| name | harness-adapters |
| description | Agent-only reference for firstmate harness operations. Use before spawning or recovering a crewmate or secondmate, handling a trust dialog, sending a harness-specific skill invocation, interrupting or exiting an agent, resuming an exited agent, or verifying a new harness adapter. Contains verified facts for claude, codex, opencode, pi, and grok. |
| user-invocable | false |
| metadata | {"internal":true} |
harness-adapters
Use this reference before any harness-specific firstmate operation: spawn, recovery, trust-dialog handling, skill invocation, interrupt, exit, resume, or adapter verification.
Crewmates default to the same harness firstmate is running on unless config/crew-harness records an adapter name.
Optional dispatch profiles in config/crew-dispatch.json can override that static default for one crewmate or scout dispatch by selecting concrete harness, model, and effort axes at intake.
The captain may override that file at session start or later; a per-task instruction such as "run this one on codex" overrides it for that dispatch only.
default means mirror firstmate's own harness.
Secondmates have their own harness knob, so a secondmate can run on a different adapter than crewmates.
config/secondmate-harness is the harness the primary uses to launch SECONDMATE agents, resolved through the fallback chain config/secondmate-harness -> config/crew-harness -> firstmate's own.
An absent or default config/secondmate-harness therefore behaves exactly as the crew harness did before this knob existed (secondmates launched on the crew harness); setting it splits the two.
config/crew-dispatch.json, config/crew-harness, and config/backlog-backend are inherited by secondmate homes.
This skill owns only the harness-relevant consequence: a secondmate's own crewmates use the primary's dispatch profiles and static harness value, while config/secondmate-harness is the primary's own setting and is never inherited - secondmates do not spawn secondmates.
Inheritance copies the literal config/crew-harness file, so for a secondmate's own crewmates to run on the primary's crewmate harness the captain must set config/crew-harness to a concrete adapter name, such as codex.
If config/crew-harness is unset or default, there is no concrete value to inherit, so the secondmate's own crewmates fall back to the secondmate's own/detected harness rather than the primary's effective crewmate harness.
Inheritance also copies the literal config/crew-dispatch.json file, so secondmates apply the same best-fit profile rules for their own crewmates.
Each adapter splits into mechanics and knowledge.
The per-task mechanics, including launch command, autonomy flag, and crewmate turn-end hook, live in bin/fm-spawn.sh.
The primary-session "no turn ends blind" guard contract and harness hook installation paths live in docs/turnend-guard.md.
The primary-session watcher wake protocols are rendered from docs/supervision-protocols/ by bin/fm-supervision-instructions.sh.
The supervision knowledge lives here: busy signature, exit command, interrupt, dialogs, resume behavior, skill invocation, and quirks.
Never dispatch a crewmate or secondmate on an unverified adapter.
If config/crew-harness or config/secondmate-harness names an unverified adapter, tell the captain and fall back to firstmate's own harness until that adapter is verified.
If the captain asks for a new harness, propose verifying it first: spawn a trivial supervised task using fm-spawn's raw-launch-command escape hatch, confirm every fact empirically, then record the mechanics in fm-spawn, the busy signature in fm-watch.sh and fm-tmux-lib.sh defaults, any needed FM_COMPOSER_IDLE_RE empty-composer override plus any novel bare agent prompt glyph in bin/fm-composer-lib.sh's shared composer classifier (the one fleet-wide owner of the empty/dead-shell/pending decision, so a new harness's own idle composer is not misread as a dead shell), the tmux agent-process liveness classification in bin/backends/tmux.sh when the harness can launch a secondmate, and the verified knowledge here.
Detection
bin/fm-harness.sh prints firstmate's own harness, using verified env markers first and then process ancestry.
bin/fm-harness.sh crew resolves the effective crewmate harness from config/crew-harness (absent or default -> own).
bin/fm-harness.sh secondmate resolves the secondmate-launch harness through the chain config/secondmate-harness -> config/crew-harness -> own, so an unset config/secondmate-harness matches the crew harness.
bin/fm-spawn.sh uses crew mode for a crewmate/scout launch and secondmate mode for a --secondmate launch, re-resolving on every spawn so the split is durable across respawns; an explicit per-spawn harness arg overrides either.
On unknown, ask the captain instead of guessing.
A captain override always beats detection.
When verifying a new adapter, record its env marker and command name in bin/fm-harness.sh.
For stuck recovery, the target window's harness is recorded as harness= in state/<id>.meta.
Use that value for interrupt, exit, resume, and skill-invocation facts.
Primary turn-end guard
Every verified primary harness has an empirically validated hook path for the "no turn ends blind" guard.
claude and codex block directly through Stop hooks that preserve exit status 2 and stderr from bin/fm-turnend-guard.sh.
opencode, pi, and grok expose passive lifecycle callbacks for this purpose, so their tracked primary adapters force one bounded follow-up or resume when the shared predicate blocks.
The exact hook files, commands, validation transcripts, scoping rules, and fail-open tradeoffs are owned by docs/turnend-guard.md.
When changing any primary turn-end hook, validate the real harness behavior in a scratch project or throwaway home before trusting it, then update that doc and the relevant concise fact below.
Primary pre-arm (PreToolUse) seatbelt
Every verified primary harness also has a wired PreToolUse-equivalent hook that denies a watcher-arm anti-pattern (shell &, truncating pipe, bundling, broad pkill -f fm-watch) before it runs.
claude and codex block directly through PreToolUse hooks; grok blocks the same way but requires every $VAR reference in its hook command string to carry an inline :-default or it fails to launch the hook entirely.
opencode and pi block by throwing from tool.execute.before / returning {block: true} from tool_call.
The exact hook files, commands, output-shaping quirks (Claude Code only honors the deny when stdout is empty), and validation transcripts are owned by docs/arm-pretool-check.md.
When changing any primary PreToolUse hook, validate the real harness behavior in a scratch project before trusting it, then update that doc.
Primary watcher supervision
At session start, bin/fm-session-start.sh prints exactly one watcher supervision block for the detected primary harness.
Do not substitute another harness's wait shape when resuming supervision.
Claude and Grok use tracked background-notify cycles around bin/fm-watch-arm.sh.
Codex uses bounded foreground checkpoints through bin/fm-watch-checkpoint.sh because Codex cannot reason while a foreground tool call is running.
OpenCode uses .opencode/plugins/fm-primary-watch-arm.js, which coordinates with the turn-end guard plugin and wakes the TUI with client.session.promptAsync.
Pi uses the tracked .pi/extensions/fm-primary-turnend-guard.ts plus the tracked .pi/extensions/fm-primary-pi-watch.ts, both project-local extensions Pi auto-discovers once trusted.
When changing any primary watcher adapter, update docs/supervision-protocols/, docs/turnend-guard.md if a shared idle or turn-end hook changed, and the relevant concise fact below.
Launch profile axes
bin/fm-spawn.sh accepts concrete --harness, --model, and --effort values chosen by firstmate at intake.
Do not make the shell scripts parse or match natural-language dispatch rules.
The supported launch-profile flags below were verified locally on 2026-06-30 with each CLI's help and parser path.
| Harness | Model flag | Effort flag | Notes |
|---|
| claude | --model <model> | --effort <low|medium|high|xhigh|max> | Verified on Claude Code 2.1.196. |
| codex | --model <model> | -c 'model_reasoning_effort="<low|medium|high|xhigh>"' | Verified on codex-cli 0.142.1. The installed binary schema contains model_reasoning_effort, the active config uses it, and the bundled model catalog advertises only low/medium/high/xhigh. max is omitted. |
| grok | --model <model> | --reasoning-effort <low|medium|high|xhigh> | Verified on grok 0.2.73. --effort parses too, but firstmate's profile axis is reasoning effort. --reasoning-effort max is rejected, so max is omitted. |
| pi | --model <model> | --thinking <low|medium|high|xhigh|max> | Verified on pi 0.80.6. max is supported and passed through for max-effort routes. |
| opencode | --model <provider/model> | none for firstmate's interactive launch | Verified on opencode 1.17.6. opencode run has --variant, but firstmate launches the interactive opencode --prompt path, which has no verified effort flag. |
When a requested effort value is outside the harness-specific accepted set, fm-spawn records the requested effort= in meta but emits no effort flag for that harness.
This preserves launch success instead of passing a known-bad value.
no-mistakes skill invocation
Send the validation skill using the target harness's skill invocation form.
Natural language is acceptable if uncertain.
- claude:
/<skill>, for example /no-mistakes.
- codex:
$<skill>, for example $no-mistakes; /<skill> is claude-only and codex rejects it as "Unrecognized command".
- opencode: no separate verified skill invocation beyond normal slash-command behavior; use natural language if the exact skill command is uncertain.
- pi: no separate verified skill invocation beyond normal command behavior; use natural language if the exact skill command is uncertain.
- grok:
/<skill>, for example /no-mistakes (same form as claude). Verified end to end: grok discovers the user-level no-mistakes skill, /no-mistakes invokes it, and grok drives a real no-mistakes axi run. Like codex's $// popups, typing /<skill> opens grok's slash-autocomplete, so a too-fast Enter selects the popup entry instead of sending, and for an argument-taking command (like /no-mistakes's optional task-first argument) that first Enter only expands the popup selection into an argument-hint placeholder rather than submitting - a genuine second Enter is required (see the grok section below for the 2026-07-03 incident and fix). fm_tmux_submit_core's retried Enter (used by fm-send on the tmux backend) already handles this correctly by reading the cursor row; the herdr backend needed a dedicated fix (fm_backend_herdr_composer_state, docs/herdr-backend.md) because its prior delta-based verification false-positived on that same popup-close content change.
claude (VERIFIED)
| Fact | Value |
|---|
| Busy-pane signature | esc to interrupt |
| Exit command | /exit |
| Interrupt | single Escape |
| Skill invocation | /<skill> (e.g. /no-mistakes) |
First launch in a fresh worktree, or first ever on a machine, may show a trust or bypass-permissions confirmation.
After every spawn, peek the pane within about 20 seconds.
If such a dialog is showing, accept it from an active firstmate session using FM_HOME=<this-firstmate-home> bin/fm-send.sh <window> --key Enter, or the choice the dialog requires, unless FM_HOME is already set to the active firstmate home; verify the brief started processing.
Claude renders a predicted-next-prompt suggestion as dim/faint text inside an otherwise-empty composer after a turn completes.
A plain tmux capture-pane cannot tell that ghost text apart from typed text.
Firstmate launches every claude crewmate and secondmate with CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION=false, scoped to firstmate-launched agents through bin/fm-spawn.sh, so it never touches the captain's global config.
The CLI's --prompt-suggestions flag is print/SDK-mode only and does not suppress the interactive composer ghost text, verified empirically on v2.1.186.
As defense in depth for any pane that flag cannot reach, including the captain's own firstmate composer that away-mode reads, the shared fm_composer_strip_ghost extractor in bin/fm-composer-lib.sh removes dim/faint SGR 2 ghost runs before pending-input classification on both ANSI-capable readers (tmux and herdr).
Its broader dark-TRUECOLOR placeholder handling and dark-theme tradeoff are documented in docs/herdr-backend.md's 2026-07-10 incident record.
That styled capture is internal to the boolean detector only.
fm-peek and every other human or LLM-facing capture path stays plain tmux capture-pane with no escape codes.
Primary-session guard fact (verified 2026-07-04, Claude Code 2.1.201; preserved 2026-07-08, Claude Code 2.1.204).
This is separate from the per-task crewmate turn-end hook above (that one just touches a marker file in a task's own .claude/settings.local.json).
The firstmate PRIMARY's own .claude/settings.json registers bin/fm-turnend-guard.sh as a Stop hook, and exiting with status 2 plus stderr reliably forces the model to continue.
Claude Code's stdin payload to a Stop hook carries a stop_hook_active boolean that is true exactly when the current stop attempt is itself a forced continuation from an earlier block this turn; a hook can and should use that as its own loop-guard (always allow the stop when it is already true) rather than tracking state itself.
A project-level .claude/settings.json only takes effect when Claude Code's project root is that exact directory - it does not walk up from a subdirectory looking for one, so firstmate launches the primary from the repo root.
After those settings are loaded, hook command resolution is still cwd-sensitive because Claude Code runs commands through /bin/sh against the session's current cwd; keep the tracked command anchored through "$CLAUDE_PROJECT_DIR"/bin/fm-turnend-guard.sh and see docs/turnend-guard.md for the verified Stop-hook details.
Claude Code's primary watcher protocol is the lowest-friction path: run bin/fm-watch-arm.sh as its own Claude Code background task and treat background-task completion as the wake.
codex (VERIFIED 2026-06-11, codex-cli 0.139.0)
| Fact | Value |
|---|
| Busy-pane signature | esc to interrupt (shown as • Working (Xs • esc to interrupt)) |
| Exit command | /quit (slash popup needs about 1 second between text and Enter; fm-send handles it) |
| Interrupt | single Escape |
| Skill invocation | $<skill> (e.g. $no-mistakes); /<skill> is claude-only and codex rejects it as "Unrecognized command" |
A $<skill> invocation opens a $-autocomplete (skill) popup, the same hazard as the / slash popup: submitting too fast lets the popup swallow the Enter, so the invocation never lands.
fm-send handles it the same way it handles / - it gives the popup a longer settle (1.2s) between typing and the first Enter, with the target backend's submit retry as the safety net - but the $ settle is scoped to harness=codex, read from the target metadata for exact task ids or legacy fm-<id> labels.
That scope matters because, unlike /, a leading $ commonly starts ordinary text ($5/month, $HOME), so a universal $ rule would needlessly slow plain steers to claude/opencode/pi; only a codex target receiving a $... message gets the popup-settle.
An explicit session:window target has no meta, so its harness is unknown and treated as non-codex (the safe fast-path default).
This is why the validation trigger ($no-mistakes) to a codex crew now lands on the first Enter instead of biting the popup.
Directory trust dialog on first run per repo root: "Do you trust the contents of this directory?"
Accept with Enter.
The decision persists for the repo, so later worktrees of the same project skip it.
Resume after exit with codex resume <session-id>.
The session id is printed on quit.
Primary-session guard fact (verified 2026-07-08, codex-cli 0.142.1).
The firstmate PRIMARY's own .codex/hooks.json registers a Stop hook that pipes Codex's Stop payload to bin/fm-turnend-guard.sh.
Codex Stop hooks block on exit 2 and expose stop_hook_active for the same one-block loop safety Claude uses.
Codex's Stop payload includes cwd, but the tracked primary hook does not use it to choose the guard executable.
Verified on 2026-07-08: Codex runs the Stop hook command with process PWD set to the hook-loaded project root, and no CODEX_PROJECT_DIR, CODEX_WORKSPACE_ROOT, or CODEX_CWD root variable is set.
The tracked hook anchors to pwd -P, verifies that root is firstmate-shaped and hook-bearing, and then invokes bin/fm-turnend-guard.sh with the original payload.
Codex's primary watcher protocol is bin/fm-watch-checkpoint.sh --seconds "${FM_CODEX_WATCH_CHECKPOINT:-180}", not bin/fm-watch-arm.sh.
The checkpoint is deliberately foreground and bounded so Codex regains control regularly to process user messages and queued wakes.
opencode (VERIFIED 2026-06-11, v1.15.7-1.17.6)
| Fact | Value |
|---|
| Busy-pane signature | esc interrupt (dotted spinner footer; note no "to") |
| Exit command | /exit |
| Interrupt | double Escape; known flaky while a long shell command runs, so a wedged pane may need /exit and relaunch |
No trust dialog.
Opencode can auto-upgrade itself in the background and the running TUI can exit mid-task, observed live from 1.15.7 to 1.17.3.
If a pane shows the exit banner, relaunch with --continue to resume the session.
--prompt does not auto-submit alongside --continue, so send the next instruction via fm-send once the TUI is up.
Primary-session guard fact (verified 2026-07-08, OpenCode 1.17.6).
The firstmate PRIMARY's own .opencode/plugins/fm-primary-turnend-guard.js listens for session.idle.
Throwing from session.idle does not block opencode run, so the primary adapter treats the event as passive and uses client.session.promptAsync to force one follow-up turn when bin/fm-turnend-guard.sh returns 2.
The companion .opencode/plugins/fm-primary-watch-arm.js owns normal TUI watcher wake supervision and coordinates with the guard plugin before the guard tries a blind-turn follow-up.
The follow-up was verified in the interactive TUI; opencode run can exit before displaying a queued follow-up, so the adapter is fail-open in headless mode.
pi (VERIFIED 2026-06-11)
| Fact | Value |
|---|
| Busy-pane signature | Working... (braille spinner prefix; no esc to interrupt text) |
| Exit command | /quit |
| Interrupt | single Escape |
Pi has no permission system, so crewmates are always autonomous.
Keep the brief as one positional argument.
Multiple positional args become separate queued messages; fm-spawn's template already does this correctly.
Project trust dialog can appear on the first pi run in any not-yet-trusted directory, observed even on clean worktrees.
Accept with Enter.
The decision persists per path in ~/.pi/agent/trust.json, so later spawns in the same worktree slot skip it.
fm-spawn keeps the turn-end extension in state/, outside the worktree, because project-local extension files make the trust gate strictly worse and pollute the project.
The extension must listen for pi's turn_end event, not agent_end, so the watcher wakes after each completed turn instead of only when the whole agent run exits.
Pi sets PI_CODING_AGENT=true for its children; this is its harness-detection env marker.
Primary-session guard fact (verified 2026-07-09, Pi 0.80.5).
The firstmate PRIMARY's own .pi/extensions/fm-primary-turnend-guard.ts listens for logical-run agent_settled, not per-tool-loop turn_end, and uses pi.sendUserMessage(..., { deliverAs: "followUp" }) to force one guarded follow-up when bin/fm-turnend-guard.sh returns 2.
Without deliverAs: "followUp", Pi rejects the send while the agent is still processing.
Pi's primary watcher protocol also requires the tracked .pi/extensions/fm-primary-pi-watch.ts extension, same trust-once discovery as the turn-end guard.
The model arms through fm_watch_arm_pi, never a foreground bash arm; the watcher tool result and clean-exit fallback are owned by docs/supervision-protocols/pi.md.
bin/fm-session-start.sh reports when the live Pi session has not loaded both the turn-end guard and watcher extensions, and points at plain pi after project trust as the fix, with -e as a trust-free fallback.
When a secondmate is launched on Pi, fm-spawn.sh --secondmate launches Pi with both -e .pi/extensions/fm-primary-turnend-guard.ts and -e .pi/extensions/fm-primary-pi-watch.ts, both already present in the secondmate home's git worktree.
grok (VERIFIED 2026-06-29, grok 0.2.73; slash-submit behavior re-verified 2026-07-03, grok 0.2.82)
Grok Build TUI (grok), a Claude-Code-compatible CLI from xAI.
Launch with a positional prompt: grok --always-approve "$(cat <brief>)".
| Fact | Value |
|---|
| Busy-pane signature | Ctrl+c:cancel (the mid-turn cancel hint in grok's keybind bar, shown iff a turn is running; the spinner line is a braille glyph + <status>… N.Ns + [stop], e.g. ⠹ Thinking… 1.1s … [stop]). Idle keybind bar shows only Shift+Tab:mode │ Ctrl+.:shortcuts. The ASCII Ctrl+c:cancel is the busy regex (avoids locale fragility of matching braille). |
| Exit command | Ctrl+Q double-press within 1000ms (it is a confirmed destructive action). Prints Resume this session with: grok --resume <session-id>. Ctrl+D is the quit key in VS Code family terminals. NOT /exit and NOT Ctrl+C. |
| Interrupt | single Ctrl+C (cancels the current turn; the footer shows Ctrl+c:cancel mid-turn). Esc only moves focus to the scrollback, it does NOT interrupt. |
| Skill invocation | /<skill> (e.g. /no-mistakes), same as claude. Opens a slash-autocomplete popup, so a too-fast Enter selects the popup entry instead of sending. For an argument-taking command that first Enter does not submit at all - it expands the selection into an argument-hint placeholder in the composer (e.g. /compact -> /compact compaction instructions, live-verified), leaving real text still sitting there unsubmitted; a genuine second Enter is required. fm-send's retried Enter lands it on BOTH backends, but only because each backend's own submit-verification correctly recognizes that placeholder-filled text as still-pending - see the incident below. |
| Autonomy | --always-approve (footer shows · always-approve); auto-approves every tool execution, verified to run fully unattended. --permission-mode bypassPermissions is the stronger equivalent. |
| Env marker | GROK_AGENT=1, set for child/tool processes. grok does NOT set CLAUDECODE despite Claude compatibility, so the marker is unambiguous. |
| Resume | grok --resume <session-id> (id printed on exit) or grok -c / --continue (most recent for the cwd); branches a new session id. |
Incident (2026-07-03, herdr backend only, grok 0.2.82): two grok/herdr crewmates were sent /no-mistakes via fm-send; both left it fully typed but unsubmitted in the composer for minutes (footer still Enter:send), and fm-send exited 0 with no error.
Reproduced live: the herdr adapter's submit-verification at the time treated ANY pane-content change after Enter as "submitted", and the popup-close-with-placeholder-fill described above IS a visible content change even though nothing was actually sent.
The tmux backend was never affected - fm_tmux_composer_state reads the actual cursor row, correctly sees the placeholder text as still-pending, and its retry loop already sends the needed second Enter.
Fixed in the herdr adapter (fm_backend_herdr_composer_state, bin/backends/herdr.sh) by classifying the composer's own row structurally instead of diffing raw content; see docs/herdr-backend.md's "Incident (2026-07-03)" section for the full account and tests/fm-backend-herdr.test.sh for the regression coverage.
Startup dialog: the "Run Grok Build in a project directory?" project picker appears ONLY when grok is launched from a non-project directory (home, Desktop, Downloads, /tmp).
fm-spawn launches inside the treehouse worktree (a git repo root), so the picker never appears and grok treats the worktree as a trusted project automatically - no post-launch keystroke is needed.
Pin [hints] project_picker_disabled = true in ~/.grok/config.toml if a non-project launch ever needs to skip it.
TRUECOLOR placeholder styling: covered (task afk-herdr-false-pending, 2026-07-10).
A freshly-dismissed, never-typed-into grok composer shows a placeholder ("Type a message...") styled with a dark 24-bit TRUECOLOR foreground, not the SGR-2 dim/faint attribute the ghost stripper originally detected.
The shared ANSI-aware owner fm_composer_strip_ghost (bin/fm-composer-lib.sh) now drops a dark/muted truecolor foreground (perceived luminance below FM_COMPOSER_GHOST_LUMA_MAX, default 128) as well as dim/faint, so the placeholder is stripped and the row reads empty on both ANSI-capable backends (tmux and herdr route through the same owner).
Verified live against grok 0.2.93: real input is the bright 38;2;224;222;244 (luminance ~225, kept), while grok's borders and placeholder/hint text are dark truecolor (38;2;50;47;70 .. 38;2;110;106;134, luminance ~51..110, dropped).
This assumes a dark terminal theme, the fleet reality; the SGR-2 signal stays theme-independent.
Regression coverage: tests/fm-composer-ghost.test.sh (test_strip_ghost_drops_dark_truecolor_ghost, test_dark_truecolor_ghost_only_composer_is_not_pending) and tests/fm-backend-herdr.test.sh (test_composer_state_grok_dark_truecolor_placeholder_is_empty, test_composer_state_grok_bright_truecolor_real_text_is_pending).
Residual gap, tmux-only (unfixed):
in that same pristine placeholder-only state, tmux's own #{cursor_y} points at the composer box's BOTTOM BORDER row, one row below the actual text row (the box appears to render one row lower before any real typing starts); once real text is typed the cursor correctly aligns with the text row again.
This is a row-SELECTION quirk, orthogonal to the styling fix above, and affects only the tmux path (herdr uses a structural composer-row scan, not cursor_y, so it is unaffected).
A correct fix needs a row-window read near cursor_y rather than the single cursor_y row.
In practice fm-spawn launches grok with the brief as its initial prompt, so a live task's composer is never observed in this pristine pre-typing state - but this is unverified for every path (e.g. a steer sent before grok's first real turn settles) and needs dedicated investigation before relying on it.
Turn-end hook: grok fires a Stop hook at every turn boundary, giving firstmate a precise per-turn wake instead of only stale-pane detection.
grok loads PROJECT hooks (<worktree>/.grok/hooks/, <worktree>/.claude/settings.local.json) only after the folder is granted hook-trust in ~/.grok/trusted_folders.toml, which is not automatic and which firstmate will not establish by editing grok's own managed trust store.
GLOBAL hooks in ~/.grok/hooks/ are always trusted and load on first launch.
So fm-spawn installs ONE firstmate-owned global hook, ~/.grok/hooks/fm-turn-end.json, plus the companion ~/.grok/hooks/fm-turn-end.sh, guarded as a no-op for every non-firstmate grok session.
Its Stop command fires only when the current workspace holds a .fm-grok-turnend token pointer that matches the firstmate-owned hook registry under ~/.grok/hooks/fm-turn-end.d/.
fm-spawn writes that per-task pointer (<worktree>/.fm-grok-turnend, gitignored via git info/exclude like the other harnesses' worktree hook files) and a matching registry entry naming this task's state/<id>.turn-ended.
The hook reads $GROK_WORKSPACE_ROOT, which is always set for hooks and equals the worktree.
This keeps the hook outside the worktree, needs no trust grant, and writes only firstmate-owned files.
fm-teardown removes the worktree pointer before returning a pooled worktree.
Secondmate spawns skip the pointer (idle panes are healthy, no stale-pane detection for them).
Primary-session guard fact (verified 2026-07-08, Grok 0.2.91).
The firstmate PRIMARY's own .grok/hooks/fm-primary-turnend-guard.json invokes bin/fm-turnend-guard-grok.sh.
Grok Stop hooks are passive for this purpose: exit 2 does not make the model continue.
The adapter therefore runs the shared predicate and, when it returns 2, forces one same-session follow-up with grok --resume <sessionId> -p <guard-reason> while setting GROK_TURNEND_GUARD_ACTIVE=1 so the nested Stop hook does not recurse.
It does not pass --permission-mode, so the passive hook cannot escalate the primary session's tool permissions.
Project-local Grok hooks require folder trust, verified with launch-time --trust; if the primary firstmate checkout is not trusted for Grok hooks, this primary guard fails open and fm-guard.sh remains the next-command alarm.
Grok's primary watcher protocol is Claude-shaped background-notify around bin/fm-watch-arm.sh; the passive Stop hook is only a backstop for blind turn ends.
