docs(comments): rewrite comments across all crates to the guidelines

Sweep every first-party crate source (1956 .rs files) to the project comment
guidelines: delete redundant restatements, decorative banners, change
narration, and end-of-line comments; keep and tighten the crucial ones
(invariants, bug rationale, SAFETY blocks, ported-source attribution).

No functional code changed. Every edit is proven comment-only against the
prior tree by a comment-stripping lexer (string/char/raw-string aware) plus a
separate doctest-fence check. Where removing a comment made rustfmt or clippy
want to re-lay-out adjacent code, the minimal triggering comment is restored so
code tokens stay byte-identical.

Gates green: cargo fmt --all --check (0 diffs), cargo check and cargo clippy
--workspace --all-targets (0 warnings).

Adds scripts/check_codegen_comment_guidelines.py — the enforcement gate for
these guidelines (flags banners, end-of-line comments, change narration, and
commented-out code).

crates/codegen/kigi-shell/tests/test_fork_session.rs

@@ -1,9 +1,4 @@
 //! Integration tests for the fork session flow.
-//!
-//! These tests verify the complete fork session flow:
-//! 1. Fork session data with parent tracking
-//! 2. Verify forked session has correct metadata
-//! 3. Test worktree creation from worktree types
 
 use agent_client_protocol as acp;
 use kigi_shell::sampling::ConversationItem;
@@ -11,7 +6,6 @@ use kigi_shell::session::info::Info;
 use kigi_shell::session::storage::{JsonlStorageAdapter, StorageAdapter};
 use tempfile::TempDir;
 
-/// Helper to create a test session in a temp directory
 async fn create_test_session(storage: &JsonlStorageAdapter, session_id: &str, cwd: &str) -> Info {
     let info = Info {
         id: acp::SessionId::new(session_id),
@@ -21,11 +15,9 @@ async fn create_test_session(storage: &JsonlStorageAdapter, session_id: &str, cw
     let model_id = acp::ModelId::new("kigi-code-fast-1");
     storage.init_session(&info, model_id).await.unwrap();
 
-    // Add some chat messages
     let msg = ConversationItem::user("Hello world");
     storage.append_chat_message(&info, &msg).await.unwrap();
 
-    // Add an update
     let notification = acp::SessionNotification::new(
         acp::SessionId::new(session_id),
         acp::SessionUpdate::AgentMessageChunk(acp::ContentChunk::new(acp::ContentBlock::Text(
@@ -48,7 +40,6 @@ async fn test_fork_session_creates_new_session_with_parent_tracking() {
     let temp_dir = TempDir::new().unwrap();
     let storage = JsonlStorageAdapter::with_root(temp_dir.path().to_path_buf());
 
-    // Create source session
     let source_info = create_test_session(&storage, "source-session-123", "/source/path").await;
 
     let target_info = Info {
@@ -68,11 +59,9 @@ async fn test_fork_session_creates_new_session_with_parent_tracking() {
         .await
         .unwrap();
 
-    // Verify result
     assert_eq!(result.chat_messages_copied, 1);
     assert_eq!(result.updates_copied, 1);
 
-    // Load the forked session and verify metadata
     let loaded = storage.load_session(&target_info).await.unwrap();
 
     assert_eq!(loaded.summary.info.id.to_string(), "fork-session-456");
@@ -84,10 +73,8 @@ async fn test_fork_session_creates_new_session_with_parent_tracking() {
     );
     assert!(loaded.summary.forked_at.is_some());
 
-    // Verify chat history was copied
     assert_eq!(loaded.chat_history.len(), 1);
 
-    // Verify updates were copied with transformed session ID
     assert_eq!(loaded.updates.len(), 1);
     match &loaded.updates[0] {
         kigi_shell::session::storage::SessionUpdate::Acp(notification) => {
@@ -102,16 +89,13 @@ async fn test_fork_preserves_session_title() {
     let temp_dir = TempDir::new().unwrap();
     let storage = JsonlStorageAdapter::with_root(temp_dir.path().to_path_buf());
 
-    // Create source session
     let source_info = create_test_session(&storage, "titled-session", "/source").await;
 
-    // Update source session with a title
     storage
         .update_session_title(&source_info, "My Important Session".to_string())
         .await
         .unwrap();
 
-    // Fork the session
     let target_info = Info {
         id: acp::SessionId::new("fork-titled"),
         cwd: "/new".to_string(),
@@ -129,7 +113,7 @@ async fn test_fork_preserves_session_title() {
         .await
         .unwrap();
 
-    // Load and verify title was preserved (generated_title is the LLM title field).
+    // display_title() surfaces generated_title, the LLM-set title field.
     let loaded = storage.load_session(&target_info).await.unwrap();
     assert_eq!(loaded.summary.display_title(), "My Important Session");
 }