feat: typing [x] at a note line start creates a to-do, and Enter continues the list unchecked (goal 0254)

[alicoding]

Owner-raised: "which one lets you do [x] todo — because none of it does right now." They were right: the engine's own task rule only fires INSIDE an existing list item, so the converged line-start syntax did nothing, and the only working path was the undiscoverable, flaky two-step (- then [ ] ).

Two pieces, both through the engine's own extension surface:

• Line-start rule: [] , [ ] , or [x] at the start of a plain paragraph wraps the line into a task item with the matching state (the Notion-family convention this WYSIWYG adopted into). Inside a list item it re-marks — covering [] and already-task items, which the stock rule structurally can't touch.
• Unchecked Enter-continuation: Enter at the end of a checked to-do now splits with the new item born unchecked, intercepted at the view level. The obvious alternative — flipping the attr after the split — was measured live to remount the checkbox widget under the caret and eat in-flight keystrokes even at human typing cadence; born-with-final-state has zero churn (verified: continuous 140ms-cadence typing of a three-item list lands every character).

Proof: new e2e in atlas-note-formatting.spec.ts (conversion, continuation, commit round-trip as real checkboxes — with the file's established settle/recovery guards for the engine's documented remount trait); the formatting-affordance cases split into their own spec along the 500-line seam; note suites + 985 unit tests green; screenshots reviewed. Userdocs names the shortcut.

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https://claude.ai/code/session_012im1JxQQV2ahnXzZDdVmZq