Markdown nested indented lists need explicit listItem.spread

Problem

serializeMd should emit tight nested lists for indented list nodes:

* parent
  * child

Instead, the serializer emitted:

* parent

  * child

The failure only showed up at the final markdown string layer. The helper that built the intermediate mdast tree still passed its existing assertions.

Root cause

The indented-list path in listToMdastTree built listItem nodes without a spread property. The classic list serializer already emitted listItem.spread: false, so the two serializer paths did not produce the same mdast shape.

That difference matters because remark-stringify treats nested lists as loose when listItem.spread is missing, even if the parent list.spread is false. The result is the extra blank line between parent and child items.

Solution

Normalize the mdast output so every generated listItem gets an explicit spread value:

const listItem: MdListItem = {
  checked: null,
  children: [
    {
      children: convertNodesSerialize(
        node.children,
        options
      ) as MdParagraph['children'],
      type: 'paragraph',
    },
  ],
  spread: options.spread ?? false,
  type: 'listItem',
};

Apply the same shape in both code paths:

• the standard indented-list builder
• the block-id wrapper path in processListWithBlockIds(...)

Next, update helper expectations so the direct mdast assertions catch this contract in the future. We also added a serializer regression for ordered nested indented lists so the fix is not bullet-only by accident.

Verification

These checks passed after the change:

bun test packages/markdown/src/lib/serializer/standardList.spec.tsx
bun test packages/markdown/src/lib/serializer/listToMdastTree.spec.ts
bun test packages/markdown/src/lib/serializer/convertNodesSerialize.spec.ts
bun test packages/markdown/src/lib/serializer
bun test packages/markdown/src
pnpm install
pnpm turbo build --filter=./packages/markdown
pnpm turbo typecheck --filter=./packages/markdown
pnpm lint:fix

Prevention

When two serializer paths are supposed to build the same mdast node type, assert the full shape in helper specs instead of checking only the final markdown string or a subset of fields.

For list serialization in particular, treat listItem.spread as part of the mdast contract, not optional metadata. If a nested list suddenly becomes loose in markdown output, compare the intermediate AST against a known-good path before changing stringify expectations.