feat: markdown → scenario-data generator (tools/)

Add a deterministic authoring tool that turns a structured scenario
markdown file into a validated scenario-data module:
- tools/scenario-md.js: pure parseScenarioMarkdown + emitScenarioModule
  (frontmatter → meta; ## Timeline/## Clues/## Cast lists → the arrays;
  auto-slugged ids; validated via validateScenario before emit).
- tools/md-to-scenario.mjs: CLI (npm run gen:scenario), file or stdout.
- tools/example-scenario.md: documented format example.

Parses a defined format, not freeform con prose. tools/ is dev-only and
never bundled. tests/tools/scenario-md.test.js round-trips + validates.
187 tests pass; build clean.

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

tests/tools/scenario-md.test.js

@@ -0,0 +1,96 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'node:fs';
+import { parseScenarioMarkdown, emitScenarioModule } from '../../tools/scenario-md.js';
+import { validateScenario } from '../../src/core/scenario.js';
+
+const MD = `---
+id: demo
+title: DEMO
+system: coc-d100
+players: 4
+playMinutes: 210
+slot: Sat · Slot 4
+---
+
+## Timeline
+- [0] The opening {hard} #open
+- [35] Interview | cut: summarise the ledger
+- [120] The reveal {hard}
+
+## Clues
+- The door-cam face {essential} {act: Act One} | fallback: the monologue cards
+- A colour detail
+
+## Cast
+- MARY FLETCHER — Innkeeper; saw the watchers | secret: she saw Crowe sew
+- DANNY TATE — Stable boy, 14
+- THE NARRATOR {pc}
+`;
+
+// Load the emitted module string as a real ES module value.
+async function importModule(js) {
+  const url = 'data:text/javascript;base64,' + Buffer.from(js).toString('base64');
+  return (await import(url)).default;
+}
+
+describe('markdown → scenario-data', () => {
+  it('parses frontmatter into meta with numeric coercion', () => {
+    const s = parseScenarioMarkdown(MD);
+    expect(s.meta).toEqual({ id: 'demo', title: 'DEMO', system: 'coc-d100', players: 4, playMinutes: 210, slot: 'Sat · Slot 4' });
+  });
+
+  it('parses timeline beats with minutes, hard triggers, cut hints and ids', () => {
+    const { timeline } = parseScenarioMarkdown(MD);
+    expect(timeline[0]).toEqual({ id: 'open', label: 'The opening', targetMin: 0, hardTrigger: true });
+    expect(timeline[1]).toEqual({ id: 'interview', label: 'Interview', targetMin: 35, cutHint: 'summarise the ledger' });
+    expect(timeline[2]).toEqual({ id: 'the-reveal', label: 'The reveal', targetMin: 120, hardTrigger: true });
+  });
+
+  it('parses clues with essential / act / fallback and auto-ids', () => {
+    const { clues } = parseScenarioMarkdown(MD);
+    expect(clues[0]).toEqual({ id: 'the-door-cam-face', label: 'The door-cam face', essential: true, act: 'Act One', fallback: 'the monologue cards' });
+    expect(clues[1]).toEqual({ id: 'a-colour-detail', label: 'A colour detail', essential: false });
+  });
+
+  it('parses cast with name/note/secret and pc/npc kind', () => {
+    const { cast } = parseScenarioMarkdown(MD);
+    expect(cast[0]).toEqual({ id: 'mary-fletcher', name: 'MARY FLETCHER', kind: 'npc', note: 'Innkeeper; saw the watchers', secret: 'she saw Crowe sew' });
+    expect(cast[1]).toEqual({ id: 'danny-tate', name: 'DANNY TATE', kind: 'npc', note: 'Stable boy, 14' });
+    expect(cast[2]).toEqual({ id: 'the-narrator', name: 'THE NARRATOR', kind: 'pc' });
+  });
+
+  it('produces a module that validates and round-trips back to the same data', async () => {
+    const parsed = parseScenarioMarkdown(MD);
+    const js = emitScenarioModule(parsed);
+    const mod = await importModule(js);
+    expect(validateScenario(mod)).toEqual([]);
+    expect(mod).toEqual(parsed);
+  });
+
+  it('dedupes ids derived from identical labels', () => {
+    const s = parseScenarioMarkdown(`---
+id: dup
+system: year-zero
+---
+## Timeline
+- [0] Beat
+- [10] Beat
+`);
+    expect(s.timeline.map((b) => b.id)).toEqual(['beat', 'beat-2']);
+  });
+
+  it('throws on missing frontmatter and on an empty timeline', () => {
+    expect(() => parseScenarioMarkdown('## Timeline\n- [0] x')).toThrow(/frontmatter/);
+    expect(() => parseScenarioMarkdown('---\nid: x\nsystem: year-zero\n---\n')).toThrow(/invalid scenario/);
+  });
+
+  it('regenerates the shipped example markdown into a valid module', async () => {
+    const md = readFileSync('tools/example-scenario.md', 'utf8'); // vitest runs from repo root
+    const mod = await importModule(emitScenarioModule(parseScenarioMarkdown(md)));
+    expect(validateScenario(mod)).toEqual([]);
+    expect(mod.meta.id).toBe('example-md');
+    expect(mod.timeline).toHaveLength(4);
+    expect(mod.clues.filter((c) => c.essential)).toHaveLength(2);
+    expect(mod.cast).toHaveLength(2);
+  });
+});