A markdown page draws task lists as read-only checkboxes and counts them in its heading #11895

A markdown file page now draws - [ ] and - [x] items as disabled checkboxes and names progress in its header. I didn't take the before/after screenshot, because my sandbox can't reach a running page. tsc, scripts/gate.ts, design-lint and the markdown tests pass; I ran 30 markdown-related test files, 437 pass and 2 skip.

What changed

• Checkboxes: in src/web/markdown.ts, a top-level bullet beginning [ ], [x] or [X] becomes <li class="task"><input type="checkbox" disabled [checked]> text</li>. The text goes through the existing escaping, and there is no form and no JavaScript.
• Left alone: fenced code, inline code, [ ] in the middle of an item, and indented or nested items.
• Progress: in src/web/render/markdown.ts, when a file has at least one task, the header reads N lines · 3 of 7 done · size. With no task the header is unchanged. The count comes from the same pass that draws the list, so it can't disagree with what's shown.
• Style: two small rules in src/web/style/content.ts drop the bullet and align the checkbox.
• Tests: test/render-markdown-tasks.test.ts covers ticked, unticked, nested, a code fence, script text escaped, and the header progress. scripts/gate.ts picks up the new test from the directory, so I didn't add it by hand.

Left out

• Nested task lists. The renderer has no nesting, so indented items stay as text.
• Task items in numbered lists. Only - and * bullets become checkboxes.

The pre-push hook wanted a Try: commit, so the branch ends with an empty one. To try it, open any .md file containing task items from a preview.

Closes #11869

A markdown file page now draws - [ ] and - [x] items as disabled checkboxes and names progress in its header. I didn't take the before/after screenshot, because my sandbox can't reach a running page. tsc, scripts/gate.ts, design-lint and the markdown tests pass; I ran 30 markdown-related test files, 437 pass and 2 skip.

What changed

• Checkboxes: in src/web/markdown.ts, a top-level bullet beginning [ ], [x] or [X] becomes <li class="task"><input type="checkbox" disabled [checked]> text</li>. The text goes through the existing escaping, and there is no form and no JavaScript.
• Left alone: fenced code, inline code, [ ] in the middle of an item, and indented or nested items.
• Progress: in src/web/render/markdown.ts, when a file has at least one task, the header reads N lines · 3 of 7 done · size. With no task the header is unchanged. The count comes from the same pass that draws the list, so it can't disagree with what's shown.
• Style: two small rules in src/web/style/content.ts drop the bullet and align the checkbox.
• Tests: test/render-markdown-tasks.test.ts covers ticked, unticked, nested, a code fence, script text escaped, and the header progress. scripts/gate.ts picks up the new test from the directory, so I didn't add it by hand.

Left out

• Nested task lists. The renderer has no nesting, so indented items stay as text.
• Task items in numbered lists. Only - and * bullets become checkboxes.

The pre-push hook wanted a Try: commit, so the branch ends with an empty one. To try it, open any .md file containing task items from a preview.

Two of the three changes are pushed. The before/after screenshot is still missing, because I can't take one from here.

• Accessible name: Each task item now renders as <li class="task"><label><input type="checkbox" disabled[ checked]> text</label></li>. The two existing assertions match the label markup. A new test asserts every checkbox sits in a label with its text, so it fails without the wrapper.
• Magic number: .prose now sets --list-indent: 24px. The ul and ol padding and the task item's offset (calc(-1 * var(--list-indent))) all read it, so they move together. The checkbox now sits exactly at the list's outer edge; before, it was 4px inside it (the old -20px against 24px padding).
• Screenshot: The sandbox can reach the preview with curl but has no browser. Someone with one should capture the before/after from https://lab--11895--forge-trevato-apps.open-platform.sh. Open a markdown file with - [ ] and - [x] items and look for "N of M done" in its header.
• Checks: tsc, the task-list tests and design-lint pass. I did not run scripts/gate.ts or scripts/fast.ts.

Left #11869 open: 1 unticked item remain (Before/after screenshot of one file page.).