feat(linkedin-studio): first-hour/reply-loop command with tracked state

Wire orphan agent #11 (engagement-coach) by giving it a command surface, and
add the tracked first-hour state the plan calls for (remediation Step 16).

- commands/firsthour.md (new, 27th command): post-publish first-hour /
  reply-loop sprint. Delegates plan construction to engagement-coach via
  Task (subagent_type: linkedin-studio:engagement-coach) — returns a grouped
  target list (whales/inner-circle/ICPs/new connections), 2-3 seed
  self-comments + 3-5 CEA replies in the user's voice, and a minute-by-minute
  timeline anchored to publish time. Presents timeline/targets/drafts +
  velocity checkpoints, auto-copies the drafts to clipboard, persists the
  plan, then hands off to post-feedback-monitor for the 48h window.
- hooks/scripts/state-updater.mjs: new pure mutation recordFirstHourPlan()
  mirroring updatePostTracking — additive by contract (inserts
  last_firsthour_date after last_post_date when absent, creates the
  ## First-Hour Plans section when absent, never touches existing fields).
  Section name is deliberately non-R-initial so it stays outside
  pruneContentHistory's "## Recent Posts ... (?=\n## [^R])" capture window.
  + a --record-firsthour CLI branch for parity with the other mutations.
- config/state-file.template.md: additive scalars (last_firsthour_date,
  firsthour_active) + the ## First-Hour Plans section.
- hooks/scripts/__tests__/state-updater.test.mjs: extend (existing file) with
  7 recordFirstHourPlan tests — section creation, field insertion vs in-place
  update (no duplication), round-trip non-interference, graceful empty
  defaults, changes array.
- CLAUDE.md: register the command (## Commands 26 -> 27, table row).
- scripts/test-runner.sh: EXPECT_COMMANDS 26 -> 27 (registration guard).

Verify: grep 'subagent_type: linkedin-studio:engagement-coach' commands/ ->
firsthour.md; node --test state-updater -> 26/26; full hook suite -> 83/83;
bash scripts/test-runner.sh -> exit 0 (62 passed, commands 27/27).

Plan Step 16 (Wave 4 S3).
[skip-docs]: tre-doc + version bump deferred to Step 21 per remediation plan.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plugins/linkedin-studio/hooks/scripts/__tests__/state-updater.test.mjs

@@ -1,6 +1,6 @@
 import { describe, test } from 'node:test';
 import assert from 'node:assert/strict';
-import { updatePostTracking, pruneContentHistory, updateFollowerCount } from '../state-updater.mjs';
+import { updatePostTracking, pruneContentHistory, updateFollowerCount, recordFirstHourPlan } from '../state-updater.mjs';
 
 const SAMPLE_STATE = `---
 last_post_date: "2026-04-05"
@@ -293,3 +293,75 @@ describe('updateFollowerCount', () => {
     assert.ok(result.content.includes('[2026-04] 920 (+70)'));
   });
 });
+
+describe('recordFirstHourPlan', () => {
+  const PLAN_OPTS = {
+    planDate: '2026-05-30 09:00',
+    postTopic: 'AI governance',
+    targets: ['Whale: @bigvoice (within 30 min)', 'Inner circle: @peer'],
+    draftComments: ['Your point about model-cards resonates — we found...'],
+    plan: ['09:00 — Post goes live', '09:10 — Add value self-comment', '09:30 — Reply to every comment']
+  };
+
+  test('creates a non-R-initial First-Hour Plans section when absent', () => {
+    // SAMPLE_STATE has no ## First-Hour Plans section → must be created (additive)
+    assert.ok(!SAMPLE_STATE.includes('## First-Hour Plans'));
+    const result = recordFirstHourPlan(SAMPLE_STATE, PLAN_OPTS);
+    assert.notEqual(result, null);
+    assert.ok(result.content.includes('## First-Hour Plans'));
+  });
+
+  test('records topic, targets, draft comments and timeline in the entry', () => {
+    const result = recordFirstHourPlan(SAMPLE_STATE, PLAN_OPTS);
+    assert.notEqual(result, null);
+    assert.ok(result.content.includes('[2026-05-30 09:00]'));
+    assert.ok(result.content.includes('AI governance'));
+    assert.ok(result.content.includes('Whale: @bigvoice (within 30 min)'));
+    assert.ok(result.content.includes('Your point about model-cards resonates'));
+    assert.ok(result.content.includes('09:10 — Add value self-comment'));
+  });
+
+  test('is additive — inserts last_firsthour_date when the field is absent', () => {
+    assert.ok(!/^last_firsthour_date:/m.test(SAMPLE_STATE));
+    const result = recordFirstHourPlan(SAMPLE_STATE, PLAN_OPTS);
+    assert.notEqual(result, null);
+    assert.match(result.content, /^last_firsthour_date: "2026-05-30 09:00"$/m);
+  });
+
+  test('updates an existing last_firsthour_date without duplicating it', () => {
+    const withField = SAMPLE_STATE.replace(
+      'last_post_date: "2026-04-05"',
+      'last_post_date: "2026-04-05"\nlast_firsthour_date: null'
+    );
+    const result = recordFirstHourPlan(withField, { ...PLAN_OPTS, planDate: '2026-05-30 11:00' });
+    assert.notEqual(result, null);
+    const hits = result.content.match(/^last_firsthour_date:/gm) || [];
+    assert.equal(hits.length, 1, 'field must not be duplicated');
+    assert.match(result.content, /^last_firsthour_date: "2026-05-30 11:00"$/m);
+  });
+
+  test('leaves existing fields and sections untouched (round-trip)', () => {
+    const result = recordFirstHourPlan(SAMPLE_STATE, PLAN_OPTS);
+    assert.notEqual(result, null);
+    assert.match(result.content, /^last_post_date: "2026-04-05"$/m);
+    assert.match(result.content, /^follower_count: 850$/m);
+    assert.ok(result.content.includes('- [2026-04-05] "AI governance is not about..."'));
+  });
+
+  test('gracefully defaults empty targets/comments/plan', () => {
+    const result = recordFirstHourPlan(SAMPLE_STATE, {
+      planDate: '2026-05-30 09:00',
+      postTopic: 'minimal'
+    });
+    assert.notEqual(result, null);
+    assert.ok(result.content.includes('## First-Hour Plans'));
+    assert.ok(result.content.includes('minimal'));
+  });
+
+  test('returns a changes array describing what changed', () => {
+    const result = recordFirstHourPlan(SAMPLE_STATE, PLAN_OPTS);
+    assert.notEqual(result, null);
+    assert.ok(Array.isArray(result.changes));
+    assert.ok(result.changes.length > 0);
+  });
+});