What probably matters to youSection of the release
What
Sometimes the same message you typed can reach Claude Code more than once. Claude Code skips the later copy. When the CLAUDE_CODE_DIAGNOSTICS_FILE environment variable is set, Claude Code now writes a line to that diagnostics file each time it skips one of these copies. An environment variable is a named value you set in your shell before starting Claude Code.
Each line records:
whether Claude had already started replying after the original message
what kind of copy was skipped
If Claude Code cannot work out whether Claude had already started replying, it writes no line for that copy.
Why
The log helps track down messages that seem to be duplicated or lost, especially in remote sessions, where Claude Code runs somewhere other than your own computer.
