Summary

This PR fixes Issue #8020 where apply_diff fails to strip line numbers from the last line in SEARCH and REPLACE blocks, particularly in Windows environments with CRLF line endings.

Root Cause

The bug occurs due to an interaction between the regex parser and line number stripping:

1. The regex in multi-search-replace.ts uses (?:\n)? which optionally consumes trailing newlines from captured content
2. In Windows environments with CRLF endings (\r\n), this can leave content ending with just \r (consuming the \n)
3. When stripLineNumbers() processes this malformed content, it splits by /\r?\n/ but the line structure is broken
4. The last line's line number prefix (e.g., 1488 |) cannot be matched and stripped properly
5. Result: Line numbers appear in the final output

Example of the bug:

Input to stripLineNumbers: "1488 | code here\r"  (missing the \n from \r\n)
After split(/\r?\n/): ["1488 | code here\r"]  (single element, no proper line split)
After strip attempt: "1488 | code here\r"  (line number remains!)

Solution

Modified stripLineNumbers() in src/integrations/misc/extract-text.ts to preserve trailing newlines when present in the original content:

// Preserve trailing newline if original content had one
if (content.endsWith("\n") || content.endsWith("\r\n")) {
    if (!result.endsWith("\n") && !result.endsWith("\r\n")) {
        result += lineEnding
    }
}

This ensures that:

• Line structure is maintained through the stripping process
• Both LF and CRLF line endings are correctly handled
• The line number regex patterns can properly match and remove prefixes from all lines including the last one

Why Not Fix the Regex Directly?

@daniel-lxs suggested modifying the regex pattern to use lookahead assertions to avoid consuming trailing newlines. However, this approach broke existing deletion tests where the replace block is empty. The current solution is more robust and doesn't require making the already complex regex even more fragile.

Changes

• Modified stripLineNumbers() to preserve trailing newlines when present in the original content
• Added comprehensive test cases for trailing newline preservation scenarios in Windows (CRLF) and Unix (LF) environments
• All existing tests pass without regression

Testing

• ✅ All existing tests pass
• ✅ New tests added for trailing newline preservation with both LF and CRLF endings
• ✅ Test case 4 specifically validates the exact scenario from issue [BUG] apply_diff fail to strip the line number at last line in SEARCH and REPLACE #8020 (Java code with line 1488)
• ✅ Tested multiple search/replace blocks
• ✅ Tested content with and without trailing newlines

Fixes #8020