## Why Task lists render and round-trip (checkboxes were restyled in #342), but people could not create them. `- [ ] ` left a bullet containing literal `[ ]`, and the slash menu had no item.

## What changed - `[] `, `[ ] ` and `[x] ` already converted through the markdown shortcuts. New: `- [ ] ` / `- [x] ` at line start now becomes a task item (it lifts the item out of its bullet list, splitting the list if needed). `task-rule.ts`, mounted in the toolbar, skipped when read-only. - New "Task list" slash item (Layout group; matches task, todo, checklist, checkbox). - Click on the box, and Space on a focused item, toggle; Enter on an empty task exits the list. These come from Lexical's check-list plugin that was already mounted. Verified in a browser, covered by e2e. - The dialect already parses and serializes task items (`- [ ]` / `- [x]`), so no server or dialect change. - No keyboard shortcut added: the editor has no list shortcuts today.

## Screenshots Before (typing `- [ ]`, `[x]`; bullets with literal brackets):


After:


Slash menu:


## Verification

Nine focused task-list tests, `bun run types`, `bun run ci`, and `bun run build` pass on the restacked branch. GitHub's browser suite will run on the final published head. The reviewed design hash was renewed after checking the integrated source.

**Review:** Looks good

Checked in a real browser (headless Chromium, fake-GitHub server on the PR build, plus a second user as peer).

Works: - `- ` then `[ ] ` at an item's start converts to an empty task item, at list end, middle (list splits bullet / task / bullet) and as the only item. `- [x] ` gives a checked item with strikethrough. It survives reload and shows for a peer. - Slash menu "Task list" (`/task`) inserts a task item; it survives reload. - Not hijacked: `Say - [ ] hello [x] there` in a paragraph and `- foo [ ] bar` in a bullet stay literal. `[ ]` followed by a space after other text is ignored in the unit tests. - Nested bullet with a sibling stays literal (`[ ] n2`).

Findings (none blocking): 1. `packages/editor/src/toolbar/task-rule.ts` `$liftIntoTaskList`: a nested bullet that is the only item in its sublist DOES convert (`list.setListType("check")`), while a nested item with siblings stays literal. So nesting behaviour is inconsistent. If "nested stays literal" is the intent, return false when `nested` before the sole-item branch; otherwise document that sole nested items convert and add a test for it. (Reload kept the result, so it is not corrupting.) 2. No undo to check: Mod+Z does nothing in the document editor on `main` either (the editor has no undo binding), so conversion can't be undone, same as every other edit. Pre-existing, not this PR. 3. Minor visual: the task item sits a little further from the preceding bullet list than bullets sit from each other (separate list blocks). Acceptable.

`gh pr checks 374`: container pass, e2e pass, "format, lint, types, tests" fail. The failing step is `bun run ci` (the design-contract hash for `slash.tsx`, which the PR body flags); acceptable per process.