fix(scripts): row 211 R4 busy check ancestor reads, denied lookups, sourced tests (#1709 )

From the GPT review of R3 (row211-r3-gpt.md, R1 to R3 and Check 5): - slot-busy.sh: every ancestor status read must give a numeric PPid. A failed ancestor or cmdline read counts as gone only when a listing of the proc root succeeds and lacks the pid; anything else is exit 2 with no CLEAR. The [ -d ] and [ -e ] tests, which can't tell a denied lookup from a missing one, are gone. - slot-busy.sh: a shell-snapshot wrapper whose text sources (source or .) a gate, test or mutant script is BUSY; one that only runs children is still skipped. - install-git-hooks.sh: the hook is staged in a mktemp file in the hooks directory, not a pid-named path. - mutants.sh: exit 1 on a survivor, NO MATCH, COPY FAILED or a timeout; nine new mutants, 30 of 30 killed. test-git-guard.sh: RED 90/14, GREEN 105/0. BUILD.md R4 has the details, including a correction to the R3 bind-mount note.
fix(scripts): row 211 R3 push guard tags, installer hooks dir, busy check errors (#1709 )
2026-11-02 14:11:47 -06:00 · 2026-11-02 13:50:11 -06:00 · 2026-11-02 13:50:11 -06:00 · 2026-11-02 13:50:11 -06:00
9 changed files with 1572 additions and 0 deletions
@@ -5816,3 +5816,43 @@ Before: agents can read the library; supporting-path and push-credential depende
 2026-10-26 | Sage | mos1884/#662 scope after330/331landing | ReadQ222/Q261/Q263 and659/660/662; posted bounded human-only factory settings/triage/defaulttwo-roundmandate/trackedno-exemptionflake scope with10acceptance criteria, task662comment1338 exactwholebody/author13GETverified. No implementation/review/gate launched.660c1335notready(review/merge, noVM); gatefacts1329/1334 retained; target integration/fullrunner confirmation follows readiness, no localfallback. Landedproduct/evidence unchanged;657/658backlog.

 2026-10-26 | Sage | Mos1909/1915/1917 real postlanding reviews | Boyd/Dewey/Filbert/Gladstone real authored candidate52ba verdictfiles independently byte/hash-verified, allAPPROVE scoped; Dewey656broaderPARTIAL retained. Formal330R1/331R4 requests failedpre-send/no comments or approvals; no borrowed/copied/mintedkeys. LegacyhelperGETname jason.woltje is NOT ownJarvis, ownslotabsent; rows tracking-open/#436, files cited via normalqueue. NewFilbertNEW-330-01 filedtask665 exactreadback, notlandingreopen/gate. Repair646-648/652-656 remainOPEN untilactualcomments;1917 conditionalbacklog routing retained. #662scope1338posted;660PR405REVISE/notready. Product1968inputs unchanged; no source/helper/test/gate edits/runs; peerjournal prefixes preserved.
+
+## 2026-11-02T19:39:18Z: row 211 (#1709, #426) R3, push guard and busy check fixes from the GPT review
+
+Before: row 211 as picked onto 09a847eda for the lead's landing batch (5734c1a80, c8f2cb70c on
+`t3/row211-push-guard-r3-fix`). The GPT review (batch1-a-gpt.md) found five gaps: slot-busy.sh read a
+failed cmdline read as an exited process and didn't check its own status read; its shell-snapshot
+exclusion matched a substring; the pre-push hook let an existing tag be re-made or moved to a descendant;
+the installer wrote through a symlinked hooks directory; the snapshot fixture didn't kill its mutant. The
+hook also took hex object names of any length.
+
+After: one R3 commit by the lead's implementation sub-agent. An unreadable live process makes slot-busy.sh
+exit 2 and never print CLEAR, and an exited one is still skipped. The exclusion matches only the wrapper's
+shape. Any change to an existing `refs/tags/*` ref is refused. The installer refuses a symlinked hooks
+directory, or one that resolves elsewhere, before any write. Object names must be 40 or 64 hex
+characters. test-git-guard.sh: RED 67 passed, 18 failed (19:27:01Z to 19:27:06Z), GREEN 85 passed, 0
+failed (19:28:58Z to 19:29:04Z). The run before GREEN gave 80/5 because the new error text said "not
+CLEAR"; it was reworded. Mutants 21 of 21 killed (19:30:11Z to 19:33:22Z, base green). No 64-hex test
+pin names a changed path. Not pushed. Gaps: the installer's resolved-path refusal has no test of its own
+(it needs a bind mount); details in agents/darkwing/work/queue-211/BUILD.md, section "R3".
+
+## 2026-11-02T20:11:25Z: row 211 (#1709, #426) R4, busy check ancestor reads, denied lookups and sourced tests
+
+Before: row 211 R3 as picked onto 09a847eda (bcd74ec33, 3a121885c, 7d03f212d on
+`t3/row211-push-guard-r4-fix`). The GPT review of R3 (row211-r3-gpt.md) found three ways slot-busy.sh could
+print CLEAR in doubt: a failed ancestor status read ended the walk without an error; `[ -e ]` read a denied
+lookup as an exited process; and a shell-snapshot wrapper that sourced a test into its own shell, with no
+child, was skipped. It also noted that mutants.sh exited 0 after a survivor, that the installer's temporary
+file had a pid name, and that the R3 note on bind mounts was wrong.
+
+After: one R4 commit by the lead's implementation sub-agent. Every ancestor read must give a numeric PPid;
+a failed read, or a failed cmdline read, counts as gone only when a listing of the proc root succeeds and
+lacks the pid, and anything else is exit 2 with no CLEAR. A wrapper whose text sources (`source` or `.`) a
+gate, test or mutant script is BUSY; a wrapper that only runs children is still skipped. mutants.sh exits 1
+on a survivor, NO MATCH, COPY FAILED or timeout (shown by hand in TMPDIR: survived exit 1, NO MATCH exit 1).
+The installer stages the hook in a mktemp file. test-git-guard.sh: RED 90 passed, 14 failed (19:57:25Z to
+19:57:37Z); the first GREEN gave 101/3 (20:01:11Z to 20:01:25Z), from a BASH_REMATCH reset in the new
+sourced() that a GREEN-time case now pins; GREEN 105 passed, 0 failed (20:02:40Z to 20:02:49Z). Mutants 30
+of 30 killed, runner exit 0 (20:02:56Z to 20:06:58Z, base green). No 64-hex test pin names a changed path.
+Not pushed. Gaps: lexical false BUSY and missed runtime-built sourced paths, and an undetected bind-mounted
+hooks directory; details in agents/darkwing/work/queue-211/BUILD.md, section "R4".
@@ -0,0 +1,573 @@
+# Row 211 (#1709, Vikunja P19 #426): a pre-push hook that refuses force-pushes, and a busy check that fails on BUSY
+
+Darkwing, 2026-10-22. Brief: `docs/plans/2026-10-20_force-push-guard.md` (blob 3a8c2cf13). Moved from Rocko
+to me by sage-2801 (Q220, mos-1301). Base: 78b69e1e6 (r2; r1 was aca16404c). Branch: `darkwing/row211-r2`
+(r1 `darkwing/row211` 6db25b1f0 stays as pushed). Reviewer: Dewey. Gate owner: Sage.
+
+## What ships
+
+- `scripts/git-hooks/pre-push` (new, `/bin/sh`). For each ref line on stdin it refuses:
+  - a delete (local sha all zeros);
+  - a remote tip that isn't in this repository (`git cat-file -e <remote>^{commit}`), with "fetch first,
+    then push again";
+  - a remote tip that isn't an ancestor of the local tip (`git merge-base --is-ancestor`), naming the ref
+    and both shas;
+  - an ancestor check that fails for any other reason (exit above 1);
+  - a short or overlong ref line, or a non-hex object name.
+
+  A new ref (remote sha all zeros) passes, and so does an empty push. It fetches nothing. On any refusal
+  it prints one line per refused ref and a closing line, and exits 1, so git pushes no ref at all.
+- `scripts/install-git-hooks.sh` (new). Installs the hook as `pre-push` in the common `.git/hooks`
+  (`git rev-parse --git-common-dir`), so a `--repo` naming a worktree lands in the shared directory.
+  It refuses (exit 2):
+  - a set `core.hooksPath` at any scope;
+  - a different installed `pre-push`, unless `--force-install` is given;
+  - a symlinked `pre-push`, even with `--force-install`;
+  - any of `GIT_DIR`, `GIT_WORK_TREE`, `GIT_COMMON_DIR`, `GIT_INDEX_FILE`, `GIT_OBJECT_DIRECTORY` or
+    `GIT_ALTERNATE_OBJECT_DIRECTORIES` in the environment;
+  - a directory that isn't a git checkout.
+
+  It never writes the installed file in place. A new hook goes in by `link()` from a temporary copy, so
+  a hook that appeared meanwhile is kept and the install refuses. A replacement goes in by `rename()`.
+  Then it compares the bytes, checks the mode, and runs a canary through `git hook run` (git 2.55 here):
+  an empty push must pass and a delete line must be refused with the guard's message.
+- `scripts/slot-busy.sh` (new). Exit 0 CLEAR, 1 BUSY, 2 its own error, one `BUSY <pid> <rule> cwd=<cwd>
+  <command>` line per match. Rules: `node ... --test`, `*gate*.sh` (after a space, `/`, `_` or `-`), a
+  `mutant` substring, `test-*.sh`, `docker compose` and `docker-compose`. It skips its own pid and its
+  ancestors, empty command lines (kernel threads) and shell-snapshot wrappers.
+- `scripts/test-git-guard.sh` (new), 61 cases, and three Maintenance rows plus a short section in
+  `docs/TOOLS.md`.
+
+## Choices
+
+1. **A separate `scripts/install-git-hooks.sh`, not `queue-commit.sh --install-push-hook`.** The brief
+   left this open. `queue-commit.sh --install-hook` is the queue guard's installer. It is tied to the
+   canonical checkout and to the lead (jason/sage) and runs the queue guard's canary. The push guard has
+   neither tie: it must also be installable in a scratch clone for the tests, and every seat worktree
+   shares it. Putting it in `queue-commit.sh` would widen that script's reach for no gain. The cost is a
+   second installer with a similar shape. The install pattern (copy beside, link or rename, verify,
+   canary) follows `queue-commit.sh`.
+2. **No privilege check in the installer.** The brief makes the canonical install a separate step with
+   Sage after landing, and the tests need to install into scratch clones as the suite's user. So the
+   script installs wherever it is told. The guard is advisory on the client in any case (`--no-verify`).
+3. **The hook source is the working file next to the installer** (`$ROOT/scripts/git-hooks/pre-push`),
+   not a blob from a ref. That lets the mutant runner install a mutated copy from its own tree, and
+   matches how `queue-commit.sh` reads its guard.
+4. **A new `scripts/test-git-guard.sh`, not more cases in `test-land-work.sh`.** The brief allowed either.
+   Land-work's suite is about `land-work.sh`, and the gate runs every `scripts/test-*.sh`, so a new file
+   gets gated with no wiring.
+5. **`--proc-root DIR` is a test seam in `slot-busy.sh`.** On a live host the real `/proc` may hold
+   other seats' runs at any time, so the suite can't demand exit 0 there. Exit 0 and every rule are
+   tested against a fake `/proc` with pids above `pid_max` (4194304), so they can't collide with the
+   ancestor set, which always comes from the real `/proc`. The real `/proc` is tested with a stand-in:
+   a `/bin/sh` script named `node`, started as `node --test standin.test.mjs` in its own cwd. The suite
+   asserts its BUSY line with that cwd, exit 1, that `slot-busy > /dev/null && echo ran` prints nothing,
+   that the suite itself (an ancestor whose command line matches `test-*.sh`) has no BUSY line, and that
+   after the stand-in exits its pid is gone. The brief's "0 without one" is the fake-`/proc` case.
+6. **Ancestors are skipped**, not only its own pid as the brief says. A gate script that runs the busy
+   check matches its own rules (`*gate*.sh`, `test-*.sh`, `mutant`), so checking only `$$` would make
+   every such caller see itself as BUSY.
+7. **The gate rule is broader than `gate.sh`**: `[ /_-]gate[^ /]*\.sh `, so `sage-gate.sh` and
+   `gate-253.sh` match too. A false BUSY costs a wait; a false CLEAR costs a broken run.
+8. **Shell-snapshot wrappers are skipped.** An agent harness runs each command as `bash -c 'source
+   .../shell-snapshots/snapshot-*.sh && eval <command text>'`, so the wrapper's command line holds the
+   text of whatever the agent typed, including a busy check that names `test-*.sh`. The real child
+   processes the wrapper starts are still matched.
+
+## Tests (`scripts/test-git-guard.sh`)
+
+Scratch bare remote, a scratch clone with the guard installed, and a worktree of that clone. Git runs
+with `GIT_CONFIG_NOSYSTEM=1` and an empty `GIT_CONFIG_GLOBAL`, as in `test-land-work.sh`. Nothing touches
+origin, `~/.mosaic`, `~/.mosaic-dev` or `~/.config/mosaic-dev`.
+
+- Install: exit 0, the canary passed, bytes and mode, no temporary file left, and the worktree's git
+  resolves `hooks/pre-push` to the common file.
+- From the worktree: a new branch and a fast-forward pass. A `--force` push of a rewritten branch, a
+  `+refspec` push and a `--force-with-lease` push are refused by the guard's message, naming the ref and
+  both shas, and the remote ref is unchanged. `:ref` and `--delete` are refused and the branch stays.
+- A second clone moves the remote; a `--force` push from the worktree is then refused with "fetch
+  first", the remote stays where the other clone put it, and the guard fetched nothing.
+- The hook fed by hand: a short line, a non-hex name and an unknown local object are refused; an empty
+  push passes.
+- The installer: `core.hooksPath` set refuses with that message and writes no hook (in `.git/hooks` or
+  the hooks path). A different hook refuses and stays byte-identical. `--force-install` replaces it, and
+  a hard link to the old file keeps the old bytes, so the replacement was a rename. A second install of
+  the same bytes exits 0. A symlinked hook refuses even with `--force-install`. A `--repo` naming a
+  worktree lands in the common directory. `GIT_DIR` set, a plain directory and an unknown argument
+  refuse.
+- `slot-busy.sh`, fake `/proc`: CLEAR with exit 0 when nothing matches (a server, a `grep gate`, a
+  snapshot wrapper whose text holds `node --test`, an empty command line). Exit 1 and the BUSY line for
+  `node --test`, with no CLEAR in the output, and `> /dev/null && echo ran` prints nothing. Each rule
+  once more (7 cases). Exit 2 for a missing root, an empty root and an unknown argument.
+- `slot-busy.sh`, real `/proc`: the stand-in cases in choice 5.
+
+## Mutants (`agents/darkwing/work/queue-211/mutants.sh`)
+
+Each mutant copies the four scripts into its own tree, edits one site there (exactly one match), and runs
+that tree's suite under `timeout -k 10 180`. The worktree's files are never edited. The unmutated suite
+runs first and a red base stops the run. The brief's five come first:
+
+| Mutant | Site |
+|---|---|
+| ancestor-dropped | pre-push: `rc=0` in place of the `merge-base --is-ancestor` call |
+| unknown-object-passes | pre-push: the missing-remote-tip branch skips the ref without refusing |
+| delete-passes | pre-push: the delete branch skips the ref without refusing |
+| install-over-hookspath | installer: the `core.hooksPath` refusal is `true \|\| die` |
+| busy-exits-0 | slot-busy: `exit 0` when BUSY |
+| differing-hook-replaced | installer: a different hook is replaced without `--force-install` |
+| replace-in-place | installer: the replacement writes into the installed file (`cat >`) instead of renaming |
+| symlink-followed | installer: no symlink refusal |
+| ancestor-error-passes | pre-push: an ancestor check exiting above 1 doesn't refuse |
+| snapshot-matched | slot-busy: no shell-snapshot skip |
+| ancestors-matched | slot-busy: no ancestor skip |
+| no-node-rule | slot-busy: the `node --test` rule removed |
+| no-compose-rule | slot-busy: the `docker compose` rule removed |
+
+`install-over-hookspath` still exits 2, because its canary then fails (git looks for the hook in the hooks
+path). The suite kills it on the message and on "no hook was written", not on the exit code.
+
+## Rebase r2 (sage-4362, 2026-10-24)
+
+r1 6db25b1f0 sat on aca16404c, 555 commits behind refactor, and overlapped it in `docs/TOOLS.md`. r2
+cherry-picks it onto 78b69e1e6 as a new commit on a new branch; no force-push. The TOOLS.md hunk merged
+without a conflict, `git patch-id --stable` is the same for both commits (db451e11), and the four scripts,
+`mutants.sh` and this file's other text are byte-identical to r1, so no assertion or reviewed line
+changed. On the new base none of the six paths existed before, `scripts/git-hooks/` holds only the queue
+guard's `pre-commit` (untouched here), and no test reads or pins `docs/TOOLS.md`.
+
+## Runs
+
+Pending: nothing has run yet. Gander held the gate slot (row 253 run 5, from 16:32Z) while this was
+written, so only `bash -n`, `sh -n` and a `DRY=1` mutant pass (every site matched once, no suite run)
+happened. The suite, the mutants and every other `scripts/test-*.sh` run in a CLEAR Sage announces, with
+`TMPDIR` under `/mnt/storage/scratch/tmp`. Results and the measured suite time go here before review.
+
+## Known limits
+
+- `git push --no-verify` skips the hook. Gitea branch protection (ops-01, through Mos) is the guard that
+  holds.
+- The hook doesn't check tags differently from branches: a moved tag is refused like a rewritten branch.
+- `slot-busy.sh` can call a process BUSY that isn't a run, for example an editor with a `test-*.sh` open.
+  It never reads files under a seat's directory, so it can't tell.
+
+## R3, the GPT review (2026-11-02)
+
+The lead's implementation sub-agent (Claude Opus 5.5, a child of Sage's T3 c5c1e8ba) wrote this round from
+the brief `/mnt/storage/scratch/mosaic-lead/briefs/row211-r3-fix.md` and the review
+`/mnt/storage/scratch/mosaic-lead/reviews/batch1-a-gpt.md` (F1 to F5 and the edge-case table). Base
+09a847eda, branch `t3/row211-push-guard-r3-fix`: dca5f10cc and 3e39689c1 picked clean as 5734c1a80 and
+c8f2cb70c, then one R3 commit. The suite goes from 61 cases to 85 and the mutants from 13 to 21. The
+sections above stay as written; where R3 changes them, it says so here.
+
+### F1: a failed read counted as a vanished process
+
+What: `slot-busy.sh` skipped any process whose cmdline read failed, so a live process it couldn't read (a
+mode-000 cmdline of a `node --test`, say) could end in CLEAR. Its own status read was unchecked too: it put
+`$$` in the skip set first, and a failed read only ended the ancestor walk.
+
+Fix: after a failed read the scan checks the pid directory. Gone means the process exited, and it's
+skipped. Still there is an error: the scan names that cmdline, counts it and goes on, so BUSY lines still
+print, then exits 2 and never prints CLEAR. Its own status must read and give a numeric PPid, or it exits 2
+before the scan. A failed read further up the walk still only ends the walk, which can give a false BUSY but
+never a false CLEAR.
+
+Tests, section "slot-busy, read errors" (fake `/proc`): "a pid directory with no cmdline: exit 2", "it
+names that cmdline and never says CLEAR", "a cmdline that can't be read (a directory): exit 2, no CLEAR", "a
+read error beside a BUSY process: exit 2, the BUSY line kept, no CLEAR", "a node --test process whose
+cmdline is unreadable (mode 000) is never CLEAR", "a failing read (tr exits 1) with every pid directory
+still there: exit 2, no CLEAR", "a process that vanishes during its read isn't an error: exit 0 and CLEAR"
+(a `tr` shim on PATH removes the pid directory, then fails) and "its own process unreadable (awk exits 1):
+exit 2, no CLEAR" (an `awk` shim).
+
+Mutants: `unreadable-read-clear` (every failed read skipped), `vanished-is-error` (no directory check, so
+an exited process is an error), `read-errors-ignored` (no final error exit) and `self-read-unchecked` (its
+own failed read ends the walk, as before).
+
+### F2: the snapshot exclusion matched a substring
+
+What: any command line holding `/shell-snapshots/snapshot-` was skipped, so a real `node --test` of a file
+under a `shell-snapshots` directory read as CLEAR.
+
+Fix: `RE_SNAPSHOT` matches only the wrapper's shape: a shell (`sh`, `bash` or `zsh`, with or without a
+path), options that include `-c`, then `source` or `.` of a `shell-snapshots/snapshot-*.sh` file as the
+first command. Any other command line that names such a path goes through the rules.
+
+Tests: "busy on: node --test /seat/tests/shell-snapshots/snapshot-guard.test.mjs (node --test)" and "busy
+on: bash /seat/shell-snapshots/snapshot-gate.sh (gate)".
+
+Mutant: `snapshot-substring` (the old substring test put back).
+
+### F3: an existing tag could be replaced or moved
+
+What: tags went through the ancestor check, and `git merge-base --is-ancestor` peels a tag. A new annotated
+tag object on the same commit, or a lightweight tag moved to a descendant, passed as a fast-forward.
+
+Fix: after the delete and new-ref checks and before the object and ancestor checks, a `refs/tags/*` ref
+whose remote object name isn't zero and differs from the local one is refused ("an existing tag can't be
+moved or replaced"). A new tag still passes, and a tag delete is still refused as a delete. This corrects
+the tag line in "Known limits" above: a moved tag was refused only when it left its line, not when
+it moved to a descendant or was re-made on the same commit.
+
+Tests, section "tags": "a new annotated tag passes", "push --force of a new tag object on the same commit
+is refused", "the remote tag is still the first tag object", "a new lightweight tag passes", "push --force
+of a lightweight tag moved to a descendant is refused", "the remote lightweight tag hasn't moved" and "a
+tag delete is refused, and the tag stays".
+
+Mutant: `tag-replace-passes`.
+
+### F4: a symlinked hooks directory
+
+What: the installer wrote through `.git/hooks` even when it was a symlink, so an install could set the hook
+of every repository sharing that directory, or write outside the repository.
+
+Fix: `own_hooks` refuses (exit 2) when `<common>/hooks` is a symlink, or when it exists and its physical
+path isn't the common directory's physical path plus `/hooks`. It runs before the pre-push symlink check
+and again after `mkdir -p`, so both checks come before the temporary file and any install write. The
+existing refusals (`core.hooksPath`, a different hook without `--force-install`, a symlinked `pre-push`)
+are unchanged.
+
+Tests: "the install refuses a symlinked hooks directory (exit 2)", "it refuses it with --force-install too"
+and "nothing was written in the directory the symlink names".
+
+Mutant: `hooks-dir-symlink-followed` (`own_hooks` returns at once).
+
+### F5: the snapshot fixture proved nothing
+
+What: the fixture wrapper ran `eval 'node --test x.test.mjs'`. There `node` follows a quote, and the node
+rule needs a space or `/` before it, so the fixture wasn't BUSY even without the exclusion and the
+`snapshot-matched` mutant survived.
+
+Fix: two wrappers whose text matches a rule without the exclusion. Pid 4194403 runs `node --test
+x.test.mjs` straight after the `source ... &&`. Pid 4194405 has the harness's real shape: `source ...
+2>/dev/null || true && eval 'bash scripts/test-x.sh > x.log' && pwd -P >| ...`. The paired BUSY case is the
+same node command under `/bin/bash -c` with no snapshot source. The F2 cases are above.
+
+Tests: "an agent's shell-snapshot wrapper isn't a match" (now neither 4194403 nor 4194405) and "busy on:
+/bin/bash -c node --test x.test.mjs (node --test)".
+
+Mutant: `snapshot-matched`, whose site is now the `RE_SNAPSHOT` test. It is killed (3 FAIL). The suite
+alone can't fail before this fix, because the old substring exclusion skips these wrappers too; the killed
+mutant is the before-and-after evidence.
+
+### Object names of the wrong length (the review's table)
+
+What: the hook took any hex string as an object name, so a remote field of `0` read as a new ref.
+
+Fix: after the non-hex check, each field must be exactly 40 or 64 characters, or the ref is refused.
+
+Tests: "a remote object name of 0 is refused, not read as a new ref", "a 39-character local object name is
+refused" and the control "a 64-character object name passes the length check (64 zeros refuse as a
+delete)".
+
+Mutant: `short-sha-accepted`.
+
+### What didn't change
+
+The earlier cases all still pass: an empty push, a new branch and a fast-forward pass; a delete, `--force`,
+`+refspec` and `--force-with-lease` rewrites are refused; a remote tip missing locally is refused with
+"fetch first", and nothing is fetched.
+
+### R3 runs
+
+`TMPDIR` was a fresh `mktemp -d /mnt/storage/scratch/tmp/XXXXXX`. Every run was in the foreground, with
+output to files there.
+
+- RED, all 24 new cases in place and no fix: 67 passed, 18 failed, 2026-11-02 19:27:01Z to 19:27:06Z. The
+  six new cases that pass there are controls that must hold before and after: both new tags pass, the tag
+  delete is refused, the 64-character control, the bare `bash -c` node case and the vanished process.
+- GREEN: 85 passed, 0 failed, 19:28:58Z to 19:29:04Z. The run before it gave 80 passed, 5 failed: the new
+  closing error said "not CLEAR", which the "no CLEAR" assertions caught. It now says "the host isn't
+  known to be idle".
+- Mutants: 19:30:11Z to 19:33:22Z, base green (85/0), runner exit 0, 21 of 21 killed, none survived, no
+  NO MATCH. Every kill exited 1.
+
+| Mutant | FAIL | First failing case |
+|---|---|---|
+| ancestor-dropped | 8 | push --force of a rewritten branch is refused |
+| unknown-object-passes | 2 | a push over a remote tip missing locally is refused, saying fetch first |
+| delete-passes | 12 | the install into a clean clone exits 0 |
+| install-over-hookspath | 2 | it says core.hooksPath is set |
+| busy-exits-0 | 14 | a node --test process: exit 1 |
+| differing-hook-replaced | 3 | the install refuses a different installed pre-push (exit 2) |
+| replace-in-place | 1 | the replacement was a rename: the old file keeps its bytes |
+| symlink-followed | 1 | the install refuses a symlinked pre-push, even with --force-install |
+| ancestor-error-passes | 1 | a failed ancestor check (an unknown local object) is refused |
+| snapshot-matched | 3 | no matching process: exit 0 and CLEAR |
+| ancestors-matched | 1 | this suite, an ancestor, has no BUSY line |
+| no-node-rule | 9 | a node --test process: exit 1 |
+| no-compose-rule | 2 | busy on: docker compose -p x up -d (docker compose) |
+| unreadable-read-clear | 6 | a pid directory with no cmdline: exit 2 |
+| vanished-is-error | 1 | a process that vanishes during its read isn't an error: exit 0 and CLEAR |
+| read-errors-ignored | 6 | a pid directory with no cmdline: exit 2 |
+| self-read-unchecked | 1 | its own process unreadable (awk exits 1): exit 2, no CLEAR |
+| snapshot-substring | 2 | busy on: node --test /seat/tests/shell-snapshots/snapshot-guard.test.mjs (node --test) |
+| tag-replace-passes | 4 | push --force of a new tag object on the same commit is refused |
+| hooks-dir-symlink-followed | 3 | the install refuses a symlinked hooks directory (exit 2) |
+| short-sha-accepted | 2 | a remote object name of 0 is refused, not read as a new ref |
+
+- Real host: `bash scripts/slot-busy.sh` on the real `/proc` exited 1 on other seats' gate and `node
+  --test` runs, with no error line. Both live shell-snapshot wrappers on the host matched `RE_SNAPSHOT`.
+- Pins: `git grep -nE '[0-9a-f]{64}' -- 'packages/*/tests/*' 'scripts/test-*.sh'` gives 33 lines (the
+  positive control). None names a path this round changes. The only test that names one is
+  `scripts/test-git-guard.sh` itself, and no test reads `docs/TOOLS.md`.
+
+### Known limits after R3
+
+- The tag line in "Known limits" above is superseded by F3. The other two lines still hold.
+- The resolved-path refusal in `own_hooks` has no test of its own. A hooks directory that isn't a symlink
+  but resolves elsewhere needs a bind mount, so root, and the symlink check catches the symlink case first.
+  `hooks-dir-symlink-followed` turns off both checks together.
+- A wrapper that sources a test script into its own shell, with no child process, is still skipped, as
+  before R3. That script's children are still matched.
+- The installer's temporary file is named by pid (`.pre-push.install-git-hooks.$$`). R3 leaves it alone.
+- The "Runs" section above was written before any run. The R3 runs here are the ones on record for this
+  round.
+
+## R4, the lead's review of R3 (2026-11-02)
+
+The lead's implementation sub-agent (Claude Opus 5.5, a child of Sage's T3 c5c1e8ba) wrote this round from
+the brief `/mnt/storage/scratch/mosaic-lead/briefs/row211-r4-fix.md` and the review
+`/mnt/storage/scratch/mosaic-lead/reviews/row211-r3-gpt.md` (R1 to R3, Check 2 and Check 5). Base 09a847eda,
+branch `t3/row211-push-guard-r4-fix`: 5734c1a80, c8f2cb70c and 4f36e3c2e picked clean as bcd74ec33,
+3a121885c and 7d03f212d, then one R4 commit. The rule for the round: an error, a denied read or a doubt ends
+in exit 2 with no CLEAR line. The suite goes from 85 cases to 105 and the mutants from 21 to 30. The
+sections above stay as written; where R4 changes them, it says so here.
+
+### The gone check (R1 and R2)
+
+Both findings come down to one question: has this pid gone, or can the scan just not see it? `gone ROOT PID`
+in `slot-busy.sh` runs `ls -f -- ROOT` and is true only when that listing succeeds and PID isn't one of its
+names. It can't read a denied lookup as gone:
+
+- When the lookup failed because ROOT lost read or search permission, `ls` can't open ROOT, exits 2, and
+  `gone` is false.
+- When ROOT still lists but the pid's entry can't be read (a pid directory or cmdline at mode 000, or ROOT
+  readable but not searchable), the name is still in the listing, so `gone` is false. `ls -f` lists in
+  directory order without a stat of each name, so a name whose lookup is denied still appears.
+- `gone` is true only when the kernel's own listing of ROOT lacks the name. The name is compared with bash
+  string matching on the captured listing, not through a pipe, so a pipe failure can't become "absent".
+- `/proc` lists only thread group leaders. The scan's pids come from a listing of the same root, and an
+  ancestor's PPid is a thread group id, so the second listing compares like with like.
+
+### R1: every ancestor read counts
+
+Was: the walk read each ancestor's PPid with awk and ended on any failure (`|| p=""`). Only the scan's own
+read was checked, so a failed read further up dropped the rest of the ancestors without an error.
+
+Fix: every ancestor read must succeed and give a numeric PPid. On a failed read or a bad PPid the walk ends
+only when `gone /proc PID` confirms the ancestor exited. Anything else prints "cannot read the status of
+ancestor PID" and exits 2. The loop runs to PPid 0; `[ -n "$p" ]` went, since p is always numeric now. The
+scan's own read is unchanged.
+
+Tests: `awkn`, an awk shim that is the real awk on call 1 (the scan's own status) and then fails ("an
+ancestor's status read that fails after its own read passed: exit 2, no CLEAR"), prints nothing ("an
+ancestor's status with no PPid: exit 2, no CLEAR"), or on call 2 prints 4194999, above pid_max, which `/proc`
+never lists ("an ancestor that has exited (its pid gone from /proc) ends the walk: exit 0 and CLEAR", the
+control for the allowed path). Each checks the shim ran at least twice, three times for the exited case, so
+the failing read is an ancestor's and not the scan's own.
+
+Mutants: `ancestor-read-unchecked` (the error becomes `break`) and `exited-ancestor-error` (no gone check, so
+an exited ancestor is an error). Both killed.
+
+### R2: a denied lookup isn't a vanished process
+
+Was: after a failed cmdline read, `[ -e "$d" ] || continue` counted the process as exited. `[ -e ]` is false
+for a missing path and for a denied lookup alike. The loop also opened with `[ -d "$d" ] || continue`, the
+same flaw before the read.
+
+Fix: after a failed read, `gone "$PROC" "$pid" && continue`; anything else is an error and exit 2. The
+`[ -d ]` line is gone. The glob's literal when nothing matches fails the numeric pid test, and every listed
+pid now goes through the read and the gone check.
+
+The read is now `{ tr '\0' ' ' < "$d/cmdline"; } 2>/dev/null`. bash prints its own "No such file or
+directory" for a failed `<` before the `2>/dev/null` on the same command applies. Without the `[ -d ]` line
+that message showed on the real `/proc` for processes that exited mid-scan. The braces send it to
+`/dev/null`. The error count and the exit code never depended on it.
+
+Tests: `denytr`, a tr shim that sets the fake proc root to mode 000 at the read of pid 4194450 (a
+`node --test`) and fails: "a lookup denied after the listing (proc root mode 000): exit 2, no CLEAR", with
+the control "the denied pid directory and its node --test cmdline were still there". `locktr` sets the root to
+000 while 4194451 is read and lets that read pass; 4194452, a `node --test`, then can't be opened: "a proc
+root that turns unreadable after one read hides no later process: exit 2, no CLEAR". Each test gives the mode
+back right after its run, and the suite's cleanup runs `chmod 0755` on every directory in `LOCKED` before
+`rm -rf`.
+
+Mutants: `denied-lookup-vanished` (back to `[ -e "$d" ] || continue`), `denied-listing-gone` (a failed
+listing counts as gone) and `dir-check-skips` (the `[ -d ]` line back before the read). All killed.
+
+Two R3 mutants had the removed `[ -e "$d" ] || continue` line as their site. They now name the gone line,
+with the same intent: `unreadable-read-clear` skips every failed read, and `vanished-is-error` makes a
+confirmed exit an error. `snapshot-matched` now deletes the new snapshot line, which removes the whole wrapper
+exclusion as before. `snapshot-substring`'s site is unchanged.
+
+### R3: a wrapper that sources a test script
+
+Was: every command line in the snapshot-wrapper shape was skipped. A wrapper that sourced a test into its own
+shell, with no child, gave CLEAR while the test ran (the review's live probe).
+
+Fix: `match()` still recognizes the wrapper by `RE_SNAPSHOT`, then passes the rest of its text, after the
+snapshot source, to `sourced()`. That prints "sourced gate", "sourced mutant" or "sourced test script" when
+the text sources one, and fails otherwise. Children's command lines play no part. A wrapper that only runs
+other commands, an external node test included, is still skipped, and its child is still matched (F2, F5).
+
+What counts as sourced (`RE_SOURCED`): the word `source` or `.`, at the start of the text or after a blank,
+one of `; & | ( ) { }`, a backtick or a quote; then blanks; an optional `--` and blanks; an optional opening
+quote; then the path, up to the next blank, shell operator, `<`, `>` or quote. The path, padded with spaces,
+goes through the gate rule, the `*mutant*` rule and the test-script rule, in that order. Every such word in
+the text is checked, not only the first. That covers `source scripts/test-x.sh`, `. ./gate.sh 253`,
+`source "scripts/test-x.sh" arg`, `eval '. ./gate.sh 253'`, `eval 'source .../mutants.sh M3'`,
+`builtin source ...` and a test sourced after other files.
+
+False BUSY it can add: the text is read as words, not parsed. Inside a wrapper, `grep x . scripts/test-x.sh`,
+`git add . scripts/test-x.sh`, `ls . gate.sh`, `echo source scripts/test-x.sh` and `cat . notes-mutant.txt`
+all read as sourcing, and so does the same text in a heredoc or a comment. A false BUSY only delays a gate.
+Missed: a path from a variable or a substitution (`source "$f"`, `. "$(pwd)/scripts/test-x.sh"`), a quoted
+path with a space in it, a file that sources a test from inside it, and a function or alias that runs one.
+Those run in the wrapper's shell too, so they remain a gap (see the limits below).
+
+Tests: rule cases on the wrapper shape: "sourced test script" four times (`source`, `.`, a quoted path with an
+argument, and a test after a file that isn't one), "sourced gate" (`eval '. ./gate.sh 253'`) and "sourced
+mutant" (`eval 'source agents/x/work/queue-1/mutants.sh M3'`). Fake pid 4194406, a wrapper that sources
+`.venv/bin/activate` and `. ./env.sh` and then runs `./gate.sh 253` as a child: "a wrapper that sources other
+files and runs a gate as a child isn't a match". The new section "slot-busy, real snapshot wrappers" starts a
+live `bash -c "source $SANDBOX/shell-snapshots/snapshot-x.sh && source $SANDBOX/scripts/test-x.sh"` whose
+test-x.sh blocks in `read -t 60 -u 3` on a fifo, and confirms its children file reads and is empty: "a live
+wrapper that sourced a test script, blocked in a builtin with no child: exit 1", "its BUSY line names the
+wrapper's pid, the sourced rule and its cwd" and "the real /proc has a BUSY line for that wrapper too". Its
+control is a live wrapper that runs a stand-in `node --test` as a child: "a live wrapper that runs node --test
+as a child: exit 1 on the child's BUSY line" and "the wrapper itself has no BUSY line". The suite kills and
+reaps both wrappers and the child, and clears `KIDS` only after a confirmed reap.
+
+The first GREEN run found a defect the RED-time cases missed. In `sourced()`, the `RE_GATE` and `RE_TEST`
+tests reset `BASH_REMATCH`. After a sourced file that wasn't a rule, the next step read an unset
+`BASH_REMATCH[0]`, and the `$(match)` subshell died on `set -u`. 4194406 printed an error line, and a wrapper
+that sourced a test after another file would have been skipped. The match is now saved before the rule tests.
+The fourth "sourced test script" case was added after RED to pin this, with the `sourced-first-only` mutant.
+
+Mutants: `sourced-test-hidden` (the snapshot branch returns 1 again), `sourced-first-only` (only the first
+sourced word is checked) and `dot-source-missed` (`.` dropped from `RE_SOURCED`). All killed.
+
+### Item 4: the mutant runner's exit status
+
+Was: exit 0 after printing "survived" or "NO MATCH".
+
+Fix: `run()` sets `bad=1` on COPY FAILED, NO MATCH, survived, and a suite exit of 124 or 137 (timeout's codes
+after TERM and after KILL). The runner ends with `exit "$bad"`. A red base still stops it with exit 3. Every
+output line reads as before; the killed line takes its exit code from a saved `rc`.
+
+Hand check, in TMPDIR only: two copies of the runner with every `run` line taken out and one line put in
+before `exit "$bad"`. A comment-only edit to `slot-busy.sh` printed "comment-only: survived" and the copy
+exited 1 (20:07:55Z). A site that isn't in the file printed "no-such-site: NO MATCH" and the copy exited 1
+(20:08:02Z). A first try cut the copies short and lost the `exit "$bad"` line, so they exited 0. That was a
+fault in the copies, not the runner, and the faithful copies above replaced them. Nothing of the check is
+left in the runner.
+
+### Item 5: the installer's temporary file
+
+Was: `tmp="$HOOKS/.pre-push.install-git-hooks.$$"`, a name known in advance. `cp` writes through a symlink
+planted there.
+
+Fix: `stage()`, called just before each copy (the `--force-install` replacement and the new install), makes the
+file with `mktemp "$HOOKS/.pre-push.install-git-hooks.XXXXXX"` (O_EXCL, a random name), then copies the hook
+into it and sets 0755. It runs after both `own_hooks` checks and the hook-symlink refusal. A failed `mktemp`
+is exit 1, "cannot create a temporary file in HOOKS". The refusals and their order are as before, and a
+refusal now creates no file at all.
+
+Test: a fresh clone with a symlink at `.git/hooks/.pre-push.install-git-hooks.<pid>` pointing to a victim
+file, and the installer started by `exec` from a subshell whose `$BASHPID` is that pid: "the install writes
+nothing through a link planted at a pid-named temporary path" and "the installed hook is a regular file with
+the repository's bytes".
+
+Mutant: `installer-fixed-tmp` (the pid name back). Killed.
+
+### Item 6: a correction to known limit 2 after R3
+
+That line says the resolved-path refusal in `own_hooks` would need a bind mount to test. That is wrong.
+`cd -P` and `pwd -P` resolve symlinks only. A bind mount shows the same path, so the comparison passes a
+bind-mounted hooks directory; it can't be tested with a bind mount because it doesn't catch one. Once
+`[ ! -L "$HOOKS" ]` has passed, `cd -P "$HOOKS"` resolves the same parents as `cd -P "$common"` plus
+`/hooks`, so the comparison fires only if the path changes between the two checks. The R3 text stays as it
+was written; this entry supersedes it.
+
+### What didn't change
+
+`scripts/git-hooks/pre-push` is untouched. Empty stdin passes, a new branch and a fast-forward pass, deletes
+and non-fast-forwards are refused, an existing tag can't change, and a remote tip missing locally is refused
+with fetch advice and no fetch. Those cases pass unchanged in GREEN. `docs/TOOLS.md` now gives 105 cases,
+the sourced-wrapper rule, the gone condition on exit 2 and the installer's `mktemp` file.
+
+### R4 runs
+
+`TMPDIR` was a fresh `mktemp -d /mnt/storage/scratch/tmp/XXXXXX`. Every run was in the foreground under
+`timeout -k 10 1800`, with output to files there.
+
+- RED, all new tests in place and no fix, 19:57:25Z to 19:57:37Z: 90 passed, 14 failed. The 14: the two
+  installer temporary-file cases, five sourced rule cases, two ancestor cases (fail, empty), two denied-lookup
+  cases and the three live sourced-wrapper cases. The five new cases that pass there are controls that must
+  hold before and after: 4194406, the exited ancestor, the denied pid directory still there, and the external
+  node wrapper's two cases.
+- GREEN, first run, 20:01:11Z to 20:01:25Z: 101 passed, 3 failed ("no matching process: exit 0 and CLEAR",
+  "a process that vanishes during its read isn't an error: exit 0 and CLEAR" and "an ancestor that has exited
+  (its pid gone from /proc) ends the walk: exit 0 and CLEAR"). All three share the fake root that holds
+  4194406, whose error line from the `BASH_REMATCH` defect above broke the exact CLEAR output. Fixed, and one
+  rule case added.
+- GREEN, 20:02:40Z to 20:02:49Z: 105 passed, 0 failed.
+- Mutants, 20:02:56Z to 20:06:58Z: base green (105/0), runner exit 0, 30 of 30 killed, none survived, no NO
+  MATCH, no timeout. Every kill exited 1.
+
+| Mutant | FAIL | First failing case |
+|---|---|---|
+| ancestor-dropped | 8 | push --force of a rewritten branch is refused |
+| unknown-object-passes | 2 | a push over a remote tip missing locally is refused, saying fetch first |
+| delete-passes | 13 | the install into a clean clone exits 0 |
+| install-over-hookspath | 2 | it says core.hooksPath is set |
+| busy-exits-0 | 23 | a node --test process: exit 1 |
+| differing-hook-replaced | 3 | the install refuses a different installed pre-push (exit 2) |
+| replace-in-place | 1 | the replacement was a rename: the old file keeps its bytes |
+| symlink-followed | 1 | the install refuses a symlinked pre-push, even with --force-install |
+| ancestor-error-passes | 1 | a failed ancestor check (an unknown local object) is refused |
+| snapshot-matched | 14 | no matching process: exit 0 and CLEAR |
+| ancestors-matched | 1 | this suite, an ancestor, has no BUSY line |
+| no-node-rule | 10 | a node --test process: exit 1 |
+| no-compose-rule | 2 | busy on: docker compose -p x up -d (docker compose) |
+| unreadable-read-clear | 8 | a pid directory with no cmdline: exit 2 |
+| vanished-is-error | 3 | a process that vanishes during its read isn't an error: exit 0 and CLEAR |
+| read-errors-ignored | 8 | a pid directory with no cmdline: exit 2 |
+| self-read-unchecked | 1 | its own process unreadable (awk exits 1): exit 2, no CLEAR |
+| snapshot-substring | 2 | busy on: node --test /seat/tests/shell-snapshots/snapshot-guard.test.mjs (node --test) |
+| tag-replace-passes | 4 | push --force of a new tag object on the same commit is refused |
+| hooks-dir-symlink-followed | 3 | the install refuses a symlinked hooks directory (exit 2) |
+| short-sha-accepted | 2 | a remote object name of 0 is refused, not read as a new ref |
+| ancestor-read-unchecked | 2 | an ancestor's status read that fails after its own read passed: exit 2, no CLEAR |
+| exited-ancestor-error | 1 | an ancestor that has exited (its pid gone from /proc) ends the walk: exit 0 and CLEAR |
+| denied-lookup-vanished | 2 | a lookup denied after the listing (proc root mode 000): exit 2, no CLEAR |
+| denied-listing-gone | 2 | a lookup denied after the listing (proc root mode 000): exit 2, no CLEAR |
+| dir-check-skips | 1 | a proc root that turns unreadable after one read hides no later process: exit 2, no CLEAR |
+| sourced-test-hidden | 9 | busy on: /bin/bash -c source /home/u/.claude/shell-snapshots/snapshot-bash-1.sh && source /seat |
+| sourced-first-only | 1 | busy on: /bin/bash -c source /home/u/.claude/shell-snapshots/snapshot-bash-1.sh && source .venv |
+| dot-source-missed | 3 | busy on: /bin/bash -c source /home/u/.claude/shell-snapshots/snapshot-bash-1.sh && . /seat/scri |
+| installer-fixed-tmp | 2 | the install writes nothing through a link planted at a pid-named temporary path |
+
+The runner cuts each first failing case at 100 characters, which is why three of them end mid-word.
+
+- Real host: `bash scripts/slot-busy.sh` on the real `/proc` exited 1 on other seats' runs, which the brief
+  expects. Before the brace fix it also printed bash's "No such file or directory" for processes that exited
+  mid-scan; after it, none.
+- Pins: `git grep -nE '[0-9a-f]{64}' -- 'packages/*/tests/*' 'scripts/test-*.sh'` gives 33 lines (the
+  positive control). None names a path this round changes, and none holds the old or new sha256 or blob id of
+  the four changed scripts. No test reads `docs/TOOLS.md` or this file.
+
+### Known limits after R4
+
+- `git push --no-verify` skips the hook. Gitea branch protection is the guard that holds (unchanged).
+- The busy rules read command lines as text. They can call a process BUSY that isn't a run, the sourced rule
+  adds the false BUSY cases above, and a test sourced by a path built at run time, by a nested file or by a
+  function is still missed.
+- A bind-mounted hooks directory isn't detected (item 6). A mount-point test, such as the hooks directory's
+  st_dev against its parent's, would catch one. Setting one up needs root. Not this round.
+- The installer has a check-then-use window after its path checks, as the review's Check 5 says. An actor who
+  can replace repository directories in it already controls the hooks.
+- A BUSY line holds the command line as it is, so a wrapper whose `-c` text has newlines prints over several
+  output lines. Chain on the exit code, never on the lines (unchanged advice).
+- The scan sees only what `/proc` lists to it. Under `hidepid=2`, another user's processes aren't listed and
+  can't make it BUSY. This host's `/proc` has no hidepid option.
@@ -0,0 +1,101 @@
+#!/usr/bin/env bash
+# Row 211 (#426) mutants. Run from the candidate worktree's root:
+#   TMPDIR=<scratch dir> LOG=<dir> bash agents/darkwing/work/queue-211/mutants.sh > mutants.txt
+# Each mutant copies the four row-211 scripts into its own tree, edits one
+# site there (exactly one match, else NO MATCH), and runs that tree's
+# scripts/test-git-guard.sh under a 180 s timeout. The worktree's files are
+# never edited. "killed" means the suite failed; "survived" means it passed.
+# The unmutated suite runs first, and a red base stops the run (exit 3).
+# Exit 0 only when every mutant is killed; 1 when any survives, has NO MATCH
+# or COPY FAILED, or times out (suite exit 124 or 137, still printed as
+# killed with that exit code).
+set -u
+LOG=${LOG:-.}
+FILES="scripts/git-hooks/pre-push scripts/install-git-hooks.sh scripts/slot-busy.sh scripts/test-git-guard.sh"
+WORK=$(mktemp -d "${TMPDIR:-/tmp}/r211-mutants.XXXXXX") || exit 2
+trap 'rm -rf "$WORK"' EXIT
+
+tree() { # $1: name. Prints the copy's root.
+  local t="$WORK/$1" f
+  for f in $FILES; do mkdir -p "$t/$(dirname "$f")" && cp -p -- "$f" "$t/$f" || return 1; done
+  echo "$t"
+}
+suite() { # $1: tree, $2: log
+  timeout -k 10 180 bash "$1/scripts/test-git-guard.sh" > "$2" 2>&1
+}
+edit() { # $1: file, $2: from, $3: to. Exit 3 unless $2 occurs exactly once.
+  python3 -B - "$1" "$2" "$3" <<'PY'
+import sys
+path, old, new = sys.argv[1:4]
+text = open(path).read()
+if text.count(old) != 1:
+    sys.exit(3)
+open(path, "w").write(text.replace(old, new))
+PY
+}
+
+base=$(tree base) || exit 2
+if [ -n "${DRY:-}" ]; then
+  echo "base: not run (DRY)"
+elif suite "$base" "$LOG/mut-base.log"; then
+  echo "base: green ($(tail -1 "$LOG/mut-base.log"))"
+else
+  echo "base: RED, stopping ($(tail -1 "$LOG/mut-base.log"))"
+  exit 3
+fi
+
+bad=0
+run() { # $1: name, $2: file, $3: from, $4: to
+  local name=$1 file=$2 t log rc
+  t=$(tree "$name") || { echo "$name: COPY FAILED"; bad=1; return; }
+  if ! edit "$t/$file" "$3" "$4"; then echo "$name: NO MATCH"; bad=1; return; fi
+  if [ -n "${DRY:-}" ]; then echo "$name: match"; return; fi
+  log="$LOG/mut-$name.log"
+  if suite "$t" "$log"; then
+    echo "$name: survived"
+    bad=1
+  else
+    rc=$?
+    echo "$name: killed (exit $rc, $(grep -c '^FAIL' "$log") FAIL; first: $(grep -m1 '^FAIL' "$log" | cut -c6-100))"
+    case $rc in 124|137) bad=1 ;; esac
+  fi
+}
+H=scripts/git-hooks/pre-push
+I=scripts/install-git-hooks.sh
+S=scripts/slot-busy.sh
+
+# The brief's five.
+run ancestor-dropped $H $'    git merge-base --is-ancestor "$rsha" "$lsha" 2>/dev/null\n    rc=$?' '    rc=0'
+run unknown-object-passes $H $'        refuse "$rref: the remote tip $rsha isn\'t in this repository; fetch first, then push again"\n        continue' '        continue'
+run delete-passes $H $'        refuse "$rref: a delete (remote $rsha); seat branches are never deleted by push"\n        continue' '        continue'
+run install-over-hookspath $I '[ -z "$out" ] || die 2 "refused: core.hooksPath' '[ -z "$out" ] || true || die 2 "refused: core.hooksPath'
+run busy-exits-0 $S 'if [ "$busy" = 1 ]; then exit 1; fi' 'if [ "$busy" = 1 ]; then exit 0; fi'
+# Further sites the suite pins.
+run differing-hook-replaced $I '[ "$FORCE" = 1 ] || die 2 "refused: a different' 'true || die 2 "refused: a different'
+run replace-in-place $I 'mv -f -- "$tmp" "$HOOK" ||' 'cat -- "$tmp" > "$HOOK" && rm -f -- "$tmp" ||'
+run symlink-followed $I 'if [ -L "$HOOK" ]; then die 2' 'if false; then die 2'
+run ancestor-error-passes $H '        *) refuse "$rref: the ancestor check failed' '        *) : "$rref: the ancestor check failed'
+run snapshot-matched $S $'  if [[ "$c" =~ $RE_SNAPSHOT ]]; then sourced "${c:${#BASH_REMATCH[0]}}"; return; fi\n' ''
+run ancestors-matched $S '  [ -z "${SKIP[$pid]:-}" ] || continue' '  :'
+run no-node-rule $S 'if [[ "$c" =~ $RE_NODE ]]; then echo "node --test"; return 0; fi' ':'
+run no-compose-rule $S 'if [[ "$c" =~ $RE_COMPOSE ]]; then echo "docker compose"; return 0; fi' ':'
+# R3, the GPT review (F1 to F5 and the object-name length check).
+run unreadable-read-clear $S '    gone "$PROC" "$pid" && continue' '    continue'
+run vanished-is-error $S $'    gone "$PROC" "$pid" && continue\n' ''
+run read-errors-ignored $S '[ "$errors" = 0 ] || {' 'true || {'
+run self-read-unchecked $S '  || { echo "slot-busy: error: cannot read its own process" >&2; exit 2; }' '  || p=""'
+run snapshot-substring $S '[[ "$c" =~ $RE_SNAPSHOT ]]' '[[ "$c" == *"/shell-snapshots/snapshot-"* ]]'
+run tag-replace-passes $H 'if [ "${rref#refs/tags/}" != "$rref" ] && [ "$lsha" != "$rsha" ]; then' 'if false; then'
+run hooks-dir-symlink-followed $I 'own_hooks() {' 'own_hooks() { return 0;'
+run short-sha-accepted $H '    if ! idlen "$lsha" || ! idlen "$rsha"; then' '    if false; then'
+# R4 (the lead's review of R3: R1 to R3 and the installer's temporary file).
+run ancestor-read-unchecked $S $'    gone /proc "$p" && break\n    echo "slot-busy: error: cannot read the status of ancestor $p" >&2; exit 2' '    break'
+run exited-ancestor-error $S '    gone /proc "$p" && break' '    :'
+run denied-lookup-vanished $S '    gone "$PROC" "$pid" && continue' '    [ -e "$d" ] || continue'
+run denied-listing-gone $S 'names=$(ls -f -- "$1" 2>/dev/null) || return 1' 'names=$(ls -f -- "$1" 2>/dev/null) || return 0'
+run dir-check-skips $S $'  pid=${d##*/}\n' $'  [ -d "$d" ] || continue\n  pid=${d##*/}\n'
+run sourced-test-hidden $S 'then sourced "${c:${#BASH_REMATCH[0]}}"; return; fi' 'then return 1; fi'
+run sourced-first-only $S '    rest=${rest#*"$m"}' '    break'
+run dot-source-missed $S '(source|\\.)[[:space:]]+' '(source)[[:space:]]+'
+run installer-fixed-tmp $I '  tmp=$(mktemp "$HOOKS/.pre-push.install-git-hooks.XXXXXX") || die 1 "cannot create a temporary file in $HOOKS"' '  tmp="$HOOKS/.pre-push.install-git-hooks.$$"'
+exit "$bad"
@@ -1879,3 +1879,6 @@ are never rewritten or removed; corrections are new entries.
 2026-10-26 | Sage | mos1884/#662 scope after330/331landing | ReadQ222/Q261/Q263 and659/660/662; posted bounded human-only factory settings/triage/defaulttwo-roundmandate/trackedno-exemptionflake scope with10acceptance criteria, task662comment1338 exactwholebody/author13GETverified. No implementation/review/gate launched.660c1335notready(review/merge, noVM); gatefacts1329/1334 retained; target integration/fullrunner confirmation follows readiness, no localfallback. Landedproduct/evidence unchanged;657/658backlog.

 2026-10-26 | Sage | Mos1909/1915/1917 real postlanding reviews | Boyd/Dewey/Filbert/Gladstone real authored candidate52ba verdictfiles independently byte/hash-verified, allAPPROVE scoped; Dewey656broaderPARTIAL retained. Formal330R1/331R4 requests failedpre-send/no comments or approvals; no borrowed/copied/mintedkeys. LegacyhelperGETname jason.woltje is NOT ownJarvis, ownslotabsent; rows tracking-open/#436, files cited via normalqueue. NewFilbertNEW-330-01 filedtask665 exactreadback, notlandingreopen/gate. Repair646-648/652-656 remainOPEN untilactualcomments;1917 conditionalbacklog routing retained. #662scope1338posted;660PR405REVISE/notready. Product1968inputs unchanged; no source/helper/test/gate edits/runs; peerjournal prefixes preserved.
+
+2026-11-02 | Sage implementation sub-agent (Claude Opus 5.5, child of T3 c5c1e8ba) | row 211 (#1709/#426) R3 from the GPT review, on t3/row211-push-guard-r3-fix over 09a847eda (picks 5734c1a80, c8f2cb70c) | F1-F5 and the object-name length check fixed with tests; suite RED 67/18, GREEN 85/0; 21 of 21 mutants killed; one local commit, not pushed
+2026-11-02 | Sage implementation sub-agent (Claude Opus 5.5, child of T3 c5c1e8ba) | row 211 (#1709/#426) R4 from the GPT review of R3, on t3/row211-push-guard-r4-fix over 09a847eda (picks bcd74ec33, 3a121885c, 7d03f212d) | R1-R3, runner exit status and installer mktemp fixed with tests; suite RED 90/14, GREEN 105/0; 30 of 30 mutants killed, runner exit 0; one local commit, not pushed
@@ -166,8 +166,46 @@ resolved through the CLI.
 | `scripts/test-conductor.sh` | Auto-apply selftests (sandboxed) | 17 cases |
 | `scripts/test-auth.sh` | Auth checkpoint selftests (no Docker) | 13 cases |
 | `scripts/test-land-work.sh` | Land-work selftests (sandboxed, fake Docker) | 84 cases |
+| `scripts/test-git-guard.sh` | Push guard, its installer and `slot-busy.sh` (scratch bare remote, fake `/proc`) | 105 cases |
+| `scripts/install-git-hooks.sh [--repo DIR] [--force-install]` | Install the push guard as `pre-push` in the common `.git/hooks` | Refuses a set `core.hooksPath`, a symlinked hooks directory or a different installed hook; exit 0 ok · 1 failed · 2 refused · 4 usage |
+| `scripts/slot-busy.sh` | Busy check: one `BUSY` line per gate or test process, or `CLEAR` | Exit 0 CLEAR · 1 BUSY · 2 error, including a process or an ancestor it can't read that isn't confirmed gone; chain on the exit code |
 | `scripts/gitea-api.sh <METHOD> <path> [body]` | Gitea API helper; reads the JSON credential file or a raw per-seat token file | Token never on argv/stdout |

+### Push guard and busy check (row 211, #426)
+
+`scripts/git-hooks/pre-push` refuses a push that deletes a branch, or that
+moves a branch to a commit that doesn't descend from the remote tip (a
+`--force`, `--force-with-lease` or `+refspec` push of a rewritten branch). A
+new branch and a fast-forward pass. It refuses any change to an existing tag,
+including a new tag object on the same commit; a new tag passes. The hook
+fetches nothing: when the remote tip isn't in the local repository it refuses
+and says to fetch first.
+`git push --no-verify` skips it, so Gitea's branch protection (ops-01) is the
+guard that holds. `scripts/install-git-hooks.sh` copies it into the common
+`.git/hooks`, which every worktree of the checkout shares, refusing a hooks
+directory that is a symlink. It stages the bytes in a new file that `mktemp`
+makes in that directory, then runs a canary
+through `git hook run`. Installing it in the canonical checkout is a step for
+the lead after the row lands.
+
+Chain the busy check on its exit code, and set `pipefail` in any script that
+pipes it:
+
+```bash
+bash scripts/slot-busy.sh > "$LOG" && gate
+```
+
+Never `bash scripts/slot-busy.sh | tail -1 && gate`: `tail` exits 0, so the
+gate runs while BUSY. It matches `node ... --test`, a `*gate*.sh`, `mutant`, a
+`test-*.sh` and `docker compose` command lines, skips itself, its ancestors
+and agent shell-snapshot wrappers (a shell whose `-c` text starts by sourcing
+`.../shell-snapshots/snapshot-*.sh`). A wrapper whose text also sources
+(`source` or `.`) a gate, test or mutant script is BUSY, because that script
+runs in the wrapper's own shell. It reads only `/proc/<pid>/cmdline`, the cwd
+link, its own and its ancestors' `status` and, after a failed read, the proc
+root's listing. A process or an ancestor it can't read makes it exit 2, never
+CLEAR, unless a listing of the proc root succeeds and no longer has that pid.
+
 ## Seat launch with registration (`scripts/mosaic`)

 ```bash
@@ -0,0 +1,64 @@
+#!/bin/sh
+# Mosaic push guard (row 211, #426). Installed as pre-push in the common
+# .git/hooks by `scripts/install-git-hooks.sh`; never edit the installed copy.
+# For each ref git is about to push, it refuses a delete and any update whose
+# remote tip isn't an ancestor of the local tip: a force-push or a +refspec.
+# It refuses any change to an existing tag, and an object name that isn't 40
+# or 64 hex characters. A new ref passes. It fetches nothing, so a remote tip
+# that isn't in this repository refuses. Any failure of the check refuses too.
+# `git push --no-verify` skips this hook; Gitea's branch protection is the
+# guard that holds (ops-01). Canon: never force-push.
+refused=0
+refuse() {
+    echo "mosaic push guard: refused: $*" >&2
+    refused=1
+}
+zero() {
+    case "$1" in *[!0]*) return 1 ;; esac
+    return 0
+}
+idlen() { # $1: an object name. True at 40 (SHA-1) or 64 (SHA-256) characters.
+    [ "${#1}" -eq 40 ] || [ "${#1}" -eq 64 ]
+}
+while read -r lref lsha rref rsha extra || [ -n "${lref:-}" ]; do
+    if [ -z "${rsha:-}" ] || [ -n "${extra:-}" ]; then
+        refuse "unreadable ref line from git: $lref ${lsha:-} ${rref:-} ${rsha:-} ${extra:-}"
+        continue
+    fi
+    case "$lsha$rsha" in
+        *[!0-9a-f]*) refuse "$rref: a ref line with a non-hex object name (local $lsha, remote $rsha)"; continue ;;
+    esac
+    if ! idlen "$lsha" || ! idlen "$rsha"; then
+        refuse "$rref: a ref line with an object name that isn't 40 or 64 hex characters (local $lsha, remote $rsha)"
+        continue
+    fi
+    if zero "$lsha"; then
+        refuse "$rref: a delete (remote $rsha); seat branches are never deleted by push"
+        continue
+    fi
+    if zero "$rsha"; then
+        continue
+    fi
+    # An existing tag never changes. A new tag object on the same commit, or
+    # a tag moved to a descendant, would pass the ancestor check below.
+    if [ "${rref#refs/tags/}" != "$rref" ] && [ "$lsha" != "$rsha" ]; then
+        refuse "$rref: an existing tag can't be moved or replaced (remote $rsha, local $lsha); push a new tag instead"
+        continue
+    fi
+    if ! git cat-file -e "$rsha^{commit}" 2>/dev/null; then
+        refuse "$rref: the remote tip $rsha isn't in this repository; fetch first, then push again"
+        continue
+    fi
+    git merge-base --is-ancestor "$rsha" "$lsha" 2>/dev/null
+    rc=$?
+    case $rc in
+        0) ;;
+        1) refuse "$rref: not a fast-forward; remote $rsha isn't an ancestor of local $lsha (a force-push or a rewritten branch)" ;;
+        *) refuse "$rref: the ancestor check failed (exit $rc) for remote $rsha and local $lsha" ;;
+    esac
+done
+if [ "$refused" != 0 ]; then
+    echo "mosaic push guard: nothing was pushed; a pushed branch only moves forward (canon: never force-push)" >&2
+    exit 1
+fi
+exit 0
@@ -0,0 +1,120 @@
+#!/usr/bin/env bash
+# install-git-hooks.sh: install the push guard (row 211, #426) as pre-push in
+# a repository's common .git/hooks, which every linked worktree shares.
+#
+# Usage:
+#   scripts/install-git-hooks.sh [--repo DIR] [--force-install]
+#
+# DIR defaults to this script's own checkout. The hook's bytes are this
+# checkout's scripts/git-hooks/pre-push. It refuses when core.hooksPath is set
+# (git would not run the hook), when the hooks directory is a symlink or
+# resolves anywhere but the common directory's hooks, and when a different
+# pre-push is installed, unless --force-install is given. It never edits an
+# installed hook in place:
+# a new hook is linked in, a replacement is renamed over the old one. The
+# bytes go first into a new file that mktemp makes in the hooks directory, so
+# nothing planted there in advance is written through. A canary then runs the
+# installed hook through git and needs a delete refused.
+#
+# Exit codes: 0 installed (or already the same bytes); 1 failed; 2 refused;
+# 4 usage. Installing in the canonical checkout is its own step with the lead.
+set -uo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd -P)"
+SRC="$ROOT/scripts/git-hooks/pre-push"
+TMPD=""
+
+say() { printf 'install-git-hooks: %s\n' "$*" >&2; }
+die() { local code=$1; shift; say "$*"; exit "$code"; }
+cleanup() { if [ -n "$TMPD" ]; then rm -rf -- "$TMPD"; fi; }
+trap cleanup EXIT
+
+usage() {
+  sed -n '5,6p' "${BASH_SOURCE[0]}" | sed 's/^# \{0,1\}//' >&2
+  exit 4
+}
+
+REPO=$ROOT
+FORCE=0
+while [ $# -gt 0 ]; do
+  case "$1" in
+    --repo) [ $# -ge 2 ] || usage; REPO=$2; shift 2 ;;
+    --force-install) FORCE=1; shift ;;
+    -h|--help) usage ;;
+    *) say "unknown argument: $1"; usage ;;
+  esac
+done
+
+for v in GIT_DIR GIT_WORK_TREE GIT_COMMON_DIR GIT_INDEX_FILE GIT_OBJECT_DIRECTORY GIT_ALTERNATE_OBJECT_DIRECTORIES; do
+  if [ -n "${!v+x}" ]; then die 2 "refused: $v is set; run with the normal git environment"; fi
+done
+[ -f "$SRC" ] && [ ! -L "$SRC" ] || die 2 "refused: $SRC is missing or not a regular file"
+
+g() { git -C "$REPO" "$@"; }
+top=$(g rev-parse --show-toplevel 2>/dev/null) || die 2 "refused: $REPO is not a git checkout"
+common=$(g rev-parse --path-format=absolute --git-common-dir) || die 1 "cannot read $REPO's git common directory"
+HOOKS="$common/hooks"
+HOOK="$HOOKS/pre-push"
+
+out=$(g config --show-scope --get-all core.hooksPath 2>/dev/null)
+[ -z "$out" ] || die 2 "refused: core.hooksPath is set ($(printf '%s' "$out" | tr '\n\t' '; ')), so git would not run the push guard; unset it first"
+
+# The hooks directory must be the common directory's own. Through a symlink
+# to a shared directory, the install would set the hook of every repository
+# that shares it. Checked before and after mkdir, before any file is written.
+own_hooks() {
+  local real want
+  [ ! -L "$HOOKS" ] || die 2 "refused: $HOOKS is a symlink; install only into the repository's own hooks directory"
+  [ -e "$HOOKS" ] || return 0
+  real=$(cd -P -- "$HOOKS" && pwd -P) && want="$(cd -P -- "$common" && pwd -P)/hooks" || die 1 "cannot resolve $HOOKS"
+  [ "$real" = "$want" ] || die 2 "refused: $HOOKS resolves to $real, not $want"
+}
+own_hooks
+if [ -L "$HOOK" ]; then die 2 "refused: $HOOK is a symlink; remove it by hand if it is not wanted"; fi
+mkdir -p "$HOOKS" || die 1 "cannot create $HOOKS"
+own_hooks
+# The hook's bytes in a new file that mktemp creates (O_EXCL, a random name)
+# in the checked hooks directory, made only once a copy is due.
+stage() {
+  tmp=$(mktemp "$HOOKS/.pre-push.install-git-hooks.XXXXXX") || die 1 "cannot create a temporary file in $HOOKS"
+  cp -- "$SRC" "$tmp" && chmod 0755 "$tmp" || { rm -f -- "$tmp"; die 1 "cannot write $tmp"; }
+}
+if [ -e "$HOOK" ]; then
+  [ -f "$HOOK" ] || die 2 "refused: $HOOK is not a regular file"
+  if cmp -s "$SRC" "$HOOK"; then
+    chmod 0755 "$HOOK" || die 1 "chmod failed"
+    note="the same bytes were already there"
+  else
+    [ "$FORCE" = 1 ] || die 2 "refused: a different pre-push hook is installed at $HOOK; compare it with $SRC, and pass --force-install to replace it"
+    stage
+    # rename() swaps the whole file; the old hook's bytes are never edited.
+    mv -f -- "$tmp" "$HOOK" || { rm -f -- "$tmp"; die 1 "cannot replace $HOOK"; }
+    note="replaced a different hook (--force-install)"
+  fi
+else
+  stage
+  # link() never replaces, so a hook that appeared meanwhile is kept.
+  if ! ln -- "$tmp" "$HOOK" 2>/dev/null; then rm -f -- "$tmp"; die 2 "refused: a pre-push hook appeared at $HOOK while installing"; fi
+  rm -f -- "$tmp"
+  note="new"
+fi
+
+cmp -s "$SRC" "$HOOK" || die 1 "$HOOK differs from $SRC after install"
+[ -x "$HOOK" ] || die 1 "$HOOK is not executable after install"
+
+# The canary: git runs the hook it would run for a push. A delete line needs
+# no objects; the guard must refuse it, and pass an empty push.
+TMPD=$(mktemp -d "${TMPDIR:-/tmp}/install-git-hooks.XXXXXX") || die 1 "mktemp failed"
+z=0000000000000000000000000000000000000000
+printf '(delete) %s refs/heads/install-canary 1%s\n' "$z" "${z#0}" > "$TMPD/delete"
+: > "$TMPD/empty"
+if ! out=$(cd "$top" && git hook run --to-stdin="$TMPD/empty" pre-push -- canary canary 2>&1); then
+  die 2 "refused: the canary's empty push failed, so git is not running the push guard as installed: $out"
+fi
+out=$(cd "$top" && git hook run --to-stdin="$TMPD/delete" pre-push -- canary canary 2>&1); rc=$?
+[ "$rc" -ne 0 ] && [[ "$out" == *"mosaic push guard: refused"* ]] \
+  || die 2 "refused: the canary's delete was not refused by the push guard (exit $rc)"
+
+printf 'ok installed the push guard at %s (%s, sha256 %s, mode 0755); canary passed\n' \
+  "$HOOK" "$note" "$(sha256sum < "$HOOK" | cut -d' ' -f1)"
+exit 0
@@ -0,0 +1,131 @@
+#!/usr/bin/env bash
+# slot-busy.sh: the shared busy check (row 211, #426). Is a gate or a test run
+# going on this host?
+#
+# Usage:
+#   scripts/slot-busy.sh [--proc-root DIR]
+#
+# It prints one BUSY line per matching process, or one CLEAR line. Exit codes:
+# 0 CLEAR, 1 BUSY, 2 its own error, which includes a process or an ancestor
+# it can't read that isn't confirmed gone (it still prints any BUSY lines,
+# never CLEAR). Gone means a listing of the proc root that succeeds and lacks
+# the pid. Chain it on the exit code, never on a filter of its output:
+#   bash scripts/slot-busy.sh > LOG && gate          (set -o pipefail if piped)
+# never `bash scripts/slot-busy.sh | tail -1 && gate`, which runs while BUSY.
+#
+# A process matches when its command line holds `node ... --test`, a
+# `*gate*.sh`, `mutant`, a `test-*.sh` or `docker compose`/`docker-compose`.
+# It skips itself and its ancestors (a gate script may run the check), and an
+# agent harness's shell-snapshot wrapper (`bash -c 'source .../shell-snapshots/
+# snapshot-*.sh ...'`), whose command line is the agent's command text; that
+# shell's real children are still matched, and so is any other command line
+# that only names a shell-snapshots path. A wrapper whose text after the
+# snapshot source also sources (`source` or `.`) a gate, test or mutant
+# script runs it in its own shell, so that wrapper is BUSY. It reads only
+# /proc/<pid>/cmdline, the cwd link, its own and its ancestors'
+# /proc/<pid>/status and, after a failed read, the proc root's listing, never
+# a file under a seat's directory.
+# --proc-root names a stand-in for /proc in the selftests.
+set -uo pipefail
+
+PROC=/proc
+while [ $# -gt 0 ]; do
+  case "$1" in
+    --proc-root) [ $# -ge 2 ] || { echo "slot-busy: error: --proc-root needs a directory" >&2; exit 2; }; PROC=$2; shift 2 ;;
+    -h|--help) sed -n '5,6p' "${BASH_SOURCE[0]}" | sed 's/^# \{0,1\}//' >&2; exit 2 ;;
+    *) echo "slot-busy: error: unknown argument: $1" >&2; exit 2 ;;
+  esac
+done
+[ -d "$PROC" ] || { echo "slot-busy: error: $PROC is not a directory" >&2; exit 2; }
+
+# gone ROOT PID: true only when ROOT lists and PID isn't in the listing. A
+# failed or denied listing is false: a lookup that fails can't tell an exited
+# process from one it may not see. `ls -f` reads the names only, no stat.
+gone() {
+  local names
+  names=$(ls -f -- "$1" 2>/dev/null) || return 1
+  [[ $'\n'"$names"$'\n' != *$'\n'"$2"$'\n'* ]]
+}
+
+# This process and its ancestors, from the real /proc. Every status read must
+# give a numeric PPid. An ancestor that exited (confirmed gone) ends the walk;
+# any other failed read is an error, never a shorter walk.
+declare -A SKIP=()
+p=$(awk '/^PPid:/{print $2; exit}' "/proc/$$/status" 2>/dev/null) && [[ "$p" =~ ^[0-9]+$ ]] \
+  || { echo "slot-busy: error: cannot read its own process" >&2; exit 2; }
+SKIP[$$]=1
+while [ "$p" != 0 ]; do
+  SKIP[$p]=1
+  if ! q=$(awk '/^PPid:/{print $2; exit}' "/proc/$p/status" 2>/dev/null) || ! [[ "$q" =~ ^[0-9]+$ ]]; then
+    gone /proc "$p" && break
+    echo "slot-busy: error: cannot read the status of ancestor $p" >&2; exit 2
+  fi
+  p=$q
+done
+
+RE_NODE='[ /]node[^ ]* (.* )?--test '
+RE_GATE='[ /_-]gate[^ /]*\.sh '
+RE_TEST='[ /]test-[^ /]*\.sh '
+RE_COMPOSE='[ /]docker( compose|-compose) '
+# The wrapper's shape: a shell, its options with -c, then `source` (or `.`)
+# of a shell-snapshots/snapshot-*.sh file as the first command.
+RE_SNAPSHOT='^ (/[^ ]*/)?(ba|z)?sh( -[a-zA-Z]+)* -[a-zA-Z]*c[a-zA-Z]*( -[a-zA-Z]+)* (source|\.) [^ ]*/shell-snapshots/snapshot-[^ /]*\.sh '
+# A sourced file in the wrapper's text: `source` or `.` after the start, a
+# blank, a shell operator or a quote, then blanks, an optional `--`, an
+# optional opening quote and the path, up to a blank, operator or quote.
+RE_SOURCED="(^|[[:space:];&|(){}\`'\"])(source|\\.)[[:space:]]+(--[[:space:]]+)?['\"]?([^[:space:];&|<>(){}\`'\"]+)"
+sourced() { # $1: the wrapper's text after the snapshot source. Prints the rule.
+  local rest=$1 m f
+  while [[ "$rest" =~ $RE_SOURCED ]]; do
+    # Saved first: the rule tests below reset BASH_REMATCH.
+    m=${BASH_REMATCH[0]} f=" ${BASH_REMATCH[4]} "
+    if [[ "$f" =~ $RE_GATE ]]; then echo "sourced gate"; return 0; fi
+    if [[ "$f" == *mutant* ]]; then echo "sourced mutant"; return 0; fi
+    if [[ "$f" =~ $RE_TEST ]]; then echo "sourced test script"; return 0; fi
+    rest=${rest#*"$m"}
+  done
+  return 1
+}
+match() { # $1: the command line, NULs as spaces. Prints the rule that matched.
+  local c=" $1 "
+  if [[ "$c" =~ $RE_SNAPSHOT ]]; then sourced "${c:${#BASH_REMATCH[0]}}"; return; fi
+  if [[ "$c" =~ $RE_NODE ]]; then echo "node --test"; return 0; fi
+  if [[ "$c" =~ $RE_GATE ]]; then echo "gate"; return 0; fi
+  if [[ "$c" == *mutant* ]]; then echo "mutant"; return 0; fi
+  if [[ "$c" =~ $RE_TEST ]]; then echo "test script"; return 0; fi
+  if [[ "$c" =~ $RE_COMPOSE ]]; then echo "docker compose"; return 0; fi
+  return 1
+}
+
+seen=0
+busy=0
+errors=0
+# No directory test before the read: `[ -d ]` is false for a denied lookup
+# too, so every listed pid goes through the read and the gone check.
+for d in "$PROC"/[0-9]*; do
+  pid=${d##*/}
+  [[ "$pid" =~ ^[0-9]+$ ]] || continue
+  seen=$((seen + 1))
+  [ -z "${SKIP[$pid]:-}" ] || continue
+  # A process can exit between the listing and the read; that's not an error.
+  # A failed read is, unless a fresh listing confirms the pid is gone: the
+  # scan can't say what that process runs.
+  # The braces send the shell's own message for a failed `<` to /dev/null too.
+  if ! cmd=$( { tr '\0' ' ' < "$d/cmdline"; } 2>/dev/null); then
+    gone "$PROC" "$pid" && continue
+    echo "slot-busy: error: cannot read $d/cmdline" >&2
+    errors=$((errors + 1))
+    continue
+  fi
+  cmd=${cmd% }
+  [ -n "$cmd" ] || continue
+  rule=$(match "$cmd") || continue
+  cwd=$(readlink "$d/cwd" 2>/dev/null) || cwd="?"
+  printf 'BUSY %s %s cwd=%s %s\n' "$pid" "$rule" "$cwd" "${cmd:0:200}"
+  busy=1
+done
+[ "$seen" -ge 1 ] || { echo "slot-busy: error: no processes under $PROC" >&2; exit 2; }
+[ "$errors" = 0 ] || { echo "slot-busy: error: $errors process(es) could not be read, so the host isn't known to be idle" >&2; exit 2; }
+if [ "$busy" = 1 ]; then exit 1; fi
+echo "CLEAR"
+exit 0
@@ -0,0 +1,502 @@
+#!/usr/bin/env bash
+# Sandboxed selftests for the push guard, its installer and the busy check
+# (row 211, #426): scripts/git-hooks/pre-push, scripts/install-git-hooks.sh
+# and scripts/slot-busy.sh.
+#
+# Pushes go from a scratch clone and its worktree to a scratch bare remote,
+# never to origin. Git sees no user or system config. The busy check runs
+# against a fake /proc (pids above pid_max) for the exit codes and rules, and
+# against the real /proc with a sleeping stand-in whose argv is `node --test`.
+set -uo pipefail
+cd "$(dirname "$0")/.."
+REPO="$(pwd)"
+unset GIT_DIR GIT_WORK_TREE GIT_COMMON_DIR GIT_INDEX_FILE GIT_OBJECT_DIRECTORY GIT_ALTERNATE_OBJECT_DIRECTORIES
+
+SANDBOX="$(cd "$(mktemp -d)" && pwd -P)"
+STANDIN=""
+KIDS=""   # wrapper shells and their children that the suite starts
+LOCKED="" # directories a test makes unreadable; cleanup gives modes back
+cleanup() {
+    if [ -n "$STANDIN" ]; then kill "$STANDIN" 2>/dev/null; wait "$STANDIN" 2>/dev/null; fi
+    for k in $KIDS; do kill "$k" 2>/dev/null; wait "$k" 2>/dev/null; done
+    for l in $LOCKED; do chmod 0755 "$l" 2>/dev/null; done
+    rm -rf "$SANDBOX"
+}
+trap cleanup EXIT
+
+PASS=0
+FAIL=0
+# Status colors: terminal-only, NO_COLOR-respecting; plain when piped.
+if [ -t 1 ] && [ -z "${NO_COLOR:-}" ]; then
+    C_OK=$'\033[0;32m'; C_FAIL=$'\033[0;31m'; C_RESET=$'\033[0m'
+else
+    C_OK=""; C_FAIL=""; C_RESET=""
+fi
+check() {
+    if [ "$2" = "0" ]; then PASS=$((PASS+1)); echo "${C_OK}OK${C_RESET}    $1"; else FAIL=$((FAIL+1)); echo "${C_FAIL}FAIL${C_RESET} $1"; fi
+}
+has() { [[ "$1" == *"$2"* ]]; }
+
+# Git sees no user or system config: no hooks path, no signing, a fixed identity.
+: > "$SANDBOX/gitconfig"
+export GIT_CONFIG_NOSYSTEM=1 GIT_CONFIG_GLOBAL="$SANDBOX/gitconfig"
+export GIT_AUTHOR_NAME=suite GIT_AUTHOR_EMAIL=suite@local GIT_COMMITTER_NAME=suite GIT_COMMITTER_EMAIL=suite@local
+
+HOOK_SRC="$REPO/scripts/git-hooks/pre-push"
+INSTALL="$REPO/scripts/install-git-hooks.sh"
+BUSY="$REPO/scripts/slot-busy.sh"
+
+B="$SANDBOX/remote.git"
+C="$SANDBOX/clone"
+W="$SANDBOX/wt"
+O="$SANDBOX/other"
+commit() { # $1: repo, $2: file and message
+    echo "$2" > "$1/$2" && git -C "$1" add "$2" && git -C "$1" commit -q -m "$2"
+}
+rtip() { git -C "$B" rev-parse -q --verify "refs/heads/$1"; }
+
+# ---- the remote, a clone with the guard, a worktree ----
+git init -q --bare -b main "$B"
+git init -q -b main "$SANDBOX/seed"
+commit "$SANDBOX/seed" base
+git -C "$SANDBOX/seed" push -q "$B" main
+git clone -q "$B" "$C"
+
+echo "== install =="
+out=$(bash "$INSTALL" --repo "$C" 2>&1); rc=$?
+check "the install into a clean clone exits 0" "$rc"
+check "it reports the install and a passed canary" "$(has "$out" "ok installed the push guard" && has "$out" "canary passed"; echo $?)"
+check "the hook is in the common .git/hooks, with the repository's bytes, executable" \
+    "$(cmp -s "$HOOK_SRC" "$C/.git/hooks/pre-push" && [ -x "$C/.git/hooks/pre-push" ]; echo $?)"
+check "no temporary file is left in .git/hooks" \
+    "$(ls -A "$C/.git/hooks" | grep -q '^\.pre-push\.install'; [ $? = 1 ]; echo $?)"
+git -C "$C" worktree add -q -b seat/w "$W" origin/main
+check "the worktree's git runs the common hook" \
+    "$([ "$(git -C "$W" rev-parse --path-format=absolute --git-path hooks/pre-push)" = "$C/.git/hooks/pre-push" ]; echo $?)"
+
+echo "== pushes from the worktree =="
+commit "$W" one
+out=$(git -C "$W" push origin seat/w 2>&1); rc=$?
+check "a new branch passes" "$rc"
+check "the remote branch is at the pushed commit" "$([ "$(rtip seat/w)" = "$(git -C "$W" rev-parse HEAD)" ]; echo $?)"
+
+commit "$W" two
+out=$(git -C "$W" push origin seat/w 2>&1); rc=$?
+check "a fast-forward passes" "$rc"
+check "the remote branch moved forward" "$([ "$(rtip seat/w)" = "$(git -C "$W" rev-parse HEAD)" ]; echo $?)"
+
+before=$(rtip seat/w)
+git -C "$W" reset -q --hard HEAD~1
+commit "$W" two-rewritten
+after=$(git -C "$W" rev-parse HEAD)
+out=$(git -C "$W" push --force origin seat/w 2>&1); rc=$?
+check "push --force of a rewritten branch is refused" "$([ "$rc" -ne 0 ]; echo $?)"
+check "the refusal is the guard's, and names the ref and both shas" \
+    "$(has "$out" "mosaic push guard: refused: refs/heads/seat/w: not a fast-forward" && has "$out" "$before" && has "$out" "$after"; echo $?)"
+check "the remote ref is unchanged after the refused --force" "$([ "$(rtip seat/w)" = "$before" ]; echo $?)"
+
+out=$(git -C "$W" push origin +seat/w:seat/w 2>&1); rc=$?
+check "a +refspec push is refused" "$([ "$rc" -ne 0 ] && has "$out" "not a fast-forward"; echo $?)"
+check "the remote ref is unchanged after the refused +refspec" "$([ "$(rtip seat/w)" = "$before" ]; echo $?)"
+
+out=$(git -C "$W" push --force-with-lease origin seat/w 2>&1); rc=$?
+check "push --force-with-lease is refused too" "$([ "$rc" -ne 0 ] && has "$out" "not a fast-forward"; echo $?)"
+
+out=$(git -C "$W" push origin :seat/w 2>&1); rc=$?
+check "a delete (:ref) is refused" "$([ "$rc" -ne 0 ] && has "$out" "mosaic push guard: refused: refs/heads/seat/w: a delete"; echo $?)"
+out=$(git -C "$W" push --delete origin seat/w 2>&1); rc=$?
+check "a delete (--delete) is refused" "$([ "$rc" -ne 0 ] && has "$out" "a delete"; echo $?)"
+check "the remote branch still exists after the refused deletes" "$([ "$(rtip seat/w)" = "$before" ]; echo $?)"
+
+# Another clone moves the remote; this clone never fetches it.
+git clone -q -b seat/w "$B" "$O"
+commit "$O" from-other
+git -C "$O" push -q origin seat/w
+moved=$(rtip seat/w)
+check "the other clone moved the remote, and this clone lacks that commit" \
+    "$([ "$moved" != "$before" ] && ! git -C "$C" cat-file -e "$moved^{commit}" 2>/dev/null; echo $?)"
+out=$(git -C "$W" push --force origin seat/w 2>&1); rc=$?
+check "a push over a remote tip missing locally is refused, saying fetch first" \
+    "$([ "$rc" -ne 0 ] && has "$out" "isn't in this repository; fetch first"; echo $?)"
+check "the remote ref is unchanged after that refusal" "$([ "$(rtip seat/w)" = "$moved" ]; echo $?)"
+check "the guard fetched nothing" "$(! git -C "$C" cat-file -e "$moved^{commit}" 2>/dev/null; echo $?)"
+
+echo "== tags =="
+# An existing tag never changes. Both cases below pass the ancestor check: a
+# new tag object on the same commit peels to that commit, and a moved
+# lightweight tag's old commit is an ancestor of its new one.
+tagtip() { git -C "$B" rev-parse -q --verify "refs/tags/$1"; }
+git -C "$W" tag -a -m first t-ann HEAD
+out=$(git -C "$W" push origin t-ann 2>&1); rc=$?
+check "a new annotated tag passes" "$([ "$rc" = 0 ] && [ "$(tagtip t-ann)" = "$(git -C "$W" rev-parse t-ann)" ]; echo $?)"
+first=$(tagtip t-ann)
+git -C "$W" tag -f -a -m second t-ann HEAD >/dev/null
+out=$(git -C "$W" push --force origin t-ann 2>&1); rc=$?
+check "push --force of a new tag object on the same commit is refused" \
+    "$([ "$rc" -ne 0 ] && has "$out" "mosaic push guard: refused: refs/tags/t-ann: an existing tag" && has "$out" "$first"; echo $?)"
+check "the remote tag is still the first tag object" "$([ "$(tagtip t-ann)" = "$first" ]; echo $?)"
+git -C "$W" tag t-light HEAD~1
+out=$(git -C "$W" push origin t-light 2>&1); rc=$?
+check "a new lightweight tag passes" "$rc"
+git -C "$W" tag -f t-light HEAD >/dev/null
+out=$(git -C "$W" push --force origin t-light 2>&1); rc=$?
+check "push --force of a lightweight tag moved to a descendant is refused" \
+    "$([ "$rc" -ne 0 ] && has "$out" "mosaic push guard: refused: refs/tags/t-light: an existing tag"; echo $?)"
+check "the remote lightweight tag hasn't moved" "$([ "$(tagtip t-light)" = "$(git -C "$W" rev-parse HEAD~1)" ]; echo $?)"
+out=$(git -C "$W" push origin :refs/tags/t-light 2>&1); rc=$?
+check "a tag delete is refused, and the tag stays" \
+    "$([ "$rc" -ne 0 ] && has "$out" "refs/tags/t-light: a delete" && [ -n "$(tagtip t-light)" ]; echo $?)"
+
+echo "== the hook, fed by hand =="
+z=0000000000000000000000000000000000000000
+hookrun() { (cd "$C" && printf '%s\n' "$1" | sh "$C/.git/hooks/pre-push" origin "$B" 2>&1); }
+out=$(hookrun "refs/heads/x $(git -C "$C" rev-parse HEAD) refs/heads/x"); rc=$?
+check "a short ref line is refused" "$([ "$rc" -ne 0 ] && has "$out" "unreadable ref line"; echo $?)"
+out=$(hookrun "refs/heads/x HEAD refs/heads/x $z"); rc=$?
+check "a non-hex object name is refused" "$([ "$rc" -ne 0 ] && has "$out" "non-hex"; echo $?)"
+out=$(hookrun "refs/heads/x $(git -C "$C" rev-parse HEAD) refs/heads/x 0"); rc=$?
+check "a remote object name of 0 is refused, not read as a new ref" \
+    "$([ "$rc" -ne 0 ] && has "$out" "isn't 40 or 64 hex characters"; echo $?)"
+out=$(hookrun "refs/heads/x $(git -C "$C" rev-parse HEAD | cut -c1-39) refs/heads/x $z"); rc=$?
+check "a 39-character local object name is refused" "$([ "$rc" -ne 0 ] && has "$out" "isn't 40 or 64 hex characters"; echo $?)"
+out=$(hookrun "refs/heads/x ${z}${z:0:24} refs/heads/x $(git -C "$C" rev-parse HEAD)"); rc=$?
+check "a 64-character object name passes the length check (64 zeros refuse as a delete)" \
+    "$([ "$rc" -ne 0 ] && has "$out" "refs/heads/x: a delete" && ! has "$out" "isn't 40 or 64"; echo $?)"
+out=$(hookrun "refs/heads/x 1234567890123456789012345678901234567890 refs/heads/x $(git -C "$C" rev-parse HEAD)"); rc=$?
+check "a failed ancestor check (an unknown local object) is refused" \
+    "$([ "$rc" -ne 0 ] && has "$out" "the ancestor check failed"; echo $?)"
+out=$(printf '' | (cd "$C" && sh "$C/.git/hooks/pre-push" origin "$B" 2>&1)); rc=$?
+check "an empty push passes" "$rc"
+
+echo "== installer refusals =="
+fresh() { rm -rf "$1"; git clone -q "$B" "$1"; }
+fresh "$SANDBOX/hp"
+git -C "$SANDBOX/hp" config core.hooksPath .husky
+out=$(bash "$INSTALL" --repo "$SANDBOX/hp" 2>&1); rc=$?
+check "the install refuses with core.hooksPath set (exit 2)" "$([ "$rc" = 2 ]; echo $?)"
+check "it says core.hooksPath is set" "$(has "$out" "core.hooksPath is set"; echo $?)"
+check "no hook was written under the hooksPath refusal" \
+    "$([ ! -e "$SANDBOX/hp/.git/hooks/pre-push" ] && [ ! -e "$SANDBOX/hp/.husky/pre-push" ]; echo $?)"
+
+fresh "$SANDBOX/df"
+printf '#!/bin/sh\nexit 0\n' > "$SANDBOX/df/.git/hooks/pre-push"
+chmod 0755 "$SANDBOX/df/.git/hooks/pre-push"
+ln "$SANDBOX/df/.git/hooks/pre-push" "$SANDBOX/df-old"
+out=$(bash "$INSTALL" --repo "$SANDBOX/df" 2>&1); rc=$?
+check "the install refuses a different installed pre-push (exit 2)" \
+    "$([ "$rc" = 2 ] && has "$out" "a different pre-push hook is installed"; echo $?)"
+check "the different hook is untouched" \
+    "$([ "$(cat "$SANDBOX/df/.git/hooks/pre-push")" = "$(printf '#!/bin/sh\nexit 0')" ]; echo $?)"
+out=$(bash "$INSTALL" --repo "$SANDBOX/df" --force-install 2>&1); rc=$?
+check "--force-install replaces it" \
+    "$([ "$rc" = 0 ] && has "$out" "replaced a different hook" && cmp -s "$HOOK_SRC" "$SANDBOX/df/.git/hooks/pre-push"; echo $?)"
+check "the replacement was a rename: the old file keeps its bytes" \
+    "$([ "$(cat "$SANDBOX/df-old")" = "$(printf '#!/bin/sh\nexit 0')" ]; echo $?)"
+out=$(bash "$INSTALL" --repo "$SANDBOX/df" 2>&1); rc=$?
+check "a second install over the same bytes exits 0" "$([ "$rc" = 0 ] && has "$out" "the same bytes"; echo $?)"
+
+fresh "$SANDBOX/ln"
+ln -s /dev/null "$SANDBOX/ln/.git/hooks/pre-push"
+out=$(bash "$INSTALL" --repo "$SANDBOX/ln" --force-install 2>&1); rc=$?
+check "the install refuses a symlinked pre-push, even with --force-install" "$([ "$rc" = 2 ] && has "$out" "is a symlink"; echo $?)"
+
+# A hooks directory that links to a shared one would put the hook outside
+# the repository, in every repository that shares it.
+fresh "$SANDBOX/sl"
+mkdir -p "$SANDBOX/shared-hooks"
+rm -rf "$SANDBOX/sl/.git/hooks"
+ln -s "$SANDBOX/shared-hooks" "$SANDBOX/sl/.git/hooks"
+out=$(bash "$INSTALL" --repo "$SANDBOX/sl" 2>&1); rc=$?
+check "the install refuses a symlinked hooks directory (exit 2)" "$([ "$rc" = 2 ] && has "$out" "/.git/hooks is a symlink"; echo $?)"
+out=$(bash "$INSTALL" --repo "$SANDBOX/sl" --force-install 2>&1); rc=$?
+check "it refuses it with --force-install too" "$([ "$rc" = 2 ] && has "$out" "/.git/hooks is a symlink"; echo $?)"
+check "nothing was written in the directory the symlink names" "$([ -z "$(ls -A "$SANDBOX/shared-hooks")" ]; echo $?)"
+
+# The temporary copy's name isn't predictable from the installer's pid. The
+# subshell plants a link at the pid-named path, then execs the installer, so
+# the installer's $$ is that pid.
+fresh "$SANDBOX/pt"
+printf 'victim\n' > "$SANDBOX/pt-victim"
+out=$(pid=$BASHPID; ln -s "$SANDBOX/pt-victim" "$SANDBOX/pt/.git/hooks/.pre-push.install-git-hooks.$pid" && exec bash "$INSTALL" --repo "$SANDBOX/pt" 2>&1); rc=$?
+check "the install writes nothing through a link planted at a pid-named temporary path" \
+    "$([ "$rc" = 0 ] && [ "$(cat "$SANDBOX/pt-victim")" = victim ]; echo $?)"
+check "the installed hook is a regular file with the repository's bytes" \
+    "$([ -f "$SANDBOX/pt/.git/hooks/pre-push" ] && [ ! -L "$SANDBOX/pt/.git/hooks/pre-push" ] && cmp -s "$HOOK_SRC" "$SANDBOX/pt/.git/hooks/pre-push"; echo $?)"
+
+fresh "$SANDBOX/wd"
+git -C "$SANDBOX/wd" worktree add -q -b seat/x "$SANDBOX/wd-wt" origin/main
+out=$(bash "$INSTALL" --repo "$SANDBOX/wd-wt" 2>&1); rc=$?
+check "an install named by a worktree path lands in the common .git/hooks" \
+    "$([ "$rc" = 0 ] && cmp -s "$HOOK_SRC" "$SANDBOX/wd/.git/hooks/pre-push"; echo $?)"
+
+out=$(GIT_DIR="$SANDBOX/wd/.git" bash "$INSTALL" --repo "$SANDBOX/wd" 2>&1); rc=$?
+check "the install refuses with GIT_DIR set" "$([ "$rc" = 2 ] && has "$out" "GIT_DIR is set"; echo $?)"
+mkdir -p "$SANDBOX/plain"
+out=$(bash "$INSTALL" --repo "$SANDBOX/plain" 2>&1); rc=$?
+check "the install refuses a directory that isn't a checkout" "$([ "$rc" = 2 ]; echo $?)"
+out=$(bash "$INSTALL" --nope 2>&1); rc=$?
+check "an unknown argument exits 4" "$([ "$rc" = 4 ]; echo $?)"
+
+echo "== slot-busy, fake /proc =="
+P="$SANDBOX/proc"
+fakeproc() { # $1: pid, $2: cwd, rest: argv
+    local pid=$1 cwd=$2; shift 2
+    mkdir -p "$P/$pid"
+    printf '%s\0' "$@" > "$P/$pid/cmdline"
+    ln -sfn "$cwd" "$P/$pid/cwd"
+}
+busyrun() { bash "$BUSY" --proc-root "$P" 2>&1; }
+fakeproc 4194401 /srv node server.mjs
+fakeproc 4194402 /srv grep -r gate .
+# Both wrappers' text would match a rule without the snapshot exclusion.
+fakeproc 4194403 /srv /bin/bash -c "source /home/u/.claude/shell-snapshots/snapshot-bash-1.sh && node --test x.test.mjs"
+fakeproc 4194405 /srv /usr/bin/bash -c "source /home/u/.claude/shell-snapshots/snapshot-bash-2-ab.sh 2>/dev/null || true && eval 'bash scripts/test-x.sh > x.log' && pwd -P >| /home/u/cwd"
+# A wrapper that sources files that aren't gates, tests or mutants, then
+# runs a gate as a child: the child is matched, the wrapper isn't.
+fakeproc 4194406 /srv /bin/bash -c "source /home/u/.claude/shell-snapshots/snapshot-bash-1.sh && source .venv/bin/activate && . ./env.sh && ./gate.sh 253"
+mkdir -p "$P/4194404"; : > "$P/4194404/cmdline"
+out=$(busyrun); rc=$?
+check "no matching process: exit 0 and CLEAR" "$([ "$rc" = 0 ] && [ "$out" = CLEAR ]; echo $?)"
+check "an agent's shell-snapshot wrapper isn't a match" "$(! has "$out" "4194403" && ! has "$out" "4194405"; echo $?)"
+check "a wrapper that sources other files and runs a gate as a child isn't a match" "$(! has "$out" "4194406"; echo $?)"
+
+fakeproc 4194410 /seat/a node --test packages/x/tests/a.test.mjs
+out=$(busyrun); rc=$?
+check "a node --test process: exit 1" "$([ "$rc" = 1 ]; echo $?)"
+check "its BUSY line names pid, rule and cwd" "$(has "$out" "BUSY 4194410 node --test cwd=/seat/a node --test"; echo $?)"
+check "BUSY output never says CLEAR" "$(! has "$out" "CLEAR"; echo $?)"
+ran=$(bash "$BUSY" --proc-root "$P" >/dev/null && echo ran)
+check "\`slot-busy > LOG && step\` doesn't run the step while BUSY" "$([ -z "$ran" ]; echo $?)"
+rm -rf "${P:?}/4194410"
+
+rule() { # $1: expected rule, rest: argv
+    local want=$1; shift
+    rm -rf "${P:?}/4194420"; fakeproc 4194420 /seat/b "$@"
+    out=$(busyrun); rc=$?
+    check "busy on: $* ($want)" "$([ "$rc" = 1 ] && has "$out" "BUSY 4194420 $want "; echo $?)"
+}
+rule "node --test" /usr/bin/node --experimental-strip-types --test a.test.ts
+rule "gate" bash /mnt/scratch/sage-gate.sh 253
+rule "gate" bash ./gate.sh
+rule "mutant" bash agents/x/work/queue-1/mutants.sh M3
+rule "test script" bash scripts/test-land-work.sh
+rule "docker compose" docker compose -p x up -d
+rule "docker compose" /usr/bin/docker-compose up
+# The snapshot exclusion is for the wrapper's shape only: the same command
+# without the snapshot source, and real runs whose arguments hold the path.
+rule "node --test" /bin/bash -c "node --test x.test.mjs"
+rule "node --test" node --test /seat/tests/shell-snapshots/snapshot-guard.test.mjs
+rule "gate" bash /seat/shell-snapshots/snapshot-gate.sh
+# A wrapper that sources a gate, test or mutant script runs it in its own
+# shell, with no child to match, so the wrapper itself is BUSY.
+SNAP="source /home/u/.claude/shell-snapshots/snapshot-bash-1.sh"
+rule "sourced test script" /bin/bash -c "$SNAP && source /seat/scripts/test-x.sh"
+rule "sourced test script" /bin/bash -c "$SNAP && . /seat/scripts/test-x.sh"
+rule "sourced test script" /bin/bash -c "$SNAP && source \"scripts/test-x.sh\" arg"
+# A sourced file that isn't one comes first; the one after it still counts.
+rule "sourced test script" /bin/bash -c "$SNAP && source .venv/bin/activate && . scripts/test-x.sh"
+rule "sourced gate" /usr/bin/bash -c "source /home/u/.claude/shell-snapshots/snapshot-bash-2-ab.sh 2>/dev/null || true && eval '. ./gate.sh 253' && pwd -P >| /home/u/cwd"
+rule "sourced mutant" /bin/bash -c "$SNAP && cd /seat && eval 'source agents/x/work/queue-1/mutants.sh M3'"
+rm -rf "${P:?}/4194420"
+
+echo "== slot-busy, read errors =="
+# A pid directory that stays while its cmdline can't be read is an error,
+# never a vanished process: exit 2 and no CLEAR.
+mkdir -p "$P/4194430"
+out=$(busyrun); rc=$?
+check "a pid directory with no cmdline: exit 2" "$([ "$rc" = 2 ]; echo $?)"
+check "it names that cmdline and never says CLEAR" "$(has "$out" "cannot read $P/4194430/cmdline" && ! has "$out" CLEAR; echo $?)"
+rm -rf "${P:?}/4194430"
+mkdir -p "$P/4194431/cmdline"
+out=$(busyrun); rc=$?
+check "a cmdline that can't be read (a directory): exit 2, no CLEAR" "$([ "$rc" = 2 ] && ! has "$out" CLEAR; echo $?)"
+fakeproc 4194410 /seat/a node --test a.test.mjs
+out=$(busyrun); rc=$?
+check "a read error beside a BUSY process: exit 2, the BUSY line kept, no CLEAR" \
+    "$([ "$rc" = 2 ] && has "$out" "BUSY 4194410 node --test" && ! has "$out" CLEAR; echo $?)"
+rm -rf "${P:?}/4194431"
+chmod 000 "$P/4194410/cmdline"
+out=$(busyrun); rc=$?
+check "a node --test process whose cmdline is unreadable (mode 000) is never CLEAR" "$([ "$rc" != 0 ] && ! has "$out" CLEAR; echo $?)"
+rm -rf "${P:?}/4194410"
+
+mkdir -p "$SANDBOX/failtr" "$SANDBOX/vanishtr" "$SANDBOX/failawk"
+printf '#!/bin/sh\nexit 1\n' > "$SANDBOX/failtr/tr"
+printf '#!/bin/sh\nexit 1\n' > "$SANDBOX/failawk/awk"
+# This tr stands in for a process that exits during the read: for pid
+# 4194440 it removes the pid directory and fails; otherwise it is tr.
+cat > "$SANDBOX/vanishtr/tr" <<EOF
+#!/bin/sh
+f=\$(readlink "/proc/\$\$/fd/0")
+case "\$f" in */4194440/cmdline) rm -rf "\${f%/cmdline}"; exit 1 ;; esac
+exec $(command -v tr) "\$@"
+EOF
+chmod +x "$SANDBOX/failtr/tr" "$SANDBOX/failawk/awk" "$SANDBOX/vanishtr/tr"
+out=$(PATH="$SANDBOX/failtr:$PATH" bash "$BUSY" --proc-root "$P" 2>&1); rc=$?
+check "a failing read (tr exits 1) with every pid directory still there: exit 2, no CLEAR" \
+    "$([ "$rc" = 2 ] && has "$out" "cannot read" && ! has "$out" CLEAR; echo $?)"
+fakeproc 4194440 /seat/v node --test v.test.mjs
+out=$(PATH="$SANDBOX/vanishtr:$PATH" bash "$BUSY" --proc-root "$P" 2>&1); rc=$?
+check "a process that vanishes during its read isn't an error: exit 0 and CLEAR" \
+    "$([ "$rc" = 0 ] && [ "$out" = CLEAR ] && [ ! -e "$P/4194440" ]; echo $?)"
+rm -rf "${P:?}/4194440"
+out=$(PATH="$SANDBOX/failawk:$PATH" bash "$BUSY" --proc-root "$P" 2>&1); rc=$?
+check "its own process unreadable (awk exits 1): exit 2, no CLEAR" \
+    "$([ "$rc" = 2 ] && has "$out" "cannot read its own process" && ! has "$out" CLEAR; echo $?)"
+
+# Every ancestor's status read counts, not only the first. The awk below is
+# the real awk for call 1 (the scan's own status) and then fails or prints
+# nothing; a third one prints a pid that isn't in /proc on call 2, so the
+# walk meets an ancestor that has exited.
+mkdir -p "$SANDBOX/awkn"
+cat > "$SANDBOX/awkn/awk" <<EOF
+#!/bin/sh
+n=\$(cat "$SANDBOX/awkn/n" 2>/dev/null || echo 0); n=\$((n + 1)); echo "\$n" > "$SANDBOX/awkn/n"
+if [ "\$n" -ge 2 ]; then
+  case \$(cat "$SANDBOX/awkn/mode") in
+    fail) exit 1 ;;
+    empty) exit 0 ;;
+    exited) if [ "\$n" = 2 ]; then echo 4194999; exit 0; fi ;;
+  esac
+fi
+exec $(command -v awk) "\$@"
+EOF
+chmod +x "$SANDBOX/awkn/awk"
+awkn() { # $1: fail, empty or exited. Runs the check on the idle fake /proc.
+    echo "$1" > "$SANDBOX/awkn/mode"; rm -f "$SANDBOX/awkn/n"
+    out=$(PATH="$SANDBOX/awkn:$PATH" bash "$BUSY" --proc-root "$P" 2>&1); rc=$?
+    calls=$(cat "$SANDBOX/awkn/n" 2>/dev/null || echo 0)
+}
+awkn fail
+check "an ancestor's status read that fails after its own read passed: exit 2, no CLEAR" \
+    "$([ "$calls" -ge 2 ] && [ "$rc" = 2 ] && has "$out" "cannot read the status of ancestor" && ! has "$out" CLEAR; echo $?)"
+awkn empty
+check "an ancestor's status with no PPid: exit 2, no CLEAR" \
+    "$([ "$calls" -ge 2 ] && [ "$rc" = 2 ] && has "$out" "cannot read the status of ancestor" && ! has "$out" CLEAR; echo $?)"
+awkn exited
+check "an ancestor that has exited (its pid gone from /proc) ends the walk: exit 0 and CLEAR" \
+    "$([ "$calls" -ge 3 ] && [ "$rc" = 0 ] && [ "$out" = CLEAR ]; echo $?)"
+
+# A lookup that is denied isn't a process that vanished. This tr makes the
+# proc root unreadable once the pid directory is listed, then fails the read;
+# the pid directory and its node --test cmdline stay where they are.
+DP="$SANDBOX/dproc"
+mkdir -p "$SANDBOX/denytr" "$DP/4194450"
+printf '%s\0' node --test d.test.mjs > "$DP/4194450/cmdline"
+cat > "$SANDBOX/denytr/tr" <<EOF
+#!/bin/sh
+f=\$(readlink "/proc/\$\$/fd/0")
+case "\$f" in */4194450/cmdline) chmod 000 "$DP"; exit 1 ;; esac
+exec $(command -v tr) "\$@"
+EOF
+chmod +x "$SANDBOX/denytr/tr"
+LOCKED="$LOCKED $DP"
+out=$(PATH="$SANDBOX/denytr:$PATH" bash "$BUSY" --proc-root "$DP" 2>&1); rc=$?
+denied=$([ ! -r "$DP" ] && echo yes); chmod 0755 "$DP"
+check "a lookup denied after the listing (proc root mode 000): exit 2, no CLEAR" \
+    "$([ "$denied" = yes ] && [ "$rc" = 2 ] && has "$out" "cannot read $DP/4194450/cmdline" && ! has "$out" CLEAR; echo $?)"
+check "the denied pid directory and its node --test cmdline were still there" \
+    "$([ "$(tr '\0' ' ' < "$DP/4194450/cmdline")" = "node --test d.test.mjs " ]; echo $?)"
+# The root turns unreadable after the first pid's read went through: the next
+# pid, a node --test, is a doubt, not a skip.
+rm -rf "${DP:?}/4194450"
+mkdir -p "$SANDBOX/locktr" "$DP/4194451" "$DP/4194452"
+printf '%s\0' sleep 60 > "$DP/4194451/cmdline"
+printf '%s\0' node --test l.test.mjs > "$DP/4194452/cmdline"
+cat > "$SANDBOX/locktr/tr" <<EOF
+#!/bin/sh
+f=\$(readlink "/proc/\$\$/fd/0")
+case "\$f" in */4194451/cmdline) chmod 000 "$DP" ;; esac
+exec $(command -v tr) "\$@"
+EOF
+chmod +x "$SANDBOX/locktr/tr"
+out=$(PATH="$SANDBOX/locktr:$PATH" bash "$BUSY" --proc-root "$DP" 2>&1); rc=$?
+denied=$([ ! -r "$DP" ] && echo yes); chmod 0755 "$DP"
+check "a proc root that turns unreadable after one read hides no later process: exit 2, no CLEAR" \
+    "$([ "$denied" = yes ] && [ "$rc" = 2 ] && has "$out" "cannot read $DP/4194452/cmdline" && ! has "$out" CLEAR; echo $?)"
+
+out=$(bash "$BUSY" --proc-root "$SANDBOX/no-such-proc" 2>&1); rc=$?
+check "a missing proc root: exit 2" "$([ "$rc" = 2 ]; echo $?)"
+mkdir -p "$SANDBOX/empty-proc"
+out=$(bash "$BUSY" --proc-root "$SANDBOX/empty-proc" 2>&1); rc=$?
+check "a proc root with no processes: exit 2" "$([ "$rc" = 2 ]; echo $?)"
+out=$(bash "$BUSY" --nope 2>&1); rc=$?
+check "an unknown argument: exit 2" "$([ "$rc" = 2 ]; echo $?)"
+
+echo "== slot-busy, real /proc =="
+mkdir -p "$SANDBOX/bin" "$SANDBOX/standin"
+cat > "$SANDBOX/bin/node" <<'EOF'
+#!/bin/sh
+trap 'exit 0' TERM
+while :; do sleep 0.2; done
+EOF
+chmod +x "$SANDBOX/bin/node"
+(cd "$SANDBOX/standin" && exec "$SANDBOX/bin/node" --test standin.test.mjs) &
+STANDIN=$!
+for _ in $(seq 50); do
+    has "$(tr '\0' ' ' < "/proc/$STANDIN/cmdline" 2>/dev/null)" "--test standin" && break
+    sleep 0.1
+done
+out=$(bash "$BUSY" 2>&1); rc=$?
+check "with a stand-in node --test running: exit 1" "$([ "$rc" = 1 ]; echo $?)"
+check "the stand-in has a BUSY line with its cwd" \
+    "$(printf '%s\n' "$out" | grep -q "^BUSY $STANDIN node --test cwd=$SANDBOX/standin "; echo $?)"
+check "this suite, an ancestor, has no BUSY line" "$(! printf '%s\n' "$out" | grep -q "^BUSY $$ "; echo $?)"
+ran=$(bash "$BUSY" >/dev/null && echo ran)
+check "\`slot-busy > LOG && step\` doesn't run the step with the stand-in up" "$([ -z "$ran" ]; echo $?)"
+kill "$STANDIN" 2>/dev/null; wait "$STANDIN" 2>/dev/null
+gone=$STANDIN; STANDIN=""
+out=$(bash "$BUSY" 2>&1); rc=$?
+check "after the stand-in exits, it has no BUSY line" "$(! printf '%s\n' "$out" | grep -q "^BUSY $gone "; echo $?)"
+check "the real-/proc run exits 0 or 1, never 2" "$([ "$rc" = 0 ] || [ "$rc" = 1 ]; echo $?)"
+
+echo "== slot-busy, real snapshot wrappers =="
+# Live wrappers, each shown to the check through a proc root that links only
+# its own real /proc directories, so other jobs on the host don't count.
+mkdir -p "$SANDBOX/shell-snapshots" "$SANDBOX/scripts" "$SANDBOX/wrap"
+: > "$SANDBOX/shell-snapshots/snapshot-x.sh"
+mkfifo "$SANDBOX/wrap/fifo"
+# Sourced: it says it's ready, then blocks in the read builtin, no child.
+cat > "$SANDBOX/scripts/test-x.sh" <<EOF
+exec 3<>"$SANDBOX/wrap/fifo"
+: > "$SANDBOX/wrap/ready"
+read -t 60 -u 3 _
+EOF
+(cd "$SANDBOX/wrap" && exec bash -c "source $SANDBOX/shell-snapshots/snapshot-x.sh && source $SANDBOX/scripts/test-x.sh") &
+WRAP=$!; KIDS="$KIDS $WRAP"
+for _ in $(seq 50); do [ -e "$SANDBOX/wrap/ready" ] && break; sleep 0.1; done
+kids=$(cat "/proc/$WRAP/task/$WRAP/children") && kids="none$kids"
+LP="$SANDBOX/lproc1"; mkdir -p "$LP"; ln -s "/proc/$WRAP" "$LP/$WRAP"
+out=$(bash "$BUSY" --proc-root "$LP" 2>&1); rc=$?
+check "a live wrapper that sourced a test script, blocked in a builtin with no child: exit 1" \
+    "$([ -e "$SANDBOX/wrap/ready" ] && [ "$kids" = none ] && [ "$rc" = 1 ] && ! has "$out" CLEAR; echo $?)"
+check "its BUSY line names the wrapper's pid, the sourced rule and its cwd" \
+    "$(printf '%s\n' "$out" | grep -q "^BUSY $WRAP sourced test script cwd=$SANDBOX/wrap "; echo $?)"
+out=$(bash "$BUSY" 2>&1); rc=$?
+check "the real /proc has a BUSY line for that wrapper too" \
+    "$([ "$rc" != 0 ] && printf '%s\n' "$out" | grep -q "^BUSY $WRAP sourced test script "; echo $?)"
+kill "$WRAP" 2>/dev/null; wait "$WRAP" 2>/dev/null; KIDS=""
+
+# External: the wrapper runs node --test as a child (`; :` keeps bash from
+# exec'ing it). The wrapper is skipped and its child is BUSY.
+(cd "$SANDBOX/wrap" && exec bash -c "source $SANDBOX/shell-snapshots/snapshot-x.sh && $SANDBOX/bin/node --test active.test.mjs; :") &
+WRAP=$!; KIDS="$KIDS $WRAP"; kid=""
+for _ in $(seq 50); do
+    kid=$(cat "/proc/$WRAP/task/$WRAP/children" 2>/dev/null); kid=${kid%% *}
+    [ -n "$kid" ] && has "$(tr '\0' ' ' < "/proc/$kid/cmdline" 2>/dev/null)" "--test active" && break
+    sleep 0.1
+done
+KIDS="$KIDS $kid"
+LP="$SANDBOX/lproc2"; mkdir -p "$LP"; ln -s "/proc/$WRAP" "$LP/$WRAP"; [ -n "$kid" ] && ln -s "/proc/$kid" "$LP/$kid"
+out=$(bash "$BUSY" --proc-root "$LP" 2>&1); rc=$?
+check "a live wrapper that runs node --test as a child: exit 1 on the child's BUSY line" \
+    "$([ -n "$kid" ] && [ "$rc" = 1 ] && printf '%s\n' "$out" | grep -q "^BUSY $kid node --test "; echo $?)"
+check "the wrapper itself has no BUSY line" "$(! printf '%s\n' "$out" | grep -q "^BUSY $WRAP "; echo $?)"
+# The wrapper exits by itself once its child has; only then are both gone.
+[ -n "$kid" ] && kill "$kid" 2>/dev/null
+for _ in $(seq 50); do kill -0 "$WRAP" 2>/dev/null || break; sleep 0.1; done
+if ! kill -0 "$WRAP" 2>/dev/null; then wait "$WRAP" 2>/dev/null; KIDS=""; fi
+
+echo "---"
+echo "git-guard selftests: $PASS passed, $FAIL failed"
+[ "$FAIL" -eq 0 ]
Author	SHA1	Message	Date
jason.woltje	fd1aa8cc81	fix(scripts): row 211 R4 busy check ancestor reads, denied lookups, sourced tests (#1709 ) From the GPT review of R3 (row211-r3-gpt.md, R1 to R3 and Check 5): - slot-busy.sh: every ancestor status read must give a numeric PPid. A failed ancestor or cmdline read counts as gone only when a listing of the proc root succeeds and lacks the pid; anything else is exit 2 with no CLEAR. The [ -d ] and [ -e ] tests, which can't tell a denied lookup from a missing one, are gone. - slot-busy.sh: a shell-snapshot wrapper whose text sources (source or .) a gate, test or mutant script is BUSY; one that only runs children is still skipped. - install-git-hooks.sh: the hook is staged in a mktemp file in the hooks directory, not a pid-named path. - mutants.sh: exit 1 on a survivor, NO MATCH, COPY FAILED or a timeout; nine new mutants, 30 of 30 killed. test-git-guard.sh: RED 90/14, GREEN 105/0. BUILD.md R4 has the details, including a correction to the R3 bind-mount note.	2026-11-02 14:11:47 -06:00
jason.woltje	7d03f212db	fix(scripts): row 211 R3 push guard tags, installer hooks dir, busy check errors (#1709 )	2026-11-02 13:50:11 -06:00
jason.woltje	3a121885cf	row 211 (#1709 ): BUILD.md records the r2 rebase onto `78b69e1e6` (sage-4362); same patch-id, no conflict; doc only (cherry picked from commit `80924f7d5d`)	2026-11-02 13:50:11 -06:00
jason.woltje	bcd74ec33d	row 211 (#1709 , #426 ): a pre-push guard that refuses deletes and non-fast-forward pushes, its installer, and slot-busy.sh that exits 1 on BUSY scripts/git-hooks/pre-push refuses a delete, a remote tip missing locally and any update whose remote tip isn't an ancestor of the local tip; a new branch and a fast-forward pass. scripts/install-git-hooks.sh puts it in the common .git/hooks, refuses a set core.hooksPath or a different hook without --force-install, and runs a canary through git hook run. scripts/slot-busy.sh exits 0 CLEAR, 1 BUSY, 2 error. scripts/test-git-guard.sh (61 cases) and the mutant runner in agents/darkwing/work/queue-211; TOOLS.md gets the usage. Not run yet: written during Gander's slot (sage-2801). (cherry picked from commit `20e885dc35`)	2026-11-02 13:50:11 -06:00