Doc-only follow-ups for review minors I1, M3, M4. No behavior change.
* I1: rustdoc on `MdHeadingV1Chunker` now records that
`policy.respect_markdown_headings` flows into `policy_hash` only;
the `md-heading-v1` variant unconditionally treats headings as
boundaries by name. To disable heading awareness, ship a different
`chunker_version` (none in P1-5).
* M3: `# Panics` rustdoc on `policy_hash` documents the
unreachable-in-practice failure mode of
`serde_json_canonicalizer::to_vec` and explains why the `expect` is
retained as future-proofing.
* M4: Inline comment at the `would_exceed` decision noting that
`acc.text_tokens` already includes the prior chunk's overlap seed,
and that the I3 clamp guarantees a flush here never produces a
chunk smaller than the seed budget.
* Heading-path bullet in the behavior contract updated to reflect the
I2 fix wording.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
altair823
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