* fix(manifest): maintain the leaf table incrementally (RS-7.3-3)

The leaf table was recomputed from scratch at the end of every crosslink batch, so a check-in lost its leaf verdict whenever a later batch linked an untagged child to it. repo-state-01 Section 7.3, as corrected, and fossil keep that verdict: a check-in and its plink parents are rechecked only when a branch tag is written to it or propagation updates or deletes its branch row (src/tag.c:195, :100-102), and the checks run when the batch ends (src/leaf.c leaf_do_pending_checks).

The rule now lives in a new internal/leaf package: Check (leaf_check), Rebuild (the explicit full rebuild) and Pending (the deferred schedule). internal/tag schedules a recheck at exactly the branch-row writes; the crosslink sweep, receive linker and repair gate apply a batch's schedule at the gate, each phantom-fill cascade transaction and each commit or tag transaction apply their own before commit, and verify.Rebuild keeps the whole-table recompute. Reparenting schedules nothing, as in fossil, so the reparent case is split into a one-batch case and a per-artifact case.

Tracked in #426.

* fix(manifest): recheck leaves a cancel reaches; drop rechecks of a failed receive tx check-in: 628f932301 user: [email protected] tags: main, trunk