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-workspace/src/foreign_sessions/codex/mod.rs

@@ -78,6 +78,8 @@ fn highest_named_state_database(root: &ApprovedRoot) -> Option<PathBuf> {
         match std::fs::symlink_metadata(&path) {
             Ok(_) => Some(path),
             Err(error) if error.kind() == std::io::ErrorKind::NotFound => None,
+            // An unreadable entry still claims its generation, so the caller
+            // falls back to rollout files instead of trusting an older database.
             Err(_) => Some(path),
         }
     })