update: entry hash chain と session_head mutex を撤廃

- HashedEntry / EntryHash / compute_hash / build_chain 撤去、JSONL は 1 行 1 LogEntry
- SessionOrigin.at_hash → at_turn_index (TurnEnd 由来) に置換
- Pod 側 SessionHead mutex を ArcSwap<SessionId> + AtomicUsize の SessionState に置換
- ensure_head_or_fork は store の entry count と writer の append tally で判定
- session-store から sha2 / hex 依存、pod から parking_lot 依存を削除

crates/pod/tests/session_metrics_test.rs

@@ -26,9 +26,7 @@ use llm_worker::llm_client::event::{Event as LlmEvent, ResponseStatus, StatusEve
 use llm_worker::llm_client::{ClientError, LlmClient, Request};
 use llm_worker::tool::{Tool, ToolDefinition, ToolError, ToolMeta, ToolOutput};
 use session_metrics::{DOMAIN, Metric, metrics_from_extensions};
-use session_store::{
-    EntryHash, FsStore, HashedEntry, LogEntry, SessionId, Store, StoreError, TraceEntry,
-};
+use session_store::{FsStore, LogEntry, SessionId, Store, StoreError, TraceEntry};
 
 use pod::{Pod, PodManifest};
 
@@ -329,32 +327,28 @@ struct MetricFailingStore {
 }
 
 impl Store for MetricFailingStore {
-    fn append(&self, id: SessionId, entry: &HashedEntry) -> Result<(), StoreError> {
-        if let LogEntry::Extension { domain, .. } = &entry.entry {
+    fn append(&self, id: SessionId, entry: &LogEntry) -> Result<(), StoreError> {
+        if let LogEntry::Extension { domain, .. } = entry {
             if domain == DOMAIN {
                 return Err(StoreError::Io(std::io::Error::other("synthetic failure")));
             }
         }
         self.inner.append(id, entry)
     }
-    fn read_all(&self, id: SessionId) -> Result<Vec<HashedEntry>, StoreError> {
+    fn read_all(&self, id: SessionId) -> Result<Vec<LogEntry>, StoreError> {
         self.inner.read_all(id)
     }
     fn list_sessions(&self) -> Result<Vec<SessionId>, StoreError> {
         self.inner.list_sessions()
     }
-    fn create_session(
-        &self,
-        id: SessionId,
-        entries: &[HashedEntry],
-    ) -> Result<(), StoreError> {
+    fn create_session(&self, id: SessionId, entries: &[LogEntry]) -> Result<(), StoreError> {
         self.inner.create_session(id, entries)
     }
     fn exists(&self, id: SessionId) -> Result<bool, StoreError> {
         self.inner.exists(id)
     }
-    fn read_head_hash(&self, id: SessionId) -> Result<Option<EntryHash>, StoreError> {
-        self.inner.read_head_hash(id)
+    fn read_entry_count(&self, id: SessionId) -> Result<usize, StoreError> {
+        self.inner.read_entry_count(id)
     }
     fn append_trace(&self, id: SessionId, entry: &TraceEntry) -> Result<(), StoreError> {
         self.inner.append_trace(id, entry)

crates/pod/tests/system_prompt_template_test.rs

@@ -184,7 +184,7 @@ async fn session_start_state_captures_rendered_prompt() {
 
     let entries = pod.store().read_all(pod.session_id()).unwrap();
     let first = entries.first().expect("at least one entry");
-    match &first.entry {
+    match first {
         LogEntry::SessionStart { system_prompt, .. } => {
             let sp = system_prompt.as_deref().expect("system prompt set");
             assert!(sp.starts_with("hello cwd="));