fix(voyage): S26 — parse plan_version prose form (S22 defect #2/#3)

The plan template (templates/plan-template.md:21) emits plan_version ONLY in
the prose blockquote metadata line:

  > Generated by trekplan v{version} on {YYYY-MM-DD} — `plan_version: 1.7`

It carries no frontmatter plan_version (the frontmatter block is trekreview-only
and holds source_findings). But PLAN_VERSION_REGEX in lib/parsers/plan-schema.mjs
was `^`-anchored (/m), matching ONLY line-start (frontmatter). The backtick-
wrapped prose form never matched → extractPlanVersion returned null → every real
generated plan got a spurious PLAN_NO_VERSION warning from plan-validator.

Not caught earlier because no test ran the parser against the actual template;
the synthetic fixtures all carry frontmatter plan_version and parse fine.

Internal source contradiction surfaced: the parser comment documents intent
"frontmatter OR doc body", planning-orchestrator.md:228 + the template place it
in the prose line, while HANDOVER-CONTRACTS.md calls it a frontmatter field.

Operator-chosen fix (parser, not template): relax the regex to
`/(?:^|`)plan_version:.../m` so it matches line-start (frontmatter) OR the
backtick-prefixed prose form. Honors the parser's own documented contract,
fixes all existing + future plans, changes no plan output, touches one code
file — vs the template-fix which would alter every plan's shape, contradict
planning-orchestrator.md, and force a 3-file doc reconciliation (scope creep).

TDD (red first): added prose-form + canonical-template regression pins in
plan-schema.test.mjs and a no-PLAN_NO_VERSION pin in plan-validator.test.mjs;
all 3 red on the `^`-anchored regex, green after the relax. The template pin
ties the parser directly to the real generated artifact.

S22 defect closed in docs/S22-happy-path-dogfood.md (§Pipeline defects + log).

Tests: 728 (726 pass / 2 skip / 0 fail; live `node --test`, = 725 baseline +3).
plugin validate passes (1 accepted CLAUDE.md-at-root warning).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LqBYc8Ltrk7LipyJmGxXiB

docs/S22-happy-path-dogfood.md

@@ -104,7 +104,7 @@ Execute succeeded (15/15, suite green, CLI works). **One finding only execute co
 ### Pipeline defects the dogfood surfaced (the bonus the S14 audit could not get — it never ran the pipeline)
 1. **`/trekplan` Phase 9 is broken as documented.** It instructs plan-critic + scope-guardian to "Write structured JSON output to `/tmp/…out.json`", then runs `plan-review-dedup.mjs` on those files. **Both agents' frontmatter grants only `Read/Glob/Grep` — no `Write`/`Bash`** — so the files are never created and the dedup step cannot run. Both agents fell back to returning JSON inline. **Severity: MAJOR** (a documented, wired step that cannot execute). Fix options: grant the reviewers `Write`, or have the orchestrator persist the returned JSON before calling the dedup helper.
 2. **Oracle-into-swarm contamination** (see caveat) — a real trap for dogfooding planning tools on their own repo.
-3. **`plan_version` not parsed.** The plan template emits `plan_version: 1.7` as prose in the "Generated by" line; `plan-validator` then warns `PLAN_NO_VERSION`. Minor template/validator mismatch — the validator looks for a frontmatter/parseable field the template doesn't emit.
+3. **`plan_version` not parsed.** ~~The plan template emits `plan_version: 1.7` as prose in the "Generated by" line; `plan-validator` then warns `PLAN_NO_VERSION`. Minor template/validator mismatch — the validator looks for a frontmatter/parseable field the template doesn't emit.~~ **RESOLVED (S26).** `PLAN_VERSION_REGEX` (`lib/parsers/plan-schema.mjs`) was `^`-anchored and only matched frontmatter; relaxed to `/(?:^|`)plan_version:.../m` so it honors the parser's documented "frontmatter or doc body" contract and parses the backtick-wrapped prose form the template emits. Regression-pinned by running `extractPlanVersion` against the actual `templates/plan-template.md`.
 4. **Version skew.** The *installed* plugin (skill the operator invokes) is cached at **v5.1.1**; the repo under development is **v5.5.0**. The dogfood ran the v5.1.1 command text against v5.5.0 `lib/`. Harmless here (the phases are stable across the bump) but worth noting: operators dogfooding the installed plugin are not testing the dev tree.
 
 ### Honest limitations
@@ -120,7 +120,7 @@ The happy path **works** and produces high-quality, executable plans — and the
 | Claim | How verified |
 |-------|--------------|
 | Brief validates clean | `node lib/validators/brief-validator.mjs --json` → `{valid:true,errors:[],warnings:[]}` |
-| Plan passes schema | `node lib/validators/plan-validator.mjs --strict --json` → `valid:true, 4 steps, 0 errors` (1 soft `PLAN_NO_VERSION` warning = defect #3) |
+| Plan passes schema | `node lib/validators/plan-validator.mjs --strict --json` → `valid:true, 4 steps, 0 errors` (1 soft `PLAN_NO_VERSION` warning = defect #3, **resolved in S26**) |
 | 15 new tests pass; suite green | `node --test` in worktree → new file 15/15; full suite 720 (718/2/0) = 705 baseline +15 |
 | CLI works on live dir | `node lib/validators/project-doctor.mjs .claude/projects/2026-06-19-voyage-doctor` → `PASS`, exit 0; `--json` → valid JSON |
 | Execute isolated; main untouched | `git worktree remove` → `git status` clean, HEAD `aeee4c6`, `lib/validators/project-doctor.mjs` absent from main |

lib/parsers/plan-schema.mjs

@@ -13,7 +13,10 @@ export const STEP_HEADING_REGEX = /^### Step (\d+):\s+(.+?)\s*$/m;
 export const STEP_HEADING_GLOBAL = /^### Step (\d+):\s+(.+?)\s*$/gm;
 export const FORBIDDEN_HEADING_REGEX = /^(?:##|###) (?:Fase|Phase|Stage|Steg) \d+/m;
 export const FORBIDDEN_HEADING_GLOBAL = /^(?:##|###) (?:Fase|Phase|Stage|Steg) \d+/gm;
-export const PLAN_VERSION_REGEX = /^plan_version:\s*['"]?([\d.]+)['"]?/m;
+// Matches plan_version in either location the schema allows: at line start
+// (frontmatter) or backtick-wrapped inside the prose "Generated by" metadata
+// line the plan template emits (`> Generated by ... — `plan_version: 1.7``).
+export const PLAN_VERSION_REGEX = /(?:^|`)plan_version:\s*['"]?([\d.]+)['"]?/m;
 
 /**
  * Find all step heading positions in plan text.

tests/lib/plan-schema.test.mjs

@@ -1,5 +1,6 @@
 import { test } from 'node:test';
 import { strict as assert } from 'node:assert';
+import { readFileSync } from 'node:fs';
 import {
   findSteps,
   findForbiddenHeadings,
@@ -135,3 +136,19 @@ test('extractPlanVersion — from frontmatter', () => {
 test('extractPlanVersion — null when absent', () => {
   assert.equal(extractPlanVersion('foo: bar\n'), null);
 });
+
+test('extractPlanVersion — from prose "Generated by" metadata line (defect S26)', () => {
+  // The plan template emits plan_version only in the prose blockquote line
+  // (`> Generated by ... — `plan_version: 1.7``), not as frontmatter.
+  // extractPlanVersion must honor its documented "frontmatter or doc body"
+  // contract and parse the backtick-wrapped prose form.
+  const prose = '> Generated by trekplan v4.1.0 on 2026-05-10 — `plan_version: 1.7`\n';
+  assert.equal(extractPlanVersion(prose), '1.7');
+});
+
+test('extractPlanVersion — recognizes the canonical plan template (regression pin S26)', () => {
+  // The real generated artifact: no test exercised the parser against the
+  // actual template, which is why defect S26 went unnoticed.
+  const tpl = readFileSync(new URL('../../templates/plan-template.md', import.meta.url), 'utf-8');
+  assert.equal(extractPlanVersion(tpl), '1.7');
+});

tests/validators/plan-validator.test.mjs

@@ -97,3 +97,17 @@ test('validatePlan — older version triggers warning', () => {
   const r = validatePlanContent(old, { strict: true });
   assert.ok(r.warnings.find(w => w.code === 'PLAN_VERSION_MISMATCH'));
 });
+
+test('validatePlan — prose plan_version line parses, no PLAN_NO_VERSION (defect S26)', () => {
+  // A plan shaped like the real template: plan_version lives only in the
+  // prose "Generated by" blockquote, not frontmatter. Must still parse.
+  const prosePlan = VALID_PLAN
+    .replace(/---\nplan_version: "1\.7"\n---\n\n/, '')
+    .replace(
+      '# Plan',
+      '# Plan\n\n> Generated by trekplan v4.1.0 on 2026-05-10 — `plan_version: 1.7`',
+    );
+  const r = validatePlanContent(prosePlan, { strict: true });
+  assert.equal(r.parsed.planVersion, '1.7');
+  assert.equal(r.warnings.find(w => w.code === 'PLAN_NO_VERSION'), undefined);
+});