fm-spawn.sh wrote the claude crewmate turn-end hook by unconditionally overwriting
<worktree>/.claude/settings.local.json:

cat > "$WT/.claude/settings.local.json" <<EOF
{"hooks":{"Stop":[{"hooks":[{"type":"command","command":"touch '$TURNEND'"}]}]}}
EOF
exclude_path '.claude/settings.local.json'

meshery/meshery (and meshery-cloud) tracks .claude/settings.local.json - a 72-line file
carrying enabledMcpjsonServers, disabledMcpjsonServers, a SessionStart hook, and several
PreToolUse hooks. Every claude spawn into such a worktree truncated that tracked file to a single
line, destroying the project's own configuration inside the worktree.

Observed repeatedly on 2026-07-21/22: four meshery worktrees each showed
M .claude/settings.local.json with a 73 +-------- diffstat. It blocked teardown three separate
times (correctly - it is indistinguishable from real uncommitted work) and any crewmate running
git add -A would have committed the truncation.

The second, subtler half: the exclude_path mitigation appends the path to .git/info/exclude,
which only suppresses untracked files. For a tracked file git still reports it modified, so the
mitigation silently did nothing in exactly the case that mattered.

Fix

Follow the precedent the codebase already set for the other harnesses - pi keeps its turn-end
extension in state/ and grok keeps its hook global under ~/.grok/hooks/, both deliberately
outside the worktree to avoid polluting the project. Claude's arm was the outlier.

• Move claude's Stop hook out of the worktree entirely. It now lives in
  state/<id>.claude-settings.json and is loaded via --settings on the launch command, so the
  worktree's own .claude/settings.local.json is never written. A project that tracks that file is
  byte-identical after a spawn; a project without one keeps working unchanged; the turn-end hook
  still fires, so supervision still wakes. Secondmates keep the plain form.
• Sibling-arm audit. The only worktree-resident hook writes left are opencode's
  .opencode/plugins/fm-turn-end.js and grok's .fm-grok-turnend; both are now guarded by
  refuse_if_tracked, which stops the spawn rather than clobber a tracked project file.
• Fix the tracked-vs-untracked assumption at the source. exclude_path is now documented as
  tidiness-only, and refuse_if_tracked is the real guard. prune_obsolete_exclude_entries removes
  the now-stale .claude/settings.local.json line firstmate used to add to the shared
  .git/info/exclude, so repos already touched heal over time - those stale lines were actively
  masking tracked-file changes in meshery and meshery-cloud.
• Guard the abort/unwind path so a refused spawn only unwinds work it created and never resets
  another task's uncommitted work or a temp root it did not create; git errors during unwind fail
  safe. Teardown cleans state/<id>.claude-settings.json at parity with the pi extension.

Tests

Regression coverage colocated in tests/, extending the existing runners rather than adding a new
one:

• tests/fm-spawn-dispatch-profile.test.sh - a spawn into a worktree where
  .claude/settings.local.json is a tracked file with existing content leaves that file
  byte-identical (the case that actually bit us), plus the no-file and untracked-file cases and the
  refuse_if_tracked sibling-arm behavior.
• tests/fm-teardown.test.sh - the dirty-copy unwind guard and claude-settings cleanup parity.
• C-locale glyph regression tests pinning LC_ALL=C for the composer prompt-classification fix.

Validation

Validated end-to-end through the no-mistakes pipeline: automated review, tests, docs, and lint all
green. Lint's local run reported only ShellCheck not found (an environment gap on the run host,
exit 127 - not a code finding); CI runs the same bin/fm-lint.sh with ShellCheck present.

Notes

• Delivered from a fork because our accounts lack direct push access to kunchenguid/firstmate.
• Out of scope and intentionally untouched: worktree allocation ignoring recorded task ownership
  (tracked separately as fm-worktree-realloc-unlanded), which touches the same file.