History of checkpoint 1 change

In crates/hub/src/flow.rs, lines 1506–1522 on v0.9.21. Every change that wrote or deleted one of these lines, or deleted a line from between them. Exact, because each line keeps its identity across edits; edits elsewhere in the file are not here. Also: oxy log -L 1506,1522:crates/hub/src/flow.rs.