feat: add pod metadata store backend

crates/session-store/tests/fs_store_test.rs

@@ -1,7 +1,8 @@
 use llm_worker::WorkerResult;
 use llm_worker::llm_client::types::{Item, RequestConfig};
 use session_store::{
-    FsStore, LogEntry, Store, TraceEntry, collect_state, new_segment_id, new_session_id,
+    FsStore, LogEntry, PodActiveSegmentRef, PodMetadata, PodMetadataStore, Store, TraceEntry,
+    collect_state, new_segment_id, new_session_id,
 };
 
 fn nil_session_start(ts: u64, session_id: uuid::Uuid) -> LogEntry {
@@ -224,3 +225,39 @@ fn lookup_session_of_finds_owning_session() {
 
     assert_eq!(store.lookup_session_of(segid).unwrap(), Some(sid));
 }
+
+#[test]
+fn pod_metadata_minimal_crud() {
+    let dir = tempfile::tempdir().unwrap();
+    let store = FsStore::new(dir.path()).unwrap();
+    let pod_name = "worker-a";
+    let sid = new_session_id();
+    let segid = new_segment_id();
+
+    assert_eq!(store.read_by_name(pod_name).unwrap(), None);
+
+    let pending = PodMetadata::new(pod_name, Some(PodActiveSegmentRef::pending_segment(sid)));
+    store.write(&pending).unwrap();
+    assert_eq!(store.read_by_name(pod_name).unwrap(), Some(pending.clone()));
+    assert!(
+        dir.path()
+            .join("pods")
+            .join(pod_name)
+            .join("metadata.json")
+            .exists(),
+        "Pod metadata must live under <data_dir>/pods/<pod_name>/"
+    );
+
+    let resolved = PodMetadata::new(
+        pod_name,
+        Some(PodActiveSegmentRef::active_segment(sid, segid)),
+    );
+    store.write(&resolved).unwrap();
+    assert_eq!(store.read_by_name(pod_name).unwrap(), Some(resolved));
+
+    store.delete_by_name(pod_name).unwrap();
+    assert_eq!(store.read_by_name(pod_name).unwrap(), None);
+
+    // Delete is idempotent for missing metadata.
+    store.delete_by_name(pod_name).unwrap();
+}