feat(phase72): HAKO_JOINIR_IF_SELECT SSOT consolidation - Test helpers

Phase 72-B: Created SSOT helper functions for HAKO_JOINIR_IF_SELECT ENV control.

Changes:
- Added set_if_select_on() and set_if_select_off() helpers to joinir_env.rs
- Replaced 13 direct std::env calls with helper functions in src/tests/mir_joinir_if_select.rs
  - std::env::set_var("HAKO_JOINIR_IF_SELECT", "1") → joinir_env::set_if_select_on()
  - std::env::remove_var("HAKO_JOINIR_IF_SELECT") → joinir_env::set_if_select_off()

Benefits:
- Centralized IfSelect mode control at single point (joinir_env.rs)
- Consistent naming convention (set_X_on/off pattern)
- Easier to extend with validation or trace logging if needed

Tests verified: cargo check --tests passed with no errors

Completed Phase 72-A+B progress:
- Phase 72-A: NYASH_JOINIR_EXPERIMENT (15 occurrences) ✅
- Phase 72-B: HAKO_JOINIR_IF_SELECT (13 occurrences) ✅
- Phase 72-C: Dev/experimental flags (pending)

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

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

src/tests/helpers/joinir_env.rs

@@ -25,3 +25,14 @@ pub fn clear_joinir_flags() {
 pub fn is_experiment_enabled() -> bool {
     std::env::var("NYASH_JOINIR_EXPERIMENT").ok().as_deref() == Some("1")
 }
+
+/// Phase 72-B: HAKO_JOINIR_IF_SELECT SSOT ヘルパー
+/// IfSelect/JoinIR If分岐選択モードをONにする
+pub fn set_if_select_on() {
+    std::env::set_var("HAKO_JOINIR_IF_SELECT", "1");
+}
+
+/// IfSelect/JoinIR If分岐選択モードをOFFにする
+pub fn set_if_select_off() {
+    std::env::remove_var("HAKO_JOINIR_IF_SELECT");
+}

src/tests/mir_joinir_if_select.rs

@@ -7,6 +7,7 @@ mod tests {
     use crate::mir::join_ir::lowering::try_lower_if_to_joinir;
     use crate::mir::join_ir::JoinInst;
     use crate::mir::{BasicBlock, BasicBlockId, MirFunction, MirInstruction, MirModule, ValueId};
+    use crate::tests::helpers::joinir_env;
     use std::collections::BTreeMap;
     use std::env;
 
@@ -148,7 +149,7 @@ mod tests {
         clear_joinir_flags();
 
         // ==== 1. Simple pattern (env ON) ====
-        std::env::set_var("HAKO_JOINIR_IF_SELECT", "1");
+        joinir_env::set_if_select_on();
 
         let func = create_simple_pattern_mir();
         let entry_block = func.entry_block;
@@ -205,7 +206,7 @@ mod tests {
 
         // ==== 3. Disabled by default (env OFF) ====
         set_core_off();
-        std::env::remove_var("HAKO_JOINIR_IF_SELECT");
+        joinir_env::set_if_select_off();
 
         let func = create_simple_pattern_mir();
         let entry_block = func.entry_block;
@@ -219,7 +220,7 @@ mod tests {
         eprintln!("✅ If/Select lowering correctly disabled by default");
 
         // ==== 4. Wrong function name (env ON) ====
-        std::env::set_var("HAKO_JOINIR_IF_SELECT", "1");
+        joinir_env::set_if_select_on();
 
         let mut func = create_simple_pattern_mir();
         func.signature.name = "WrongName.test/1".to_string();
@@ -545,7 +546,7 @@ mod tests {
         use crate::mir::join_ir::JoinInst;
 
         let _env = strict_if_env_guard();
-        std::env::set_var("HAKO_JOINIR_IF_SELECT", "1");
+        joinir_env::set_if_select_on();
 
         let func = create_if_merge_simple_pattern_mir();
         let entry_block = func.entry_block;
@@ -578,7 +579,7 @@ mod tests {
             panic!("Expected JoinInst::IfMerge, got {:?}", result);
         }
 
-        std::env::remove_var("HAKO_JOINIR_IF_SELECT");
+        joinir_env::set_if_select_off();
     }
 
     /// Phase 33-7: Test IfMerge lowering for 3-variable pattern
@@ -587,7 +588,7 @@ mod tests {
         use crate::mir::join_ir::JoinInst;
 
         let _env = strict_if_env_guard();
-        std::env::set_var("HAKO_JOINIR_IF_SELECT", "1");
+        joinir_env::set_if_select_on();
 
         let func = create_if_merge_multiple_pattern_mir();
         let entry_block = func.entry_block;
@@ -620,7 +621,7 @@ mod tests {
             panic!("Expected JoinInst::IfMerge, got {:?}", result);
         }
 
-        std::env::remove_var("HAKO_JOINIR_IF_SELECT");
+        joinir_env::set_if_select_off();
     }
 
     /// Phase 63-2: Helper to create a simple pattern MIR with Const instructions
@@ -683,7 +684,7 @@ mod tests {
         use crate::mir::MirType;
 
         let _env = strict_if_env_guard();
-        std::env::set_var("HAKO_JOINIR_IF_SELECT", "1");
+        joinir_env::set_if_select_on();
 
         let func = create_simple_pattern_mir_with_const();
         let entry_block = func.entry_block;
@@ -708,7 +709,7 @@ mod tests {
             panic!("Expected Select instruction with type_hint");
         }
 
-        std::env::remove_var("HAKO_JOINIR_IF_SELECT");
+        joinir_env::set_if_select_off();
     }
 
     /// Phase 63-6-4: A/B テスト - Route A (legacy) vs Route B (type hint)
@@ -721,7 +722,7 @@ mod tests {
         use crate::mir::MirType;
 
         let _env = strict_if_env_guard();
-        std::env::set_var("HAKO_JOINIR_IF_SELECT", "1");
+        joinir_env::set_if_select_on();
 
         // P1 Simple pattern で Select 生成
         let func = create_simple_pattern_mir_with_const();
@@ -748,7 +749,7 @@ mod tests {
         eprintln!("✅ Phase 63-6-4 Step 2: P1 function name filter: IfSelectTest.* ✓");
         eprintln!("✅ Phase 63-6-4: A/B test passed - JoinIR type hint available for lifecycle.rs");
 
-        std::env::remove_var("HAKO_JOINIR_IF_SELECT");
+        joinir_env::set_if_select_off();
     }
 
     /// Phase 64-2-2: A/B テスト - P2 IfMerge Simple 型ヒント検証