Fixes #4852: Add performance safeguards to prevent apply_diff hanging on large XML files

[roomote]

Summary

This PR fixes issue #4852 where would hang indefinitely when processing large or complex XML files.

Root Cause

The issue was in the function used by both diff strategies. The middle-out search algorithm could potentially run millions of iterations on large files without any performance constraints, leading to indefinite hanging.

Solution

Added comprehensive performance safeguards to the function:

1. Maximum iteration limit: Capped at 10,000 iterations to prevent infinite loops
2. Timeout mechanism: 5-second timeout for very large files
3. Early exit optimization: Immediately exit when perfect matches (100% similarity) are found
4. Performance logging: Added warnings for debugging large file issues

Changes Made

• Modified function in
• Modified function in
• Added comprehensive test suite in

Testing

• Added performance tests that verify the fix works on large XML files (1000+ lines)
• Tests confirm operations complete within reasonable time limits (< 10 seconds)
• All existing tests continue to pass
• Verified both successful matches and failed searches are handled correctly

Impact

• Resolves hanging issues on large XML files
• Maintains existing functionality for normal-sized files
• Improves overall performance through early exit optimization
• Provides better debugging information for performance issues

Fixes #4852

[ellipsis-dev]

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[daniel-lxs]

Closing temporarily in favor of #4854.

This PR addresses the findBestMatch performance but doesn't fix the actual root cause. The issue analysis in #4851 identified that the hang occurs during XML parsing and HTML entity processing in the apply_diff tool itself, not in the fuzzy search.

PR #4854 directly addresses these root causes:

• XML parsing timeouts that were causing indefinite hangs
• HTML entity double-processing corrupting XML content
• Regex operations hanging on complex XML patterns

While the 10k iteration limit would help with search performance, it doesn't solve the actual hanging issue users are experiencing with XML files.