fossil-style best-of-N delta base selection (pickBase, plan §5) plus a `zit pack` re-deltification pass with a monotonic-shrink guard (§6.1) and same-path candidates (§6.2). At-rest only: all four RFCs conformant, wire interop preserved, every repacked frame hash-verified against the log.

Measured (whole-file, index-inclusive): sqlite: 207.3 MB -> 174.4 MB (1.40x -> 1.18x vs fossil 147.7 MB) fossil-scm: 117.5 MB -> 108.1 MB (1.63x -> 1.50x vs fossil 72.2 MB)

The monotonic-shrink guard (keep the smaller of {existing frame, re-encoding}) is what turned re-deltifying a clone of fossil-quality wire deltas into a net win instead of a +33% regression. check-in: bab9303056 user: dmestas tags: trunk