fix(lists): expand tabs in the indentation to four-column stops

[delphinus]

Everything that measures indentation counts spaces, so a list item indented with a tab was one column deep instead of four. A tab-indented item under another item did not nest:

- outer
	- inner item long enough to wrap onto a second line

• its continuation lines hung from the parent's column, not the nested item's text;
• the tab itself reached the buffer, where 'tabstop' (8 by default) pushed the marker further right than the hanging indent assumed.

The fix

render_document expands tabs in each line's leading whitespace before anything measures it, with tab stops every four columns as CommonMark specifies. \t- item now renders exactly as - item does, and \t stops at column 4. Fenced code is left alone, since its tabs are content.

Tests

tests/list_indent_test.lua gains Test 10:

• a tab-indented nested item renders the same as a four-space one;
• its wrapped continuation hangs under its own text;
• no tab reaches the output;
• a tab after spaces stops at column four;
• a tab inside fenced code stays.

Four of these assertions fail without the fix. make test passes.

🤖 Generated with Claude Code