`# ` (a heading with no following text) used to seed the heading
stack with `Some("")`, which then propagated into every child block's
`heading_path` as a `""` segment — visibly polluting the path that
downstream consumers index by.
Filter empty entries from both `heading_path()` and the in-line
ancestor collection at heading-end. We deliberately keep `Some("")`
in the stack rather than skipping the assignment so the slot remains
occupied and a subsequent deeper heading is still positioned
correctly relative to its level — only the visible path drops the
empty.
New tests:
- empty_heading_does_not_pollute_path
- empty_h1_then_h2_does_not_break_stack
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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