Add typed crsql changes extraction

AGENTS.md

@@ -120,8 +120,9 @@ Roadmap items should be actionable and checkable:
   `cas cleanup` evicts unpinned blobs while retaining pinned blobs.
 - DB resources can be registered locally and report local-only status plus a
   read-only SQLite schema summary/hash and `crsql_changes` metadata when
-  present. cr-sqlite loading, typed change extraction, and sync are still
-  roadmap work.
+  present. The DB crate can extract typed read-only `crsql_changes` batches for
+  future sync messages. cr-sqlite loading, applying remote changes, and sync are
+  still roadmap work.
 - KV stores support local SQLite-backed create/set/get. Iroh Documents
   replication and command-level prefix-capability enforcement are still roadmap
   work. The auth evaluator already understands `kv.write_prefix:<prefix>`