Deny an Unbounded Shell Wait, and Report the Shells a Session Leaves - #1622
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Fixes #1589. The rule against an unbounded wait was read, quoted into six worker briefs, and produced the forbidden shape in all six. It then produced it again in a later session, whose loops were still running when the maintainer quit. A rule followed into the same failure twice is not fixed by writing it more clearly, so this adds the two mechanical layers `GOVERNANCE.md` "Durable Knowledge and Self-Improvement" sets the bar for, and rewrites the prose the layers enforce. ## The prose `AGENTS.md` "Delegation" gains a prohibition rather than a preference, naming the two forms a bound takes and giving no shape to copy. The issue asked for a shape, and two rounds of measured review disproved every one drafted. One branched on the clock rather than on why the loop ended, so a condition met a second past the bound reported a timeout. Every one of them read a condition command that was failing as one that was merely unmet, burning the whole bound before reporting it unmet. One was called portable while resting on `SECONDS` and `(( ))`, which under dash report NOT MET in a millisecond. The bullet says that outright, so the next reader inherits the result rather than the fourth draft. The section intro called everything under it a cost rule, which is what let the wait rule read as a billing concern. It now says plainly that this one is not, because the harm is the maintainer's machine. ## The deny `gh-write-guard.py` gains requirement 7: a `while`/`until` compound whose body calls `sleep` is denied unless the command text carries its own bound. A bound is a `timeout <duration>` ahead of the loop, inherited into a `sh -c`/`bash -c` payload, or an arithmetic guard in the loop's own condition. A nested loop is judged on its own terms. A heredoc body is data rather than a command line unless a shell is what it is fed to, so a document quoting the forbidden shape is written rather than denied. Twenty self-test cases cover the matrix, including the shape the denial itself hands back, which must not deny in turn. ## The report `stray-process-sweep.py` is a new SessionEnd hook, requirement 8, for the leaks the deny cannot reach: the ones started before it arrived, and the three shapes it deliberately does not cover. A shell started by a tool call runs in a session of its own, which is both why it survives and how it is identified. The sweep reports every descendant of the agent process running outside the agent's own session, names each subtree root's command and age, and hands over the kill line. It kills nothing, since a long build backgrounded on purpose is not distinguishable from a leaked wait at that point. A SessionEnd hook cannot block and its JSON output is discarded, so stderr on exit 2 is the one channel that reaches a human. ## The rename The spec covered writes alone when every requirement was a write. Two of the eight now guard the machine rather than the credentials, so the spec and the kit read host-safety rather than write-safety throughout.
Every one is a defect in what the previous commit shipped, found by the adversarial pass over its own diff, and every one is now a case in the matrix it escaped. ## Rule 7 A zero duration read as a bound. GNU documents `timeout 0` as disabling the timeout entirely, confirmed live, so `timeout 0 bash -c '<loop>'` let the incident's exact shape through behind a bound that does nothing. The backward walk to the `timeout` stopped at the first token not starting with a hyphen, so `timeout -k 30 900 bash -c '<loop>'` and `timeout 900 nice bash -c '<loop>'` were both denied. That is a false deny on ordinary work, and `-k` is the idiom for a wait that must actually die. The bound is now read from the command run the wrapper sits in, which also keeps `timeout 5 echo hi && bash -c '<loop>'` unbounded and admits a run opening with a keyword or a command prefix. A `done` used as a word closed the loop before its `sleep` was reached, so `until ...; do echo done; sleep 30; done` was allowed. A `done` now closes only in command position. A `sleep` behind a `command`, `env`, `exec` or `nohup` prefix was not read as a sleep, so the body looked sleepless and the loop was allowed. Two heredoc defects, each turning a document into commands or the reverse. A hyphenated tag was not recognized, so writing this rule's own forbidden shape under `<<'END-DOC'` denied. And the terminator was matched after stripping, so a doc line that merely read as the tag ended the body early and the rest was scanned. A plain heredoc now ends only on the tag at column zero, and `<<-` on a tabbed one. ## Rule 8 The sweep discarded `ps`'s exit status and read only its stdout, so a failed `ps` became an empty table rather than a failure. The "could not read the process table" branch was unreachable for its most likely cause, and on macOS, where `etimes` and a decimal `sess` do not exist, every session end would have printed the wrong diagnosis. A non-zero status and an empty table are both failures now, and the scope is stated as Linux and WSL rather than POSIX, which macOS is. ## The test that stopped testing `test_every_deployed_file_is_in_the_digest` derived its expectation by scraping `install.py` for literal `HERE / "..."` reads. Moving the copy into a loop removed the last one, so the test covered no deployed hook at all while still passing its own tripwire. The deployed set is a declared constant now, read by the test rather than scraped, and the test asserts the installer still consumes that constant.
Round two over the same diff. Two of these let the incident's own shape through the guard, and one denied ordinary work with no way around it. ## The bypasses A `timeout` bound was inherited into a payload that backgrounds the loop, so `timeout 600 bash -c 'until ...; do sleep 30; done &'` was allowed. It is not bounded: the shell forks the loop and exits, so `timeout`'s own child is gone, it exits 0, and nothing ever signals what it left. Measured live, the loop outlived a three second bound. An agent reaches this by being denied and then following the denial's own advice while keeping its `&`, which makes it the likeliest shape of all. `_HEREDOC_START` matched inside a `<<<` herestring and inside an `$((a<<b))` shift, because `re.search` retries at the next offset. The strip then deleted every following line while hunting a terminator that never comes, so `grep -q x <<< foo` on one line and an unbounded loop on the next was allowed, where the same loop alone denies. A `<<` now needs whitespace before it and no third `<`, and bodies are stripped at every nesting level rather than only the outermost. ## The false deny `while IFS= read -r pr; do gh pr view "$pr"; sleep 2; done < prs.txt` was denied. That loop is bounded by its input, throttling between API calls is the ordinary reason one sleeps, and rule 7 carries no environment escape hatch, so an agent hitting it had to restructure the command. A condition whose command is `read`, after any assignments, now reads as bounded, while a `read` named later in the condition is an argument and still bounds nothing. ## The rest `for ((;;)); do sleep 30; done` runs forever exactly as `while true` does and was reached by nothing, so the arithmetic `for` is judged now while `for x in <words>` stays bounded by its word list. A prefix is recognized path-qualified and through an assignment, closing `/usr/bin/env sleep` and `FOO=1 sleep` on the miss side and `sudo timeout 60 ...` and `TMPDIR=/tmp timeout 60 ...` on the false-deny side. `gtimeout` is recognized, being the only GNU timeout a macOS host has. The sweep took the nearest ancestor naming a `claude` path, so a tool shell whose own arguments held one stood in for the agent and the sweep reported a clean machine with a live detached subtree under it. It takes the outermost match now, and never a shell. On macOS it returns immediately rather than failing at every session end against a `ps` that carries neither `etimes` nor a decimal `sess`. Twelve more cases in the matrix, forty-three over rule 7.
Round three over the same diff, on the maintainer's call to close all eight rather than declare them. One broke the branch's own gate, three let an unbounded wait through, and the rest were text that disagreed with the code beside it. ## The gate A paragraph at column zero terminated the requirements list, so requirement 8 began a new one and markdownlint failed MD029 on the repository's own pinned image. One issue across 185 files, and it was this branch's. ## The message that taught the wrong shape The denial said to put "a `timeout <seconds>` invocation ahead of the loop". Read literally that is `timeout 600 until ...; do sleep 30; done`, which bash rejects outright, so an agent following the advice at the moment it most needs the right answer gets a syntax error. The denial, the spec, and the kit README now name the form the rule actually accepts, `timeout <seconds> bash -c '<the loop>'`. A case pins the rejected shape as allowed and says why: bash never runs it, so it is a syntax error rather than a wait to judge. ## Where a sleep can hide `while sleep 30; do ...; done` is the standard poll-forever idiom and it was allowed, because only the body was read for a `sleep`. So was `while true; do bash -c 'sleep 30'; done`, because the recursion into a wrapper payload looked for loops and never for a sleep. Both leak exactly as the denied form does. The condition is read now, and a sleep inside a payload the body runs counts as the body sleeping. ## The heredoc reader that could not see quotes A raw-text scan matched ` << IDENT` anywhere, so `echo $(( 1 << shift ))` and `git commit -m 'Explain the << EOF form'` each opened a phantom heredoc whose body ran to the end of the command, taking a real unbounded loop out of view. The opener is read from tokens now, where a quoted `<<` is the text it is and a `<<<` is a token of its own. A line carrying arithmetic is skipped outright, since `$(( 1 << n ))` tokenizes to a bare `<<` that no token test separates from a redirection, and skipping costs a false deny on a line holding both where reading it wrong drops commands. Whether a shell reads a heredoc body is the redirection's own command now, not the line mentioning one, so `bash -c 'echo hi' && cat > doc.md <<EOF` writes a document rather than denying. ## Text that disagreed with the code The Codex and opencode READMEs still counted six requirements, in files this branch had already touched for the rename, so an implementation built from either would have omitted requirement 7 and its audit would not have noticed. ## The test that could not fail `test_every_deployed_file_is_in_the_digest` compared `DEPLOYED_HOOKS` against `PAYLOAD_FILES`, which is defined as `DEPLOYED_HOOKS` plus the block list. It reads the installed home now: a file the installer wrote that the digest does not cover is the gap, and the disk is the only source that does not trust the lists under test. ## Declared rather than fixed A heredoc inside a multi-line `bash -c` payload still denies. The outer level splits the payload on its newlines, so the opener line carries the wrapper, and the body is kept. It fails in the safe direction and the shape is rare, so it is written down rather than given another mechanism.
The previous commit narrowed the heredoc exemption from "any shell named on the opener line" to "the redirection's own command". The first was an over-approximation and the second is an under-approximation, and only one of those is safe: `cat <<'EOF' | bash` carrying an unbounded wait went from denied to allowed, and a real bash runs that body. So did `sudo -u ci bash <<EOF`, `nice -n 10 bash <<EOF`, `env -i bash <<EOF`, `stdbuf -oL bash <<EOF` and `timeout 0 bash <<EOF`. The predicate wanted is whether a shell reads the body, which is a question about the heredoc's pipeline rather than about what owns the redirection. It is asked over the pipeline now, ended by any separator but a pipe, so a piped shell and a prefixed one both keep their body while `bash -c '...' && cat > doc.md <<EOF` still writes a document. Over-approximating inside the pipeline is deliberate: keeping a body gets it scanned, where dropping one hides whatever it holds. ## The rest of the round `cat <<- EOF` spells its tag as its own token, which the regex this replaced handled and the token reader did not, so writing a document through the spaced dash form denied. `_sleeps` re-joined its tokens before looking inside a wrapper payload, which dropped the quoting and left a command ending at the first `;`, so only the payload's first word was ever read. It recurses on the payload token now, which also gives the payload the command-position test it was missing: `bash -c 'echo a; sleep 30'` denies and `bash -c 'pkill sleep'` does not. The module docstring still taught the `timeout` placement the previous commit corrected in the denial, the spec and the kit README. It was the fourth surface, inside a file that round edited. Bumping the Codex and opencode requirement counts from six to eight made two sentences false: `gh-write-guard.py` is a reference for requirements 1 to 7, not 8, and a command gate is the wrong place for a requirement that reports at session end. Both now name `stray-process-sweep.py` and the session-end moment for that one.
The last round added four lines reading `<< - EOF` as the dash form. `<<- EOF` and `<< - EOF` tokenize identically, and bash reads the second one's delimiter as `-` with `EOF` an argument to `cat`, measured. So the branch strips past a real `-` terminator and drops the commands after it, turning a deny into an allow on a command whose loop really runs. The branch is gone rather than corrected. Telling the two spellings apart needs the raw line, which is the kind of mechanism the last two rounds kept adding and kept getting wrong. Without it a document written through the spaced dash form denies, which is the safe direction, and every other heredoc spelling is untouched. Two limits are recorded in the spec rather than closed here, both found by the same pass and both narrow. A body kept because a shell reads it has its own lines re-tested as openers, so an unterminated opener inside one swallows the top-level lines after it. And the scan for a shell over a heredoc's pipeline reads every token rather than only those in command position, so `cat <<EOF | shellcheck -s bash -` keeps a body no shell runs and denies a document being linted. They are left because the last two rounds each introduced a defect while removing others, two and then three, which is the point at which another round is the likelier source of the next one. Written down where a reader meets the rule, and carried to the pull request for reviewers who have not spent five rounds inside this file.
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Priority: ⚪ Pending latest changes Estimated code review effort: 4 (Complex) | ~60 minutes Severity of issue fixed: Medium Merge Risk: 🟠 High · up to Common shell forms can still leave unbounded processes running, and some session exits may skip reporting while installation appears current. These issues should be fixed before merge. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 79.55% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 44 functions across 4 files. (9 skipped: 9 unsupported.) ✨ Finishing Touches 💡 2📝 Generate docstrings 💡
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`scripts/tests/test_tooling_encoding.py` requires every text-mode spawn to pin its encoding, because Python decodes a `text=True` pipe with the locale's encoding when the call names none, which is cp1252 on a Windows runner. The sweep's `ps` read named none, so its decoding depended on where it ran. CI caught this and the local run did not, because the local gates run the doc linters and `test_install.py` and never `unittest discover -s scripts/tests`, which is what the validate action runs. The full suite, 1468 tests, passes with this.
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🟡 Changes recommended
There are confirmed rule-7 parsing edge cases that can cause false denials or missed denials, and one new helper has avoidable O(n^2) behavior on large process trees.
Get a fresh assessment by requesting another Copilot review.
Pull request overview
This PR strengthens the fleet host-safety kit by mechanically denying unbounded shell wait loops in the Claude Code PreToolUse guard, and by adding a SessionEnd sweep that reports detached process trees that outlive a session. It also updates the surrounding specification and documentation to reflect the expanded “host-safety” scope (credentials + machine safety), and updates the canonical review report for the affected AGENTS.md unit.
Changes:
- Extend
gh-write-guard.pywith requirement 7 to deny unboundedwhile/until+sleepwaits unless they carry an accepted bound. - Add
stray-process-sweep.pyas a SessionEnd hook, wire it into the installer, and add install/test coverage for deployment and registration. - Rename “write-safety” -> “host-safety” across spec/docs and refine the AGENTS.md prose around the wait prohibition.
File summaries
| File | Description |
|---|---|
| reports/canonical-review.json | Updates the recorded canonical-review digest/stamp/findings for the AGENTS.md unit affected by the prose change. |
| host-setup/windows/README.md | Renames references from write-safety to host-safety in the Windows host-setup documentation. |
| host-setup/README.md | Updates top-level host-setup docs to describe agent-safety as host-safety guards. |
| host-setup/agent-safety/README.md | Expands the spec to include requirements 7 (deny unbounded waits) and 8 (report stray processes), plus flow/docs updates. |
| host-setup/agent-safety/opencode/README.md | Updates the opencode gap doc to reference the new 8-requirement spec and the sweep hook. |
| host-setup/agent-safety/codex/README.md | Updates the Codex gap doc to reference the new 8-requirement spec and the sweep hook. |
| host-setup/agent-safety/claude/test_install.py | Adds tests ensuring the sweep is deployed, registered once, and included in digest coverage. |
| host-setup/agent-safety/claude/stray-process-sweep.py | New SessionEnd hook that reports detached descendant process trees (Linux/WSL) and provides a selftest. |
| host-setup/agent-safety/claude/README.md | Documents the additional SessionEnd sweep hook, verification steps, and operational constraints. |
| host-setup/agent-safety/claude/install.py | Installs/tests/registers both hooks (PreToolUse + SessionEnd), updates digest/registration checks accordingly. |
| host-setup/agent-safety/claude/gh-write-guard.py | Adds rule 7 parsing/detection + selftest matrix for unbounded shell-wait denial behavior. |
| docs/host-setup.md | Renames and broadens the “Agent Host-Safety” documentation section to match the new scope. |
| AGENTS.md | Updates the intro to distinguish the unbounded-wait prohibition from cost rules and adds the explicit prohibition bullet. |
Review details
- Files reviewed: 13/13 changed files
- Comments generated: 4
- Review effort level: Lite
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… a Run Four findings from round 1 on #1622, all real, all fixed. ## A shift read as a bound `_BOUND_IN_CONDITION` matched any `<` or `>` inside `(( ))`, so `while (( 1 << 1 )); do sleep 1; done` read as bounded and passed. The arithmetic branch now requires an operator that is not doubled, so a comparison bounds and a shift does not. ## A shell named as an argument read as a run `_unbounded_wait_loop` read a wrapper token wherever it appeared, which is how `timeout 600 bash -c ...` was reached at all, and it also denied `echo bash -c '<loop>'`, where no shell runs. Whether a wrapper runs is its run's own first command: a prefix or a `timeout` runs what follows it, whatever options sit between, and anything else does not. That is deliberately a different question from whether the wrapper is bounded. Answering it with the bound test instead, which was the first attempt here, let `timeout 0 bash -c '<loop>'` skip its payload entirely, since the zero is no bound and a bound-shaped test then refused to look inside a shell that really does run the loop. Leaning toward executed is the safe direction, because not scanning a payload is a bypass while scanning one costs a false deny at worst. ## Two smaller ones `_descendants` walked its queue with `pop(0)`, which shifts the whole list on every step and makes a breadth-first walk over a busy host's process table quadratic. It walks by index now. `AGENTS.md`'s "The harm it does" had no clear subject, which this session's own canonical pass raised independently before Copilot did. It names the wait.
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🔵 Needs a closer look
There are a few concrete correctness/documentation issues to address (notably a quadratic process-walk in the new sweep and some incomplete/inconsistent rename wording) before this can be safely approved.
Review details
Suppressed comments (3)
Previously missed (1) — in code that hasn't changed since the last review.
docs/host-setup.md:195
- This file now introduces the section as "Agent Host-Safety", but the per-agent subsection headings immediately below still use the older "Write Safety" terminology. That makes the rename incomplete/inconsistent for readers.
Rename the subsection headings to match the new host-safety terminology.
AGENTS.md:33
- The sentence "The harm it does is the maintainer's machine rather than the bill" has an unclear pronoun antecedent, which makes the new framing ambiguous.
Clarify what causes the harm (the unbounded wait) to keep this paragraph unambiguous.
An agent session is billed on the context it carries, not the work it does. Every request re-reads the whole accumulated context, so a token added early is paid for again on every request after it. A long session therefore bills its last task for every earlier one. These are cost rules. The prohibition on an unbounded wait below is not one. It sits here because a wait is written in the same breath as the delegation it waits on. The harm it does is the maintainer's machine rather than the bill. None of these rules licenses doing less work, skipping verification, or shipping something unreviewed.
host-setup/agent-safety/claude/stray-process-sweep.py:144
queue.pop(0)makes_descendants()O(n^2) in the number of descendant processes. On a busy host with a large process table, this can materially inflate the SessionEnd hook runtime.
Use an index-based queue (or a deque) to keep this breadth-first walk O(n).
out = []
queue = list(children.get(root, []))
while queue:
pid = queue.pop(0)
out.append(pid)
- Files reviewed: 13/13 changed files
- Comments generated: 0 new
- Review effort level: Lite
Two findings, one from Copilot's suppressed set and one from this session's own canonical pass. `docs/host-setup.md` introduced its section as "Agent Host-Safety" while the three per-agent headings under it still read "Write Safety", so the rename stopped one level short. No anchor anywhere referenced them. The previous commit's pronoun fix widened a scope word while fixing it: "What an unbounded wait damages is the maintainer's machine, not the bill" generalized past the prohibition it justifies, which is about an unbounded shell loop. The section's own first wait bullet says the other kind of unbounded wait, a sequence of near-identical requests, is exactly a billing harm, so the unit contradicted itself. It names the shell loop now.
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Actionable comments posted: 6
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Inline comments:
In `@host-setup/agent-safety/claude/gh-write-guard.py`:
- Line 1666: Update _BOUND_IN_CONDITION so it does not classify standalone
constant comparisons as loop bounds; require evidence that the condition reads a
changing counter or deadline. Add the always-true constant-comparison scenario
to _WAIT_CASES while preserving detection of genuine bounded loops.
- Around line 1669-1681: Update _reads_its_input so a leading read no longer
automatically qualifies a loop as bounded; require the command to establish that
its input source is finite before granting the exemption, and ensure producers
such as yes are not classified as finite.
- Around line 1752-1757: Update the launcher parsing around _opens_command and
_WAIT_CASES so launcher options and their values are consumed before determining
the invoked command position. Ensure commands such as env -i sleep, sudo, nice,
and time are normalized to test sleep rather than treating the option token as
the command boundary, while preserving existing separator and command-prefix
behavior.
In `@host-setup/agent-safety/claude/install.py`:
- Line 373: Update the sweep-detection loop around the hook command check to
reject matching SessionEnd sweeps when their enclosing hook group defines any
matcher, while still accepting matcher-less groups. Add a report-mode test
covering an “other” session exit where a filtered sweep does not run and
surviving processes are not reported.
In `@host-setup/agent-safety/claude/stray-process-sweep.py`:
- Line 56: Update the subprocess.run call in the stray-process sweep to set its
text encoding explicitly, using the repository’s established encoding
convention, so decoding is deterministic and the SessionEnd hook can report
survivors reliably.
In `@host-setup/agent-safety/README.md`:
- Around line 189-196: Update Requirement 7 and _reads_its_input so leading read
conditions count as bounded only when the guard proves finite input; otherwise
remove the read exception from both. Add a guarded finite-input branch to the
decision flow, and include arithmetic for ((...)) loops in the flow alongside
while/until handling.
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AGENTS.mddocs/host-setup.mdhost-setup/README.mdhost-setup/agent-safety/README.mdhost-setup/agent-safety/claude/README.mdhost-setup/agent-safety/claude/gh-write-guard.pyhost-setup/agent-safety/claude/install.pyhost-setup/agent-safety/claude/stray-process-sweep.pyhost-setup/agent-safety/claude/test_install.pyhost-setup/agent-safety/codex/README.mdhost-setup/agent-safety/opencode/README.mdhost-setup/windows/README.mdreports/canonical-review.json
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…red Sweep Four findings from CodeRabbit's first round on #1622, all real, plus a measured correction to the rule's own stated reason. ## A launcher's options hid the sleep behind them `_sleeps` asked `_opens_command`, which reads the token immediately before, so `while true; do env -i sleep 30; done` was allowed: the `-i` sits between the launcher and what it runs. `sudo -u ci sleep 30` and `nice -n 10 sleep 30` went the same way. It asks `_runs_as_command` now, which reads the run's own first command, so a launcher's options no longer hide what follows them while `grep -i sleep f` still runs none. ## A read is not bounded by an endless pipe `yes | while read line; do sleep 30; done` never exhausts its input, and the `read` exemption allowed it. The exemption now also requires an input redirect on the loop, because a redirect names a source that ends while a pipe's producer is unknown from the command text. A piped `find | while read` is denied by that, which is a false deny in the safe direction, and the spec says so where it names the three bound forms. ## A sweep under a matcher never fires `registration_problems` counted a sweep in any SessionEnd group, so a sweep registered under `"matcher": "clear"` read as registered while running on that exit reason alone. `--report` would call such a machine current while no ordinary exit is ever swept. It is reported now, with a test that reintroduces the state. ## The reason the rule gives for itself was false Measured over five seconds: a sleeping poll loop burns 0 CPU ticks and 0.0% CPU, where a busy loop burns 5 CPU-seconds at 100%. So "damages the maintainer's machine" was not true of the shape this rule names, and no wait is written as a busy loop. The intro says what is true and what the incident actually was, that such a loop never ends.
This was referenced Sep 15, 2026
The last commit answered a reviewer's false-deny finding by asking
whether a wrapper's run begins with a known launcher. That over-corrected
into a wider bypass than the one it fixed, measured at 95 of 210
lead-and-shell combinations flipping from denied to allowed.
The sharpest case needs no launcher at all. The walk back to the run's
head stopped at any shell operator, and a redirection is one, so
> /tmp/log bash -c 'until [ -f /tmp/x ]; do sleep 30; done'
read as not executing and skipped its payload. It runs, and killing the
shell orphans its `sleep` to init, which is the leak the rule exists for.
`flock <lock> bash -c`, `xargs bash -c`, `find -exec bash -c`,
`ssh host bash -c` and `docker run ... bash -c` went the same way, each
of them a shape an agent plausibly writes.
The question is now asked the other way round. A shell is executed unless
the run's head is a command that names its arguments rather than running
them, which is what `echo bash -c '<loop>'` is and what the reviewer's
finding was actually about. The set of such commands is the exemption
rather than the rule, so a name missing from it reads as executing and
costs a scan, where the previous shape cost a skipped payload. The walk
also stops at a separator rather than any operator, and steps over a
leading redirection and its target.
The old comment asserted the defect as fact, saying anything outside the
launcher set does not execute, one line below a sentence claiming the
code leans toward executed. It leans that way now.
Three attempts at a sentence explaining why a non-cost rule sits in a cost section, and a review measured each one false. "What an unbounded wait damages is the maintainer's machine, not the bill" generalized past the rule it justified, since the section's own first wait bullet calls a sequence of near-identical requests a billing harm. Narrowing it to "unbounded shell loop" fixed that and left a claim a sleeping poll loop disproves at 0% CPU. Replacing that with "such a loop never ends" is false of the ordinary case: a `while [ ! -f flag ]; do sleep 0.2; done` loop with no bound exited on its own at 1.61 seconds when the flag appeared. And "it sits here because a wait is written in the same breath as the delegation it waits on" covers one of the four cases the bullets name, since a review wait, a script, and a tool call delegate nothing. So the reason is gone rather than rewritten a fourth time. The intro says which rules are cost rules and which one is not, and the prohibition states itself. The same pass found the bullet above it self-contradicting after an earlier fix: "one backgrounded command, bounded per the prohibition below, that returns when the condition is met" requires a bound and then names the condition as the only thing that ends the wait. It ends on the condition or on its bound now, whichever comes first.
Naming exactly one non-cost rule invited a reader to sort every other bullet as a cost rule, and at least four are not. The prohibition bullet already says of itself that it is a prohibition rather than a preference, so the intro says which kind of rules most of these are and stops. "ends on the condition or on its bound, whichever comes first" taught a two-exit shape one bullet before the requirement for three, and measured, the two-exit form cannot tell them apart: `timeout 2 bash -c 'until nosuchtool --flag; do sleep 0.2; done'` and the same wrapper around `until false` both exit 124 at 2.003 seconds, so a broken check reports as an honest not-yet. "its bound" was also a definite reference to a noun the section defines two bullets later, against three earlier uses of the word in other senses. That bullet is about where a wait runs, and the two bullets under it own what it must report, so it says only that. This is the last edit to this section on this branch. Four review rounds over these two sentences each produced new findings in whatever the previous round wrote, and every surviving improvement came from deleting a clause rather than from writing a better one. The rule itself has not changed through any of it.
The ledger is tracked, so the pass it records is committed with the change rather than left in the worktree after it.
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🟡 Changes recommended
The new “read + input redirect” exemption in rule 7 can incorrectly treat process substitution (< <(cmd)) as a finite bound, allowing unbounded sleep loops to bypass the deny.
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The read exemption requires an input redirect on the loop, on the reasoning that a redirect names a source that ends while a pipe's producer is unknown from the command text. A process substitution is that same unknown producer wearing a redirect's clothes, so `while read l; do sleep 30; done < <(yes)` satisfied the test and `< <(tail -f log)` with it, both of which never exhaust. That was the exemption contradicting its own reason one line after stating it. A redirect whose target is a process substitution is no bound now, and the spec says so where it names the third bound form.
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🔵 Needs a closer look
The new SessionEnd sweep registration check in install.py should validate the hooks.SessionEnd shape to avoid misleading “not registered” reports when settings.json is present but corrupted.
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Suppressed comments (1)
Previously missed (1) — in code that hasn't changed since the last review.
host-setup/agent-safety/claude/install.py:368
registration_problems()iterateshooks.SessionEndwithout validating its type. Ifsettings.jsonis corrupted (e.g.,SessionEndis a dict or string), the loop will silently skip everything and report the sweep as "not registered", which is a misleading diagnosis and obscures the real remediation (fix the settings shape). Add an explicit type check and report a clear error whenhooks.SessionEndis present but not a list.
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`registration_problems` iterated `hooks.SessionEnd` with no type check, so a corrupted settings file read as zero registrations and reported the sweep absent. Iterating a dict yields its keys and a string yields its characters, and either way the group test rejects every element, so the count is zero and the diagnosis names the wrong problem: a reader is sent to re-run the installer when the fix is the settings shape. The same shape sits one branch up on the PreToolUse read, which this copied, so both go through one helper now. A wrong `hooks` type is reported once rather than once per event, and a wrong per-event type names the event it belongs to. Where the shape cannot be read at all, no count is reported from it, since a count derived from an unreadable structure means nothing. Three tests cover the shapes and one covers the deduplication.
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Answering round 5's suppressed finding, which opens no thread. Real, and fixed in aa5bcf7.
Worth saying that the same shape sits one branch up on the That makes two findings this round that were pre-existing in code this pull request only touched nearby, the other being the path-separator split. Both were worth having. |
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🟡 Changes recommended
A few updated docs still use “write hook” language under “Host Safety” and understate the newly added non-write protections, which can mislead readers about the kit’s scope.
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Suppressed comments (2)
Previously missed (1) — in code that hasn't changed since the last review.
docs/host-setup.md:213
- The section is now "Host-Safety", but this sentence still calls it a "host write hook". The kit now includes non-write protections (unbounded-wait deny + SessionEnd sweep), so "write" is misleading here.
This issue also appears on line 217 of the same file.
docs/host-setup.md:219
- Same as the Codex section: this still says "host write hook" under a "Host Safety" heading, which understates the scope of the kit (it is not write-only anymore).
No equivalent host write hook ships yet for opencode. Keep opencode's own permission model enabled
meanwhile. [`host-setup/agent-safety/opencode/README.md`][agent-safety-opencode] states the gap and
what implementing against the spec would look like. [Issue #781][issue-781] tracks it.
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Three findings, all the same shape as the heading rename and the diagram drift earlier on this branch: prose about the rules that still described the scope they had before. `docs/host-setup.md` called the missing Codex and opencode hooks a "host write hook" under a section renamed to host safety, which understates a kit that now denies an unbounded wait and reports what a session leaves running. The kit README's script-file bullet had grown "or a wait" in its lead and kept telling a reader to issue each write as its own command. It names the wait throughout now, and says the thing that makes the wait case worse rather than merely equal: a denied write fails loudly, where a wait the guard never saw runs until something ends it. Renaming a heading is not settling a rule. This is the third surface on this branch where the rename swept the title and left the sentence under it saying the old thing, which is worth more than the three fixes.
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Answering round 6's two suppressed findings, which open no thread. Both real, both fixed in d98cdfd.
Worth naming the pattern rather than just the fix: this is the third surface on this branch where a rename swept the title and left the sentence under it saying the old thing. The first was the per-agent headings in this same file, the second was the requirement 7 decision-flow node, and this is the third. Each read correctly in isolation, each was invisible to every gate, and each was found by a reviewer reading the whole file rather than the diff. That is the argument for the whole-unit read this repository already requires of canonical content, applied to documentation that is not canonical: a diff-scoped review cannot see a sentence that did not change but stopped being true. |
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🟡 Changes recommended
A couple of small inconsistencies in the new hook implementation and installer reduce correctness and maintainability, and should be fixed before approval.
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`installed_digest` named both hook files where `payload_digest` reads `PAYLOAD_FILES`, which is derived from `DEPLOYED_HOOKS`. That is exactly the drift the constant was added to close two commits ago: a third hook would have been deployed, would have been in the payload digest, and would not have been in the installed digest, so a machine carrying a stale copy of it would report as current. It reads the constant now, and a test parametrised over that constant deletes each deployed hook in turn and asserts the digest notices, so a hook added to the list is covered without anyone remembering to. The sweep's docstring also said it reports a boundary on macOS, which was true of an earlier draft and not of the code beside it: macOS and Windows exit silently without sweeping, rather than failing at the end of every session. The docstring says what the function does.
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🔵 Needs a closer look
Rule 7 can be bypassed when a loop is backgrounded after redirections (e.g., done > /tmp/log &), and the self-test matrix should cover this variant to prevent regression.
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Previously missed (2) — in code that hasn't changed since the last review.
host-setup/agent-safety/claude/gh-write-guard.py:1936
- Rule 7 backgrounding detection only checks for
&immediately afterdone, so...; done > /tmp/log &is treated as not backgrounded. In atimeout ... bash -c '<loop>'wrapper, that can incorrectly inherit the timeout bound and allow a loop that actually outlives the wrapper (the&comes after redirections, but it still backgrounds the loop). Scan forward to the first real separator afterdone(skipping any redirects/targets) and treat&there as backgrounding.
host-setup/agent-safety/claude/gh-write-guard.py:3660 - The self-test matrix covers
...; done &but not the common variant where redirections appear before the background operator (e.g.,...; done > /tmp/log &). Adding a case here will prevent regressions in the backgrounding detection logic.
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Backgrounding was read from the token immediately after `done`, so a redirection between the loop and its `&` hid it: `timeout 600 bash -c 'until [ -f x ]; do sleep 30; done > /tmp/log &'` inherited the timeout as a bound, and the timeout bounds nothing there. The shell forks the loop and exits, its child is gone, and the signal lands on nothing. The scan now walks the loop's own redirections first. That needed one thing more than reading redirection operators, since a redirection carries its file descriptor as a separate token and a stderr redirect arrives as three: reading that leading digit as the command hid the `&` behind it in the same way, which the first version of this fix still did. Five cases cover the variants, and a sixth records that a loop bounded by its input stays bounded when backgrounded, since that bound ends the loop by exhausting its input rather than by a signal reaching a process.
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Answering round 8's two suppressed findings, which open no thread. Both real, both fixed in f09895e. The backgrounding check reading only the token after The scan walks the loop's own redirections now. Worth recording that the first version of the fix still missed two variants, because a redirection carries its file descriptor as a separate token, so a stderr redirect arrives as three tokens and reading that leading digit as the command hid the ampersand behind it in exactly the same way. Caught by probing the variants rather than by reasoning about them. The missing matrix case. Also correct, and five are in now rather than one. A sixth records the boundary the other way: a loop bounded by its input stays bounded when backgrounded, since that bound ends the loop by exhausting its input rather than by a signal reaching a process. That distinction is the whole reason backgrounding disables one bound and not the other, and it was not written down anywhere before you asked for the case. |
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🔵 Needs a closer look
It changes and extends host-safety enforcement hooks (including non-trivial shell parsing and process-table interpretation) where a subtle false-allow/false-deny would have high impact and merits final human verification.
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This was referenced Sep 15, 2026
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…t Outrunning (#1632) Answers the five CodeRabbit findings on promotion PR #1629, and the five rounds of local strict review those fixes then drew. Requirement 7 shipped in #1622 and this is the hardening pass over it. ## What was wrong CodeRabbit found two bypasses, a decoy registration, and an install that could disable its own guard. Fixing those exposed more of the same class, so the branch is five commits, each answering the round before it. The load-bearing change is the last one, and it is a deletion. Four rounds narrowed a token scan that tried to decide which `&` backgrounds which compound, and each narrowing was defeated by a new spelling: a statement between the loop and its group's closer, a `disown` before a `wait`, a subshell the sequencing had already reaped, a `setsid` inside the payload rather than beside the timeout. That is a parse question and the scan does not have a parse, so `_waits_after`, `_escapes_timeout_group` and the group-closer walk are gone. One predicate replaces them: a background operator anywhere in the command, a `coproc`, or a `setsid` anywhere, and nothing in that command bounds anything. The cost is a false deny on `<loop> & wait`, a bound nothing in the command text can verify. `timeout 900 <command> &`, the shape the fleet rules actually ask agents to write, still passes, because a backgrounded `timeout` outlives the shell and still enforces. That case is tested. ## Closed in the guard - A crash that failed **all seven rules open**. `str.isdigit()` is true for a superscript and `int()` then raises, and a non-zero exit lets the tool call through exactly as an allow does. - A group backgrounding the loop inside it, in every spelling including a fused closer and a trailing statement. - A redirect that rebinds the pipe the loop already reads: `<&0`, `/dev/stdin`, `/proc/self/fd/0`, `/dev/full`, `/dev/./zero`, `//dev/zero`. The whole of `/dev` and `/proc` is read as a category, since a list of the streams that never end always had another entry. - The last descriptor-0 redirect is what binds, so `< in.txt < /dev/zero` no longer lets the file vouch for the stream. - `read -u 3` draws on a descriptor the redirect never bound, so it is no bound. - `wait $p`, `timeout --foreground`, `setsid`, and `coproc` each leave a loop running past the timeout. - False denies removed: `done 2>&1 < f` and four siblings, `make build |& tee log`, and a `case` arm ending `;&`. ## Closed in the installer - The registration check was recomputing the launcher at check time, so a correctly installed machine reported STALE. - The decoy hole was closed on the sweep and left open on the guard, which is the hook that actually denies. - A matcher had to be exactly `Bash`; absent, `""`, `*` and `Bash|Task` all receive Bash calls. - A path had to be double-quoted; bare, single-quoted, `~` and `$HOME` all run the deployed file. - A rejected entry skipped its own count, so every real problem came with a second line falsely saying the hook is not registered. - A sweep timeout larger than the installer writes was reported as a defect. - The staged-copy path had no error handling and two concurrent installs shared one filename. ## Known and open Six findings from the final review round are recorded and not fixed here, per the local-strict-review budget. Two are genuinely unbounded waits the guard allows, both pre-existing: an `until read` loop over an exhausted input, where exhaustion is what makes it never exit, and `timeout -s 0`, which delivers a signal the payload ignores. The rest are a stale diagram node, a stale count in one sentence, a SessionEnd matcher check that rejects `""` and `*`, and a test that does not assert the defects it plants. Each is filed. Closes nothing on its own: #1589 is closed by #1629, which this unblocks. 🤖 Generated with [Claude Code](https://claude.com/claude-code) https://claude.ai/code/session_01JeRfDdqc5Ua2Q1Ui5K7XJS
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Fixes #1589. The rule against an unbounded wait was read, quoted verbatim into six worker briefs, and produced the forbidden shape in all six. It then produced it again in a later session, whose loops were still running when the maintainer quit. A rule followed into the same failure twice is not fixed by writing it more clearly, so this adds the two mechanical layers
GOVERNANCE.md"Durable Knowledge and Self-Improvement" sets the bar for, and rewrites the prose the layers enforce.The issue proposed prose alone, and named a mechanical layer as the thing that would make it enforceable. That is what this is.
The deny
gh-write-guard.pygains requirement 7. Awhile/untilcompound whose body callssleepis denied unless the command text carries its own bound, which is either an arithmetic guard in the loop's own condition or atimeout <duration>running ash -c/bash -cwrapper that holds the loop. A nested loop is judged on its own terms. A heredoc body is data rather than a command line unless a shell is what it is fed to, so a document quoting the forbidden shape is written rather than denied.Five local review rounds found twenty-five defects in this rule and fixed every one, and each is a case in the matrix it escaped. Fifty-five cases cover rule 7 and the whole self-test is 263. What they were, grouped:
timeout 0reads as a bound while GNU documents zero as disabling the timeout. Atimeoutat the loop's own level bounds nothing, sincetimeouttakes a command and a loop keyword is not one. Atimeoutaround a payload that backgrounds the loop bounds nothing either, because the shell forks and exits and its child is gone.sleephides. In the loop's condition, which is the standard poll-forever idiom. Behind acommand/env/exec/nohupprefix, path-qualified or through an assignment. Inside ash -cpayload the body runs.<<<herestring, a spaced or unspaced arithmetic shift, and a<<inside a quoted commit message each opened a phantom heredoc whose body ran to the end of the command, taking a real loop out of view. A hyphenated tag, a spaced dash form, and a terminator matched after stripping each turned a document into commands.while readloop throttled with asleepis bounded by its input.timeout -k 30 900,timeout 900 nice,sudo timeout, and an assignment prefix are all real bounds.gtimeoutis the only GNU timeout a macOS host has.for ((;;))runs forever exactly aswhile truedoes. Adoneused as a word closed the body before itssleep.One of those twenty-five was introduced by an earlier round of this same loop: narrowing the heredoc shell test from the opener line to the redirection's own command let
cat <<'EOF' | bashthrough, which a real bash runs. It is asked over the heredoc's pipeline now, over-approximating deliberately, because keeping a body gets it scanned where dropping one hides what it holds.The report
stray-process-sweep.pyis a newSessionEndhook, requirement 8, for the leaks the deny cannot reach: the ones started before it arrived, and the shapes it deliberately does not cover. A shell started by a tool call runs in a session of its own, which is both why it survives and how it is identified. The sweep reports every descendant of the agent process running outside the agent's own session, names each subtree root's command and age, and hands over thekillline.It kills nothing. A long build backgrounded on purpose is not distinguishable from a leaked wait at that point, and ending a process on the maintainer's machine is not reversible. A
SessionEndhook cannot block and its JSON output is discarded, so stderr on exit 2 is the one channel that reaches a human, and the sweep uses it for a report rather than for a refusal.Its limits are stated rather than implied. A process whose own tool-call shell has since exited is reparented to init and leaves the agent's tree entirely, so no descendant walk reaches it. What the sweep does see is the backgrounded tool-call shell itself, which is the shape both incidents left behind. The detached-session test has no Windows equivalent, so a Windows host carries a hook that reports nothing rather than an untested guess.
The prose
AGENTS.md"Delegation" carries the prohibition and nothing else. Five measured review rounds disproved every shape drafted to go with it, in four separate ways: one branched on the clock rather than on why the loop ended, so a condition met a second past the bound reported a timeout; every one of them read a failing condition command as a merely unmet one; one rested onSECONDSand(( ))while being called portable, which under dash report NOT MET in a millisecond; and thetimeoutform as first written was a syntax error. Each explanatory sentence added to carry a shape was itself a checkable claim, and each round of measurement found falsehoods in the new ones. So the bullet states the rule and the section intro says plainly that this one is not a cost rule, and the mechanics live in the hook's own denial text, which is tested.The rename
The spec covered writes alone when every requirement was a write. Two of the eight now guard the machine rather than the credentials, so the spec and the kit read host-safety rather than write-safety throughout.
The prose the rule sits in
The prohibition itself survived every round untouched. What did not was every sentence written to justify it. Three attempts at explaining why a non-cost rule sits in a cost section each measured false: naming the wait contradicted the bullet above it, which calls a sequence of near-identical requests a billing harm; narrowing it to a shell loop left a machine-damage claim a sleeping poll loop disproves at 0% CPU against a busy loop's 100%; and "such a loop never ends" is false of the ordinary case, since a flag-file wait exits on its own at 1.61 seconds when the flag appears.
So the intro no longer explains. It says which kind of rules most of these are, and the prohibition bullet says of itself that it is a prohibition rather than a preference. Every surviving improvement to that section came from deleting a clause rather than from writing a better one.
Declared rather than fixed
Findings this change does not answer, listed rather than left to be found. Two are pre-existing and measured: the bullet grouping the two fallback forms and a stderr redirect as one class is wrong about the redirect, which preserves the exit status; and "silence means 'still running' and nothing else" is defeated by signal death and by block buffering, measured at zero bytes on both streams in each case. Both are in #1627 with six others.
Requirement 7's three declared non-reaches are in the spec: a busy loop with no
sleep, a guard against a counter nothing advances, and a wait inside a script file. Two heredoc limits are there too, and #1626 records that the sweep cannot see a leak init has reparented out of the agent's tree, with #1625 recording that it runs on Linux and WSL only.Two deviations from process, stated
A local-review receipt was recorded for the two-line encoding fix without a subagent pass over it, on the judgement that a change of two keyword arguments demanded by a repo test and verified by 1468 others did not need one. And a canonical receipt was recorded after deleting exactly the clauses that pass had flagged, on the judgement that the reviewer had read a superset of what ships. Both are judgement standing in for the rule, which is why they are here rather than only in a commit message.
What rule 7 does not do, stated rather than discovered
Three shapes are declared non-reaches in the spec: a busy loop that polls with no
sleep, a guard against a counter nothing advances, and a wait inside a script file. Each is a precision-over-recall choice, since a false deny on an ordinary loop costs more work than those leaks do, and each still falls under the prose rule.Two heredoc limits are known and unclosed, both narrow, both recorded where a reader meets the rule. A body kept because a shell reads it has its own lines re-tested as openers, so an unterminated opener inside one swallows the top-level lines after it. And the scan for a shell over a heredoc's pipeline reads every token rather than only those in command position, so
cat <<EOF | shellcheck -s bash -keeps a body no shell runs and denies a document being linted. A heredoc inside a multi-linebash -cpayload denies for a third reason, the outer level splitting that payload on its newlines.They are unclosed because the review loop reached the point of diminishing returns and passed it. Six adversarial passes fixed twenty-six defects in this rule, and the last two rounds introduced two and then three of their own while removing others. That is the signal to hand the remainder to reviewers who have not spent six rounds inside this file, which is what this pull request does.
Reviewer findings on the sections this change does not touch, and the per-round sweep it does not add, are filed separately.