feat(joinir): Phase 185 Strict Mode Semantics Cleanup

Remove redundant strict checks from If lowering (3 → 1 check point):
- mod.rs: Remove 2 strict panic blocks from try_lower_if_to_joinir()
- mod.rs: Comment out unused strict_on variable
- Keep single strict check at caller level (if_form.rs)

This aligns If lowering architecture with Loop lowering:
- Lowerers are thin Result-returning boxes (no policy decisions)
- Strict mode check happens at router/caller level (single source of truth)
- Fail-Fast principle: panic at ONE location when strict=ON

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

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

CURRENT_TASK.md

@@ -1,5 +1,59 @@
 # Current Task
 
+## ✅ Phase 185: JoinIR Strict Mode Semantics Cleanup (Completed - 2025-12-04)
+
+**Status**: ✅ **All Tasks Completed** → Clean Architecture Established
+
+**Key Achievement**: Strict mode semantics unified between Loop/If lowering. If lowering now has SINGLE strict check point (like Loop), eliminating double/triple-invocation problem.
+
+### Completed Tasks
+
+✅ **Task 1-2**: Strict flow inventory and design
+- Created comprehensive flow inventory document
+- Identified problem: If lowering had 3 strict check points vs Loop's 1
+- Document: `docs/private/roadmap2/phases/phase-185-joinir-strict-mode/strict_flow_inventory.md`
+
+✅ **Task 3**: If lowering strict check consolidation
+- **Removed 2 strict checks** from `try_lower_if_to_joinir()` (lines 296, 314)
+- **Kept 1 strict check** at caller level in `if_form.rs` (line 311)
+- Pattern now matches Loop lowering: Result-returning box + single check at router
+
+✅ **Task 4**: Representative strict tests verified
+- Loop (reference): `loop_min_while.hako` ✅ Passes with NYASH_JOINIR_STRICT=1
+- If Select: `joinir_if_select_simple.hako` ✅ Passes with NYASH_JOINIR_STRICT=1
+- If Merge: `joinir_if_merge_simple.hako` ✅ Passes with NYASH_JOINIR_STRICT=1
+- Fallback: All tests pass without strict mode (backward compatibility maintained)
+
+✅ **Task 5**: Documentation updated
+- Phase 185 implementation complete
+- Phase 184 Known Issues resolved (double-invocation problem fixed)
+- CURRENT_TASK.md updated with completion status
+
+### Implementation Summary
+
+**Architecture Change**: Strict check consolidation
+
+| Component | Before (Problem) | After (Fixed) |
+|-----------|-----------------|---------------|
+| **try_lower_if_to_joinir** | 2 panic points (lines 296, 314) | 0 panic points (thin Result box) |
+| **if_form.rs caller** | 1 panic point (line 311) | 1 panic point (SINGLE source) |
+| **Total** | **3 check points** ❌ | **1 check point** ✅ |
+
+**Pattern Now Matches Loop Lowering**:
+- Loop: `LoopToJoinLowerer::lower()` → Result → Single check in `join_ir_vm_bridge_dispatch`
+- If: `try_lower_if_to_joinir()` → Option → Single check in `if_form.rs`
+
+**Modified Files**:
+- `src/mir/join_ir/lowering/mod.rs` (removed 2 strict checks, -8 lines)
+- `src/mir/builder/if_form.rs` (kept 1 strict check at caller level, 0 changes)
+
+**Semantic Guarantee**:
+- strict=OFF: Lowering failure → fallback to traditional path (dev/test)
+- strict=ON: Lowering failure → panic with clear message (production gate)
+- Fail-Fast principle: ONE check point = ONE source of truth
+
+---
+
 ## ✅ Phase 184: JoinIR If Lowering Mainline (Completed - 2025-12-04)
 
 **Status**: ✅ **All Tasks Completed** → Phase 185+ Ready
@@ -54,7 +108,7 @@
 
 ### Known Issues (Non-blocking)
 
-1. **Double-invocation in strict mode**: NYASH_JOINIR_STRICT=1 can panic even when lowering succeeds (skeleton + lowering passes). Workaround: use NYASH_JOINIR_DEBUG=1 instead.
+1. ~~**Double-invocation in strict mode**: NYASH_JOINIR_STRICT=1 can panic even when lowering succeeds (skeleton + lowering passes). Workaround: use NYASH_JOINIR_DEBUG=1 instead.~~ ✅ **FIXED in Phase 185**
 2. **Test output formatting**: Tests show "RC: 0" instead of expected print output (unrelated to If lowering infrastructure).
 
 ### Verification Commands

src/mir/join_ir/lowering/mod.rs

@@ -202,7 +202,8 @@ pub fn try_lower_if_to_joinir(
         return None;
     }
     let core_on = crate::config::env::joinir_core_enabled();
-    let strict_on = crate::config::env::joinir_strict_enabled();
+    // Phase 185: strict check moved to caller (if_form.rs)
+    // let strict_on = crate::config::env::joinir_strict_enabled();
 
     // Phase 33-9.1: Loop専任関数の除外（Loop/If責務分離）
     // Loop lowering対象関数はIf loweringの対象外にすることで、
@@ -248,7 +249,7 @@ pub fn try_lower_if_to_joinir(
             return None;
         }
     }
-    let strict_allowed = strict_on && core_on && is_allowed;
+    // Phase 185: strict_allowed removed (strict check moved to caller: if_form.rs)
 
     if debug_level >= 1 {
         eprintln!(
@@ -286,6 +287,8 @@ pub fn try_lower_if_to_joinir(
         if_select::IfSelectLowerer::new(debug_level)
     };
 
+    // Phase 185: Remove strict checks from lowerer (thin Result-returning box)
+    // Strict mode panic should happen at caller level (if_form.rs), not here
     if !if_select_lowerer.can_lower_to_select(func, block_id) {
         if debug_level >= 1 {
             eprintln!(
@@ -293,12 +296,6 @@ pub fn try_lower_if_to_joinir(
                 func.signature.name
             );
         }
-        if strict_allowed {
-            panic!(
-                "[joinir/if] strict mode: pattern not matched for {}",
-                func.signature.name
-            );
-        }
         return None;
     }
 
@@ -311,13 +308,6 @@ pub fn try_lower_if_to_joinir(
         );
     }
 
-    if result.is_none() && strict_allowed {
-        panic!(
-            "[joinir/if] strict mode: lowering failed for {}",
-            func.signature.name
-        );
-    }
-
     result
 }