When a user ID is not in the in-memory cache, message rendering
degrades to raw IDs and paramFormatUser fails the tool call
entirely. This is common on Enterprise Grid workspaces where the
user cache (50K+ users) can be hours stale.
On cache miss, fetch the single user via users.info and patch the
snapshot atomically. This costs one API call instead of rebuilding
the entire user cache. Disk persistence is skipped; the next full
refresh cycle handles it.
Fixes#268
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Greg Katz