Pre-landing review findings (security + checklist), all reproduced before the fix:
- A checked-out branch could commit `.claude/skills/impeccable/scripts/bin/<os>-<arch>/impeccable`
and the probe would report READY and `scan` would run it, with the agent's full
environment. Launchers and sibling engines under the repo or cwd now count as
"skill present" only (IMPECCABLE_NOT_CACHED: repository-local install, and the
hint never names a repository-local launcher to run); only HOME-rooted installs,
IMPECCABLE_BIN, the cache, and PATH entries outside the repo qualify, all by
realpath. The engine now sees a minimal environment (PATH, HOME, TMPDIR, locale,
IMPECCABLE_*), never the agent's tokens.
- `scan --changed <base>` pushed git-derived paths without the allow-list, so a
committed symlink with a frontend extension handed a file outside the repo to
the engine. Derived targets now go through the same allow-list as explicit ones
and symlinks named by git are refused outright.
- A repo-controlled `scripts/VERSION` with embedded newlines forged probe lines;
the version is trusted only when it is semver, and every printed version is
sanitized. Engine text containing the untrusted-content fence or a
`SENTINEL:` prefix is neutralized with a zero-width space
(neutralizeSentinels in the contract), so page text cannot close the envelope
or forge a probe line.
- A failing `git diff <base>...HEAD` (unknown or unfetched base) was swallowed
and read as "no frontend changes"; it is now DETECT_REFUSED with exit 1.
- The scan allow-list root follows `${GSTACK_HOME:-$HOME/.gstack}` like the
templates and gstack-slug (config.yaml keeps gstack-config's STATE_ROOT
precedence); a quoted or commented design_detector value reads correctly.
Smaller: raw engine chunks are kept only in --format raw; diagnostics are
capped (200 kept, 20 echoed); the engine identity hash reads size + 4 MB, not
the whole binary; PROBE_STEP and ENGINE_STDERR are contract sentinels; the
--verbose gate covers every probe step; analytics use one sentinel vocabulary;
bare limits live in DETECT_LIMITS. The fake engine's knobs are IMPECCABLE_FAKE_*
(so they pass the minimal env) and a shared test helper installs it. New tests
cover each item above plus clean runs, `{}` parse errors, missing paths, and the
50 MB stdout cap.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
bin/gstack-design-detect.ts finds and runs an impeccable engine the user
installed; it never installs, downloads, or executes anything that could
download. `probe` reads only: config (design_detector off → DISABLED),
IMPECCABLE_BIN (absolute, realpath outside the repo and cwd), a PATH walk
(absolute entries outside the repo; a #! shim counts as launcher-present,
never READY), the ~/.impeccable/bin/<newest semver>/ cache, and the engine
installed beside a skill launcher (scripts/bin/<os>-<arch>/impeccable, the
layout a real install produced). It reports IMPECCABLE_SKILL, host-aware
IMPECCABLE_HOOK (+ HOOK_OTHER), the ignore lists from .impeccable/config*.json,
IMPECCABLE_ENGINE_UNTESTED for versions outside the fixture set, and a hint
only when a launcher exists without its engine. `scan` re-probes, refuses
URLs and anything outside the repo root or the design-report allow-list
(realpath, so symlinks cannot escape), derives `--changed <base>` targets
NUL-safely through git and lib/frontend-scope.ts, batches 100 absolute paths
per engine call with stdin ignored, a SIGKILL timeout, a 50 MB stdout cap, and
sanitized length-capped fields, then prints one normalized JSON document
(--format gstack) or the engine's bytes (--format raw); DETECT_TOP (fenced as
untrusted content), DETECT_SUMMARY, and DETECT_EXIT go to stderr; exit code
passes through with 1 over 2 over 0; exit 3 is a gstack bug. `rules` prints
the mapped set. Every run appends a content-free line to the local analytics
file.
lib/design-detect-contract.ts owns every sentinel string, the limits, and the
normalized-finding shape (pure module); test/design-detect-contract.test.ts
asserts every sentinel-shaped token the agent can read exists there.
lib/frontend-scope.ts mirrors gstack-diff-scope's frontend arm, pinned by a
parity test that runs the bash script. bin/gstack-config gains
design_detector (auto | off, default auto, invalid values rejected with the
file unchanged). test/fixtures/fake-impeccable.ts is the env-driven engine
stand-in; test/gstack-design-detect.test.ts covers READY/NOT_CACHED/
NOT_AVAILABLE/DISABLED, env trust (.env never loaded, in-repo IMPECCABLE_BIN
ignored), newest-semver cache, hook and ignore detection, refusals, exit
passthrough, raw byte-identity, normalization, the display cap, timeout,
parse errors, diagnostics, --changed, and analytics. The egress scanner test
records the wrapper as a documented non-sink.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
