Status: rejected — the separate persistence interface package is the intended modular capability seam for durable backends. Folding it into `dsh-session` would reduce package count at the cost of a cleaner backend boundary.
`dsh-session-persistence` is an interface package whose main concepts are already owned by `dsh-session`: `SessionHeader`, `SessionEvent`, `SessionId`, `session/event`, and `session/flush`. The package adds the abstract `SessionPersistence` service, the shared write coordinator, and contract helpers. Backend packages depend on it, and `agent-loop` has to optionally find a sibling service for resume.
The capability-seam split made sense when persistence was a new swappable backend design. After the mutable summary was removed, the interface package mostly wraps the session log's own storage concern. Keeping it separate may be more ceremony than clarity.
## Proposal
Move the abstract `SessionPersistence` service, the coordinator, and persistence contract helpers into `dsh-session`. Keep JSONL and SQLite as separate backend packages that register the session-owned service. This preserves backend swappability while deleting one support package and one cross-package seam.
The implementing PR should update the [capability seams](../../implemented/architecture/2026-06-13-capability-seams.md) guidance with the exception: persistence is not like bash or LLM because its vocabulary and lifecycle events are already the session package's core domain.
`dsh-session` becomes heavier: it owns both the in-memory log and the persistence interface. That is the trade. If third-party persistence backends were already a public ecosystem, the separate interface package would be a cleaner SDK boundary; pre-release, the extra package looks like abstraction before there is an external consumer.
