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-interjection-core/src/buffer.rs

@@ -3,30 +3,27 @@ use serde::{Deserialize, Serialize};
 use crate::events::EventQueue;
 use crate::format::format_interjection;
 
-/// A buffered mid-turn interjection awaiting the next safe drain point.
-/// `Attachment` is host-defined (inline images, asset IDs); core never reads it.
+/// Mid-turn interjection waiting for the next safe drain point.
+/// `Attachment` is host-defined; core never inspects it.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct PendingInterjection<Attachment> {
     pub text: String,
     pub attachments: Vec<Attachment>,
 }
 
-/// A drained entry, wrapped and ready to emit as a synthetic user message.
+/// Drained entry, framed as a synthetic user message.
 #[derive(Debug, Clone, PartialEq)]
 pub struct FormattedInterjection<Attachment> {
     pub text: String,
     pub attachments: Vec<Attachment>,
 }
 
-/// A queue of pending interjections — just an [`EventQueue`] of
-/// [`PendingInterjection`]. Use [`drain_formatted`] to drain + frame them as
-/// synthetic user messages.
+/// Queue of [`PendingInterjection`] values. Drain via [`drain_formatted`].
 pub type InterjectionBuffer<Attachment> = EventQueue<PendingInterjection<Attachment>>;
 
-/// Drain `buffer`, framing each entry as a synthetic user message (FIFO, one
-/// message per entry, never merged). `sanitize_text` runs on the raw text first
-/// (hosts strip artifacts like image placeholder paths; pass
-/// `std::convert::identity` if none).
+/// Drain `buffer` FIFO, one synthetic user message per entry (never merged).
+/// `sanitize_text` runs on raw text first (e.g. strip image placeholders);
+/// pass `std::convert::identity` when none is needed.
 pub fn drain_formatted<Attachment>(
     buffer: &InterjectionBuffer<Attachment>,
     sanitize_text: impl Fn(String) -> String,