Document DB sync prototype scope

docs/adr/0010-crsqlite-db-sync.md

@@ -6,11 +6,25 @@ Accepted.
 
 ## Decision
 
-Database sync will use local SQLite databases with cr-sqlite. Changes from
-`crsql_changes` will be exchanged over Iroh and applied through cr-sqlite, with
-schema hash gating and resource authorization.
+Database sync uses local SQLite databases with cr-sqlite-compatible
+`crsql_changes` tables or views. Geth extracts typed change batches, exchanges
+them over the protected Iroh control path, checks schema metadata before
+application, and applies compatible batches through the local `crsql_changes`
+interface.
+
+The prototype does not add a second snapshot transport for DBs. CAS-backed DB
+snapshots or change-batch blobs are deferred until the change path proves too
+large for the control path or until initial peer catch-up needs snapshots.
 
 ## Consequences
 
-The MVP stores DB resource metadata and leaves synchronization as explicit future
-work.
+The prototype has deterministic fixture coverage for extraction, application,
+two-node Iroh exchange, authorization, schema mismatch detection, and live-sync
+watermarks.
+
+A real cr-sqlite extension integration test is intentionally not marked done in
+this environment because there is no `sqlite3` CLI or cr-sqlite extension
+artifact available to load. The blocker is environmental, not a protocol
+decision. When the extension is available, add a two-node test that creates a
+real cr-sqlite-enabled table, mutates one node, runs `geth db sync`, and proves
+the second node applies the change through cr-sqlite.