BlockStart API Hard Cut

Goal

Remove the leaky blockStart rule contract where custom rules have to manually thread range and other base match data through resolveMatch. Core should provide the base block-start match payload by default and merge custom match extras on top.

Phases

• [in_progress] Inspect current core input-rule types/runtime and related learnings.
• [pending] Add or adjust core tests to lock merged block-start match behavior.
• [pending] Implement the hard cut in core.
• [pending] Simplify affected rules in list and basic-nodes to use the new API.
• [pending] Verify with targeted tests, build, typecheck, and lint.
• [pending] Document the learning if the API cut exposes a reusable rule.

Findings

• blockStart already had a base match shape in core: { range, text }.
• The leaky part was resolveMatch, which replaced that base payload instead of contributing extras on top.
• That forced custom rules to manually preserve range, which is why list and blockquote rules accumulated pointless resolveMatch: ({ range }) => ({ range }) boilerplate.
• The durable API cut is: resolveMatch returns extras, core merges them with the base block-start match before apply.

Progress

• Loaded hard-cut, north-star, major-task, learnings-researcher, planning-with-files, testing, tdd, and task.
• Framed this as a core API fix, not another local rule patch.
• Added a core regression proving custom block-start extras merge with the base match payload.
• Hard-cut the API in core types and runtime.
• Simplified modern and classic list rules plus blockquote rules to stop threading range manually.
• Added the API learning in docs/solutions/best-practices/block-start-resolve-match-should-return-extras-while-core-provides-base-match.md.

Errors

• None yet.