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/ptyctl/src/session.rs

@@ -102,7 +102,7 @@ impl PtySession {
         let alive = Arc::new(AtomicBool::new(true));
         let exit_code: Arc<std::sync::Mutex<Option<u32>>> = Arc::new(std::sync::Mutex::new(None));
 
-        // --- PTY Reader Thread (blocking) ---
+        // PTY Reader Thread (blocking)
         let alive_reader = alive.clone();
         std::thread::Builder::new()
             .name("pty-reader".into())
@@ -128,7 +128,7 @@ impl PtySession {
             })
             .context("failed to spawn PTY reader thread")?;
 
-        // --- PTY Writer Task (async) ---
+        // PTY Writer Task (async)
         tokio::spawn(async move {
             loop {
                 tokio::select! {
@@ -151,7 +151,7 @@ impl PtySession {
             }
         });
 
-        // --- Terminal Feeder Task (async) ---
+        // Terminal Feeder Task (async)
         let terminal_feeder = terminal.clone();
         let output_tx_feeder = output_tx.clone();
         let raw_tail_feeder = raw_tail.clone();
@@ -172,7 +172,7 @@ impl PtySession {
             }
         });
 
-        // --- Child Process Waiter ---
+        // Child Process Waiter
         let alive_waiter = alive.clone();
         let exit_code_waiter = exit_code.clone();
         tokio::spawn(async move {