* fix(manifest): link a check-in atop an absent parent despite absent files

The crosslink deferral held back a check-in until every F-card blob was stored. When the primary parent's manifest is itself absent, no mlink row depends on those files (fossil's add_mlink returns before reading one, and the parent's crosslink derives the transition once it arrives), so the wait could never complete for files the repository will not receive. The libfossil repository holds one such check-in, a fossil-scm commit imported without its history; the sweep lost its event and plink rows that fossil rebuild writes (RS-4.2-2).

missingCheckinRefs now skips the F-cards when the primary parent is unavailable; the baseline is still required. Adds conformance case repostate.4.2.phantom-parent-absent-file and a unit test that also checks the child's mlink is derived once the parent arrives.

Tracked in #398.

* fix(manifest): record the remaining crosslink deferral gaps

Adds gap case repostate.4.2.root-absent-file, a receive-linker ordering test for the child-before-parent path, and notes the narrowed exemption. Tracked in #398 and #406. check-in: 15762adeb6 user: [email protected] tags: main, trunk