Return byte prefixes with tagged read outcomes and exact causes. Share those facts across partial journals and captures, preserve typed primary failures and successful siblings, and keep zero-byte failures unavailable. Retain failed descriptor and root owners through retry.
Fixes#5058
Derive the read limit from the accepted safe decimal PID plus a tolerated CRLF and overflow sentinel. Retain short-read handling, cached valid facts and existing descriptor ownership and handshake semantics.
Fixes#5057