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-memory/src/text_utils.rs

@@ -2,24 +2,16 @@
 //! (`session::helpers::memory_flush`) and dream (`session::memory::dream`)
 //! response-processing paths.
 //!
-//! These live here, in the memory subsystem, so `dream` no longer reaches
-//! *up* into `session::helpers::memory_flush` for them — which removes the
-//! `dream` <-> `memory_flush` module dependency cycle and is a prerequisite
-//! for extracting the memory subsystem into its own crate.
+//! They live down here rather than in `memory_flush` so that `dream` need not
+//! reach *up* into it, which would form a `dream` <-> `memory_flush` cycle.
 
-/// Check if text contains at least one markdown header (`#` or `##`).
-///
-/// Used by both flush and dream response processing to ensure the model
-/// produced structured output.
 pub fn has_markdown_headers(text: &str) -> bool {
     text.contains("## ") || text.contains("# ")
 }
 
-/// Check if the response matches the NO_REPLY convention.
-///
-/// Strips all non-alphanumeric characters, lowercases, and checks if the
-/// remainder is exactly `"noreply"`. This handles common separator variants:
-/// `"no reply"`, `"no_reply"`, `"no-reply"`, `"NO REPLY"`, etc.
+/// Matches the NO_REPLY convention across separator variants — `"no reply"`,
+/// `"no_reply"`, `"no-reply"`, `"NO REPLY"` — by comparing only the
+/// lowercased alphanumerics.
 pub fn is_no_reply(text: &str) -> bool {
     let normalized: String = text
         .to_lowercase()