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/common/kigi-tool-protocol/src/session_event.rs

@@ -98,8 +98,6 @@ mod tests {
     use super::*;
     use serde_json::json;
 
-    // ── SessionEvent round-trip tests ────────────────────────────────
-
     #[test]
     fn turn_started_round_trip() {
         let event = SessionEvent::TurnStarted {
@@ -226,8 +224,6 @@ mod tests {
         }
     }
 
-    // ── #[serde(other)] backward-compat ─────────────────────────────
-
     #[test]
     fn unknown_event_type_deserializes_as_unknown() {
         let v = json!({ "event_type": "some_future_event", "extra": 123 });
@@ -242,8 +238,6 @@ mod tests {
         assert_eq!(event, SessionEvent::Unknown);
     }
 
-    // ── ToolCallOutcome serialization ───────────────────────────────
-
     #[test]
     fn tool_call_outcome_snake_case() {
         for (variant, expected) in [
@@ -259,8 +253,6 @@ mod tests {
         }
     }
 
-    // ── SessionPhase serialization ──────────────────────────────────
-
     #[test]
     fn session_phase_snake_case() {
         for (variant, expected) in [
@@ -277,8 +269,6 @@ mod tests {
         }
     }
 
-    // ── Forward-compat: inner enum Unknown ──────────────────────────
-
     #[test]
     fn tool_call_outcome_unknown_variant_on_future_value() {
         let back: ToolCallOutcome = serde_json::from_value(json!("timeout")).unwrap();
@@ -327,16 +317,12 @@ mod tests {
         );
     }
 
-    // ── Unknown variant serialization ───────────────────────────────
-
     #[test]
     fn unknown_variant_serializes_as_expected() {
         let v = serde_json::to_value(SessionEvent::Unknown).unwrap();
         assert_eq!(v, json!({"event_type": "unknown"}));
     }
 
-    // ── Extra/unknown fields on known variants ──────────────────────
-
     #[test]
     fn extra_fields_ignored_on_known_variant() {
         let v = json!({
@@ -356,8 +342,6 @@ mod tests {
         );
     }
 
-    // ── Negative: missing required fields ───────────────────────────
-
     #[test]
     fn turn_ended_missing_required_field_rejected() {
         let v = json!({
@@ -371,8 +355,6 @@ mod tests {
         assert!(serde_json::from_value::<SessionEvent>(v).is_err());
     }
 
-    // ── Boundary values ─────────────────────────────────────────────
-
     #[test]
     fn turn_number_zero_and_max() {
         for turn_number in [0, u64::MAX] {