When a Heading block opens a chunk and is followed by another Heading
or an atomic block (Code, Table, ImageRef, AudioRef) with no
intervening prose, the prior fallback used `common.heading_path` from
the heading itself — which per kb-normalize convention does NOT
include the heading's own text. Result: heading-only and heading-led
chunks for `# Alpha\n## Beta\n...` patterns landed with
`heading_path = []`, losing citation context.
Synthesize the leading heading into the chunk's heading_path when
blocks[0] is a Heading: parent path + heading.text. The first
non-Heading branch (existing logic for normal mid-section chunks) is
unchanged.
`chunk_id` recipe is `(doc_id, chunker_version, block_ids,
policy_hash)` — `heading_path` is not in the recipe, so this fix does
NOT shift chunk_ids. Snapshot baseline `long-section.chunks.snapshot.json`
also unchanged because every heading in that fixture is followed by a
paragraph (the bug only triggers on direct heading→heading or
heading→atomic adjacency).
Adds `heading_with_parents` test helper and a regression test pinning
the `# Alpha\n## Beta\n[code]` pattern.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
altair823
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