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-tui/src/app/dispatch/session/fork.rs

@@ -15,32 +15,18 @@ use crate::scrollback::blocks::SessionEvent;
 use crate::scrollback::state::ScrollbackState;
 use agent_client_protocol as acp;
 use std::time::Instant;
-/// Top-level `/fork` dispatcher. Resolves the worktree decision: an
-/// explicit `--worktree` / `--no-worktree` flag short-circuits to
-/// [`dispatch_fork_resolved`]. When no flag is given and a persisted
-/// `fork_worktree_mode` preference is set (`Always` / `Never`), the
-/// popup is skipped and the corresponding path is taken directly. The
-/// `Ask` default opens the [`open_fork_question`] modal so the user is
-/// asked.
+/// Top-level `/fork` dispatcher, resolving the worktree decision (explicit
+/// flag, persisted `fork_worktree_mode`, or the [`open_fork_question`] modal).
 ///
-/// When the parent session's working directory is **not** inside a git
-/// repository (indicated by the absence of a `git_head_changed`
-/// notification — `current_branch` is `None`):
-/// - `--worktree` is rejected with a toast (nothing to create a worktree from).
-/// - No flag (regardless of `fork_worktree_mode`): the worktree question
-///   is skipped and the fork proceeds with `worktree = false`.
+/// A parent outside a git repository has `current_branch == None` (no
+/// `git_head_changed` notification): `--worktree` is rejected and every other
+/// path forks with `worktree = false`. That fallback is safe even if the
+/// notification simply has not arrived yet — the worktree can be created
+/// manually afterwards.
 ///
-/// Note: if the notification has not arrived yet (rare — user forks
-/// before the shell sends `git_head_changed`), the fallback to
-/// `worktree = false` is safe and the worktree can be created manually
-/// afterwards.
-///
-/// Two failure surfaces:
-/// - Active view is not an agent: toast and return.
-/// - Active agent has no `session_id` (still being created): toast and
-///   return. Both rejections are deliberate -- queueing the fork until
-///   `SessionLoaded` would require persisting `ForkArgs` across the
-///   `TaskResult` and is deferred to v2.
+/// A missing agent or a parent with no `session_id` are rejected rather than
+/// queued: queueing until `SessionLoaded` would mean persisting `ForkArgs`
+/// across the `TaskResult`, deferred to v2.
 pub(in crate::app::dispatch) fn dispatch_fork(
     app: &mut AppView,
     args: crate::slash::commands::fork::ForkArgs,

crates/codegen/kigi-tui/src/app/dispatch/session/load.rs

@@ -495,16 +495,6 @@ pub(in crate::app::dispatch) fn reanchor_grouped_selection<T>(
     }
     state.selected = sel;
 }
-/// Trigger a deep content search when the session picker query changes.
-///
-/// Any query of 2+ chars searches content — title matches never suppress
-/// it. Forced (Ctrl+/) searches fire immediately; keystrokes otherwise
-/// coalesce through [`Effect::DebounceSessionSearch`], whose expiry runs
-/// the search only if its seq is still current. Shorter queries clear the
-/// content results.
-///
-/// Checks the active agent's modal first; if no modal session picker
-/// exists, falls back to the welcome-screen picker state.
 pub(in crate::app::dispatch) fn dispatch_cycle_session_source_filter(
     app: &mut AppView,
 ) -> Vec<Effect> {
@@ -544,6 +534,16 @@ pub(in crate::app::dispatch) fn dispatch_cycle_session_source_filter(
     }
     vec![]
 }
+/// Trigger a deep content search when the session picker query changes.
+///
+/// Any query of 2+ chars searches content — title matches never suppress
+/// it. Forced (Ctrl+/) searches fire immediately; keystrokes otherwise
+/// coalesce through [`Effect::DebounceSessionSearch`], whose expiry runs
+/// the search only if its seq is still current. Shorter queries clear the
+/// content results.
+///
+/// Checks the active agent's modal first; if no modal session picker
+/// exists, falls back to the welcome-screen picker state.
 pub(in crate::app::dispatch) fn dispatch_trigger_deep_search(
     app: &mut AppView,
     force: bool,

crates/codegen/kigi-tui/src/app/dispatch/session/modal.rs

@@ -1,7 +1,4 @@
 //! Session rename / close helpers (shared with the dashboard).
-//!
-//! The `/sessions` picker modal was removed; rename-via-slash and
-//! dashboard close still use these dispatchers.
 use crate::app::actions::Effect;
 use crate::app::agent::AgentId;
 use crate::app::app_view::{ActiveView, AppView};