`session[.vN].jsonl` was assembled independently by the JSONL provider
(twice), the session-log export archive, and the recorded-session fixture
helpers. `dsh-session-format` now owns `sessionFormatLogFilename` and
`parseSessionFormatLogFilename`; the three consumers append only their
compression suffix, and the migration note names the owner.
`snapshotSessionFormatJson` re-implemented the lossless JSON walk that
`dsh-util-values` already publishes as `snapshotJsonValue` + `deepFreeze`,
and the frozen v0 relationship validator carried a third structural JSON
comparison next to `deepEqualJson`. Both now delegate; the format package
reports one `is not lossless JSON` diagnostic per labelled subject instead
of ten member-specific ones, and enumerable accessors whose values survive
a JSON round trip are accepted like `JSON.stringify` accepts them.
`ensureJsonlGenerationCurrent` returned a live Zstandard body iterator that
every production caller disposed unread before decoding the same bytes again;
the header read now decodes only the first frame and owns no decoder past its
return. The JSONL backend reuses the generation module's stable-revision read
instead of keeping a second copy, `encodeCurrent` encodes the validated
current artifact it is documented to receive instead of re-running the
migration chain on it, and the test-only `inspectVersion` catalog method and
the `migrateSessionSnapshotFixture` duplicate of
`prepareSessionSnapshotFixtureForComparison` are removed.
imccyu