feat: plan-mode handshake for interactive review skills

Add a preamble-level STOP-Ask handshake that fires when the user invokes any
of the 4 interactive review skills (plan-ceo-review, plan-eng-review,
plan-design-review, plan-devex-review) while their Claude Code session is
in plan mode. Without this gate, plan mode's "this supercedes any other
instructions" system-reminder outranked the skills' interactive STOP gates
and the skills silently wrote plan files without any per-finding AskUserQuestion.

The handshake offers 2 options (exit-and-rerun, cancel) — the original
third "stay and batch" option was dropped after two independent reviewers
flagged it as a silent bypass of the skills' anti-skip rule.

Architecture decisions (CEO+Eng review):
- Preamble-level resolver, not per-template injection (Codex finding #2)
- Position 1 in preamble composition: after bash block (_SESSION_ID live),
  before onboarding AskUserQuestion gates (so fresh-install users see the
  handshake first, not drowned in telemetry/proactive/routing prompts)
- Generator-only `interactive: true` frontmatter flag, following the
  `preamble-tier` precedent (no host-config frontmatter allowlist edits)
- Host-scoped to Claude via `ctx.host === 'claude'` check inside the
  resolver (simpler than `suppressedResolvers` which only gates `{{}}`
  placeholders)
- One-way-door classification in scripts/question-registry.ts for all 4
  skills so question-tuning `never-ask` preferences can't suppress the gate
- Synchronous telemetry write to ~/.gstack/analytics/skill-usage.jsonl on
  handshake fire (captures A-exit and C-cancel outcomes that terminate the
  skill before end-of-run telemetry runs)

Also adds an explicit STOP block to plan-ceo-review Step 0C-bis so the
approach-selection question can't silently skip to mode selection.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/resolvers/preamble.ts

@@ -22,6 +22,7 @@ import { generateQuestionTuning } from './question-tuning';
 
 // Core bootstrap
 import { generatePreambleBash } from './preamble/generate-preamble-bash';
+import { generatePlanModeHandshake } from './preamble/generate-plan-mode-handshake';
 import { generateUpgradeCheck } from './preamble/generate-upgrade-check';
 import { generateCompletionStatus } from './preamble/generate-completion-status';
 
@@ -78,6 +79,13 @@ export function generatePreamble(ctx: TemplateContext): string {
   }
   const sections = [
     generatePreambleBash(ctx),
+    // Plan-mode handshake at position 1: after bash (so _SESSION_ID / _BRANCH /
+    // _TEL env vars are live for the synchronous telemetry write) and before
+    // all onboarding AskUserQuestion gates (so fresh-install users in plan mode
+    // see the handshake first, not drowned in telemetry / proactive / routing
+    // prompts). Host-scoped to Claude + interactive-frontmatter-scoped inside
+    // the resolver — no-op for every other skill/host combination.
+    generatePlanModeHandshake(ctx),
     generateUpgradeCheck(ctx),
     generateWritingStyleMigration(ctx),
     generateLakeIntro(),