update: SessionId / SessionStart / SessionOrigin 等を Segment 系名称へ

- Type/Function/Variantを Segment* 系へ統一
  - SessionId/SessionStart/SessionOrigin/SessionStartState/SessionState/SessionLogSink/SessionLockInfo
  - new_session_id / session_id / create_session* / list_sessions / lookup_session / update_session / find_by_session
  - protocol Event::SessionRotated → SegmentRotated、CompactDone.new_session_id → new_segment_id
- Module: session_log → segment_log / session → segment (file mv 含む)
  pod 側の session_log_sink → segment_log_sink も同様
- crate 名 (session-store)、CLI flag (--session)、ResumeWithSession (CLI tied) は据え置き
- session-tests/session_metrics_test 等の Store impl も追従

crates/session-store/src/lib.rs

@@ -1,4 +1,4 @@
-//! Session persistence via append-only JSONL logs.
+//! Segment persistence via append-only JSONL logs.
 //!
 //! # Architecture
 //!
@@ -11,15 +11,15 @@
 //! functions after state-mutating operations.
 //!
 //! Debug-mode [`TraceEntry`] records capture raw stream events in a separate
-//! `.trace.jsonl` file, independent of the session log.
+//! `.trace.jsonl` file, independent of the segment log.
 //!
 //! # Quick start
 //!
 //! ```ignore
-//! use session_store::{create_session, restore, save_delta, FsStore, SessionStartState};
+//! use session_store::{create_segment, restore, save_delta, FsStore, SegmentStartState};
 //!
 //! let store = FsStore::new("./sessions")?;
-//! let session_id = create_session(&store, SessionStartState {
+//! let segment_id = create_segment(&store, SegmentStartState {
 //!     system_prompt: None,
 //!     config: &config,
 //!     history: &[],
@@ -29,8 +29,8 @@
 pub mod event_trace;
 pub mod fs_store;
 pub mod logged_item;
-pub mod session;
-pub mod session_log;
+pub mod segment;
+pub mod segment_log;
 pub mod store;
 pub mod system_item;
 
@@ -39,23 +39,23 @@ pub use fs_store::FsStore;
 pub use llm_worker::UsageRecord;
 pub use llm_worker::llm_client::types::{ContentPart, Item, Role};
 pub use logged_item::{LoggedContentPart, LoggedItem, LoggedRole, from_logged, to_logged};
-pub use session::{
-    SessionStartState, append_entry, append_system_item, classify_history_item,
-    create_compacted_session, create_session, create_session_with_id, ensure_head_or_fork, fork,
+pub use segment::{
+    SegmentStartState, append_entry, append_system_item, classify_history_item,
+    create_compacted_segment, create_segment, create_segment_with_id, ensure_head_or_fork, fork,
     fork_at, restore, save_config_changed, save_delta, save_extension, save_pod_scope,
     save_run_completed, save_run_errored, save_turn_end, save_usage, save_user_input,
 };
-pub use session_log::{
-    LogEntry, POD_SCOPE_EXTENSION_DOMAIN, PodScopeSnapshot, RestoredState, SessionOrigin,
+pub use segment_log::{
+    LogEntry, POD_SCOPE_EXTENSION_DOMAIN, PodScopeSnapshot, RestoredState, SegmentOrigin,
     collect_state,
 };
 pub use system_item::{SystemItem, render_pod_event};
 pub use store::{Store, StoreError};
 
-/// Session identifier. UUID v7 (time-ordered, lexicographically sortable).
-pub type SessionId = uuid::Uuid;
+/// Segment identifier. UUID v7 (time-ordered, lexicographically sortable).
+pub type SegmentId = uuid::Uuid;
 
-/// Generate a new session ID.
-pub fn new_session_id() -> SessionId {
+/// Generate a new segment ID.
+pub fn new_segment_id() -> SegmentId {
     uuid::Uuid::now_v7()
 }