Enhance tool documentation and add new features

- Added module-level documentation for memory tools (`remember`, `recall`, `forget`) to clarify their purpose.
- Improved documentation in `recall.rs` and `remember.rs` to describe the functionality and flow of memory entry operations.
- Updated `mod.rs` to include descriptions for the tool trait and execution context.
- Enhanced `plan.rs` with detailed comments on plan-mode signaling tools.
- Documented text search tools in `search.rs` to explain their functionality.
- Improved sequential-thinking tool documentation in `seqthink.rs`.
- Added safety filter documentation in `shell_filter` for credential and git operations.
- Enhanced utility tools documentation, including `cd`, `dir_cache_update`, and `todowrite`.
- Improved rendering documentation in view modules (`chat`, `markdown`, `status`, `workflow`) to clarify rendering flows and purposes.

src/model/session.rs

@@ -1,7 +1,12 @@
+//! Session metadata: id, title, workspace roots, and message/token counts,
+//! persisted as `session.json` per session directory.
+
 use std::path::{Path, PathBuf};
 use serde::{Deserialize, Serialize};
 use chrono::Utc;
 
+/// Metadata for one conversation session (distinct from the message
+/// history itself, which lives in `Conversation`/the msglog).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Session {
     pub id: String,
@@ -17,6 +22,8 @@ pub struct Session {
 }
 
 impl Session {
+    /// Create a new session with the given id/title, defaulting the
+    /// model, workspace root (current dir), and counters.
     pub fn new(id: String, title: String) -> Self {
         let now = Utc::now().timestamp_millis();
         Session {
@@ -33,14 +40,25 @@ impl Session {
         }
     }
 
+    /// Compute this session's directory under `<base_dir>/sessions/<id>`.
     pub fn session_dir(&self, base_dir: &Path) -> PathBuf {
         base_dir.join("sessions").join(&self.id)
     }
 
+    /// Compute this session's `conversation.json` path.
     pub fn conversation_path(&self, base_dir: &Path) -> PathBuf {
         self.session_dir(base_dir).join("conversation.json")
     }
 
+    /// Persist this session's metadata to `session.json`, atomically.
+    ///
+    /// Flow: ensure the session directory exists → serialize to pretty
+    /// JSON → write to `session.json.tmp` → rename over `session.json`.
+    ///
+    /// Why: write-then-rename avoids a torn/partial `session.json` if
+    /// interrupted mid-write.
+    ///
+    /// Return: `Ok(())` on success, or an `io::Error` from any step.
     pub fn save(&self, base_dir: &Path) -> std::io::Result<()> {
         let dir = self.session_dir(base_dir);
         std::fs::create_dir_all(&dir)?;
@@ -52,6 +70,10 @@ impl Session {
         Ok(())
     }
 
+    /// Load a session's metadata by id from `<base_dir>/sessions/<id>/session.json`.
+    ///
+    /// Return: the parsed `Session`, or an `io::Error` if the file is
+    /// missing or malformed.
     pub fn load(id: &str, base_dir: &Path) -> std::io::Result<Self> {
         let path = base_dir.join("sessions").join(id).join("session.json");
         let data = std::fs::read_to_string(path)?;
@@ -59,6 +81,14 @@ impl Session {
         Ok(session)
     }
 
+    /// List all loadable sessions under `<base_dir>/sessions/`.
+    ///
+    /// Flow: read the sessions directory → keep subdirectories → attempt
+    /// `Session::load` for each by its directory name, discarding any
+    /// that fail to load.
+    ///
+    /// Return: a `Vec<Session>`, empty if the directory can't be read or
+    /// contains no valid sessions.
     pub fn list(base_dir: &Path) -> Vec<Self> {
         let sessions_dir = base_dir.join("sessions");
         let entries = match std::fs::read_dir(&sessions_dir) {