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+## Description
+
+Fixes #5633
+
+This PR resolves the critical HTML entity escaping/unescaping issue that was causing diff search/replace operations to fail or produce unintended content modifications.
+
+## Problem
+
+The apply_diff tools were unescaping HTML entities (e.g., & → &) in search content for non-Claude models, but the actual file content still contained the escaped entities. This caused:
+
+1. **Search failures**: When LLMs provided search content with HTML entities, the unescaping made it not match the actual file content
+2. **Unintended modifications**: Partial matches could lead to incorrect replacements in files
+
+## Solution
+
+- **Removed HTML entity unescaping logic** from applyDiffTool.ts and multiApplyDiffTool.ts for non-Claude models
+- **Preserved HTML entities** in search content to ensure exact matching with file content
+- **Removed unused imports** of unescapeHtmlEntities from both files
+- **Added comprehensive test coverage** to prevent regression
+
+## Changes Made
+
+- src/core/tools/applyDiffTool.ts:
+
+    - Removed HTML entity unescaping for non-Claude models (lines 26-28)
+    - Removed unused import of unescapeHtmlEntities (line 13)
+
+- src/core/tools/multiApplyDiffTool.ts:
+
+    - Replaced HTML entity unescaping logic with simple assignment (lines 414-418)
+    - Removed unused import of unescapeHtmlEntities (line 13)
+
+- src/core/tools/**tests**/applyDiffHtmlEntity.spec.ts:
+    - Added comprehensive test suite with 5 test cases
+    - Tests verify HTML entities are preserved in search/replace operations
+    - Tests cover various entity types: &, <, >, ', "
+    - Tests verify both Claude and non-Claude model behavior
+
+## Testing
+
+- [x] All existing tests pass
+- [x] Added comprehensive tests for HTML entity handling scenarios:
+    - [x] HTML entities preserved in search content for non-Claude models
+    - [x] HTML entities still unescaped for Claude models (backward compatibility)
+    - [x] Various entity types tested (&, <, >, ', ")
+    - [x] Both single and multiple entity scenarios covered
+- [x] Manual testing completed:
+    - [x] Verified search operations work with HTML entities in content
+    - [x] Confirmed no unintended content modifications occur
+- [x] All linting and type checking passes
+
+## Verification of Acceptance Criteria
+
+- [x] **Search failures resolved**: HTML entities in search content now match file content exactly
+- [x] **Unintended modifications prevented**: No more partial matches causing incorrect replacements
+- [x] **Backward compatibility maintained**: Claude model behavior unchanged
+- [x] **No regressions**: All existing functionality preserved
+- [x] **Comprehensive test coverage**: Edge cases and scenarios covered
+
+## Related Issues
+
+This issue was previously attempted to be fixed in:
+
+- PR #5608 (closed without merging)
+- Issue #4077 (related HTML entity handling)
+
+This PR provides a complete and tested solution that addresses the root cause.
+
+## Checklist
+
+- [x] Code follows project style guidelines
+- [x] Self-review completed
+- [x] Comments added for complex logic
+- [x] Documentation updated (test documentation)
+- [x] No breaking changes
+- [x] All tests passing
+- [x] Linting and type checking passes