On BASE the #95514 stream-recovery rebound final_response inline, before
the tail-closing / persist-override / micro-compaction / _persist_session
calls inside the guarded persist try-block, so a raise in any of them left
the caller with the streamed text (cleanup_errors reported the failure).
HEAD's _close_transcript_tail returned the recovered value only on normal
completion; an exception in the same block dropped it and the user-visible
answer regressed to the pre-recovery '' (then rewritten by the explainer).
Split the helper into _drop_transcript_scaffolding / _recover_final_from_stream
/ _close_transcript_tail and rebind final_response in the guarded step as soon
as it is computed, restoring BASE ordering. Adds a regression test.
c65aebccf0