`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.
`session-log-export` names its archive entry after `SESSION_FORMAT_VERSION`,
a runtime value of the shared `dsh-session` instance, so `dsh-session` becomes
a peer dependency and the export is classified as peer-required in the package
dependency policy. The three Session format packages take the `0.1.2-rc.1`
root version that master now requires.
The persistence seam is now create/open/stat/list returning per-session
SessionHandles (read/append/flush/close); every log read and write flows
through the owning handle. The seam package exports only the service and
handle contracts, consumer-visible errors, and pure durable-data
validation helpers; each backend owns its complete storage runtime, and
the shared contract suites pin equivalent observable behavior. The
backend routes published sessions' live events by id into the active
write handle; agent-loop only acquires, seeds, and closes the handle.
Resume appends interruptedTurnClosers through its write handle;
session-query owns the revision-keyed cold cache. Legacy-only surfaces
are removed in the same swap: locate/readRaw/supportsRawArtifacts, the
legacy event-shape read migration, zstd torn-frame salvage,
DSH_SESSION_JSONL, and hook transcript_path population; a torn final
zstd frame is discarded whole; the session-list cold blank probe returns
on stat metadata (eventCount derived from the last physical row,
sizeBytes). The WebUI ZIP export serializes the logical log from a read
handle, so both backends export identically.
Refs #3245
imccyu