fix(run-shape-guard): register it, and refuse a timer wearing a wait's clothes

[wenzowski]

The gate that was never wired, and the timer it would not have caught

Two defects at one edit site in mise-tasks/run-shape-guard.

It had never been registered

git log -S'run-shape-guard' -- .claude/settings.json returns zero commits. In
267 lines, two bats suites, a MUTANT_GATES row, five workflow comments, two
memories and an AGENTS.md claim to gate the rule, the guard had never been wired
to anything. Every refusal it can emit had been delivered to nobody.

Its own header says "prose is feedforward only (non-negotiable rule 2), and the
session that hit this had read the prose." It then shipped as prose itself — the
mechanism landed, the wiring didn't. AGENTS.md's "Gated by run-shape-guard"
was the worst half: a reader who checks the claim stops looking.

It is now a PreToolUse/Bash entry with its owning row in
hooks-wiring-check's DECLARED table, so the registration is decided in both
directions by an existing gate — a missing row is wiring-sibling-command, a
missing entry is wiring-declaration-stale.

Registering by path meant clearing hook-pin-check first

A by-path hook does not get mise's env. The guard's three jq calls would have
resolved to nothing, and since every read here is fail-open by design, that is not
an error — it is a silent allow: the whole guard reporting clean while judging
nothing.

The two payload reads move to mise-tasks/payload-field, and deny()
hand-escapes its document the way fanout-guard's decide() does. Deliberately
not the #PIN-OK: exemption, which exists for reads no extraction surface can
serve (mcp-attach-check's settings file); a hook payload is precisely what
payload-field serves.

That left one read payload-field could not answer — run_in_background, which
CLOUD-613 named as a fact the mediated envelope hides. hook::Field is a fixed
allowlist and its doc says "growing it is a deliberate edit here, which is the
point", so this is that edit.

run_in_background was standing in for the thing that actually matters

The flag used to skip the foreground-sleep family outright. That reasoning is right
about the case it had in mind — a background until <test>; do sleep 1; done is
the documented form and denying it would be the false positive CLOUD-199 measured
— but the flag is the wrong proxy for it, and the guard's own remedy sentence
already said so: what makes a wait correct is a command that EXITS when the
condition holds.

Measured 2026-08-21, one session landing CLOUD-776:

	count
backgrounded sleep 590; tail -6 land.log	490
mise run verify calls	5
polls that changed a decision	2
backgrounded tasks that re-invoked the session on exit	523 / 524

The notification those 490 calls were duplicating already existed and fired every
time, failures included. The flag had moved the poll out of the guard's view rather
than making it correct.

So the exemption now asks for the exit condition itself: a background call carrying
an until/while construct is exempt as before; a background bare sleep is
refused as a timer.

What the predicate deliberately does not do

The loop test is over the whole scrubbed command, never the element. The list
split turns until <test>; do sleep 5; done into three elements and the one
carrying the sleep has no keyword in it — an element-scoped test would deny every
correct wait, which is exactly the false positive that gets a guard bypassed.

It is coarse in the allowing direction on purpose: for i in $(seq 60); do sleep 10; done is a timer too and is not caught. Narrowing that costs a real
parser, and CLOUD-199's bar is that a guard be 100% right on a narrow shape rather
than 80% right on a broad one.

Matched with <<< and never a pipe — grep -q exits on its first match, which
SIGPIPEs the producer, and under pipefail a MATCH would have read as "no
keyword" and denied every correct wait. pipefail-grep-check caught that shape
in the first commit attempt.

The refusals name the remedy

Both texts now point at the two real affordances: the exit notification (523 of
524, measured) and mise run alive for "is it still going" rather than "has
it finished". An agent refused without being told what to do instead writes a
differently-spelled poll.

Tests

Nine new rows, five of them allows, because the allows are what keep the rule
from being bypassed — a while loop, a curl wait on genuinely external state, a
backgrounded long-running command with no sleep, a foreground call with no sleep,
and the shape written inside a commit message. #MUTANT background-timer-exempt
restores the old unconditional skip, so the timer rows go red when the rule is
removed (CLOUD-418).

Doctrine

AGENTS.md's conflated sentence — "Backgrounding keeps the session alive and
re-invokes you on exit; an idle turn gets the VM reclaimed" — is split. The
measured session collapsed it into "stay busy or die" and satisfied the imagined
requirement with make-work sleeps. It now says the exit notification is the
wake-up, that "idle" means a turn with nothing backgrounded, and that it is
committed-and-pushed rather than activity that survives a reclaim. Its nohup/&
bullet now names verdict-not-discarded, where those shapes moved with CLOUD-443,
instead of this guard.

Risk, stated

plan-hold (CLOUD-491/515) was a gate in exactly this area built on an unmeasured
premise; it was measured twice, failed twice, and was removed. The premise here
is measured. The falsifier to watch is unchanged: if this deny fires on a
well-formed wait it will be bypassed and is then worse than nothing, which is why
the allow rows are not padding.

Not here, deliberately

CLOUD-489's two families — a loop whose condition polls this session's own process
or its own task-output file — are a different predicate over the same line and stay
on their own issue. This one unblocks them: neither enforced anything while the
guard was unregistered.

Verification

mise run hook-pin-check, mise run hooks-wiring-check, mise run pipefail-grep-check, batten policy budget, both guard bats suites (30/30), and
mise run verify.

Closes CLOUD-821

Summary by CodeRabbit

• New Features

  • Added run-in-background as an available payload field in command output and shell completions.
  • Background polling loops using until or while remain supported.

• Bug Fixes

  • Standalone background timers and backgrounded sleeps that do not monitor a condition are now blocked.
  • Improved guidance explains exit notifications, status checks, and appropriate background execution.

• Documentation

  • Updated command references and behavior documentation for background execution safeguards.

[linear-code]

CLOUD-821 `run-shape-guard` has never been registered, so AGENTS.md's "Gated by `run-shape-guard`" is prose, and its `run_in_background` exemption passes a timer with no exit condition

Why

Landing CLOUD-776 took ~950 tool calls in one session, and almost none of them were work. Measured from that session's own transcript:

	count
sleep N; tail <log> calls	490
background tasks launched	524
median launch → completion notice	590s — i.e. exactly the nominal sleep
content-free replies to task notifications	40
mise run verify calls	5
polls that changed a decision	2

The mechanism being hand-rolled already existed and demonstrably fired: 523 of 524 backgrounded tasks re-invoked the session on exit, including every land failure and its final success. Every genuine intervention came from a task exiting, never from a poll. This is the same duplication CLOUD-489 measured, in a shape CLOUD-489's predicate does not reach — see Relation to CLOUD-489 below.

Two defects, one file, one edit site.

Defect A — the guard has never been registered.

git log -S'run-shape-guard' -- .claude/settings.json returns zero commits: the string has never appeared there. The wired PreToolUse entries are the engine dispatcher, issue-search-guard, issue-read-guard, board-move-guard, connector-verb-guard, connector-allow-guard, fanout-guard. Every other reference to run-shape-guard in the repo is prose — two memories, five workflow comments, a MUTANT_GATES row, a doc comment in exec.rs, and AGENTS.md:144's claim "Gated by run-shape-guard."

So mise-tasks/run-shape-guard is 267 lines with two bats suites and a mutation census row, enforcing nothing. Its foreground-sleep deny text (:213) is precisely the coaching that would have redirected the measured session — "act on its exit; the harness re-invokes you … never poll in the foreground" — and it has never been delivered to anybody.

This is non-negotiable rule 2 failing one level up. The guard's own header says "Prose is feedforward only (non-negotiable rule 2), and the session that hit this had read the prose." The guard then shipped as prose itself: the mechanism landed, the wiring didn't. AGENTS.md:144 asserting a gate that does not exist is the worst half of it — a reader who checks the claim stops looking. CLOUD-400 is the same shape one layer down (batten hook wired into no harness, every mediated_call row gating nothing) and was closed as a duplicate of the cutover; this is that class recurring for a shell guard that the cutover leaves in place.

Note what this does not say: foreground sleep is still refused in practice, by the harness's own block. That block is what redirected the measured session into run_in_background: true — out of a gated shape and into an ungated one — which is Defect B.

Defect B — run_in_background: true is treated as proof the wait is well-formed.

run-shape-guard:197 skips the entire foreground-sleep family whenever the flag is set. The comment at :193 explains why the flag was chosen, and it is right about the case it has in mind. But :213 states what actually makes a wait correct:

background a command that EXITS when the condition holds (until <test>; do sleep 1; done), which is a background wait and is allowed.

sleep 590; tail -6 /tmp/land.log has no exit condition. It is a wall clock standing in for an event — the exact defect mem:workflow/landing-loop names ("a guessed sleep standing in for 'the background thing has happened'"), and it is what was written 490 times. The flag moved the poll out of the guard's view rather than making it correct. The predicate the comment already describes — is there an exit condition — is decidable from the command string.

Relation to CLOUD-489 (In Progress, no branch, no code on main)

CLOUD-489 narrows the same :197 exemption and its argument is adopted here unchanged. Its predicate is over loop conditions: family 1, a loop whose condition invokes pgrep/kill -0/ps; family 2, a loop whose condition reads a harness task-output path. Both require a loop construct to be present. The measured shape here has no loop at all — a bare sleep, then a tail. CLOUD-489's families do not match it, and its own carve-out language ("a command that exits when the condition holds") presumes the loop this shape omits.

So this is the complement, not a duplicate: CLOUD-489 refuses the wrong thing to wait on, this refuses waiting on nothing. They meet at the same line and want the same deny text. Defect A blocks both — neither predicate enforces anything until the guard is registered — hence blocks CLOUD-489.

Refinement — Ready

• Source of truth (§1). mise-tasks/run-shape-guard, which already owns every run-shape refusal and already reads tool_input.run_in_background; .claude/settings.json plus hooks-wiring-check's DECLARED table for the registration. No new task, no second guard.
• Mechanism as a computable predicate (§2). Two parts.
  1. Registration. A PreToolUse entry on matcher Bash in .claude/settings.json pointing at $CLAUDE_PROJECT_DIR/mise-tasks/run-shape-guard, plus its mise-tasks/run-shape-guard <this-key> row in hooks-wiring-check's DECLARED (:105-116). Without the row the entry is wiring-sibling-command; without the entry the row is wiring-declaration-stale. Both directions already gate, so the registration is decided by an existing check rather than by review (CLOUD-713/777).
  2. The exemption narrows from "run_in_background is set" to "run_in_background is set and the stage resolving to sleep is inside an until/while loop". Judged per stage after the existing heredoc-drop and quote-scrub, over the already-scrubbed element, using resolve() and the elements[]/seps[] split the file already has. A predicate over the scrubbed element, not a new parser.
• Blocker to clear in the same change (§8, a precondition rather than a dependency). hook-pin-check refuses a hook registered by path that shells out to a mise-pinned tool, because a by-path invocation does not get mise's env and every read here is fail-open — it would silently allow. run-shape-guard:50-51 and :197 read the payload with jq. The three routes, and why the third:
  • #PIN-OK: jq — the exemption exists for reads that no extraction surface can serve (mcp-attach-check's settings/log files). A hook payload is exactly what payload-field serves, so claiming it here is claiming the wrong exemption.
  • register as mise run -q run-shape-guard — unblocked (hook-pin-check does not judge mise run registrations), but pays ~203ms of task-runner startup on every Bash call, which is the hot path CLOUD-479/435 measured and moved three hooks off.
  • payload-field for all three reads. command and hook_event_name are already served. run_in_background is not: hook::Field (hook.rs:1396) is a fixed allowlist with no such variant — which is CLOUD-613's observation that "the last two families need facts the mediated envelope hides: the call's run_in_background." The enum is #[non_exhaustive] and its doc states "Growing it is a deliberate edit here, which is the point", so adding Field::RunInBackground is the sanctioned edit, not a workaround. It is a boolean about the call, never content, so rule 4 holds: Field's safety argument is that it can never name Envelope::input, and a bool cannot carry a secret.
• Effect (§3). run-shape-guard is a PreToolUse guard reading a payload on stdin; it adds no command to the surface, so no effect declaration and no change to the derived read-only allowlist. batten payload field run-in-background is a read on an existing read-only verb.
• Output & exit contract (§5). Unchanged shape: permissionDecision: "deny" JSON on stdout, exit 0, fails open on anything unparseable, honours BATTEN_RUN_SHAPE_BYPASS=1. Pointer-only. The deny text gains the remedy half — the completion notification already wakes you (measured 523/524 this session, and CLOUD-489's three-arm controlled measurement showed even a near-idle backgrounded loop is notified and not evicted), and mise run alive (CLOUD-425) for a single push-based phase read when the question is "is it still going" rather than "has it finished". An agent refused without being told what to do instead writes a different poll.
• Commit / bump (§6). fix(run-shape-guard) for the guard, wiring and doctrine → patch. feat(hook) for Field::RunInBackground → non-breaking (#[non_exhaustive]); mise run semver decides, not this paragraph.
• Test obligation (§7). tests/run-shape-guard.bats, in the suite's existing idiom (:14-25: synthesize with jq -nc, pipe to the script, assert on $output — never exit status, since the guard always exits 0). Mutation-checked per CLOUD-418: a new #MUTANT slug|sed|case-substring row beside :44-45, since MUTANT_GATES (mise.toml:316) already lists this task and a new family with no row fails no-mutant-declared.
  • THE MEASURED SHAPE: — backgrounded sleep 590; tail -6 /tmp/land.log is denied. Pins this incident, matching the naming convention at :39 and :105.
  • Backgrounded bare sleep 300 — denied; waits for nothing and reports nothing.
  • The allows carry equal weight (CLOUD-199 — a guard with false positives gets bypassed): backgrounded until mise run alive | grep -q land; do sleep 5; done stays allowed; until curl -sf …; do sleep 5; done stays allowed; a backgrounded long-running command with no sleep stays allowed; a foreground command with no sleep stays allowed; sleep inside a quoted span or heredoc is untouched.
  • The denial names the remedy — assert the text contains mise run alive and the exit-notification sentence, not merely that it refused.
  • Wrapper trio (gh-guard.bats:105-125 convention): allow is silent, fails open on unparseable input, honours BATTEN_RUN_SHAPE_BYPASS=1.
  • mise run hook-pin-check green with the guard registered by path — the blocker, asserted rather than remembered.
  • mise run hooks-wiring-check green — the DECLARED row and the entry agree, in both directions.
• Doctrine, the feedforward half (rule 2: prose ships with its mechanism, never instead of it). AGENTS.md:138-139 — "Backgrounding keeps the session alive and re-invokes you on exit; an idle turn gets the VM reclaimed" — is two clauses that the measured session collapsed into "stay busy or die", then satisfied with make-work sleeps. Split them so they cannot be read as one: a backgrounded task's exit notification is the wake-up, and idling until it arrives is the designed state; "an idle turn" means a turn with nothing backgrounded; and per AGENTS.md:147 it is committed-and-pushed, not activity, that survives a reclaim. Verify AGENTS.md:144's gate claim is true once the registration lands, and correct .claude/rules/toolchain.md's guard bullet to the new predicate and bypass.

Acceptance

• run-shape-guard is registered and fires: a Bash call carrying sleep 590; tail -6 /tmp/land.log with run_in_background: true comes back refused, with text naming mise run alive and the exit notification. Behavioural, end to end — not "the bats suite passes".
• hook-pin-check and hooks-wiring-check are both green with it registered by path.
• Every genuinely-well-formed wait stays allowed, pinned by test in both directions. If this deny fires on a correct wait it will be bypassed and is then worse than nothing — which is why the allow rows are not padding. plan-hold (CLOUD-491/515) was a gate in exactly this area built on an unmeasured premise; it was measured twice, failed twice, and was removed. The premise here is measured: 490 polls, two of which changed a decision.
• AGENTS.md:144's claim is true rather than aspirational, and :138's sentence no longer licenses the misread.
• Anti-vacuity per CLOUD-418: removing the rule turns the new cases red under mise run mutant.

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📝 Walkthrough

Walkthrough

The change exposes run-in-background payload metadata and updates run-shape-guard to deny backgrounded sleep timers unless they use until or while conditions. It adds hook wiring, shell completions, documentation, and regression tests.

Changes

Background execution guard

Layer / File(s)	Summary
Background execution payload field crates/batten/src/hook.rs, completions/batten.*, man/batten-payload-field.1	The payload field API exposes run-in-background from snake_case or camelCase boolean input. Shell completions and the manual list the field.
Timer guard enforcement .claude/settings.json, mise-tasks/run-shape-guard, tests/run-shape-guard.bats	The Bash PreToolUse hook invokes the guard. The guard reads background metadata through payload-field, allows condition-driven background loops, denies bare background timers, escapes denial JSON, and tests the updated behavior.
Guard guidance and registration .claude/rules/toolchain.md, AGENTS.md, mise-tasks/hooks-wiring-check	Documentation describes exit notifications, mise run alive, background command requirements, guard registration, and the declared wiring exception.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 50efe

The change wires the guard into Bash hook processing and rejects background bare sleeps while preserving loop-based waits; no actionable merge-blocking risk remains, so it is merge-ready after normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant BashPreToolUse
  participant runShapeGuard
  participant payloadField
  BashPreToolUse->>runShapeGuard: invoke for Bash command
  runShapeGuard->>payloadField: read run-in-background
  payloadField-->>runShapeGuard: return true or false
  alt backgrounded sleep without until or while
    runShapeGuard-->>BashPreToolUse: deny with timer guidance
  else condition-driven background loop or unrelated command
    runShapeGuard-->>BashPreToolUse: allow
  end

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Check name	Status	Explanation	Resolution
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Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the guard registration and the new refusal of timer-like background commands.
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Inline comments:
In `@mise-tasks/run-shape-guard`:
- Around line 86-87: Remove the duplicate background-field extraction in the
Bash hook flow, keeping a single assignment that invokes payload-field
run-in-background and preserves the existing empty fallback behavior.

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