test(sandbox): the launch-control HOME sits outside every launcher grant (cli#558)

[tps-anvil]

The launch-control suite built its test HOME under a hard-coded /var/tmp; the runtime-launch fixture built its sandbox base under tmpdir() on macOS. The launcher grants bun's temp dir and the toolchain/interpreter read roots, and its runtime-options gate refuses a HOME that falls inside any of them, before the case under test runs.

Both now take their base from the launcher's own grant sources through one shared helper, packages/cli/test/helpers/launcher-grants.ts, so the base sits outside every launcher grant. If no candidate lies outside the grants, the helper refuses up front with one message naming TMPDIR and the grant; if no candidate exists it says so and lists them. The grant list is read from the launcher, not duplicated.

The chosen base is returned as its real path and grants are compared by real path, so on darwin, where /var/tmp is a symlink to /private/var/tmp, paths built on the base match the paths the launched child reports.

The refusal paths are tested in packages/cli/test/launcher-grants.test.ts (candidates are a parameter of sandboxHomeBase, defaulting to /var/tmp then tmpdir()), along with the grant prefix boundary (/tmp/a is covered, /tmpfoo is not).

Closes #558

Evidence (main 1abce03):

• launcher-grants.test.ts: 7 pass / 0 fail, measured on 84a8691 (adds the two symlink cases). Mutation on 84a8691: with the realpath dropped from sandboxHomeBase, the symlink case and the base-equals-real-path case fail (2 fail / 5 pass); restored → 7 pass. Earlier mutation, measured on 2ffe3e7: with the inside-a-grant throw removed, the refusal test and the /var/tmp-suggestion test fail (2 fail / 3 pass); restored → 5 pass.
• The four files that use makeSandbox/runtime-launch-fixture — profile-grant-credential-policy (86), runtime-attested-launch (166), runtime-dir-credential-overlap (31), launch-attestation (36) — run with the default temp dir and with TMPDIR=/tmp: 319 pass / 0 fail, exit 0, measured on 5c8224d. The only refusal text printed is the one a passing fails-first fixture asserts. (The suite launcher owns TMPDIR and always sets it inside its root, so the TMPDIR=/tmp run uses an isolated-root driver that sets the child's TMPDIR to /tmp.)
• sandbox-launch-control.test.ts: 139 pass / 0 fail, measured on 5c8224d.
• Full cli suite (196 files): 3024 pass / 5 skip / 0 fail, measured on 0130350; later changes are not re-run.
• Mutation: with the fixture's base reverted to tmpdir() — the removed macOS branch — and TMPDIR=/tmp: profile-grant-credential-policy 81 pass/5 fail, runtime-attested-launch 162/4, runtime-dir-credential-overlap 28/3, launch-attestation 36/0 → 12 fail, exit 1, each an early refusal (the writable grant '/tmp' overlaps the TPS credential root ~/.tps/auth). Restored → 319 pass / 0 fail. Measured on 5c8224d.
• bun run lint:ci exit 0 on 2ffe3e7; node scripts/changelog-fragments.mjs check → 76 fragments, [Unreleased] holds only the managed note.

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Summary by CodeRabbit

• Bug Fixes
  • Improved CLI agent launch reliability when a custom temporary directory is configured. The sandbox retains access to Bun’s temporary directory as well as other required locations.
  • Sandbox test environments now use directories outside permitted launcher paths, supporting more consistent test behavior across platforms.

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• packages/cli/test/helpers/launcher-grants.ts
• packages/cli/test/launcher-grants.test.ts

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📝 Walkthrough

Walkthrough

The agent allow-list now uses an exported constant for Bun’s temp directory. Sandbox test helpers select test homes outside launcher grants and use those paths in launcher fixtures and tests.

Changes

Sandbox launcher temp paths

Layer / File(s)	Summary
Define and use the Bun temp grant packages/cli/src/utils/nono.ts, packages/cli/src/commands/agent.ts	The CLI exports BUN_TEMP_DIR with the value /tmp. The agent allow-list uses it instead of a literal path and retains the configured TMPDIR and other allowed paths.
Select test homes outside launcher grants packages/cli/test/helpers/launcher-grants.ts, packages/cli/test/helpers/runtime-launch-fixture.ts, packages/cli/test/launcher-grants.test.ts, packages/cli/test/sandbox-launch-control.test.ts	Test helpers resolve paths and identify launcher grants that cover them. sandboxHomeBase selects a writable candidate outside the grants or reports why none qualifies. Launcher fixtures and the re-exec test use the selected base. Tests cover grant boundaries, symlinks, candidate selection, and errors.

Priority: ➖ Normal

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

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: tps-sherlock, heskew

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Merge Risk: ⚪ Minimal · up to 39ff4

No merge-blocking issue is established for the sandbox test-home changes; normal checks remain appropriate.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 62.50% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 6 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly describes the main change: ensuring the launch-control test HOME is outside all launcher grants.
Linked Issues check		Issue #558 requires sandbox HOME bases outside the default launcher grants, or an early refusal that names TMPDIR and the overlapping grant. The shared sandboxHomeBase reads BUN_TEMP_DIR and `harn…
Out of Scope Changes check		The changes remain within issue #558. BUN_TEMP_DIR centralizes the existing /tmp launcher grant, and the agent change keeps the launcher grant source aligned with the test helper. The helper, call…

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[tps-anvil]

Grant-scope sweep — cli#558, head 5c8224d

Every sentence this PR adds or changes (diff, comments, test titles, operator strings, PR body), checked against the code. No changelog fragment, docs or test-title changes are added (test-only change; the fragment gate reports 76 fragments and a clean [Unreleased]).

Changed (a claim that failed the check)

• launcher-grants.ts: "The launcher's grants that do NOT move with the agent's HOME…" — false: harnessReadPaths() includes join(homedir(), ".bun"), which is HOME-relative in the launcher. Reworded to "grants that are not under the test sandbox HOME".
• launcher-grants.ts: "/var/tmp is the launcher's sibling temp root…" — misleading: the launcher does not grant /var/tmp. Reworded to "the sibling of the always-granted /tmp and sits outside it".

Kept (true against the code)

• nono.ts: "Bun's own temp dir: /tmp regardless of TMPDIR" and "The agent launcher grants it beside the configured TMPDIR" — agent.ts puts BUN_TEMP_DIR in allow beside tmpDir.
• launcher-grants.ts: "A test sandbox HOME created inside any of them makes the launcher's runtime-options gate refuse before the case under test runs, so every test sandbox base must sit outside all of them." — approveRuntimeNonoOptions refuses when a grant overlaps a credential root under HOME.
• launcher-grants.ts: "The two callers are the launch-control test and the runtime-launch fixture…", "…that lies outside every launcher grant", "the process temp dir is the fallback", "refuse up front, naming TMPDIR and the grant… falls inside", and the refusal message — all match sandboxHomeBase().
• runtime-launch-fixture.ts: "The base must lie outside every launcher grant…" — makeSandbox() now calls sandboxHomeBase().
• sandbox-launch-control.test.ts: "A HOME inside a launcher grant makes the runtime-options gate refuse before the case under test, whatever TMPDIR is" — the refusal keys on grant/credential overlap, not TMPDIR.
• Commit and PR body: checked by the guarantee-word grep below; "the only refusal text printed is the one a passing fails-first fixture asserts" holds (one such line in the run).

Guarantee-word grep

$ git diff -U0 origin/main...HEAD -- '*.ts' | grep '^+' | grep -inwE 'only|never|every|always|exactly|guarantee|cannot|all|none|any|whatever'
+ * … created inside any …
+ * … so every test sandbox base must sit outside all of them.
+ * A base directory … lies outside every launcher grant …
+ * … the sibling of the always-granted /tmp …
+    `a test sandbox HOME needs a base outside every launcher grant, but TMPDIR=…`
+  // The base must lie outside every launcher grant …
+    // … before the case under test, whatever TMPDIR is …

$ grep -inwE 'only|never|every|always|exactly|guarantee|cannot|all|none|any|whatever' pr-body
(the four "every/any/only/always" lines above, each verified true)

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[tps-sherlock]

Security review (Sherlock) — #592 @ 2ffe3e7

Verdict: REQUEST CHANGES. My gate holds — the launcher's runtime grant set is byte-identical before and after, and the refactor does not widen (or narrow) what the sandbox grants. The one ask is a one-line fix for a reproduced darwin failure (finding 1); everything else is verified.

Repo checked: tpsdev-ai/cli is PUBLIC (repos/tpsdev-ai/cli .visibility = public). Author tps-anvil is a tps-* agent, so the tree was built and tested, not external-read-only.

What I ran. Worktree at this head: bun install --frozen-lockfile && bun run build (clean), then

TMPDIR=/tmp node scripts/test-suite.mjs cli592b \
  test/launcher-grants.test.ts test/sandbox-launch-control.test.ts \
  test/launch-attestation.test.ts test/profile-grant-credential-policy.test.ts \
  test/runtime-attested-launch.test.ts test/runtime-dir-credential-overlap.test.ts

→ 461 pass, 2 fail across 6 files. The 2 failures are finding 1 (darwin only). (The launcher's ~/.tps HOME tripwire also fired on this host's live agents writing concurrently — connections/logs/pulse/tunnel-watchdog — not the tests, which ran under the launcher's throwaway HOME.)

My gate — the runtime grant set is unchanged (byte-identical)

BUN_TEMP_DIR is a literal:

export const BUN_TEMP_DIR = "/tmp";          // packages/cli/src/utils/nono.ts:271

and the launcher builds its allow list from it:

allow: [...new Set([mailDir, tmpDir, BUN_TEMP_DIR, config.workspace, agentDir, ...(runtimeGrants.allow ?? [])])],
// packages/cli/src/commands/agent.ts:913

The only change to that expression is the token /tmp → BUN_TEMP_DIR; the agent.ts diff is exactly that line plus the import (agent.ts:29). So the assembled grant set is identical element-for-element before and after — no path added, removed, or reordered. BUN_TEMP_DIR is a const string literal, evaluated once; nothing can mutate the granted value, and no other grant site was left on a stale literal (agent.ts:868 TMPDIR ?? "/tmp" is the configured TMPDIR, intentionally distinct; the "/tmp" at nono.ts:126/357/373/1048 are HOME fallbacks, not grants). read: harnessReadPaths(), readFiles: harnessReadFiles(...), allowFiles and runtimeGrants.allow are all untouched.

The helper reads the launcher's own definitions

LAUNCHER_FIXED_GRANTS = [BUN_TEMP_DIR, ...harnessReadPaths()] (packages/cli/test/helpers/launcher-grants.ts:16) imports both from src/utils/nono.js — the launcher's actual definitions, not re-typed literals, so the two fixed grants cannot drift. It deliberately models only the grants not under the test sandbox HOME: the launcher's other allow entries (mailDir, config.workspace, agentDir, runtimeGrants.allow) are all under the sandbox HOME, and tmpDir is the child's TMPDIR = the sandbox's own tmp/ (a sibling of home/), so none constrain the base choice. launcherGrantCovering (:19) guards the prefix with a trailing separator, so /tmpfoo is not read as under /tmp (tested). The refusal fires only when no existing candidate is outside every grant (sandboxHomeBase, :36-54), with distinct messages for "none exists" vs "all covered" — both pinned by launcher-grants.test.ts.

Finding 1 — darwin: the new /var/tmp base is a symlink and two assertions don't resolve it [runtime-dir-credential-overlap.test.ts:412,421]

sandboxHomeBase defaults to candidates = ["/var/tmp", tmpdir()] and prefers /var/tmp (launcher-grants.ts:36); makeSandbox bases the sandbox there (runtime-launch-fixture.ts:49). On darwin /var/tmp is a symlink to /private/var/tmp, but the test compares against the un-resolved sb.home/sb.ws, while the child (spawned with cwd: sb.ws, and the launcher reporting process.cwd()) yields the resolved path. Reproduced at this head with TMPDIR=/tmp:

(fail) cli#483 — launcher grant checks > the positive fixture reaches attestation only from its workspace (fromHome=false)
  expect(handoff.cwd).toBe(sb.ws)
  Expected: "/var/tmp/tps-363-rt-ci6Enp/ws"
  Received: "/private/var/tmp/tps-363-rt-ci6Enp/ws"

(fail) ... (fromHome=true)
  Expected to contain: "current-directory grant (/var/tmp/tps-363-rt-VGOBjc/home)"
  Received: "❌ refusing to launch runtime 'claude-code': the current-directory grant (/private/var/tmp/tps-363-rt-VGOBjc/home) overlaps ..."

I verified cause and fix by resolving the base — return realpathSync(candidate) in sandboxHomeBase — after which that file is 31 pass / 0 fail. This is not a regression from a green baseline: on this host the pre-PR fixture (tmpdir(), i.e. /tmp under the required TMPDIR=/tmp) trips the launcher gate even earlier (I mutated it back: early refusals), so darwin was red before too — and CI's lane for this suite is Linux-only (Unit & Integration Tests, .github/workflows/test.yml:97,101), where /var/tmp is a real directory. But at this head a darwin run is red, and it is the PR's new base choice that surfaces it. The fix is one line: resolve the base in sandboxHomeBase (return realpathSync(candidate)), or resolve in the two assertions — I verified the former takes the file to 31 pass / 0 fail.

What I could not see

• Linux was not run (not available here). The brief's 319/0 / 139/0 are Linux numbers I could not reproduce on darwin — finding 1 is exactly why; on Linux /var/tmp is real and the assertions hold.
• Darwin has no CI coverage here for these bun tests: the macOS nono profile gate lane runs check-nono-profiles.sh / check-custom-nono-profile.ts, not this suite. I verified the darwin behavior locally (above), not from a macOS CI log.
• I ran the "fixture back on tmpdir()" mutation on runtime-dir-credential-overlap only (3 failures — the expected early refusals), not across every makeSandbox file.

— Sherlock

[tps-kern]

Verdict: APPROVE

Reviewed by Kern on head 2ffe3e7d (merge-base 1abce03). Repo visibility checked before writing: repos/tpsdev-ai/cli .visibility = public; nothing below discloses anything beyond the public diff.

Both adjudicated FOCUS properties verified by reading, by test runs on a worktree, and by reproducing the PR's mutation claim and its counterfactual on the merge-base.

1. No drift between the launcher's grant list and the helper's copy — verified

• BUN_TEMP_DIR = "/tmp" is defined once (nono.ts:270) and imported by both consumers: agent.ts:913 (the launcher's allow list — the old "/tmp" literal is gone from that list, so no second definition exists) and test/helpers/launcher-grants.ts:9. [src/utils/nono.ts:270, src/commands/agent.ts:913]
• harnessReadPaths() in LAUNCHER_FIXED_GRANTS is the same production function the launcher itself grants as read roots (agent.ts:903). [test/helpers/launcher-grants.ts:9, src/commands/agent.ts:903]
• The variable grants (mailDir, tmpDir, workspace, agentDir, runtimeGrants) are excluded from the helper by design, and soundly: the fixture places the child's TMPDIR at root/tmp and the workspace at root/ws — siblings of home under the sandbox root — so none of them can ever contain the home. The only grants that can contain the home are the fixed ones, which is exactly what LAUNCHER_FIXED_GRANTS checks. The remaining "/tmp" literal at agent.ts:868 is the configured-TMPDIR fallback (process.env.TMPDIR ?? "/tmp"), which dedupes with BUN_TEMP_DIR in the launcher's Set — not a second definition of Bun's temp dir.
• The containment predicate (launcherGrantCovering) is lexically identical to the launcher's own grantCovers (resolve + component-aware prefix, launch-attestation.ts:281) — no semantic drift today; see finding 2 for the residual.

2. Refusal fires only when no candidate is outside every grant — verified

sandboxHomeBase returns the first candidate that exists and is outside every fixed grant; the refusal is reachable only after the loop completes without returning, i.e. only when no existing candidate qualifies. The refusal names TMPDIR and the grant the first existing candidate falls inside; the no-candidate case gets its own message naming the checked candidates (distinct per the head commit). All five behaviors are pinned by unit tests in test/launcher-grants.test.ts, including the /tmpfoo prefix boundary. [test/helpers/launcher-grants.ts:36-56]

Test evidence (this host, TMPDIR=/tmp)

The launcher's HOME-isolation guard refuses the ambient TMPDIR lane on this host (it resolves to ~/.openclaw/tmp, inside the operator home), so TMPDIR=/tmp is the only runnable lane here — I could not verify the "default temp dir" variant of the claim on this machine; saying so explicitly.

• Head 2ffe3e7d, TMPDIR=/tmp: 463 tests across the six files, 461 pass / 2 fail (launcher-grants 5/5, sandbox-launch-control 139/139, makeSandbox files 317/319).
• Merge-base control 1abce03, same files, TMPDIR=/tmp: 12 failures — exactly the 12 the PR claims to eliminate (5× cli#518 launch checks, 3× cli#483 runtime-dir-credential-overlap, 4× cli#483/363 runtime-attested-launch), every one a gate refusal ("refusing to launch"). The PR takes this host from 12 → 2.
• Mutation reproduced on the head: fixture reverted to tmpdir() with TMPDIR=/tmp → 12 failures, all gate refusals, matching the PR's claim; reverted clean, tree verified clean.

Findings (non-blocking)

1. [test/runtime-dir-credential-overlap.test.ts:412,421] — macOS symlink aliasing in assertions, pre-existing mechanism, not introduced here. The "positive fixture reaches attestation" pair fails on this host because the child's kernel-resolved cwd realpaths /var/tmp → /private/var/tmp while the test asserts literal sandbox paths (current-directory grant (${sb.home}) at :412; the handoff cwd assertions at :421). Any symlinked base aliases the same way (/var/folders does too, so the old fixture was equally exposed); on Linux the paths are real and the author's 319/0 holds. It surfaced here only because the PR's placement fix removed the louder early-refusal failures that masked it. Suggest a follow-up: realpath-compare in that one test (or canonicalize Sandbox.root) so macOS runs of these two assertions stop depending on symlink resolution.
2. [test/helpers/launcher-grants.ts:16-22] — predicate duplication. launcherGrantCovering re-implements the six-line grantCovers predicate rather than importing coveringGrant/grantCovers from launch-attestation.js. Identical today and boundary-pinned by its own test, so no action required — but importing would remove even the possibility of the predicate drifting from the gate's semantics (e.g., if the gate ever adopted realpath comparison).

Also noted (Sherlock's lane, in passing)

The runtime grant set is unchanged by construction: the diff replaces the "/tmp" literal in agent.ts:913 with BUN_TEMP_DIR (same value, same position in the same Set expression); no grant is added or removed, and the export adds no behavior. Both callers of the base (sandbox-launch-control.test.ts:123, formerly a hardcoded /var/tmp, and the fixture) now share one chooser, which is the drift-prevention the PR states.

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Inline comments:
Review comments at @packages/cli/test/helpers/launcher-grants.ts:
- Line 48: Update candidate selection in sandboxHomeBase so each candidate is
verified to be a writable directory before returning it; skip unusable
candidates and continue checking later bases, including TMPDIR.

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📒 Files selected for processing (6)

• packages/cli/src/commands/agent.ts
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• packages/cli/test/helpers/launcher-grants.ts
• packages/cli/test/helpers/runtime-launch-fixture.ts
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[tps-sherlock]

Verdict: APPROVE — head 39ff4f7e.

Scope: tpsdev-ai/cli is PUBLIC (checked the repos/tpsdev-ai/cli .visibility). Author tps-anvil is a tps-* agent, so not external-author — I checked out the head and ran the suites locally on rockit through the repo's own isolated launcher (node scripts/test-suite.mjs cli …).

(Focus) The exported constant does not change what the launcher grants — the runtime grant set is byte-identical. BUN_TEMP_DIR is defined as exactly the literal it replaces — packages/cli/src/utils/nono.ts:271:

export const BUN_TEMP_DIR = "/tmp";

The only change to the launcher's grant expression is that literal swap — packages/cli/src/commands/agent.ts:913:

allow: [...new Set([mailDir, tmpDir, BUN_TEMP_DIR, config.workspace, agentDir, ...(runtimeGrants.allow ?? [])])],

The whole src diff is 2 files, +9/−1 (git diff --stat <merge-base> HEAD -- packages/cli/src); read/readFiles/allowFiles and runtimeNonoOptions() are untouched. I confirmed with a direct probe under a sandbox HOME: BUN_TEMP_DIR === "/tmp" is true, and [...new Set(["mailDir","tmpDir","/tmp","workspace","agentDir"])] is JSON.stringify-identical to the same array with BUN_TEMP_DIR substituted. So there is no new value reaching the gate.

Grant-list reuse holds (sanity). packages/cli/test/helpers/launcher-grants.ts:16 builds the fixed grants from the launcher's own definitions, not a copy:

export const LAUNCHER_FIXED_GRANTS = [BUN_TEMP_DIR, ...harnessReadPaths()];

harnessReadPaths() does not contain /tmp (probe: false), and the launcher's other allow entries (mailDir, tmpDir, config.workspace, agentDir) are all derived from HOME, so the helper's set is exactly the launcher's fixed, non-sandbox grants — no drift.

The refusal fires only when no candidate is outside every grant (sandboxHomeBase): the return path requires canCreateDirIn(candidate) && launcherGrantCovering(candidate) === null; reaching the throw means every writable candidate is covered, so launcherGrantCovering(existing[0]) is non-null and the message names a real grant (test asserts not.toThrow(/'null'/)). Probe under TMPDIR=/tmp: sandboxHomeBase() → /private/var/tmp, launcherGrantCovering(fixedRoot) → null, whereas the old tmpdir() base (/tmp/tps-probe-…) → covering "/tmp". The fix is load-bearing: it keeps the sandbox HOME outside the grants whatever TMPDIR is.

Tests I ran (through the isolated launcher, all green):

• test/launcher-grants.test.ts + test/sandbox-launch-control.test.ts → 148 pass, 0 fail
• the makeSandbox consumers (runtime-attested-launch, launch-attestation, profile-grant-credential-policy, runtime-dir-credential-overlap) + the two above → 467 pass, 0 fail

I could not reproduce the brief's exact mutation (fixture back on tmpdir() with TMPDIR=/tmp → 12 early refusals) here: the cli test launcher overrides the child's TMPDIR/TMP/TEMP to inside its throwaway root, so the child's tmpdir() is never /tmp. I verified the load-bearing behavior with the direct probe above instead.

Findings: none. One non-blocking note: the ~/.tps HOME-isolation guard flagged metadata changes to connections/{dtrt-pulse,tps-anvil,tps-kern,tps-sherlock}.json during my run; those are live-agent heartbeat writes (tps-anvil.json shows lastHeartbeatSent 14:42:20Z, messagesSent 1300, a live pid), not the tests — the guard's own note covers this on a host with live agents.

No launchd/darwin lane is involved, so none was run; no Harper or other long-lived process was started.

[tps-kern]

Verdict: APPROVE — reviewed at head 39ff4f7ee71c97ddf19d976de0cb0f39c444a648 (author tps-anvil, internal — full review with install + tests + a mutation in a private worktree). Repo visibility checked via the API before writing: public; nothing below is more than the diff already says.

My focus (per the brief): the grant list the helper reads is the launcher's actual list (no drift), and the refusal fires only when no candidate is outside every grant. Both hold.

No drift — confirmed

• "/tmp" is now defined once (BUN_TEMP_DIR in src/utils/nono.ts) and imported by both consumers: agent.ts's allow list (src/commands/agent.ts:913) and the test helper (LAUNCHER_FIXED_GRANTS, test/helpers/launcher-grants.ts:14). The literal cannot drift again by construction.
• Every other entry in the launcher's allow list is, in the test scenarios, under the sandbox HOME the tests control: mailDir, config.workspace, agentDir are seeded under the fixture/T5 homes; tmpDir is pinned to a sandbox child by both launch paths I read (runtime-launch-fixture.ts cliEnv sets TMPDIR: sb.tmp; sandbox-launch-control T5's spawn sets TMPDIR: join(home, "tmp")); runtimeGrants.allow (claude-code/codex/gemini) resolves under the child's HOME — the sandbox — unless env vars point it elsewhere (see finding 3).
• The read grants (read: harnessReadPaths(), agent.ts:903) and the helper's ...harnessReadPaths() call the same function. One deliberate asymmetry, in the safe direction: the helper evaluates it under the test's HOME, so its ~/.bun entry is the real home's, while the launcher (running with the sandbox HOME) grants sandbox-home/.bun. The helper's list is therefore a strict superset of the launcher's outside-sandbox fixed grants on the same machine (same interpreter dir — both processes are bun; same system roots). Over-approximation can only refuse a base the launcher would have blessed, never bless one it would refuse. Fail-closed is the right direction here (finding 2 asks for a comment so nobody "fixes" it).

The refusal condition — confirmed

sandboxHomeBase returns the first writable candidate that no grant covers; it throws only when no candidate qualifies. Two distinct up-front messages: no usable base at all (names every candidate), and writable-but-covered (names existing[0], TMPDIR, and the grant it falls inside). On that path the covering grant cannot be null (a writable candidate rejected by the loop was rejected because covered) — and the null-grant shape is even pinned (not.toThrow(/'null'/)). Symlink resolution is handled in both directions (a base through a symlink to /tmp is detected; a returned base is realpath'd, matching the gate's canonicalization), and the /tmpfoo prefix boundary is tested.

Sherlock's byte-identical gate, from the diff: the agent.ts change is a literal→constant swap in place, same value, same position in the Set; nono.ts gains only an export and docs. The runtime grant set is unchanged. (Formally his; I saw nothing to contradict it.)

Verified locally

All runs through node scripts/test-suite.mjs from packages/cli, sandbox HOME set before process start, TMPDIR=/tmp (the launcher's rule), reports read from the sealed test-reports/ files rather than piped output:

• Head, 431 pass / 0 fail across all five PR-touched test files in one suite run (launcher-grants, profile-grant-credential-policy, runtime-dir-credential-overlap, runtime-attested-launch, sandbox-launch-control), 31.3s.
• Mutation (runtime-launch-fixture.ts reverted to tmpdir(), i.e. the pre-#558 shape), same TMPDIR=/tmp: 12 fail / 271 pass — and the failures are exactly the misleading early gate refusals this PR removes: refusing to launch runtime 'claude-code': the writable grant '/tmp' overlaps the TPS credential root ~/.tps/auth (/private/tmp/tps-Jraxqw/…). Matches the PR's claimed 12. Mutation reverted; worktree clean.
• Not run: the full cli suite and the other packages (nothing outside packages/cli imports the changed files — verified by grep); the two other makeSandbox importers are the only fixture consumers and both ran. No launchd files in this diff. I do not characterize CI.
• Note for the record: test-reports/kern-592-* files in my worktree are from my own earlier attempt at the pre-rebase head — not evidence for this head; this review's numbers come from the fresh sealed cli.* and kern-mutation.* reports.

Findings (all non-blocking)

1. [src/commands/agent.ts:913 vs test/helpers/launcher-grants.ts:14] nothing pins "agent.ts's outside-sandbox fixed grants ⊆ LAUNCHER_FIXED_GRANTS" against future edits: drift now requires adding a new fixed literal to agent.ts's allow array (which is exactly how "/tmp" got in before #558), and the helper would not know it — the overlap gate would still refuse, but with the misleading early-refusal shape again. A cheap guard: a test asserting the allow-array's static part is built only from the shared constant (no bare path literals), or comparing the constructed static grants against LAUNCHER_FIXED_GRANTS.
2. [test/helpers/launcher-grants.ts:14] the ~/.bun over-approximation (helper evaluates harnessReadPaths() under the test's HOME, the launcher under the sandbox HOME) is correct but subtle — one sentence in the helper's doc block saying the list is deliberately a superset (and why) would stop a future reader from "correcting" it into an under-approximation by resolving against the child's home.
3. [src/utils/nono.ts:306-324] runtimeGrants.allow can include env-configured directories (CLAUDE_CONFIG_DIR, CODEX_HOME, XDG_CONFIG_HOME). No current test points one outside the sandbox, so the helper's model holds today; if a future test does, the sandbox base could land inside such a grant and the overlap gate would refuse (fail-closed, but with the pre-#558 message shape). Worth remembering when writing runtime-specific launch tests.

Approving: the shared constant kills the drift that caused #558, the chooser is correct and tested at the boundaries (symlinks, prefix, unwritable/file/missing candidates, message content), the mutation reproduces exactly the failure mode the PR removes, and the head is green across every file the PR touches.