Strategy 9 (context_aware, the last-resort fuzzy strategy used by
patch_replace, V4A UPDATE hunks, and skill_manage) had two serious flaws,
both reproduced live against current main:
1. CORRECTNESS: it accepted a block when >=50% of its lines were >=0.80
similar. A 2-line pattern with one real line and one garbage line matched,
silently deleting the non-matching line and persisting a wrong edit as
success. Now requires the first AND last lines to anchor-match and EVERY
non-blank pattern line to be >=0.80 similar — one garbage line disqualifies
the block.
2. PERFORMANCE: it scored every content window with per-line SequenceMatcher,
so every failed match paid O(file_lines x pattern_lines) — measured ~5.5s
for a single 40-line no-match on a 10k-line file, per hunk. The first/last
line anchor pre-filter skips non-candidate windows: same case now ~160ms
(34x faster).
Also gate replace_all: a similarity-based strategy (block_anchor,
context_aware) with multiple matches under replace_all would overwrite every
approximate block, not just exact ones. Now refused with a clear error
directing the caller to precise text.
All verified with sabotage-checked regression tests (fail against the old
50% logic). 158 file/patch/fuzzy tests pass; legit fuzzy edits (indent drift,
unique near-match) unaffected.
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