feat(trekplan): Regression and On failure step rules, and trial 2's minor fixes

The minor points (B8-B12, C13, C14, C16, C17) of the second voyage-lekerepo
trial (2026-10-08), each verified against the code and started with a test
that failed first.

- K10: optional step field `Regression:` - one command the criteria runner
  allows, unpiped; plan-validator refuses one that can never run
  (PLAN_STEP_REGRESSION_NOT_RUNNABLE). Any plan_version, no bump.
- K11: `On failure:` opens with revert | retry | skip | escalate, or the
  validator warns (PLAN_STEP_ON_FAILURE_UNKNOWN); onFailureAction in
  plan-schema.
- B8 (operator decision 2026-10-08): minors open after the last critic round
  are listed numbered in the Phase 10 summary; the ones the operator picks are
  fixed and get one more round (--extra-round when the 3 are spent).
- B11: plan-review dedup merges two reviewers' findings on the same file:line
  with the same content (trial pair: Jaccard 0.44, overlap 0.83); the Jaccard
  threshold for every other pair is unchanged.
- B12: /trekbrief Step 4c says the reviewer runs in the background and is
  waited for, not "foreground, blocking".
- C13: the Phase 4 size count includes .mjs, .cjs, .mts, .cts.
- C14: --evidence shows the first output line on PASS rows.
- C16: findings-schema checks path:line citations in finding prose (error) and
  in the prose around the block (warning) against the file.
- C17: git-historian gets the brief, never proposes changing a frozen file,
  and names the remote from `git remote -v`.

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

README.md

@@ -297,7 +297,8 @@ Every plan includes:
 Every implementation step includes:
 - **Test first:** — the test the step makes pass (required from `plan_version 1.8`)
 - **Interface in:** / **Interface out:** / **Review focus:** — optional: what the step consumes and produces, and the untested inputs it pins to a test
-- **On failure:** — what to do when verification fails (revert / retry / skip / escalate)
+- **Regression:** — optional: one runnable suite command (`npm test`, no pipe, no `&&`) run green before the checkpoint, while `Verify:` stays the step's own red-first test; the validator refuses one that can never run
+- **On failure:** — what to do when verification fails; it opens with `revert`, `retry`, `skip` or `escalate`, or the validator warns
 - **Checkpoint:** — git commit after success
 - **Manifest:** — the objective completion predicate (Hard Rule 17)
 
@@ -305,7 +306,7 @@ One step per plan is the "run the thing" step (`End-to-end:`): the product run t
 
 Exploration uses 6–8 agents in parallel (architecture-mapper, dependency-tracer, task-finder, test-strategist, git-historian, risk-assessor, plus convention-scanner on medium+ codebases and research-scout when unfamiliar tech is detected). Adversarial review then runs `brief-reviewer`, `plan-critic` (12 dimensions, no-placeholder enforcement, manifest audit, interfaces and slices, design and architecture rules), and `scope-guardian` (creep + gap detection, ceremony match). Per-agent details in [`agents/`](agents/).
 
-**The plan gate.** Each critic round is written into the plan by `lib/validators/plan-gate.mjs --record`; `plan-gate.mjs <plan.md>` then exits 0 (go on), 1 (stop: invalid plan, no verdict, a verdict the plan has changed since, or an open BLOCKER) or 2 (could not run). After 3 rounds with a BLOCKER open, `/trekplan` stops and asks; it never continues silently, and "execute" is offered only when the gate exits 0. In Claude Code's plan mode the plan is written to Claude Code's plan file and approved through its own approval prompt (that `/trekplan` runs cleanly inside plan mode is not verified yet).
+**The plan gate.** Each critic round is written into the plan by `lib/validators/plan-gate.mjs --record`; `plan-gate.mjs <plan.md>` then exits 0 (go on), 1 (stop: invalid plan, no verdict, a verdict the plan has changed since, or an open BLOCKER) or 2 (could not run). After 3 rounds with a BLOCKER open, `/trekplan` stops and asks; it never continues silently, and "execute" is offered only when the gate exits 0. Minors still open after the last round are listed numbered in the summary; the ones you pick are fixed and get one more round, the rest are carried. In Claude Code's plan mode the plan is written to Claude Code's plan file and approved through its own approval prompt (that `/trekplan` runs cleanly inside plan mode is not verified yet).
 
 **Checks the plan hands on** (0 / 1 / 2, and 2 = "not measured", never green): `lib/verification/arch-rules.mjs --repo <dir>` runs the target repo's own dependency-cruiser or import-linter — Voyage installs nothing — and `--prove` shows a rule pass, fail on a planted violation, and pass again; `lib/verification/plan-scope-sweep.mjs --plan <plan.md> --base <ref>` lists changed files that no step names.