When a transcript's session ID fails the adoption check during resume, Claude Code now logs an explicit diagnostic message identifying the rejected session ID and falls back to treating the resume as a fork under a fresh session ID, instead of failing silently.
Session adoption gate logs a rejection reason when a custom ID is refused
Resume now logs why a custom session ID was rejected before falling back to a fresh forked session.
Under the hoodTier: how much it should matter to you
1Useful: my rating, 1 to 5
1Signal: worth watching, 1 to 5
SessionsArea: what it touches
ImprovementsKind: in v2.1.261,
ImprovementsSection of the release