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-agent-lifecycle/src/send/contributors/turn_input.rs

@@ -1,20 +1,17 @@
 use async_trait::async_trait;
 
-/// Turn facts supplied when the host pulls extension input at its sampling chokepoint.
 pub struct TurnInputContext {
-    /// Stable host-owned turn identifier.
     pub turn_id: String,
     /// True when the harness produced the turn (auto-wake, drain, cron, continuation), not the user.
     pub synthetic: bool,
 }
 
-/// A model-visible input fragment contributed into the active turn. The host owns wrapping, origin stamping, and placement.
+/// Raw fragment text: the host owns wrapping, origin stamping, and placement.
 pub struct TurnInputFragment {
     pub text: String,
 }
 
-/// Contributes model-visible input fragments into the active turn when the host pulls at its sampling chokepoint.
-/// Fragments land in the same turn, never a new one.
+/// Fragments land in the turn the host is already sampling, never a new one.
 #[async_trait]
 pub trait TurnInputContributor: Send + Sync {
     async fn contribute_turn_input(&self, _input: &TurnInputContext) -> Vec<TurnInputFragment> {