Addresses @teknium1's second review round on #63144:
1. _is_compacted_message now checks both active=0 AND compacted=1.
Previously checked active=0 alone, which also matched rewind/undo rows
(active=0, compacted=0) that must stay hidden.
2. Added _is_compression_ended() — checks only the session's own
end_reason, not the lineage-wide has_compression_hop flag. This prevents
delegation children living under a compression continuation from leaking
through the lineage filter.
3. _discover lineage skip now uses is_ended_session (session-level check)
instead of has_compression (lineage-level flag).
New tests:
- TestRewindExclusion: rewind rows stay hidden alongside compacted rows
- TestCompressionEndedHelper: session-level end_reason checks
- TestLegacyContinuationPlusDelegation: delegate child excluded while
compression ancestors surface
78 passed (71 + 7 new).
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