update: session-grouping review follow-up

- PickerOutcome::Picked から未使用の session_id を除去（pod-cli が lookup_session_of で再解決）
- picker preview が singular AssistantItem も拾うように
- fs_store layout doc に migration（後方互換なし、旧 flat sessions は破棄）を明記
- TaskStore は Session-lifetime、ScopedFs/Tracker は Pod-process lifetime と用語整理
- Pod::session_id / from_manifest_spawned のコメント補強

crates/tools/src/lib.rs

@@ -4,12 +4,12 @@
 //! `llm-worker` `Tool` infrastructure. Filesystem access is mediated by
 //! two orthogonal concerns:
 //!
-//! - [`ScopedFs`] — pod-lifetime, expresses the write-block boundary for
-//!   the current scope. Derived from the manifest and shareable across
-//!   sessions.
-//! - [`Tracker`] — session-lifetime, enforces the "read before edit"
+//! - [`ScopedFs`] — Pod-process lifetime, expresses the write-block
+//!   boundary for the current scope. Derived from the manifest; not
+//!   persisted across Pod restart.
+//! - [`Tracker`] — Pod-process lifetime, enforces the "read before edit"
 //!   policy via content hashes and tracks the recency of touched files.
-//!   Recreated fresh per session.
+//!   Recreated fresh on each Pod start (including resume).
 //!
 //! The Pod layer owns both instances and passes them to
 //! [`builtin_tools`] when registering tools on a `Worker`.
@@ -42,11 +42,11 @@ pub use tracker::Tracker;
 pub use write::write_tool;
 
 /// Register all builtin tools, wiring them to a shared `ScopedFs`
-/// (pod-lifetime) and `Tracker` (session-lifetime).
+/// (Pod-process lifetime) and `Tracker` (Pod-process lifetime).
 ///
 /// All returned factories share the same tracker instance so that
 /// `Read` / `Write` / `Edit` see a consistent history across tool
-/// invocations within a single session.
+/// invocations within a single Pod run.
 ///
 /// `bash_output_dir` is where the Bash tool spills long outputs. The
 /// caller is responsible for adding that path to the readable scope

crates/tools/src/task.rs

@@ -1,8 +1,9 @@
-//! Pod-lifetime TaskStore and builtin task tools.
+//! Session-lifetime TaskStore and builtin task tools.
 //!
-//! The store is Pod/session-lifetime state shared by the four Task* tools. It
-//! is reconstructed on resume by replaying TaskCreate / TaskUpdate tool-call
-//! arguments from persisted history.
+//! The store survives compaction and Pod restart — it is reconstructed
+//! on resume by replaying TaskCreate / TaskUpdate tool-call arguments
+//! from persisted history, so its effective lifetime is the
+//! [`session_store::SessionId`] (the conversation), not the Pod process.
 
 use std::sync::{Arc, Mutex};
 

crates/tools/src/tracker.rs

@@ -18,11 +18,13 @@
 //!
 //! # Lifetime
 //!
-//! A `Tracker` is **session-scoped**: the Pod layer creates a fresh
-//! instance at the start of each agent session and discards it when the
-//! session ends. The `ScopedFs` write boundary, by contrast, is
-//! pod-lifetime (derived from the manifest). The two are orthogonal and
-//! the Pod wires them together when registering builtin tools.
+//! A `Tracker` is **Pod-process scoped**: the Pod layer creates a fresh
+//! instance at the start of each Pod run (including resume) and discards
+//! it when the process exits — it is not persisted, so a resumed
+//! conversation starts with an empty read/edit history. The `ScopedFs`
+//! write boundary is likewise Pod-process scoped (derived from the
+//! manifest). The two are orthogonal and the Pod wires them together
+//! when registering builtin tools.
 //!
 //! ```no_run
 //! # use std::path::PathBuf;