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-pager-pty-harness/tests/empty_enter_send_now.rs

@@ -5,7 +5,8 @@
 //! ```
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-#[ignore] // opt-in: real pager binary in a PTY (CI runs with --ignored)
+// opt-in: real pager binary in a PTY (CI runs with --ignored)
+#[ignore]
 async fn empty_enter_force_sends_top_queued() {
     kigi_pager_pty_harness::scenarios::empty_enter_send_now::assert_empty_enter_force_sends_top_queued()
         .await

crates/codegen/kigi-pager-pty-harness/tests/prompt_history_durable_quit.rs

@@ -34,7 +34,8 @@ const SIGINT_CANARY: &str = "SIGINTCANARY7";
 const ACK: &str = "ACKSENTINEL";
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-#[ignore] // opt-in: spawns the real pager binary in a PTY (CI runs with --ignored)
+// opt-in: spawns the real pager binary in a PTY (CI runs with --ignored)
+#[ignore]
 async fn prompt_history_durable_after_double_ctrl_c_and_recallable_on_resume() {
     run().await.expect("prompt-history durable-quit e2e");
 }
@@ -43,7 +44,8 @@ async fn prompt_history_durable_after_double_ctrl_c_and_recallable_on_resume() {
 /// same graceful quit: the prompt stays durable and the process exits 0.
 #[cfg(unix)]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-#[ignore] // opt-in: spawns the real pager binary in a PTY (CI runs with --ignored)
+// opt-in: spawns the real pager binary in a PTY (CI runs with --ignored)
+#[ignore]
 async fn prompt_history_durable_after_real_sigint_graceful_quit() {
     run_sigint().await.expect("sigint graceful-quit e2e");
 }
@@ -197,7 +199,8 @@ fn submit_and_settle(
     pager
         .wait_for_text(ACK, Duration::from_secs(30))
         .context("turn response rendered")?;
-    pager.update(Duration::from_millis(1000)); // let the short turn finish (idle)
+    // let the short turn finish (idle)
+    pager.update(Duration::from_millis(1000));
     Ok(pager)
 }
 

crates/codegen/kigi-pager-pty-harness/tests/scroll_correctness_ptyctl.rs

@@ -98,7 +98,8 @@ async fn scroll_up_from_follow_bottom_then_back_down() -> Result<()> {
         }
     }
     // Wheel over mid-screen scrollback (1-indexed SGR coords).
-    harness.inject_keys(&sgr_scroll(64, 15, 40, 50))?; // 64 = wheel up
+    // 64 = wheel up
+    harness.inject_keys(&sgr_scroll(64, 15, 40, 50))?;
     harness.update(Duration::from_millis(200));
     harness.update(Duration::from_millis(300));
     let mid = harness.screen_contents();
@@ -126,7 +127,8 @@ async fn scroll_up_from_follow_bottom_then_back_down() -> Result<()> {
             bail!("pager exited while PageDown scrolling");
         }
     }
-    harness.inject_keys(&sgr_scroll(65, 15, 40, 50))?; // 65 = wheel down
+    // 65 = wheel down
+    harness.inject_keys(&sgr_scroll(65, 15, 40, 50))?;
     harness.update(Duration::from_millis(200));
     harness.update(Duration::from_millis(400));
     let back_bottom = harness.screen_contents();

crates/codegen/kigi-pager-pty-harness/tests/scroll_matrix_curated.rs

@@ -89,7 +89,7 @@ async fn c1_auto_g8_midstream() {
     assert_cell_passes("c1_auto_g8_midstream").await;
 }
 
-/// The formerly-declared bug: the finalize-decel fix landed, so the G4 jerk
+/// The once-declared bug: the finalize-decel fix landed, so the G4 jerk
 /// cell passes outright — I-SMOOTH-COAST (post-input motion at most one
 /// tapered cap) and I-NO-DROP (finalize discards nothing) moved from the
 /// xfail set to ordinary pass rows. The cell id keeps its historical name