fix(layout): leave headerless documents and auto-spaced Hangul paragraphs to Hancom

[airmang]

무엇

두 가지 "모르면 멈추거나 쓰지 않기" 고침.

1. 머리 정보 파트 없는 문서: Contents/header.xml이 없는 HWPX에서 estimate_pages가 IndexError로 멈췄다(_Measure가
   root.headers[0]을 읽음). 이제 지원 밖으로 알리고(a document without a header part (Contents/header.xml)),
   write_line_caches도 아무것도 쓰지 않는다.
2. 한글·영문/숫자 자동 간격: 문단 모양이 hh:autoSpacing(eAsianEng/eAsianNum)을 켜면 한/글은 한글 음절과 영문 글자·숫자
   사이를 넓힌다. FormFit은 아직 그 폭을 모르므로, 그런 문단(한글 바로 옆에 영문 글자 또는 숫자)에는 줄 배치 정보를 쓰지
   않는다. 쓰면 한/글이 그 줄 나눔을 그대로 믿어 글자가 눌릴 수 있었다.

시험

• test_a_document_without_a_header_part_is_left_unsupported(고치기 전 IndexError).
• test_a_paragraph_with_automatic_spacing_beside_hangul_is_left_for_hancom(4가지: 영문 간격 + 빈칸 옆만 → 씀, 영문 간격 + 한글 옆 영문 → 안 씀,
  숫자 간격 + 한글 옆 숫자 → 안 씀, 간격 꺼짐 → 씀; 안 씀 둘은 고치기 전 실패).

🤖 Generated with Claude Code

[airmang]

Reviewed exact head 394ad26.

Reviewed header absence handling before _Measure construction and the cache writer's unsupported early return. Reviewed the per-measure auto-spacing map, enabled-flag parsing and bidirectional Hangul/ASCII-letter-or-digit adjacency guard, including cell paths through _lines. Tests cover headerless ZIP input, no cache mutation, enabled/disabled spacing and non-adjacent Latin text. All 1,524 local line-cache/page-estimate tests pass. No unresolved code finding. All 13 current CI checks pass; verified workflow head SHA and read its test/lint/type/hygiene log (6,934 passed, 18 skipped, 1 xfailed; coverage 90.04%).

Merge held: after #506 and #512 merged, git merge-tree against current main 73d68a7 reproduces content conflicts in CHANGELOG.md. Resolve preserving both PRs' changes and fixture coverage, then revalidate the updated head and combined tree. No conflicted integration-test pass is claimed. COMMENT because this account owns the PR.

[airmang]

Re-reviewed exact head 9ce2f46. Range-diff shows the header guard correctly moved into _estimate after #506's refactor, while automatic-spacing paragraph exclusion and other reviewed behavior are preserved. Inspected the header guard before _Measure construction, unsupported/no-write return, and per-measure bidirectional Hangul/Latin-or-digit adjacency lookup. No unresolved finding. All 1,526 local cache/page-estimate tests pass. All 13 exact-head checks pass; workflow SHA verified and logs inspected (6,937 passed, 18 skipped, 1 xfailed; lint/types/hygiene pass).

Merge held: git merge-tree with current main 45b9541 after #508/#513 reproduces a CHANGELOG.md conflict. Preserve both changes and rerun latest-head checks/integration after resolution. This remains the safety prerequisite for #515's incomplete automatic-spacing tab-width path. No conflicted integration-test pass is claimed. COMMENT because this account owns the PR.

[airmang]

Re-reviewed exact head c60fbf9. Range-diff confirms the previously reviewed headerless-document guard in _estimate and automatic-spacing cache exclusion are unchanged apart from base/CHANGELOG resolution. Rechecked the guard before _Measure construction, public/private estimate entry points, unsupported no-write return and per-measure Hangul/Latin-or-digit adjacency lookup. No unresolved finding; previous conflict is resolved.

All 1,527 local cache/page-estimate tests pass on this head. All 13 current checks pass; CI workflow head SHA verified and test/lint/type/hygiene logs read (6,942 passed, 18 skipped, 1 xfailed; coverage 90.05%). After #509 merged, scratch integration with main 469aa3c was clean; all 1,682 FormFit/cache/page-estimate/body-patch tests pass. Tested tree 7416496072ead57cf906af3b7c406da7828cb3dd. Ready for expected-head-SHA squash merge. COMMENT because this account owns the PR.