Check-in [4deb9d870f]

- A clone to a client the 7.2 gate refuses could name a withheld tree as a delta source: walkCloneChain never asked the gate, and a refused artifact was still recorded as sent. A flat check-in stored as a delta of a tree manifest -- the normal flat-to-tree transition -- then reached a 2.28 client as a cfile it could never apply. A withheld source is now unforwardable, so its dependent goes out whole, and a refused artifact is not recorded as sent. Gimme answers and pushes already send full content, and igot only announces, so the clone was the one path. - The gate armed only once a crosslink set the seen-submanifest indicator, so a tree a sync had stored but not yet linked went out ungated. Every receive path now sets it as the artifact is stored -- checkDelta hands back the content it rebuilt, so a verified delta costs no second expansion -- and a repository an earlier version swept, which may hold trees that version filed as unparseable, arms the gate until the next sweep re-examines them. - The three sub-manifest settings are written inside one savepoint, so a database error partway leaves none of them applied. - The 22900 threshold is zit's and is also what an unreleased fossil 2.29 announces without reading trees. The constant says so, and the conformance suite records SM-7.2-1 as a deviation with a case that shows such a peer being sent a tree. check-in: 4deb9d870f user: [email protected] tags: feat/submanifest-reader, main, trunk