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-chat-state/src/commands.rs

@@ -37,7 +37,7 @@ impl std::error::Error for RepairHistoryBlocked {}
 
 /// Commands sent to the ChatStateActor via mpsc channel.
 pub enum ChatStateCommand {
-    // ═══ Mutations (fire-and-forget) ═══
+    // Mutations (fire-and-forget)
     /// Push a user message into the conversation.
     PushUserMessage { item: ConversationItem },
 
@@ -64,7 +64,7 @@ pub enum ChatStateCommand {
     RecordTokenUsage { total_tokens: u64 },
 
     /// Stash the per-turn `TokenUsage` from the most recent model response.
-    /// Overwrites any previously stashed value.
+    /// Overwrites any earlier stashed value.
     RecordLastTurnUsage { usage: TokenUsage },
 
     RecordModelCallUsage {
@@ -176,7 +176,7 @@ pub enum ChatStateCommand {
     /// Repair dangling tool calls after a harness-initiated halt.
     RepairDanglingAfterHarnessHalt { class: &'static str },
 
-    // ═══ Queries (request/response via oneshot) ═══
+    // Queries (request/response via oneshot)
     /// Build a ConversationRequest ready to send to the API.
     /// Clones the conversation, prunes old tool results, repairs dangling
     /// tool calls, injects memory reminder, and assembles the request.
@@ -280,7 +280,7 @@ pub enum ChatStateCommand {
         reply: oneshot::Sender<Vec<Vec<ConversationItem>>>,
     },
 
-    // ═══ Narrow targeted queries (avoid full-conversation clone) ═══
+    // Narrow targeted queries (avoid full-conversation clone)
     /// Get the number of items in the conversation.
     /// Cheaper than `GetConversation` when only the length is needed.
     GetConversationLen { reply: oneshot::Sender<usize> },