test(git-sync): exhaustive converter coverage + fix 3 round-trip data-loss bugs

Coder↔reviewer design loop (9 rounds, reviewer verdict: exhaustive) produced
92 specs; implemented +123 tests (465 -> 588 passing). The new round-trip
coverage exposed three genuine data-loss bugs in the Markdown<->ProseMirror
converter, all now FIXED (round-trip is lossless for these):

1. pageBreak was lost on export (no converter case -> rendered to "" and the
   node vanished). Now emits <div data-type="pageBreak"></div>, which the schema
   parses back -> round-trips.
2. A block image between blocks left an empty <p> artifact after import-hoisting,
   producing a phantom blank-gap diff on every sync. markdownToProseMirror now
   strips content-less paragraphs after generateJSON — with a schema-validity
   guard that keeps the obligatory single empty paragraph in `content: "block+"`
   containers (tableCell/tableHeader/blockquote/column/callout/doc), so empty
   cells/quotes never become an invalid `content: []`.
3. The `code` mark combined with another mark was not byte-stable (emitted nested
   HTML that the schema's `code` `excludes:"_"` collapsed on import). The
   converter now emits code-only when `code` co-occurs, matching the editor.

New coverage spans media/diagram/details/columns/math/mention attribute
round-trips, converter emission branches, git error paths, and engine decision
branches. A dedicated test pins the empty-container schema validity (the review
catch on the bug-2 fix).

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

packages/git-sync/test/docmost-schema-attrs.test.ts

@@ -0,0 +1,75 @@
+import { describe, expect, it } from 'vitest';
+import {
+  sanitizeCssColor,
+  clampCalloutType,
+} from '../src/lib/docmost-schema.js';
+
+// These tests pin the two security/normalization helpers that Docmost
+// interpolates into inline style and the callout banner type on re-render.
+// They are the allowlist guard (XSS/style-breakout boundary) and the
+// case-insensitive callout normalizer, both otherwise only exercised
+// indirectly through parseHTML/renderHTML.
+
+describe('sanitizeCssColor', () => {
+  it('accepts a plain named color unchanged', () => {
+    expect(sanitizeCssColor('red')).toBe('red');
+  });
+
+  it('accepts 3-digit and 6-digit hex colors unchanged', () => {
+    expect(sanitizeCssColor('#abc')).toBe('#abc');
+    expect(sanitizeCssColor('#aabbcc')).toBe('#aabbcc');
+  });
+
+  it('accepts well-formed functional notation unchanged', () => {
+    expect(sanitizeCssColor('rgb(1,2,3)')).toBe('rgb(1,2,3)');
+    expect(sanitizeCssColor('rgba(0,0,0,0.5)')).toBe('rgba(0,0,0,0.5)');
+    expect(sanitizeCssColor('hsl(120,50%,50%)')).toBe('hsl(120,50%,50%)');
+  });
+
+  it('trims surrounding whitespace before matching', () => {
+    // '  blue  ' trims to 'blue', which is a valid named color.
+    expect(sanitizeCssColor('  blue  ')).toBe('blue');
+  });
+
+  it('rejects a style-injection payload (returns null)', () => {
+    expect(sanitizeCssColor('red; --x: url(x)')).toBeNull();
+  });
+
+  it('rejects an attribute-breakout payload (returns null)', () => {
+    expect(sanitizeCssColor('red"><script>')).toBeNull();
+  });
+
+  it('rejects the empty string (returns null)', () => {
+    expect(sanitizeCssColor('')).toBeNull();
+  });
+
+  it('rejects non-string input via the typeof guard (returns null)', () => {
+    // @ts-expect-error deliberately passing a non-string to exercise the guard
+    expect(sanitizeCssColor(123)).toBeNull();
+  });
+});
+
+describe('clampCalloutType', () => {
+  it('lowercases an uppercase valid type', () => {
+    expect(clampCalloutType('INFO')).toBe('info');
+  });
+
+  it('lowercases a mixed-case valid type', () => {
+    expect(clampCalloutType('Warning')).toBe('warning');
+  });
+
+  it('passes through already-lowercase valid types', () => {
+    expect(clampCalloutType('danger')).toBe('danger');
+    expect(clampCalloutType('success')).toBe('success');
+  });
+
+  it('falls back to "info" for unknown types', () => {
+    expect(clampCalloutType('note')).toBe('info');
+    expect(clampCalloutType('tip')).toBe('info');
+  });
+
+  it('falls back to "info" for empty string and null', () => {
+    expect(clampCalloutType('')).toBe('info');
+    expect(clampCalloutType(null)).toBe('info');
+  });
+});