What probably matters to youSection of the release
Unclear What Claude Code does with the Project ID once it is set is not shown.
What
Claude Code now recognises an environment variable called CLAUDE_CODE_ATTRIBUTION_PROJECT. An environment variable is a named value set in your shell before Claude Code starts. It appears in the lists of variables Claude Code passes along and in the shell setup it writes out.
When a job is saved, its environment is filtered before it is written to the job's state.json file. If the value of CLAUDE_CODE_ATTRIBUTION_PROJECT does not look like a claude.ai Project ID, it is dropped with the reason "not a claude.ai Project ID".
Why
The variable links a session to a claude.ai Project, and a malformed value is thrown away rather than stored. If you set it, use the exact Project ID, or it will not be kept with saved jobs.
