Add deterministic CAS tree objects

AGENTS.md

@@ -118,6 +118,9 @@ Roadmap items should be actionable and checkable:
   `keychain status`. SSH signature capture/verification is still roadmap work.
 - Local CAS supports pin/unpin metadata, surfaced through `cas list`, and
   `cas cleanup` evicts unpinned blobs while retaining pinned blobs.
+- The CAS crate can build deterministic tree objects for local file trees and
+  store those manifests as CAS blobs. File roots, scan workflows, and sync
+  conflict handling are still roadmap work.
 - 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. The DB crate and daemon can extract typed read-only `crsql_changes`