feat(plan-eng/design-review): auto-select B in plan mode at the scope gate

In plan mode the scope gate's "What should I review? A/B/C" question is pure
friction: there is no branch diff and the target is the plan being drafted.
Both gates gain an ordered exceptions block, checked BEFORE asking:

1. Plan mode → auto-select B: review the active plan (in context or pasted),
   announce it in one line ("Scope gate: plan mode — auto-selected B
   (reviewing <target>)") so the user can interrupt; an explicitly different
   user-named target still wins; no plan drafted yet → ask as normal.
2. User-named target (outside plan mode): explicit-only — a path, a pasted
   doc, or the literal words "branch diff". A passing mention is not naming;
   when in doubt, ask.

Outside plan mode with no explicitly-named target, nothing changes. Plan-mode
is checked FIRST because the PTY harness seeds drafts as pasted user messages
(claude-pty-runner.ts:1600) — ordering makes the seeded smokes deterministic.

Pinning: seeded plan-mode smokes assert no gate render + announcement rendered
(eng test 2; new design seeded test); plan-mode-no-op extends to eng/design
(bypass must not misfire outside plan mode; first question must be the gate)
plus a named-target case proving the pasted target is consumed; a drift-guard
asserts the two hand-duplicated exceptions blocks stay identical modulo the
two variant slots and carry the announcement string the detectors pin.

Skeleton ceilings ratcheted with comments (eng 68k, design 89k; eng union
ratio 1.08→1.09) — measured 67,006 B / 88,226 B after regen.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/helpers/carve-guards.ts

@@ -164,7 +164,8 @@ export const CARVE_GUARDS: Record<string, CarveGuard> = {
     },
     behavioral: 'plan',
     // v1.2.0 activation lift (shared first-run-guidance preamble) + #2077 ask-first scope gate.
-    maxSkeletonBytes: 67_000,
+    // +~1 KB: plan-mode auto-select-B scope-gate exceptions (2026-08).
+    maxSkeletonBytes: 68_000,
     minUnionBytes: 70_000,
     mustContain: ['Architecture', 'Code Quality', 'Test', 'Performance'],
     // Cross-cutting preamble growth (v1.57.2.0 AUQ-failure prose fallback + the
@@ -172,7 +173,9 @@ export const CARVE_GUARDS: Record<string, CarveGuard> = {
     // default-on Codex outside-voice (codexPreflight block + CODEX_MODE branch
     // prose, replacing the smaller opt-in question) land this at ~6.6% over the
     // v1.53.0.0 baseline. Headroom for those intentional additions.
-    maxSizeRatio: 1.08,
+    // 1.08 → 1.09: the scope-gate exceptions block put the union ~95 B over
+    // the 1.08 line (123,440 / 114,209 baseline = 1.0808).
+    maxSizeRatio: 1.09,
   },
   'plan-design-review': {
     skill: 'plan-design-review',
@@ -189,7 +192,8 @@ export const CARVE_GUARDS: Record<string, CarveGuard> = {
     // +Conductor AUQ-default-prose rule + one-way/continuation safety in the
     // always-loaded AskUserQuestion Format section.
     // v1.2.0 activation lift (shared first-run-guidance preamble) + #2077 ask-first scope gate.
-    maxSkeletonBytes: 88_000,
+    // +~1.3 KB: plan-mode auto-select-B scope-gate exceptions (2026-08).
+    maxSkeletonBytes: 89_000,
     minUnionBytes: 70_000,
     mustContain: ['design', 'visual'],
     maxSizeRatio: 1.07,

test/helpers/touchfiles.ts

@@ -102,7 +102,10 @@ export const E2E_TOUCHFILES: Record<string, string[]> = {
   'plan-eng-review-plan-mode':    ['plan-eng-review/**', 'scripts/resolvers/preamble/generate-completion-status.ts', 'scripts/resolvers/question-tuning.ts', 'scripts/resolvers/preamble/generate-ask-user-format.ts', 'scripts/resolvers/preamble.ts', 'scripts/resolvers/review.ts', 'test/helpers/claude-pty-runner.ts', 'test/skill-e2e-plan-eng-plan-mode.test.ts'],
   'plan-design-review-plan-mode': ['plan-design-review/**', 'scripts/resolvers/preamble/generate-completion-status.ts', 'scripts/resolvers/question-tuning.ts', 'scripts/resolvers/preamble/generate-ask-user-format.ts', 'scripts/resolvers/preamble.ts', 'scripts/resolvers/review.ts', 'test/helpers/claude-pty-runner.ts', 'test/skill-e2e-plan-design-plan-mode.test.ts'],
   'plan-devex-review-plan-mode':  ['plan-devex-review/**', 'scripts/resolvers/preamble/generate-completion-status.ts', 'scripts/resolvers/question-tuning.ts', 'scripts/resolvers/preamble/generate-ask-user-format.ts', 'scripts/resolvers/preamble.ts', 'scripts/resolvers/review.ts', 'test/helpers/claude-pty-runner.ts'],
-  'plan-mode-no-op':              ['plan-ceo-review/**', 'scripts/resolvers/preamble/generate-completion-status.ts', 'scripts/resolvers/preamble.ts', 'test/helpers/claude-pty-runner.ts'],
+  // Covers ceo (preamble misfire) + eng/design (scope-gate bypass must not
+  // fire outside plan mode) + the named-target exception case. 4 sequential
+  // PTY runs (~+10 min, ~+$2 vs the pre-bypass single run).
+  'plan-mode-no-op':              ['plan-ceo-review/**', 'plan-eng-review/**', 'plan-design-review/**', 'scripts/resolvers/preamble/generate-completion-status.ts', 'scripts/resolvers/preamble.ts', 'test/helpers/claude-pty-runner.ts', 'test/skill-e2e-plan-mode-no-op.test.ts'],
 
   // v1.21+ AskUserQuestion-blocked regression tests — Conductor launches
   // claude with `--disallowedTools AskUserQuestion --permission-mode default`