Storage hub (ctx.storage) for non-session data: a named backend registry plus mounted data-form facilities. The hub performs no IO itself — backends own media, data forms own semantics. Design and trade-offs: domain KV storage Agent Note.

Shape

ctx.storage.backend — name → backend table. Multiple backends stay mounted side by side (json, sqlite); which backend serves a consumer is that consumer's configuration (the domain layer's route table), never a hub-global choice. register() returns the disposer; duplicate names and unknown lookups fail loud.
ctx.storage.mount(form, facility) / ctx.storage.form(form) — data-form mounting. StorageForms is merge-extensible; the domain layer merges domain and is reached as ctx.storage.domain.
A backend owns one medium (file-tree root, database file) and exposes optional data-shape facets — kv today; an append-log facet is reserved for the future session-backend migration. src/backend.ts is the normative contract text; tests/contract.ts exports the shared conformance suite every backend runs.

Packages in this group

Package	Role
`dsh-storage`	The hub service + backend vocabulary + shared conformance suite
`dsh-storage-json`	JSON backend: one unit per human-readable file, atomic whole-file rewrite
`dsh-storage-sqlite`	SQLite backend: one database hosting all routed units, document-per-row
`dsh-storage-domain`	Domain data form (`ctx.storage.domain`): typed schemas, write chain, change events

Model Experience

Backend and form registrations

What the model sees

Nothing. ctx.storage is a host-side registration table; the hub registers no tools, injects no prompts, and writes no session events.

Token effect

Zero direct tokens on every request.

KV Cache effect

Independent of live requests: the hub never touches a request prefix, so it cannot invalidate provider cache reuse.

Known Limitations and Deferred Work

kv is the only data shape — the append-log facet the future session-backend migration needs is reserved in the design note but not yet defined; backends currently have exactly one facet to implement.
Forms resolve lazily — reading ctx.storage.domain before the domain plugin mounts throws form-not-mounted; assemblies order plugins accordingly (misconfiguration fails loud rather than silently deferring).