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-sampler/src/commands.rs

@@ -1,8 +1,8 @@
 //! Internal actor protocol.
 //!
 //! `SamplerCommand` is `pub(crate)` because it is the wire between
-//! [`SamplerHandle`](crate::handle::SamplerHandle) and the actor task,
-//! not a public type. External callers always go through `SamplerHandle`.
+//! [`SamplerHandle`](crate::handle::SamplerHandle) and the actor task.
+//! External callers always go through `SamplerHandle`.
 
 use tokio::sync::oneshot;
 
@@ -12,15 +12,12 @@ use crate::config::SamplerConfig;
 use crate::metrics::InferenceLatencyStats;
 use crate::types::RequestId;
 
-/// Commands sent from a [`SamplerHandle`](crate::handle::SamplerHandle)
-/// to the actor task.
-///
-/// Large payloads (`ConversationRequest`, `SamplerConfig`) are boxed so
-/// every command stays cheap to copy through the mpsc channel.
+/// Large payloads (`ConversationRequest`, `SamplerConfig`) are boxed so every
+/// variant stays cheap to move through the mpsc channel.
 pub(crate) enum SamplerCommand {
-    /// Submit a new sampling request. Fire-and-forget — results come via
-    /// events. When `completion_tx` is set the per-request task also
-    /// signals that channel for `submit_and_collect` callers.
+    /// Fire-and-forget — results arrive as events. When `completion_tx` is set
+    /// the per-request task also signals that channel, for
+    /// `submit_and_collect` callers.
     Submit {
         request_id: RequestId,
         request: Box<ConversationRequest>,
@@ -33,10 +30,9 @@ pub(crate) enum SamplerCommand {
     /// Cancel an in-flight request.
     Cancel { request_id: RequestId },
 
-    /// Update the default sampling config (model switch, auth refresh).
+    /// Sent on a model switch or an auth refresh.
     UpdateConfig { config: Box<SamplerConfig> },
 
-    /// Query: is a specific request still in flight?
     IsActive {
         request_id: RequestId,
         reply: oneshot::Sender<bool>,