fix(watchlist): preserve custom body sections through sync rewrite

renderNote wiped any ## heading not owned by the renderer (Synopsis,
Cast, Links, My Notes) on every sync, destroying user content like
## Collection graph-link sections. extractCustomSections now pulls
non-owned sections out of the existing body before rewrite, and
renderNote re-emits them verbatim, in original order, between Links
and My Notes.

packages/obsidian/src/watchlist/SyncEngine.ts

@@ -1,4 +1,4 @@
-import { parseNote, extractMyNotes, noteTmdbRef } from 'packages/obsidian/src/watchlist/parse';
+import { parseNote, extractMyNotes, extractCustomSections, noteTmdbRef } from 'packages/obsidian/src/watchlist/parse';
 import { buildRecord } from 'packages/obsidian/src/watchlist/build';
 import { renderNote } from 'packages/obsidian/src/watchlist/render';
 
@@ -80,7 +80,7 @@ export async function syncFolder(deps: SyncDeps, opts: SyncOptions = {}): Promis
 			}
 			const detail: any = await withRateLimitRetry(() => deps.fetchDetail(ref.tmdbId, ref.isMovie), deps.sleep);
 			const record = buildRecord(detail, ref.isMovie, frontmatter);
-			const rendered = renderNote(record, extractMyNotes(body));
+			const rendered = renderNote(record, extractMyNotes(body), extractCustomSections(body));
 			report.synced++;
 			if (strip(frontmatter['watch_status']) === 'Watched' && record.watchStatus === 'Unwatched') {
 				report.flipped.push(note.path);

packages/obsidian/src/watchlist/parse.ts

@@ -22,6 +22,37 @@ export function extractMyNotes(body: string): string {
 	return m ? m[1].trim() : '';
 }
 
+const OWNED_HEADINGS = new Set(['Synopsis', 'Cast', 'Links', 'My Notes']);
+
+export interface CustomSection {
+	heading: string;
+	content: string;
+}
+
+export function extractCustomSections(body: string): CustomSection[] {
+	const lines = (body ?? '').split('\n');
+	const sections: CustomSection[] = [];
+	let heading: string | null = null;
+	let buf: string[] = [];
+	const flush = (): void => {
+		if (heading === null) return;
+		const content = buf.join('\n').replace(/(\n\s*)+$/, '');
+		if (!OWNED_HEADINGS.has(heading)) sections.push({ heading, content });
+	};
+	for (const line of lines) {
+		const m = /^##\s+(.*)$/.exec(line);
+		if (m) {
+			flush();
+			heading = m[1].trim();
+			buf = [];
+		} else if (heading !== null) {
+			buf.push(line);
+		}
+	}
+	flush();
+	return sections;
+}
+
 export function stripQuotes(s: string | undefined): string {
 	return (s ?? '').trim().replace(/^"|"$/g, '');
 }

packages/obsidian/src/watchlist/render.ts

@@ -1,9 +1,10 @@
 import type { WatchlistRecord } from 'packages/obsidian/src/watchlist/schema';
 import { yamlList, yamlScalar, quotedOrNull } from 'packages/obsidian/src/watchlist/yaml';
+import type { CustomSection } from 'packages/obsidian/src/watchlist/parse';
 
 const CATEGORY_TAG: Record<string, string> = { Movie: 'movie', Series: 'series', Anime: 'anime' };
 
-export function renderNote(r: WatchlistRecord, myNotes: string): string {
+export function renderNote(r: WatchlistRecord, myNotes: string, customSections: CustomSection[] = []): string {
 	const tag = CATEGORY_TAG[r.category];
 	const stars = r.ratingStars;
 	const fm = [
@@ -67,6 +68,7 @@ export function renderNote(r: WatchlistRecord, myNotes: string): string {
 	if (r.homepage) links.push(`- [Homepage](${r.homepage})`);
 	if (r.notionUrl) links.push(`- [Original Notion entry](${r.notionUrl})`);
 	if (links.length) b.push('## Links', ...links, '');
+	for (const s of customSections) b.push(`## ${s.heading}`, s.content, '');
 	b.push('## My Notes', '', myNotes);
 	if (myNotes) b.push('');
 	return fm.join('\n') + '\n' + b.join('\n');

tests/watchlist-parse.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from 'bun:test';
-import { parseNote, extractMyNotes, noteTmdbRef } from 'packages/obsidian/src/watchlist/parse';
+import { parseNote, extractMyNotes, noteTmdbRef, extractCustomSections } from 'packages/obsidian/src/watchlist/parse';
 
 const NOTE = `---
 type: watchlist_item
@@ -55,3 +55,32 @@ describe('noteTmdbRef', () => {
 		expect(noteTmdbRef({ type: 'list' })).toBeNull();
 	});
 });
+
+describe('extractCustomSections', () => {
+	test('extracts non-owned section', () => {
+		const body = `\n# Loki\n\n## Links\n- [IMDb](x)\n\n## Collection\nPart of [[Movies]]\n\n## My Notes\n\ngreat finale\n`;
+		expect(extractCustomSections(body)).toEqual([{ heading: 'Collection', content: 'Part of [[Movies]]' }]);
+	});
+	test('owned headings excluded (Synopsis, Cast, Links, My Notes)', () => {
+		const body = `\n## Synopsis\nblah\n\n## Cast\nA, B\n\n## Links\n- x\n\n## My Notes\n\nnote\n`;
+		expect(extractCustomSections(body)).toEqual([]);
+	});
+	test('two custom sections keep order', () => {
+		const body = `\n## Collection\nPart of [[Movies]]\n\n## Rewatch Log\n- 2024-01-01\n- 2025-02-02\n\n## My Notes\n\nnote\n`;
+		expect(extractCustomSections(body)).toEqual([
+			{ heading: 'Collection', content: 'Part of [[Movies]]' },
+			{ heading: 'Rewatch Log', content: '- 2024-01-01\n- 2025-02-02' },
+		]);
+	});
+	test('preserves internal blank lines, trims trailing', () => {
+		const body = `\n## Collection\nline one\n\nline two\n\n\n## My Notes\n\nnote\n`;
+		expect(extractCustomSections(body)).toEqual([{ heading: 'Collection', content: 'line one\n\nline two' }]);
+	});
+	test('no custom sections → empty array', () => {
+		const body = `\n# Loki\n\n## Links\n- x\n\n## My Notes\n\nnote\n`;
+		expect(extractCustomSections(body)).toEqual([]);
+	});
+	test('empty/missing body → empty array', () => {
+		expect(extractCustomSections('')).toEqual([]);
+	});
+});

tests/watchlist-render.test.ts

@@ -37,3 +37,28 @@ describe('renderNote golden', () => {
 		expect(renderNote(r, '')).not.toContain('**Rating:**');
 	});
 });
+
+describe('renderNote custom sections', () => {
+	test('no custom sections → output unchanged (golden)', () => {
+		const expected = readFileSync(join(import.meta.dir, 'fixtures', 'canonical-series.md'), 'utf-8');
+		expect(renderNote(LOKI, '', [])).toBe(expected);
+	});
+	test('single custom section placed after Links, before My Notes', () => {
+		const out = renderNote(LOKI, '', [{ heading: 'Collection', content: 'Part of [[Movies]]' }]);
+		const linksIdx = out.indexOf('## Links');
+		const collectionIdx = out.indexOf('## Collection');
+		const myNotesIdx = out.indexOf('## My Notes');
+		expect(linksIdx).toBeGreaterThan(-1);
+		expect(collectionIdx).toBeGreaterThan(linksIdx);
+		expect(myNotesIdx).toBeGreaterThan(collectionIdx);
+		expect(out).toContain('## Collection\nPart of [[Movies]]\n');
+	});
+	test('multiple custom sections keep relative order', () => {
+		const out = renderNote(LOKI, '', [
+			{ heading: 'Collection', content: 'Part of [[Movies]]' },
+			{ heading: 'Rewatch Log', content: '- 2024-01-01' },
+		]);
+		expect(out.indexOf('## Collection')).toBeLessThan(out.indexOf('## Rewatch Log'));
+		expect(out.indexOf('## Rewatch Log')).toBeLessThan(out.indexOf('## My Notes'));
+	});
+});

tests/watchlist-sync-engine.test.ts

@@ -22,6 +22,13 @@ keep me
 
 const AIRING_NOTE = ENDED_NOTE.replace('status: Ended', 'status: Returning Series').replace('last_air_date: 2023-11-09', 'last_air_date: 2023-10-01');
 
+const NOTE_WITH_COLLECTION = ENDED_NOTE.replace('## My Notes', '## Collection\nPart of [[Movies]]\n\n## My Notes');
+
+const NOTE_WITH_TWO_CUSTOM_SECTIONS = ENDED_NOTE.replace(
+	'## My Notes',
+	'## Collection\nPart of [[Movies]]\n\n## Rewatch Log\n- 2024-01-01\n- 2025-02-02\n\n## My Notes',
+);
+
 function makeDeps(notes: { path: string; content: string }[], detail: any = tvDetail) {
 	const contents = new Map(notes.map(n => [n.path, n.content]));
 	const writes: { path: string; content: string }[] = [];
@@ -163,6 +170,38 @@ describe('syncFolder', () => {
 		expect(report.errors[0].path).toBe('Bad.md');
 		expect(report.synced).toBe(1);
 	});
+	test('custom section round-trips through rewrite, positioned after Links and before My Notes', async () => {
+		const { deps, writes } = makeDeps([{ path: 'Loki.md', content: NOTE_WITH_COLLECTION }]);
+		await syncFolder(deps, { full: true });
+		const out = writes[0].content;
+		expect(out).toContain('## Collection\nPart of [[Movies]]\n');
+		const linksIdx = out.indexOf('## Links');
+		const collectionIdx = out.indexOf('## Collection');
+		const myNotesIdx = out.indexOf('## My Notes');
+		expect(collectionIdx).toBeGreaterThan(linksIdx);
+		expect(myNotesIdx).toBeGreaterThan(collectionIdx);
+	});
+	test('two custom sections keep relative order through rewrite', async () => {
+		const { deps, writes } = makeDeps([{ path: 'Loki.md', content: NOTE_WITH_TWO_CUSTOM_SECTIONS }]);
+		await syncFolder(deps, { full: true });
+		const out = writes[0].content;
+		expect(out.indexOf('## Collection')).toBeLessThan(out.indexOf('## Rewatch Log'));
+		expect(out.indexOf('## Rewatch Log')).toBeLessThan(out.indexOf('## My Notes'));
+	});
+	test('idempotence: custom section stable across two sync passes (render→parse→extract→render byte-identical)', async () => {
+		const { deps, writes } = makeDeps([{ path: 'Loki.md', content: NOTE_WITH_COLLECTION }]);
+		await syncFolder(deps, { full: true });
+		const rendered = writes[0].content;
+		const second = makeDeps([{ path: 'Loki.md', content: rendered }]);
+		const report = await syncFolder(second.deps, { full: true });
+		expect(second.writes.length).toBe(0);
+		expect(report.written).toBe(0);
+	});
+	test('golden: note with no custom sections unaffected by custom-section plumbing', async () => {
+		const { deps, writes } = makeDeps([{ path: 'Loki.md', content: ENDED_NOTE }]);
+		await syncFolder(deps, { full: true });
+		expect(writes[0].content).not.toContain('## Collection');
+	});
 	test('stale-read guard: content edited mid-sync is re-read fresh, not clobbered by early snapshot', async () => {
 		const { deps, writes, contents } = makeDeps([
 			{ path: 'A.md', content: AIRING_NOTE },