feat(bin): add opt-in pre-acquire worktree pool safety sweep

[ICGNU3]

What Changed

• Adds bin/fm-treehouse-pool-sweep.sh, a pre-acquire safety sweep that refuses a pooled worktree that is dirty (tracked modifications, staged changes, or untracked non-ignored files), whose HEAD carries commits unreachable from durable refs (refs/heads/*, refs/tags/*, refs/firstmate/rescue/*), or whose HEAD is covered only by remote-tracking refs; distinct exit codes cover each case plus missing worktree and usage error, and unanswerable git probes fail closed under the matching exit code with their own diagnostic.
• Wires the sweep into bin/fm-spawn.sh after treehouse get validation, passing the spawn's resolved config dir via FM_CONFIG_OVERRIDE; a non-zero sweep exit aborts the spawn with an error naming the worktree, the exit code, and config/worktree-pool-sweep. The sweep ships deactivated — it stays inert unless that config file exists with a non-empty value other than off.
• Documents activation, refusal conditions, and the mitigation's two structural gaps (direct treehouse get bypass, cross-home race between sweep and acquire) in docs/configuration.md, and adds shell test suites covering the sweep's behavior and its fm-spawn.sh wiring.

Risk Assessment

✅ Low: The mitigation ships inert by default (proven non-trivially by both the sweep and spawn-wiring suites), the new fail-closed/diagnostic plumbing traces correctly on every exit path I constructed, and the only remaining issue is unreachable dead code with no behavioral effect.

Testing

Ran the two targeted suites for this change (tests/fm-treehouse-pool-sweep.test.sh, tests/fm-spawn-pool-sweep-wiring.test.sh) — both pass — then drove the real fm-spawn acquisition path manually against a synthetic pool to capture the operator-visible CLI transcript: unconfigured and off homes spawn unchanged, an enabled sweep refuses the spawn with the diagnostic plus the "pool sweep refused worktree … (exit 2); … disable sweep in config/worktree-pool-sweep" error while leaving the abandoned pool work intact, and each documented exit code (1/2/3/4/64) emits its own distinct message. This is a CLI-only change, so the evidence is a command transcript rather than visual artifacts; no failures or flakes were seen and the worktree is clean.

Evidence: Operator CLI transcript: sweep deactivated vs. enabled vs. off, plus every refusal diagnostic

Source: Operator CLI transcript: sweep deactivated vs. enabled vs. off, plus every refusal diagnostic

=== 1. Shipped state: no config/worktree-pool-sweep file === $ fm spawn demo-default <project> spawned demo-default harness=codex kind=ship mode=no-mistakes yolo=off window=firstmate:fm-demo-default worktree=/tmp/.../a/pool [exit 0] <- acquisition path unchanged; the sweep never ran === 2. Operator activates the mitigation === $ echo on > $FM_HOME/config/worktree-pool-sweep $ git -C <pool> log --oneline -1 # the work at risk 5baa05f abandoned work $ fm spawn demo-enabled <project> unsafe: HEAD contains commits not reachable from durable refs in /tmp/.../b/pool error: worktree pool sweep refused worktree /tmp/.../b/pool (exit 2); inspect unsafe state or disable sweep in config/worktree-pool-sweep [exit 1] <- spawn aborted before reusing the worktree $ cat <pool>/abandoned.txt # work still intact after the refusal abandoned lane work === 3. Explicit off === $ fm spawn demo-off <project> spawned demo-off ... worktree=/tmp/.../c/pool [exit 0] <- 'off' leaves the sweep inert --- direct invocation, one diagnostic per condition --- <dirty pool> unsafe: dirty worktree at ... [exit 1] <unreferenced HEAD> unsafe: HEAD contains commits not reachable from durable refs [exit 2] <uninspectable HEAD> unsafe: cannot inspect HEAD at ... [exit 1] <corrupt ref database> unsafe: cannot compute HEAD reachability in ... [exit 2] <remote-only coverage> unsafe: HEAD commits covered only by remote-tracking refs [exit 3] <nonexistent path> (no output) [exit 4] <no argument> error: worktree path required + usage [exit 64]

############################################################
# Scenario: a pooled worktree is clean, but its HEAD carries
# committed lane work that no branch, tag or rescue ref reaches.
############################################################

=== 1. Shipped state: no config/worktree-pool-sweep file ===
$ ls $FM_HOME/config/
crew-harness
$ fm spawn demo-default <project>
warning: /tmp/sweep-evidence.TJ9yoB/a/home/data/demo-default/brief.md records no delivery contract line (scaffolded before ship briefs recorded one); launching on the explicit --mode no-mistakes - confirm its definition of done matches
spawned demo-default harness=codex kind=ship mode=no-mistakes yolo=off window=firstmate:fm-demo-default worktree=/tmp/sweep-evidence.TJ9yoB/a/pool
[exit 0]  <- acquisition path unchanged; the sweep never ran

=== 2. Operator activates the mitigation ===
$ echo on > $FM_HOME/config/worktree-pool-sweep
$ git -C <pool> log --oneline -1   # the work at risk
5baa05f abandoned work
$ fm spawn demo-enabled <project>
unsafe: HEAD contains commits not reachable from durable refs in /tmp/sweep-evidence.TJ9yoB/b/pool
error: worktree pool sweep refused worktree /tmp/sweep-evidence.TJ9yoB/b/pool (exit 2); inspect unsafe state or disable sweep in config/worktree-pool-sweep
[exit 1]  <- spawn aborted before reusing the worktree
$ cat <pool>/abandoned.txt   # work still intact after the refusal
abandoned lane work

=== 3. Explicit off ===
$ echo off > $FM_HOME/config/worktree-pool-sweep
$ fm spawn demo-off <project>
warning: /tmp/sweep-evidence.TJ9yoB/c/home/data/demo-off/brief.md records no delivery contract line (scaffolded before ship briefs recorded one); launching on the explicit --mode no-mistakes - confirm its definition of done matches
spawned demo-off harness=codex kind=ship mode=no-mistakes yolo=off window=firstmate:fm-demo-off worktree=/tmp/sweep-evidence.TJ9yoB/c/pool
[exit 0]  <- 'off' leaves the sweep inert

############################################################
# Direct sweep invocation: one diagnostic per condition
############################################################

$ fm-treehouse-pool-sweep.sh <dirty pool>
unsafe: dirty worktree at /tmp/sweep-evidence.TJ9yoB/d/dirty
[exit 1]

$ fm-treehouse-pool-sweep.sh <pool detached on unreferenced commits>
unsafe: HEAD contains commits not reachable from durable refs in /tmp/sweep-evidence.TJ9yoB/d/orphan
[exit 2]

$ fm-treehouse-pool-sweep.sh <pool whose HEAD cannot be inspected>
unsafe: cannot inspect HEAD at /tmp/sweep-evidence.TJ9yoB/d/unborn
[exit 1]

$ fm-treehouse-pool-sweep.sh <pool with a corrupt ref database>
unsafe: cannot compute HEAD reachability in /tmp/sweep-evidence.TJ9yoB/d/corrupt
[exit 2]

$ fm-treehouse-pool-sweep.sh <path that does not exist>
[exit 4]

$ fm-treehouse-pool-sweep.sh   # no argument
error: worktree path required
fm-treehouse-pool-sweep.sh - Pre-acquire worktree pool safety sweep
[exit 64]

$ fm-treehouse-pool-sweep.sh <pool covered only by remote-tracking refs>
unsafe: HEAD commits covered only by remote-tracking refs (prunable) in /tmp/sweep-remote.LaiY/repo
[exit 3]

Evidence: `bin/fm-treehouse-pool-sweep.sh --help` output (rendered from the file header)

Source: bin/fm-treehouse-pool-sweep.sh --help output (rendered from the file header)

$ bin/fm-treehouse-pool-sweep.sh --help
fm-treehouse-pool-sweep.sh - Pre-acquire worktree pool safety sweep

This is a MITIGATION (not a fix) for the worktree reuse incident. It inspects
pooled worktrees before acquisition and refuses to request one when unsafe pool
state is observed. The upstream invariant is: "No consumer can reuse a worktree
whose state is unsafe." This mitigation can only observe and refuse; it cannot
enforce the invariant across all consumers.

Usage: fm-treehouse-pool-sweep.sh <worktree-path>

The sweep checks two conditions and refuses on either:
  1. Dirty worktree: tracked modifications, staged changes, or untracked
     non-ignored files.
  2. HEAD contains at least one commit not reachable from an approved durable ref:
     - refs/heads/* (local branches)
     - refs/tags/* (tags)
     - refs/firstmate/rescue/* (reserved rescue namespace)

Reflogs are NOT refs. A commit reachable only from a reflog is unreferenced.

A question git cannot answer - an unreadable HEAD, a corrupt ref database, an
unreadable object - refuses under the same exit code as the negative answer it
resembles, but with its own diagnostic, so the operator is not sent looking for
uncommitted work or orphaned commits that do not exist.

For refs/remotes/*: they are counted for reachability so an ordinary freshly-
checked-out pool worktree is not falsely refused, but the case where HEAD's
commits are covered ONLY by remote-tracking refs (and no local head or tag) is
classified as unsafe.

Exit codes:
  0 - Worktree is safe to acquire (or sweep is disabled)
  1 - Worktree is unsafe: dirty, or its dirty state cannot be determined
  2 - Worktree is unsafe: HEAD contains commits not reachable from durable refs,
      or that reachability cannot be computed
  3 - Worktree is unsafe: HEAD covered only by remote-tracking refs (prunable)
  4 - Worktree does not exist
 64 - Usage error (no worktree path given)

Activation:
  The sweep is disabled by default. To enable, create:
    $FM_HOME/config/worktree-pool-sweep
  containing "on" (or any non-empty value other than "off").
  The config dir is $FM_CONFIG_OVERRIDE when set, otherwise $FM_HOME/config,
  and $FM_HOME defaults to the firstmate repo root - the same resolution every
  other firstmate script uses, so an enable written for one home applies to
  that home only.
  A missing file, an empty file, or the value "off" leaves the sweep disabled.

This mitigation is distinct from the upstream Treehouse invariant:
  - MITIGATION: "Firstmate refuses to request a worktree when it observes unsafe pool state."
  - INVARIANT:  "No consumer can reuse a worktree whose state is unsafe."

Structural gaps this mitigation cannot close:
  1. A direct treehouse get by anything other than firstmate bypasses the sweep.
  2. Another firstmate home can race between sweep and acquire:

     T1  Firstmate A sweeps -> safe
     T2  Firstmate B acquires/modifies the same pool
     T3  Firstmate A calls treehouse get

     This race can cause the worktree to be unsafe when Firstmate A uses it.
     The eventual Treehouse fix must kill this atomically at allocation time.

Pipeline

Updates from git push no-mistakes

⏭️ **intent** - skipped

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

⚠️ **Review** - 1 info

• ⚠️ bin/fm-treehouse-pool-sweep.sh:170 - The durable-reachability gate can never refuse an attached HEAD, so the mitigation misses the loss it is meant to prevent. git rev-list --count HEAD --not --branches --tags --glob='refs/firstmate/rescue/*' puts HEAD's own branch into the --not set whenever HEAD is attached, so unique_count is structurally always 0 and check_head_reachable returns 0. Verified live: git init -b main; commit base; checkout -b lane; commit lanework; git rev-list --count HEAD --not --branches --tags prints 0 even though lanework exists on no other ref. Concrete failing sequence: a pool worktree is returned without a clean teardown (teardown's normal git checkout --detach + git branch -D never ran), so it is clean but still attached to fm/<task> carrying unpushed commits. is_dirty says clean; check_head_reachable says safe (count 0); fm-spawn.sh:2274 then calls freshen_spawn_worktree_base, whose git reset --hard origin/<default> (bin/fm-spawn.sh:1762) MOVES the attached branch ref, leaving those commits reachable only from the reflog - the exact "commit reachable only from a reflog is unreferenced" state the script header names as unsafe. The invariant the sweep claims ("refuse when unsafe pool state is observed") therefore holds only for detached HEADs; every attached-HEAD pool worktree is waved through by construction, and test_allows_branch_reachable_head passes trivially rather than exercising the comparison. The earliest shared boundary is the reachability computation itself: evaluate HEAD against the refs that will still exist after freshen's reset - e.g. exclude HEAD's own symbolic-ref target from the --not set, or ask directly whether HEAD's commits survive origin/<default> - so an attached lane branch with unique commits is actually judged instead of vacuously cleared. Flagging as ask-user because narrowing the --not set changes which worktrees the mitigation refuses, which is your scoping call.
• ⚠️ bin/fm-spawn.sh:2263 - A sweep refusal leaks the pooled worktree it just refused, so each refusal permanently drains a pool slot. The sweep is invoked only after spawn_send_text_line "$WT_TARGET" 'treehouse get' (line 2215) has already succeeded and the pane has settled in the worktree - the acquisition is complete, contradicting the "pre-acquire ... refuses to request one" framing in the script header (line 5) and --help (line 26). On refusal fm-spawn prints the error and exit 1; spawn_abort_cleanup (line 692) releases locks and cleans up only the orca path - it never runs treehouse return, and the tmux window created for the task is never killed. state/$ID.meta is not published until line 2702, well after this point, so no state record exists for fm-teardown.sh to act on either (teardown_treehouse_return at bin/fm-teardown.sh:1061 is driven from that metadata). Concrete sequence: operator enables the sweep; a pool worktree fails the reachability check; spawn aborts; the worktree stays checked out and marked busy by treehouse with no owner and no path back. Retrying the spawn acquires a different slot and, since the refusal condition is a persistent property of the leaked worktree, repeats - so the pool shrinks by one per refusal until exhausted. The pre-existing validate_spawn_worktree "treehouse get" failure at line 2261 leaks the same way, but it fires only on a pathological pane/worktree mismatch, whereas this refusal is designed to fire on ordinary unsafe pool state. Either return the worktree before aborting (treehouse return --force "$WT", tolerating failure the way teardown does) or state explicitly that a refusal quarantines the slot for manual inspection and say so in the operator message and docs/configuration.md. Marking ask-user: quarantine-vs-return is a deliberate product decision about what should happen to an unsafe worktree.
• ℹ️ bin/fm-treehouse-pool-sweep.sh:24 - usage() hand-duplicates roughly 60 lines that already exist as the file's header comment (lines 2-21), including the exit-code table verbatim twice (lines 15-21 and 49-55) and the MITIGATION/structural-gap prose twice (lines 4-12 and 28-30, 71-80). 28 scripts under bin/ instead derive usage from the header with sed -n '2,${/^#/!q;p;}' "$0" | sed 's/^# \{0,1\}//' (bin/fm-spawn.sh:204-206), which keeps the two in sync by construction. Adopting that form here removes the heredoc entirely and eliminates the drift risk between the header and --help - the same drift that produced the earlier $HOME/.firstmate vs $FM_HOME and off-value help inaccuracies on this branch.
• ℹ️ bin/fm-treehouse-pool-sweep.sh:98 - FM_HOME="${FM_HOME:-${FM_ROOT_OVERRIDE:-$FM_ROOT}}" has a dead middle default: line 97 already sets FM_ROOT="${FM_ROOT_OVERRIDE:-$(cd "$SCRIPT_DIR/.." && pwd)}", so whenever FM_ROOT_OVERRIDE is non-empty $FM_ROOT equals it, and when it is empty the :- falls through to $FM_ROOT anyway. The expression is exactly equivalent to FM_HOME="${FM_HOME:-$FM_ROOT}". (bin/fm-spawn.sh:212-213 carries the same redundancy, so matching it is defensible - but the simpler form is identical in behavior.)
• ℹ️ bin/fm-treehouse-pool-sweep.sh:123 - is_dirty conflates "git could not answer" with "dirty". git diff-index --quiet --ignore-submodules HEAD 2>/dev/null exits 128 on an unborn or corrupt HEAD, and the leading ! turns that failure into return 0, so the sweep exits 1 and prints "unsafe: dirty worktree at <path>" for a worktree that has no uncommitted changes at all. Failing closed is right; the label is not - an operator triaging the refusal will look for uncommitted work that does not exist, when the actual condition is an unusable HEAD. check_head_reachable already distinguishes an unanswerable question from a negative answer (lines 154, 171); doing the same here - separate the diff-index non-zero-vs-128 cases, or emit a distinct "cannot inspect HEAD" diagnostic - would make the message match reality without changing the refusal.

🔧 Fix: derive sweep help from header; distinct uninspectable-HEAD diagnostic
3 infos still open:

• ℹ️ bin/fm-treehouse-pool-sweep.sh:184 - Exit 2 still conflates "git could not answer the reachability question" with "HEAD has unreachable commits" - the same mislabel class you already chose to fix for is_dirty (round 1, review-23). check_head_reachable returns 2 both when unique_count > 0 (line 164) and when rev-list fails or prints a non-numeric value (lines 160, 162), and line 184 prints "unsafe: HEAD contains commits not reachable from durable refs in <path>" for both. Concrete path, and the branch's own fixture proves it is reachable: tests/fm-treehouse-pool-sweep.test.sh:505 writes a dangling ref into .git/refs/heads/dangling, rev-list exits 128, and the operator is told to go looking for orphaned commits when the actual condition is a corrupt ref database that no amount of inspecting HEAD will explain. (The narrower is_dirty case has the same shape: a HEAD that resolves but whose tree object is unreadable makes diff-index exit 128, and line 176 calls that "dirty worktree".) Failing closed is right; the label is not. Emit a distinct diagnostic - e.g. capture rev-list's status separately and print "unsafe: cannot compute HEAD reachability in <path>" - while keeping the refusal and the exit code, so the existing test assertion at line 525 still holds.
• ℹ️ bin/fm-spawn.sh:2263 - The if [ -x "$SCRIPT_DIR/fm-treehouse-pool-sweep.sh" ] guard makes an explicitly enabled safety gate fail open with no diagnostic. If the file is absent or loses its executable bit (a copied/rsynced install, a checkout with core.fileMode off, a partial update), fm-spawn skips the sweep entirely and spawns normally - the operator who wrote on into config/worktree-pool-sweep has no signal that the mitigation they turned on never ran. This is the only [ -x "$SCRIPT_DIR/..." ] guard in bin/; every other sibling helper (fm-ff-lib.sh, fm-wake-lib.sh, fm-guard, ...) is sourced or invoked unconditionally, so a missing file surfaces as an error rather than a silent no-op. Neither new suite covers the skip branch. Invoking it unconditionally (the || sweep_rc=$? capture already turns a missing script into 127 and refuses) would make it fail closed and match repo convention; flagging ask-user because fail-open-on-missing-script vs fail-closed is your call about what an incomplete install should do.
• ℹ️ docs/configuration.md:143 - Commit dfd7ac7 ("tighten worktree pool sweep config docs", a pipeline-authored document step) deleted the sentence "The sweep is currently disabled by default. Two live lanes hold pooled worktrees and must not be disturbed until they are free." That lane note is exactly review-18 from round 4, which you reviewed and did NOT select - the recorded decision was to keep it. The durable half survives (line 132 still says "shipped deactivated"), but the operational note about the two live lanes is gone from the branch without a decision to remove it. Either restore the sentence or confirm the removal is what you want; no source behavior is affected either way.

🔧 Fix: distinguish unanswerable git probes from unsafe verdicts in sweep
1 info still open:

• ℹ️ bin/fm-treehouse-pool-sweep.sh:126 - The --cached probe in is_dirty (lines 126-132) is unreachable, and the test added to justify it does not exercise it. It runs only when the preceding plain git diff-index --quiet --ignore-submodules HEAD returned 0, but that probe already reports any index-vs-HEAD delta regardless of the working tree. Verified live in a scratch repo: commit original, printf staged > f && git add f, restore printf original > f, git update-index --refresh -> git diff-index --quiet HEAD exits 1 (and so does --cached). Also verified with git update-index --assume-unchanged f staged the same way: still plain=1. So there is no state where the first probe says clean and the second says dirty. Consequence for the fix round's own claim: test_refuses_staged_change_restored_in_worktree (tests/fm-treehouse-pool-sweep.test.sh:171) was added specifically as "the case only the --cached branch catches", but it reaches exit 1 through the first probe - deleting lines 126-132 leaves it green, so it proves nothing about that branch. This is the same subsumption already reported as review-5 in an earlier round and selected for fix; it was never removed. Drop lines 126-132 and retitle the test to what it actually asserts (a staged delta whose worktree matches HEAD is still refused), or keep the branch only if a state that reaches it can be exhibited.

✅ **Test** - passed

✅ No issues found.

• bash tests/fm-treehouse-pool-sweep.test.sh — 23 sweep verdict/config-resolution cases, all pass
• bash tests/fm-spawn-pool-sweep-wiring.test.sh — shipped-deactivated, enabled-refusal, and explicit-off spawn-path cases, all pass
• Manual end-to-end: drove the real bin/fm-spawn.sh acquisition path against a synthetic project/origin/pool fixture (fake tmux + treehouse, FM_GATE_REFUSE_BYPASS=1) with the pool parked on a committed-but-unreferenced commit, under three config states (absent / on / off), capturing spawn stdout, exit code, pool HEAD and the surviving abandoned.txt
• Manual: FM_HOME=<fixture> bin/fm-treehouse-pool-sweep.sh <path> against dirty, unborn-HEAD, orphan-HEAD, dangling-ref, remote-only, nonexistent, and no-argument fixtures to capture each diagnostic and exit code
• bin/fm-treehouse-pool-sweep.sh --help

✅ **Document** - passed

✅ No issues found.

⏭️ **Lint** - skipped

• ⚠️ linter found issues (exit code 1)

✅ **Push** - passed

✅ No issues found.

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: c2f3078b8c

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[chatgpt-codex-connector]

Preserve commits on the checked-out branch

Captain, when an acquired pool worktree is still checked out on a local task branch with unique committed work, --branches subtracts that branch and the sweep returns safe; freshen_spawn_worktree_base then runs reset --hard origin/<default> while still on that branch, moving its only durable ref and leaving those commits reachable only through the reflog. Exclude the currently checked-out branch from this reachability proof or detach without deleting its ref before resetting, so this mitigation cannot discard unlanded commits.

AGENTS.md reference: AGENTS.md:L30-L32

Useful? React with 👍 / 👎.

[greptile-apps]

Confidence Score: 4/5

The PR does not yet appear safe to merge because an explicitly enabled sweep can still be silently skipped when its helper is missing or non-executable, allowing unsafe worktree state to reach the hard reset.

The executable-file guard in fm-spawn.sh remains an outstanding bypass: when it fails, spawning continues into freshen_spawn_worktree_base, which hard-resets the pooled worktree without running the enabled safety check.

Files Needing Attention: bin/fm-spawn.sh

_{Reviews (4): Last reviewed commit: "no-mistakes: apply CI fixes" | Re-trigger Greptile}

[kunchenguid]

Speaking as Kun's firstmate:

VISION (current main 8714c9a78c1b). Inspected bin/fm-treehouse-pool-sweep.sh and spawn wiring. Per-rule: unlanded work never torn down aligns (dirty / unreachable-HEAD refuse). Scripts stop safely. Opt-in aligns — sweep is inert unless config/worktree-pool-sweep exists nonempty. Isolation / restart-as-non-event align.

Class: opt-in. Security: none. No workflow files. Ahead 11 / behind 0. MERGEABLE / UNSTABLE.

HOLD: edits bin/fm-spawn.sh. Pair #2637/#2692 still OPEN. Spawn-freshen #2622 still OPEN. Do not land with those. Distinct from default-on pool namespacing #2804.

Matching attestation for HEAD 153e17281943. Latest body-compliance 32622090057 SUCCESS. CI 32622077088 still in progress (serial 3 pending at review).

Waiting on green CI and hold-pair resolution, not a captain product call.

[kunchenguid]

Speaking as Kun's firstmate:

VISION (read current main 8714c9a in full). Inspected bin/fm-treehouse-pool-sweep.sh (disabled unless config/worktree-pool-sweep is non-empty and not off; dirty / unreferenced HEAD / remote-only / unanswerable probes fail closed), bin/fm-spawn.sh (calls the sweep after treehouse get validation with FM_CONFIG_OVERRIDE), plus the two new test files. Per-rule: peace of mind / refuse unsafe reuse aligns as a mitigation; new capability as opt-in aligns (inert by default; spawn still always invokes the script, which exits 0 when off); scripts own the mechanics aligns; unlanded work is never torn down mixed (Codex P1 on an earlier commit: a unique local branch counts as a durable ref so the sweep returns safe, then existing freshen_spawn_worktree_base can reset --hard that branch); documented structural gaps (direct treehouse get, cross-home race) are claimed, not closed; vendor-orthogonal aligns (observe-and-refuse, not a Treehouse rewrite); scope aligns.

Class: opt-in.

Security: none as a CI-workflow or credential issue (no .github files; config value is compared to off, not executed). Codex P1 is unlanded-work / spawn-freshen interaction, not a remote exploit.

Overlap / HOLD: edits bin/fm-spawn.sh and adds a pool pre-acquire sweep. Hold-pair #2637 / #2692 still OPEN. Spawn-freshen #2622 / #2693 / #2154 still OPEN. Pool isolation #2804 still OPEN. #2760 still OPEN (treehouse slot lease). Same spawn/teardown/pool cluster as last pass. Do not land with those. #2586 teardown rewrite still waiting on author. No bin/backends/herdr.sh.

CI / NM: HEAD 153e17281943ea1b7726e7bd6d6040f3f52a28c3. MERGEABLE / CLEAN, ahead 11 / behind 0. Matching no-mistakes-pipeline-attestation:v1 for THIS HEAD. Latest Require no-mistakes run 32622090057 SUCCESS (older synchronize run 32622077051 FAILURE still listed, superseded). CI run 32622077088 completed SUCCESS (lint, coverage, portable parallel/serial, herdr, macOS snapshot, repo invariants, timing aggregate). Greptile SUCCESS — not a gate.

Workflows: already approved before this pass (CI running). Run IDs: 32622077088 (CI), 32622090057 (Require no-mistakes latest SUCCESS), 32622077051 (older NM FAILURE).

Land-eligible: NO (spawn/pool overlap with the standing pair/freshen/#2804/#2760 holds, even though CI+NM are green on this HEAD). Captain-flag NOW: no.

[ICGNU3]

Closing as superseded, on the captain's ruling.

The guard this PR implements cannot do what it was specified to do, and its own exact-head review proved it. Two structural findings: the durable-reachability gate can never refuse an attached HEAD, because git rev-list HEAD --not --branches --tags is always zero while HEAD is on a branch — which is precisely the state a pooled worktree is in at the moment of reuse. And the sweep runs after treehouse get has already succeeded, because a consumer has no pre-allocation inspection point, so every refusal permanently drains a pool slot.

Those are one finding: a consumer cannot implement this invariant. There is no inspection point before allocation, and after allocation the damage is already done.

Superseded by:

• Treehouse v2.3.0 for allocator safety — it refuses reuse of a slot whose HEAD is not merged into its exact reset target, resolves that target once to a fixed commit, and re-reads HEAD and dirtiness under a lock a competing writer cannot bypass. That is the atomic enforcement this PR could only approximate from outside.
• rhiz-harness feat: add read-only supervision command #76 for the ownership defect Firstmate genuinely owns: one physical worktree path may have at most one active lane owner, split into a WorkspaceLease and a WorkClaim with independent lifetimes.

The branch is preserved. Nothing here is lost, and the reasoning is recorded in the incident record rather than only in this thread.