The indent trigger was using .abs() which fired on both increased indent
(non-indented → indented) AND decreased indent (indented → non-indented).
This caused drop-cap style paragraphs (indented first line, flush-left
continuation) to incorrectly split into two blocks.
Per plan Phase 4.4 heuristic #2, indent change should only trigger when the
current line is MORE indented (to the right, larger x0) than the block
average - i.e., a new paragraph starting after non-indented text. It should
NOT trigger for decreased indent (first line indented, rest flush-left).
Fix: Remove .abs() and only check if line_x0 - block_avg_x0 > threshold.
Tests:
- test_indented_first_line_new_block: PASS (non-indented → indented splits)
- test_indented_first_line_of_paragraph_not_split: PASS (drop cap stays together)
- All 179 line module tests: PASS
The bead description mentioned compile errors in hash.rs from API drift,
but those errors were either already fixed or misattributed. The API usage
was already correct:
- compute_fingerprint already takes 3 arguments with source
- len() already propagates Result with ?
- read_at method already used correctly
- Catalog fields accessed via trailer correctly
Only cleanup: removed unused std::fs::File and std::io imports.
Verification: notes/bf-4mkhv.md
