feat(trekexecute): couple the executor to the review gate, the plan approval and the step checks

Wave 2, order 6. /trekexecute now:
- refuses a plan whose logged approval does not cover its current sha256
  (K2, approval-log verify --kind plan), before step 1;
- runs the step check (K9) and the step's optional Regression: (K10, new
  lib/verification/regression-check.mjs through the criteria runner) at step
  end, before the checkpoint; exit 2 is "not measured", never green;
- runs the architecture rules (K5) and the plan-file sweep (K6) after the last
  step; a violation or a file outside the plan turns completed into partial;
- reviews by itself in the closing run (Phase 7.2): run the thing, /simplify,
  /trekreview, verdict-gate; a BLOCK adds the review's remediation steps after
  the plan validator accepts them and the operator re-approves the plan, capped
  at TREKEXECUTE_MAX_REVIEW_ROUNDS (3);
- makes the main-merge gate a lock on the verdict: BLOCK or undecided keeps
  the merge closed; when open, the executor merges and the guard's question is
  the one question (operator decision 2026-10-08). The --gates pause before
  the wave merge-back is gone for the same reason.

The guard refuses a merge into main and a push in the permission mode that
shows no prompts, since no one can be asked (operator decision 2026-10-09; two
mode-read exemptions approved by the operator).

progress.json gains optional coupling fields (Handover 5); the validator
rejects the runner's exitCode in plan_verification.failed_criteria (C15).
Pointer lines name the skills test-first and debugging (S2).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -32,7 +32,7 @@ Voyage — a contract-driven Claude Code pipeline: brief, research, plan, execut
 | `/trekbrief` | Brief — one question round sized by class (`ceremony: small\|bounded\|architectural`, heaviest in doubt, said aloud, only moved up) produces a task brief with explicit research plan; ends with the operator explicitly approving `## Intent` + `## Goal` («høres bra ut» is not approval), logged in the target repo's hash-chained approval log and committed (the brief too when `artifact_store: git`) (`--approve <dir>` does only the approval, then writes the trekbrief record); optionally orchestrates the pipeline | session |
 | `/trekresearch` | Research — deep local + external research, produces structured research brief. Opt-in `--engine {swarm\|deep-research}` delegates the external phase to Claude Code's built-in `/deep-research` workflow (swarm default) | session |
 | `/trekplan` | Plan — brief-reviewer, explore, plan, review. Requires `--brief` or `--project`; halts unless the brief's intent is approved (hash-bound, stale on edit). Auto-discovers `architecture/overview.md` if present. Plan 1.8: `Test first:` per step + one `End-to-end:` step; a design part for `ceremony: architectural` (absent = architectural); critic loop of max 3 rounds, recorded in the plan, and `plan-gate.mjs` (0 go / 1 stop / 2 could not run) decides | session |
-| `/trekexecute` | Execute — disciplined plan/session-spec executor: one fresh `step-implementer` helper per plan step, one controller that reads the diff (spec + quality verdicts), proof of red / floor guard / done line as commands, fix rounds that go up (max 5: helper → plan → operator), closed stop list + decision log in the final report | session |
+| `/trekexecute` | Execute — disciplined plan/session-spec executor: refuses a plan whose logged approval does not cover its current sha256 (K2); one fresh `step-implementer` helper per plan step, one controller that reads the diff (spec + quality verdicts), proof of red / floor guard / step check (K9) / `Regression:` (K10) / done line as commands, fix rounds that go up (max 5: helper → plan → operator), architecture rules (K5) + plan-file sweep (K6) after the last step, then its own review (`/simplify` → `/trekreview` → verdict gate, K7; BLOCK keeps the merge into main closed), closed stop list + decision log in the final report | session |
 | `/trekreview` | Review — a gate: Claude Code's `/code-review` + `/security-review` as engine, then Voyage's brief control (which stops); writes `review.md` with a required verdict that `lib/review/verdict-gate.mjs` decides on (0 ALLOW/WARN · 1 BLOCK · 2 never green); proposes recurring finding classes as project memory, line by line (Handover 6) | session |
 | `/trekcontinue` | Continue — resumes the next session of a multi-session voyage project. Reads `.session-state.local.json` (Handover 7) and immediately begins executing | session |
 | `/trekendsession` | End-session — mark the current session complete and write session-state pointing at the next session. Helper for informal multi-session flows | session |
@@ -74,6 +74,11 @@ Full flag reference for each command (modes, `--gates`, `--profile`, breaking ch
 > logged", never green. Voyage's guards are deterministic only when no
 > installed mod handles `tool.check`.
 
+> **One question per merge (operator decision, 2026-10-08).** Where the guard
+> asks (merge into main, push), `/trekexecute` never asks the same thing: its
+> main-merge gate is a lock on the review verdict, and the guard's prompt is
+> the one question. Exit 2 from K5/K6/K7/K9 is "not measured", never green.
+
 ## Agents
 
 | Agent | Model | Role |