feat(cms): implement RewindBlobRepository for managing binary blobs

crates/zesdex-cms/src/domain/repository.rs

@@ -63,6 +63,19 @@ pub trait MemoryRepository {
     fn delete(&self, memory_dir: &Path, name: &str) -> Result<()>;
 }
 
+/// Repository for rewind-snapshot binary blobs, keyed by an arbitrary
+/// caller-supplied key (e.g. a tool-call id) within a session.
+pub trait RewindBlobRepository {
+    /// Store (or overwrite) a blob under `blob_key` for this session.
+    fn store_blob(&self, session_dir: &Path, blob_key: &str, data: &[u8], mime_type: Option<&str>) -> anyhow::Result<()>;
+
+    /// Retrieve a blob's bytes by key, or `None` if not found.
+    fn retrieve_blob(&self, session_dir: &Path, blob_key: &str) -> anyhow::Result<Option<Vec<u8>>>;
+
+    /// List all blob keys for this session, oldest first.
+    fn list_blob_keys(&self, session_dir: &Path) -> anyhow::Result<Vec<String>>;
+}
+
 /// Persistence contract for `EditLog`.
 pub trait EditLogRepository {
     /// Open (or start tracking) the edit log for a session directory.