[codex] Fix markdown list roundtrips

[samuelstroschein]

Summary

Fixes Markdown list roundtripping in the editor:

• Prevents collapsed toolbar clicks inside active bullet/numbered lists from unwrapping the current list item and dropping bullet syntax on save.
• Preserves manually typed checklist markers such as - [], - [ ], and - [x] when serializing Markdown.
• Keeps checklist toolbar state distinct from plain bullet-list state.
• Adds a long-document persistence regression for the issue Editor deletes content below edit point in long Markdown document #129 shape so mid-document edits do not truncate content below the edit point.
• Adds a patch changenote for the user-facing fix.

Root Cause

TipTap represents checklists on top of bullet-list/list-item nodes, while the Markdown serializer did not emit task markers from listItem.checked. The toolbar also treated collapsed clicks inside active lists as unwrap commands, which could convert an existing one-item bullet list back into a paragraph before persistence.

Validation

• pnpm test
• pnpm run typecheck
• git diff --check
• Manual Electron verification against /Users/samuel/Desktop/flash_kb/new-file.md
• Manual Electron long-document roundtrip check for the issue Editor deletes content below edit point in long Markdown document #129 reproduction shape

---

Note

Medium Risk
Touches the Markdown save path and list editing UX; wrong behavior could corrupt saved file content, though changes are scoped and heavily tested.

Overview
Fixes Markdown save roundtrips for bullet lists, checklists, and toolbar behavior so list syntax is not dropped accidentally.

Serialization: serializeAst now injects [ ] / [x] markers from listItem.checked before the Rust serializer runs, so checked tasks roundtrip through the editor.

Formatting toolbar: Collapsed clicks on bullet/numbered list buttons no longer unwrap the current item; unwrap only happens with an explicit text selection. Bullet vs checklist aria-pressed state is split so task items are not shown as plain bullets.

Typing shortcuts: Checklist triggers inside an existing list only flip checked on the first paragraph of the item, avoiding false task conversion when [ ] is typed in a continuation line.

Adds regression coverage (toolbar, shortcuts, editor persistence including a long-document mid-edit case) and a patch changenote.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Treat mixed-list plain items as bullets

When the cursor is on the plain bullet item in a mixed list like - plain followed by - [ ] todo, astToTiptapDoc marks the whole bulletList as isTaskList if any sibling has checked, so computeTaskListActive returns true even though the current listItem.checked is null. With this new && !isTaskList gate, the Bullet button is no longer pressed and the Checklist button is shown as active for that plain item, so the toolbar state no longer matches the selected item in mixed lists.

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