feat(joinir): Phase 248 - Normalized JoinIR infrastructure

Major refactoring of JoinIR normalization pipeline:

Key changes:
- Structured→Normalized→MIR(direct) pipeline established
- ShapeGuard enhanced with Pattern2 loop validation
- dev_env.rs: New development fixtures and env control
- fixtures.rs: jsonparser_parse_number_real fixture
- normalized_bridge/direct.rs: Direct MIR generation from Normalized
- pattern2_step_schedule.rs: Extracted step scheduling logic

Files changed:
- normalized.rs: Enhanced NormalizedJoinModule with DevEnv support
- shape_guard.rs: Pattern2-specific validation (+300 lines)
- normalized_bridge.rs: Unified bridge with direct path
- loop_with_break_minimal.rs: Integrated step scheduling
- Deleted: step_schedule.rs (moved to pattern2_step_schedule.rs)

New files:
- param_guess.rs: Loop parameter inference
- pattern2_step_schedule.rs: Step scheduling for Pattern2
- phase43-norm-canon-p2-mid.md: Design doc

Tests: 937/937 PASS (+6 from baseline 931)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/mir/join_ir/normalized/dev_env.rs

@@ -1,38 +1,111 @@
 #![cfg(feature = "normalized_dev")]
 
 use once_cell::sync::Lazy;
-use std::sync::Mutex;
+use std::sync::{Mutex, MutexGuard};
 
 /// RAII guard for normalized_dev env toggling (NYASH_JOINIR_NORMALIZED_DEV_RUN).
-/// 汚染防止のため tests/runner の両方で再利用できるようにここに置く。
+/// ネストを許可し、最初の呼び出し時の状態だけを保存・復元する。
 pub struct NormalizedDevEnvGuard {
-    _lock: std::sync::MutexGuard<'static, ()>,
-    prev: Option<String>,
+    active: bool,
 }
 
-static NORMALIZED_ENV_LOCK: Lazy<Mutex<()>> = Lazy::new(|| Mutex::new(()));
+#[derive(Default)]
+struct EnvState {
+    stack: Vec<Option<String>>,
+}
+
+static NORMALIZED_ENV_STATE: Lazy<Mutex<EnvState>> = Lazy::new(|| Mutex::new(EnvState::default()));
+static NORMALIZED_TEST_LOCK: Lazy<Mutex<()>> = Lazy::new(|| Mutex::new(()));
 
 impl NormalizedDevEnvGuard {
     pub fn new(enabled: bool) -> Self {
-        let lock = NORMALIZED_ENV_LOCK
+        let mut state = NORMALIZED_ENV_STATE
             .lock()
             .expect("normalized env mutex poisoned");
+
+        // Save current value before overriding.
         let prev = std::env::var("NYASH_JOINIR_NORMALIZED_DEV_RUN").ok();
+        state.stack.push(prev);
+
         if enabled {
             std::env::set_var("NYASH_JOINIR_NORMALIZED_DEV_RUN", "1");
         } else {
             std::env::remove_var("NYASH_JOINIR_NORMALIZED_DEV_RUN");
         }
-        Self { _lock: lock, prev }
+
+        Self { active: true }
     }
 }
 
 impl Drop for NormalizedDevEnvGuard {
     fn drop(&mut self) {
-        if let Some(prev) = &self.prev {
-            std::env::set_var("NYASH_JOINIR_NORMALIZED_DEV_RUN", prev);
-        } else {
-            std::env::remove_var("NYASH_JOINIR_NORMALIZED_DEV_RUN");
+        if !self.active {
+            return;
+        }
+        let mut state = NORMALIZED_ENV_STATE
+            .lock()
+            .expect("normalized env mutex poisoned");
+        if let Some(prev) = state.stack.pop() {
+            if let Some(prev) = prev {
+                std::env::set_var("NYASH_JOINIR_NORMALIZED_DEV_RUN", prev);
+            } else {
+                std::env::remove_var("NYASH_JOINIR_NORMALIZED_DEV_RUN");
+            }
         }
     }
 }
+
+/// normalized_dev feature + env の ON/OFF をまとめた判定。
+pub fn normalized_dev_enabled() -> bool {
+    crate::config::env::normalized_dev_enabled()
+}
+
+/// normalized_dev かつ test/debug ログが有効なときだけ true。
+pub fn normalized_dev_logs_enabled() -> bool {
+    crate::config::env::normalized_dev_enabled() && crate::config::env::joinir_test_debug_enabled()
+}
+
+/// テスト用コンテキスト：env を ON にしつつロックで並列汚染を防ぐ。
+pub struct NormalizedTestContext<'a> {
+    _lock: MutexGuard<'a, ()>,
+    _env_guard: NormalizedDevEnvGuard,
+}
+
+impl<'a> NormalizedTestContext<'a> {
+    fn new(lock: MutexGuard<'a, ()>) -> Self {
+        let env_guard = NormalizedDevEnvGuard::new(true);
+        NormalizedTestContext {
+            _lock: lock,
+            _env_guard: env_guard,
+        }
+    }
+}
+
+/// テストで使う共通ガード。
+pub fn test_ctx() -> NormalizedTestContext<'static> {
+    let lock = NORMALIZED_TEST_LOCK
+        .lock()
+        .unwrap_or_else(|e| e.into_inner());
+    NormalizedTestContext::new(lock)
+}
+
+/// 簡易ラッパー：クロージャを normalized_dev ON で実行。
+pub fn with_dev_env<F, R>(f: F) -> R
+where
+    F: FnOnce() -> R,
+{
+    let _ctx = test_ctx();
+    f()
+}
+
+/// env が既に ON のときはそのまま、OFF のときだけ with_dev_env を噛ませる。
+pub fn with_dev_env_if_unset<F, R>(f: F) -> R
+where
+    F: FnOnce() -> R,
+{
+    if normalized_dev_enabled() {
+        f()
+    } else {
+        with_dev_env(f)
+    }
+}