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-shell/src/bin/chat-history-downgrade.rs

@@ -1,5 +1,4 @@
 //! normalize chat_history.jsonl, convert any v1 (ConversationItem) to v0 (ChatRequestMessage) format.
-//! Used for data processing pipeline.
 //!
 //! Usage:
 //!   chat-history-downgrade <INPUT> <OUTPUT>
@@ -176,10 +175,8 @@ fn main() -> anyhow::Result<()> {
     Ok(())
 }
 
-// ============================================================================
-// Tests — hardcoded JSON fixtures so schema changes in either
+// Hardcoded JSON fixtures so schema changes in either
 // ConversationItem (v1) or ChatRequestMessage (v0) will break these.
-// ============================================================================
 
 #[cfg(test)]
 mod tests {
@@ -195,7 +192,6 @@ mod tests {
             .expect("convert_line should succeed")
             .expect("v1 line should produce a v0 message (not a buffered Reasoning)");
         let out = serde_json::to_string(&v0).expect("v0 should serialize");
-        // Verify the output is valid v0
         let _: ChatRequestMessage =
             serde_json::from_str(&out).expect("v0 output should round-trip");
         out

crates/codegen/kigi-shell/src/bin/trace_classify.rs

@@ -13,11 +13,6 @@
 //!       [--include-reasoning true] \
 //!       [--kigi-home <path>]
 //!
-//! The binary name is `trace_classify` (underscore) — that's the file
-//! name in `src/bin/`, which cargo's auto-discovery uses verbatim.
-//! The task brief calls it `trace-classify` (hyphen) in prose; the
-//! canonical CLI invocation is the underscore form.
-//!
 //! Each JSONL line carries the per-turn gate decision, the parsed
 //! classifier verdict (or the abort/parse error if the call failed),
 //! and the inputs that drove them.
@@ -61,7 +56,7 @@ struct Cli {
     /// Override the LazinessDetector min-confidence threshold (default
     /// matches production's `LAZINESS_DEFAULT_MIN_CONFIDENCE`). Must
     /// be a finite float in `[0.0, 1.0]`. Use this to mirror a
-    /// per-model override from the production models catalog. (F6/N5)
+    /// per-model override from the production models catalog.
     #[arg(long, value_parser = validate_min_confidence)]
     min_confidence: Option<f32>,