feat(design): {{DESIGN_DETECTOR}} wired into design-review, ship review-lite, review army, design-html

The user-installed impeccable engine becomes a deterministic pre-pass in four
skills, through one resolver with three renders: {{DESIGN_DETECTOR}} (the probe
block and how to read every sentinel), {{DESIGN_DETECTOR:phase0}} (design-
review's mechanical scan), {{DESIGN_DETECTOR:gate}} (design-html's bounded slop
gate). Every rendered invocation is `bun --no-env-file run <bin>/gstack-design-
detect.ts ... --host <host>` and every scan ends with the DETECT_EXIT_CODE echo
so exit 2 (findings) never aborts a block.

design-review: probe in Setup; Phase 0 picks DOM mode (URL target) or source
mode (diff-aware, no URL) once; source mode scans the changed frontend files in
Setup, DOM mode never reads source (Rule 4). Phase 3 gains a DOM-dump step per
page: both browser engines load the shared script from lib/dom-dump.js (Aside
splices it into a double-quoted repl script; the fallback engine copies it into
a temp dir for `$B eval --out --raw`), the dump is size-capped, run through
gstack-redact (a HIGH finding skips the page), and persisted under
$REPORT_DIR/dom/$RUN_ID/; one scan runs after the last page, labeled "static
scan of the rendered DOM; cross-origin CSS not resolved". REPORT_DIR honors
GSTACK_HOME so the wrapper's allow-list and the report dir agree; RUN_ID is set
once in Setup. design-baseline.json is schemaVersion 2 with runId, targetSet,
base, and a detector block (mode, engine, byRule, byPage), written temp+rename
with a per-run copy; Regression Output diffs ids only when mode and target set
match, caveats an engine change, and calls live-page count deltas advisory.
Phase 7 hands deferred detector findings to the `handoff=` command the scan
printed; Phase 9 recomputes the same way and deletes the dumps unless
--keep-dom; Phase 10 reports `Detector: N → M`.

ship review-lite gains step 0 (probe, `scan --changed <base>`, tier buckets,
detector + checklist dedupe, advisory and ignored never count) and a
`detector` count in its log payload; the PR body gets a Detector line (rule
ids and counts only). The Review Army Design specialist runs the mechanical
pass at the top of review/design-checklist.md, which now carries it. design-
html probes after DESIGN_SETUP and runs the one-pass gate before screenshots.

lib/dom-dump.js is generated by gen-skill-docs from lib/dom-dump-script.ts
(Claude host, --out-dir aware, dry-run freshness) and pinned byte-equal, so the
prose never carries the script. The contract gains DETECT_JSON, DOM_DUMP_OK,
and the self-describing set; its test now checks both directions.

Budget: design-review eager 25.6K → 28.5K. The plan's target was +2.5K; after
the levers it named (ids-only detector rules, no inline script, trimmed prose)
it lands at +2.87K, and the remainder is doctrine and detector wiring, so the
ceiling moves to the captured 31,319 for design-review only (the full capture
would also have loosened 21 ceilings this branch never touched; those stay).
design-html skeleton re-baselined to 54,000 (measured 53,592). Codex and
Factory ship goldens refreshed (review-lite step 0 and the PR-body line render
inline there).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

lib/design-detect-contract.ts

@@ -40,6 +40,10 @@ export const SENTINEL = {
   DETECT_PARSE_ERROR: 'DETECT_PARSE_ERROR',
   DETECT_OUTPUT_TOO_LARGE: 'DETECT_OUTPUT_TOO_LARGE',
   INTERNAL_ERROR: 'DESIGN_DETECT_INTERNAL_ERROR',
+  /** printed by rendered bash: the temp file holding a scan's JSON */
+  DETECT_JSON: 'DETECT_JSON',
+  /** printed by rendered bash after a DOM dump is persisted */
+  DOM_DUMP_OK: 'DOM_DUMP_OK',
   DOM_DUMP_REDACTION_BLOCKED: 'DOM_DUMP_REDACTION_BLOCKED',
   DOM_DUMP_TOO_LARGE: 'DOM_DUMP_TOO_LARGE',
   DESIGN_MD_FORMAT: 'DESIGN_MD_FORMAT',
@@ -50,6 +54,18 @@ export const SENTINEL = {
 
 export type SentinelName = keyof typeof SENTINEL;
 
+/**
+ * Sentinels whose line explains itself after the colon (a path, a version, a
+ * reason). Prose need not teach them; the agent notes them and moves on. The
+ * contract test requires every OTHER sentinel to be taught somewhere the agent
+ * reads.
+ */
+export const SELF_DESCRIBING_SENTINELS: readonly string[] = [
+  SENTINEL.HOOK_OTHER, SENTINEL.IGNORED_FILES, SENTINEL.CONFIG_UNREADABLE, SENTINEL.ENV_IGNORED,
+  SENTINEL.ENGINE_UNTESTED, SENTINEL.DETECT_EXIT, SENTINEL.DETECT_REFUSED, SENTINEL.DETECT_NO_TARGETS,
+  SENTINEL.DETECT_TIMEOUT, SENTINEL.DETECT_PARSE_ERROR, SENTINEL.DETECT_OUTPUT_TOO_LARGE,
+];
+
 /** Engine versions the committed fixtures were captured from. */
 export const TESTED_ENGINE_VERSIONS: readonly string[] = ['0.1.3'];