feat: add pod metadata store backend

crates/session-store/src/fs_store.rs

@@ -3,6 +3,7 @@
 //! Layout:
 //! - Segment log: `{root}/{session_id}/{segment_id}.jsonl`
 //! - Event trace: `{root}/{session_id}/{segment_id}.trace.jsonl`
+//! - Pod metadata: `{root}/pods/{pod_name}/metadata.json`
 //!
 //! The per-Session directory makes `list_segments(session_id)` an O(dir)
 //! scan and gives the fork tree a visible grouping in the filesystem.
@@ -16,6 +17,7 @@
 //! enumerable by the picker.
 
 use crate::event_trace::TraceEntry;
+use crate::pod_metadata::{PodMetadata, PodMetadataStore, validate_pod_name};
 use crate::segment_log::LogEntry;
 use crate::store::{Store, StoreError};
 use crate::{SegmentId, SessionId};
@@ -55,6 +57,19 @@ impl FsStore {
             .join(format!("{segment_id}.trace.jsonl"))
     }
 
+    fn pods_dir(&self) -> PathBuf {
+        self.root.join("pods")
+    }
+
+    fn pod_dir(&self, pod_name: &str) -> Result<PathBuf, StoreError> {
+        validate_pod_name(pod_name)?;
+        Ok(self.pods_dir().join(pod_name))
+    }
+
+    fn pod_metadata_path(&self, pod_name: &str) -> Result<PathBuf, StoreError> {
+        Ok(self.pod_dir(pod_name)?.join("metadata.json"))
+    }
+
     fn append_line(&self, path: &Path, line: &str) -> Result<(), StoreError> {
         if let Some(parent) = path.parent() {
             fs::create_dir_all(parent)?;
@@ -84,6 +99,41 @@ impl FsStore {
     }
 }
 
+impl PodMetadataStore for FsStore {
+    fn write(&self, metadata: &PodMetadata) -> Result<(), StoreError> {
+        let path = self.pod_metadata_path(&metadata.pod_name)?;
+        if let Some(parent) = path.parent() {
+            fs::create_dir_all(parent)?;
+        }
+        let content = serde_json::to_vec_pretty(metadata)?;
+        fs::write(path, content)?;
+        Ok(())
+    }
+
+    fn read_by_name(&self, pod_name: &str) -> Result<Option<PodMetadata>, StoreError> {
+        let path = self.pod_metadata_path(pod_name)?;
+        let content = match fs::read_to_string(path) {
+            Ok(content) => content,
+            Err(err) if err.kind() == std::io::ErrorKind::NotFound => return Ok(None),
+            Err(err) => return Err(StoreError::Io(err)),
+        };
+        Ok(Some(serde_json::from_str(&content)?))
+    }
+
+    fn delete_by_name(&self, pod_name: &str) -> Result<(), StoreError> {
+        let path = self.pod_metadata_path(pod_name)?;
+        match fs::remove_file(&path) {
+            Ok(()) => {}
+            Err(err) if err.kind() == std::io::ErrorKind::NotFound => return Ok(()),
+            Err(err) => return Err(StoreError::Io(err)),
+        }
+        if let Some(parent) = path.parent() {
+            let _ = fs::remove_dir(parent);
+        }
+        Ok(())
+    }
+}
+
 impl Store for FsStore {
     fn append(
         &self,