## Why
A failed rollout append can leave a rejected line before a valid same-ordinal
retry. Advancing the byte checkpoint past that line without also advancing the
ordinal checkpoint can prevent subsequent history from being projected.
## What changed
- Defer rejected and unknown rollout lines until a later valid ordinal shows
whether they were replaced by a retry or consumed an ordinal.
- Advance skipped ordinal ranges together with the durable byte checkpoint,
while rejecting gaps that cannot be explained by rejected lines.
- Prefer item event timestamps and parse the rollout timestamp only when an
item needs it as a fallback.
## Testing
Added coverage for same-ordinal retries, inferred ordinal gaps, unknown and
malformed records, invalid fallback timestamps, and unexplained gaps.
GitOrigin-RevId: 374beda316c605d562bd9526abed19916598d69f
6256a7ccc7