refactor(joinir): unify policy decisions and trim routing

src/mir/builder/control_flow/joinir/patterns/policies/README.md

@@ -85,8 +85,8 @@
 - Reject理由は`error_tags::freeze()`でタグ付与
 
 ### Decision型の統一
-- `Decision` enum（None / Use(...) / Reject(String)）を統一パターンとして使用
-- 例: `P5bEscapeDerivedDecision`, `TrimDecision`（将来）
+- `PolicyDecision<T>`（Use / Reject / None）をSSOTにする
+- 例: `P5bEscapeDerivedDecision = PolicyDecision<BodyLocalDerivedRecipe>`, `TrimPolicyResult`
 
 ## 使用パターン
 

src/mir/builder/control_flow/joinir/patterns/policies/mod.rs

@@ -8,6 +8,10 @@
 //! - ルーティング決定: 適用可能なLoweringパターンを決定
 //! - Recipe生成: Pattern固有の情報（ConditionOnlyRecipe, BodyLocalDerivedRecipe, etc.）を生成
 //!
+//! ## 決定型のSSOT
+//! - `PolicyDecision<T>` に統一（Use / Reject / None）
+//! - BodyLocal, Trim, P5b escape などすべてここ経由で route することで Pattern2 側の分岐を簡潔に保つ
+//!
 //! ## 設計原則
 //! - **単一判断の原則**: 各policy箱は1つのパターン判断のみ
 //! - **非破壊的判断**: 入力を変更せず、Decision型で結果を返す
@@ -17,11 +21,14 @@
 //! policies/ は「認識とルーティング決定（policy）」を分離する受け皿です。
 //! Phase 94（P5b derived）から段階的に移設を開始しました。
 //!
-//! ### 段階的な移行計画
-//! - Phase 1: ディレクトリ準備 ✅
-//! - Phase 2: 既存policy箱の移動（進行中）
-//! - Phase 3: インターフェース統一（将来）
-//!
 //! 詳細は [README.md](README.md) を参照してください。
 
+#[derive(Debug, Clone)]
+pub enum PolicyDecision<T> {
+    Use(T),
+    Reject(String),
+    None,
+}
+
 pub(in crate::mir::builder) mod p5b_escape_derived_policy;
+pub(in crate::mir::builder) mod trim_policy;

src/mir/builder/control_flow/joinir/patterns/policies/p5b_escape_derived_policy.rs

@@ -13,13 +13,9 @@ use crate::config::env::joinir_dev;
 use crate::mir::builder::control_flow::joinir::patterns::escape_pattern_recognizer::EscapeSkipPatternInfo;
 use crate::mir::join_ir::lowering::common::body_local_derived_emitter::BodyLocalDerivedRecipe;
 use crate::mir::join_ir::lowering::error_tags;
+use super::PolicyDecision;
 
-#[derive(Debug)]
-pub enum P5bEscapeDerivedDecision {
-    None,
-    UseDerived(BodyLocalDerivedRecipe),
-    Reject(String),
-}
+pub type P5bEscapeDerivedDecision = PolicyDecision<BodyLocalDerivedRecipe>;
 
 /// Detect a P5b derived body-local (`ch`) recipe from a Pattern2 loop body.
 ///
@@ -43,7 +39,7 @@ pub fn classify_p5b_escape_derived(
     }
 
     match build_recipe_from_info(body, &info) {
-        Ok(Some(recipe)) => P5bEscapeDerivedDecision::UseDerived(recipe),
+        Ok(Some(recipe)) => P5bEscapeDerivedDecision::Use(recipe),
         Ok(None) => {
             // Escape pattern exists but there is no body-local reassignment to cover.
             P5bEscapeDerivedDecision::None
@@ -257,7 +253,7 @@ mod tests {
         ];
 
         match classify_p5b_escape_derived(&body, "i") {
-            P5bEscapeDerivedDecision::UseDerived(recipe) => {
+            P5bEscapeDerivedDecision::Use(recipe) => {
                 assert_eq!(recipe.name, "ch");
                 assert_eq!(recipe.loop_counter_name, "i");
                 assert_eq!(recipe.pre_delta, 1);

src/mir/builder/control_flow/joinir/patterns/policies/trim_policy.rs

@@ -0,0 +1,51 @@
+//! Trim pattern policy box (判定専用)
+//!
+//! 目的: Trim 形状かどうかを判定し、ConditionScope を返すだけに責務を絞る。
+//! 生成（lowering）は従来通り TrimLoopLowerer 側が担当する。
+
+use crate::ast::ASTNode;
+use crate::mir::builder::control_flow::joinir::patterns::trim_loop_lowering::TrimLoopLowerer;
+use crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape;
+use crate::mir::loop_pattern_detection::loop_condition_scope::{
+    CondVarInfo, CondVarScope, LoopConditionScope, LoopConditionScopeBox,
+};
+
+use super::PolicyDecision;
+
+/// 判定結果（生成に必要な最小情報だけ運ぶ）
+#[derive(Debug, Clone)]
+pub struct TrimPolicyResult {
+    pub cond_scope: LoopConditionScope,
+    pub condition_body_locals: Vec<CondVarInfo>,
+}
+
+pub fn classify_trim_like_loop(
+    scope: &LoopScopeShape,
+    loop_cond: &ASTNode,
+    break_cond: &ASTNode,
+    loop_var_name: &str,
+) -> PolicyDecision<TrimPolicyResult> {
+    let cond_scope =
+        LoopConditionScopeBox::analyze(loop_var_name, &[loop_cond, break_cond], Some(scope));
+
+    if !cond_scope.has_loop_body_local() {
+        return PolicyDecision::None;
+    }
+
+    let condition_body_locals: Vec<_> = cond_scope
+        .vars
+        .iter()
+        .filter(|v| v.scope == CondVarScope::LoopBodyLocal)
+        .filter(|v| TrimLoopLowerer::is_var_used_in_condition(&v.name, break_cond))
+        .cloned()
+        .collect();
+
+    if condition_body_locals.is_empty() {
+        return PolicyDecision::None;
+    }
+
+    PolicyDecision::Use(TrimPolicyResult {
+        cond_scope,
+        condition_body_locals,
+    })
+}