The earlier removal fix invalidated parentAvailable immediately and queued a trailing subagent.list request, but it still applied the already in-flight success verbatim. That stale success reopened the composer and became the trailing request baseline. If the trailing request failed, its error snapshot preserved parentAvailable:true indefinitely.
Record a false-only parent availability override on the exact in-flight catalog request when the owner removal frame arrives. Successful and failed responses now replay that request-local invalidation before publishing a snapshot, and addressed child Sessions receive the same effective value. The trailing request therefore starts from a false baseline and a later transport or business failure cannot resurrect the removed parent.
Strengthen the regression to assert the catalog and selected child remain read-only immediately after a stale parentAvailable:true success, then fail the trailing pull and assert the error snapshot remains unavailable. The complete SessionManager test file passes all 39 tests, and the client runtime TypeScript project builds cleanly.
Tianyi Cui
069f2644ff