Copilot CLI grep compaction corrupts filenames and line numbers, and merges distinct files #5318

Validate a suspected Copilot CLI grep-output compaction bug using this existing file:
/path/to/rg-compactor-repro.log-3

Do not modify the file. Use its full absolute path: output length affects whether compaction activates. The file contains 20 identical RG_REPRO lines.

Perform these checks using the built-in rg tool (functions.rg), NOT shell ripgrep or another search tool:

1. Control: pattern="RG_REPRO", paths="<file_path>, output_mode="content", head_limit=19, -n=true.
2. Reproduction: use exactly the same arguments, except head_limit=20.

Then independently obtain the correct baseline using Bash:
rg -H -n -m 20 RG_REPRO <file_path>

Compare the literal tool responses, without silently correcting filenames or line numbers.

On the affected CLI 1.0.105 build, the control retains the filename ending in .log-3 and actual line numbers 1 through 19. The reproduction instead groups results under rg-compactor-repro.log (losing -3), gives every result apparent line number 3, and moves the real line number into the text, such as "3: 1:RG_REPRO". The Bash baseline retains .log-3 and actual line numbers 1 through 20.

Report REPRODUCED only if that corruption is observed. Otherwise report NOT REPRODUCED or INCONCLUSIVE and explain the actual results. Merely grouping results is not a failure if filenames and line numbers remain correct. Preserve the tool responses as evidence; do not assume a different CLI version has the same defect.