edit tool: fuzzy replacer chain silently overwrites previous edits in same file #32559

Description

The fuzzy replacer chain in edit.ts (BlockAnchorReplacer, WhitespaceNormalizedReplacer, IndentationFlexibleReplacer, ContextAwareReplacer) allows stale edits to silently overwrite previous changes to the same file.

Concrete example

1. File contains: return calculate()
2. Edit 1 succeeds: return calculate() becomes return calculate() + 1
3. Edit 2 proposes oldString return calculate() which is stale
4. BlockAnchorReplacer matches the already-modified content at 81.8% similarity (threshold 65%) and applies Edit 2 silently reverting Edit 1

Root causes

• Fuzzy thresholds too permissive: 0.65 Levenshtein similarity, 50% line-match
• No staleness check before fuzzy matching
• Replacer chain degrades to loose matching instead of failing

Related issues

Related to but distinct from:

• [BUG] V1 edit.ts isDisproportionateMatch bypasses all safety checks for single-line oldString #31785 which covers isDisproportionateMatch bypass for single-line oldString (a secondary guard) while this issue targets the replacer thresholds that cause overwrites on multi-line edits
• [BUG] File modification tools (edit/write/apply_patch/shell) lack data-loss prevention guards #31248 a broader umbrella. This issue drills into one specific mechanism with a concrete reproduction and measured similarity (81.8%)

Additional design notes

• Lock map never evicts entries
• No built-in undo
• Double diff not cached