feat(storage): sqlite backend — one database hosting all routed units

node:sqlite DatabaseSync with the session-persistence-sqlite open
sequence (0o700 dir, exclusive 0o600 create, foreign_keys, configurable
journal mode, user_version stamp-or-reject). STRICT tables throughout:
units/unit_globals meta tables plus one document-per-row table per
declared unit table, keeping per-key durable updates precise.

packages/storage/storage-sqlite/README.md

@@ -0,0 +1,39 @@
+# @deepseek-ai/dsh-storage-sqlite
+
+SQLite backend for the [storage hub](../storage/README.md): registers as backend `sqlite`, serving the `kv` facet over one `node:sqlite` database file (or `:memory:`). Design and trade-offs: [domain KV storage Agent Note](../../../.agents/notes/proposed/architecture/2026-07-24-domain-kv-storage-and-workspace.zh.md).
+
+## Storage model
+
+Document-per-row: each unit table becomes a physical `"u_<unit>_<table>" (key TEXT PRIMARY KEY, value TEXT)` STRICT table whose `value` is the record's JSON text, so one key updates one row (the reason to route a high-churn domain here instead of the JSON backend). Unit identity lives in two metadata tables — `units` stamps each unit's format version at first open and rejects a differing descriptor with `version-mismatch`; `unit_globals` holds each unit's global singleton row. The physical layout version lives in `PRAGMA user_version`; any other stamped value rejects (unreleased format, no migrations). Unit and table names are validated against the hub's `UNIT_NAME_RE` before they reach DDL, so no external input is ever interpolated into SQL identifiers.
+
+Every write primitive is a single prepared statement — SQLite's per-statement atomicity satisfies the KV contract without explicit transactions, and write ordering stays the caller's responsibility (the domain layer's write chain). Missing directories and database files are created owner-only (`0o700`/`0o600`), matching the session-persistence SQLite backend, whose open sequence this package copies verbatim until the planned media-layer extraction.
+
+## Configuration (schemastery)
+
+```ts
+interface Config {
+  path: string   // SQLite database file path, or ':memory:' for an in-process DB
+  journalMode?: 'wal' | 'delete' | 'truncate' | 'persist'   // journal_mode pragma; default 'wal'
+}
+```
+
+## Model Experience
+
+### What the model sees
+
+Nothing. This backend contributes no prompt, tool, or schema; it persists non-session domain data for host-side consumers.
+
+### Token effect
+
+Zero live-request tokens.
+
+### KV Cache effect
+
+None — no live request prefixes are touched.
+
+## Known Limitations and Deferred Work
+
+- **`DatabaseSync` is synchronous** — each write blocks the event loop for its (single-statement) duration; acceptable at domain-data scale.
+- **No busy-wait or retry policy** — another connection holding a write transaction rejects the operation immediately; multi-process write protection is on the design's future-work list.
+- **Only the current `STORAGE_SQLITE_SCHEMA_VERSION` opens** — any other stamped version is rejected rather than migrated (pre-release stance).
+- **`openDatabase` duplicates the session-persistence SQLite open sequence** — extraction into a shared media layer is deferred to the planned session-backend migration (see the Agent Note's reuse audit).