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-agent-lifecycle/src/local/contributors/command.rs

@@ -4,8 +4,9 @@ use crate::send::contributors::command::{
     CommandAction, CommandContributor, CommandInvocation, CommandSpec,
 };
 
-/// `?Send` twin of [`CommandContributor`] for single-threaded hosts like kigi build's TUI agent, whose session state is `Rc`/`RefCell`-based and can
-/// never satisfy the `Send` bounds the send flavor bakes into its boxed hook futures.
+/// `?Send` twin of [`CommandContributor`] for single-threaded hosts like kigi build's TUI agent,
+/// whose session state is `Rc`/`RefCell`-based and can never satisfy the `Send` bounds the send
+/// flavor bakes into its boxed hook futures.
 #[async_trait(?Send)]
 pub trait LocalCommandContributor {
     fn advertised_commands(&self) -> Vec<CommandSpec>;
@@ -14,7 +15,8 @@ pub trait LocalCommandContributor {
     -> Result<CommandAction, String>;
 }
 
-/// Send contributors work in single-threaded hosts as-is, so shared logic implements [`CommandContributor`] once and both hosts can register it.
+/// Send contributors work in single-threaded hosts as-is, so shared logic implements
+/// [`CommandContributor`] once and both hosts can register it.
 #[async_trait(?Send)]
 impl<T: CommandContributor> LocalCommandContributor for T {
     fn advertised_commands(&self) -> Vec<CommandSpec> {

crates/codegen/kigi-agent-lifecycle/src/local/contributors/session_lifecycle.rs

@@ -5,7 +5,8 @@ use crate::send::contributors::session_lifecycle::{SessionIdleInput, SessionLife
 /// `?Send` twin of [`SessionLifecycleContributor`].
 #[async_trait(?Send)]
 pub trait LocalSessionLifecycleContributor {
-    /// Fired when the session settles idle (no running turn or queued work); the host owns the check.
+    /// Fired when the session settles idle (no running turn or queued work); the host owns the
+    /// check.
     async fn on_session_idle(&self, _input: &SessionIdleInput) {}
 }
 

crates/codegen/kigi-agent-lifecycle/src/local/contributors/turn_input.rs

@@ -4,8 +4,9 @@ use crate::send::contributors::turn_input::{
     TurnInputContext, TurnInputContributor, TurnInputFragment,
 };
 
-/// `?Send` twin of [`TurnInputContributor`] for single-threaded hosts like kigi build's TUI agent, whose session state is `Rc`/`RefCell`-based
-/// and can never satisfy the `Send` bounds the send flavor bakes into its boxed hook futures.
+/// `?Send` twin of [`TurnInputContributor`] for single-threaded hosts like kigi build's TUI agent,
+/// whose session state is `Rc`/`RefCell`-based and can never satisfy the `Send` bounds the send
+/// flavor bakes into its boxed hook futures.
 #[async_trait(?Send)]
 pub trait LocalTurnInputContributor {
     async fn contribute_turn_input(&self, _input: &TurnInputContext) -> Vec<TurnInputFragment> {
@@ -13,7 +14,8 @@ pub trait LocalTurnInputContributor {
     }
 }
 
-/// Send contributors are usable in single-threaded hosts as-is, so shared logic implements [`TurnInputContributor`] once for both hosts.
+/// Send contributors are usable in single-threaded hosts as-is, so shared logic implements
+/// [`TurnInputContributor`] once for both hosts.
 #[async_trait(?Send)]
 impl<T: TurnInputContributor> LocalTurnInputContributor for T {
     async fn contribute_turn_input(&self, input: &TurnInputContext) -> Vec<TurnInputFragment> {

crates/codegen/kigi-agent-lifecycle/src/local/registry.rs

@@ -6,7 +6,6 @@ use crate::local::contributors::{
     LocalTurnLifecycleContributor,
 };
 
-/// Mutable registry used while hosts register typed runtime contributions.
 #[derive(Default)]
 pub struct LocalExtensionRegistryBuilder {
     turn_lifecycle_contributors: Vec<Rc<dyn LocalTurnLifecycleContributor>>,
@@ -67,7 +66,6 @@ impl LocalExtensionRegistryBuilder {
     }
 }
 
-/// Immutable typed registry produced after extensions are installed.
 #[derive(Default)]
 pub struct LocalExtensionRegistry {
     turn_lifecycle_contributors: Vec<Rc<dyn LocalTurnLifecycleContributor>>,
@@ -94,7 +92,6 @@ impl LocalExtensionRegistry {
         &self.command_contributors
     }
 
-    /// The one contributor owning `name`, or `None` when no extension advertised it.
     pub fn command_handler(&self, name: &str) -> Option<&Rc<dyn LocalCommandContributor>> {
         self.command_handlers.get(name)
     }