feat(joinir): Phase 61-4-F ToplevelOps and production path integration

Phase 61-4-F: Loop-outside If JoinIR production path

Changes:
- F.1: Add ToplevelOps struct implementing PhiBuilderOps for MirBuilder
  - Enables emit_toplevel_phis() to emit PHI instructions via MirBuilder
  - Uses insert_phi_at_head_spanned for proper PHI placement
  - ~70 lines, thin wrapper following box theory

- F.2: Integrate production path with emit_toplevel_phis
  - Replace TODO with actual PHI emission call
  - Build IfShape from branch blocks
  - Log PHI count on dry-run

- Add IfToplevelTest.* to try_lower_if_to_joinir allowed list
  - Fixes function name guard that blocked testing

Note: Pattern matching currently only supports return patterns
(IfMerge/IfSelect). Local variable assignment patterns fall back
to existing PHI generation, which correctly produces valid MIR.

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

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

src/mir/builder/if_form.rs

@@ -1,6 +1,79 @@
 use super::{MirBuilder, ValueId};
 use crate::ast::ASTNode;
+use crate::mir::control_form::IfShape;
 use crate::mir::loop_api::LoopBuilderApi; // for current_block()
+use crate::mir::phi_core::phi_builder_box::PhiBuilderOps;
+use crate::mir::{BasicBlockId, ConstValue, MirInstruction};
+
+/// Phase 61-4-F: MirBuilder 用 PhiBuilderOps 実装
+///
+/// ループ外 if の JoinIR 経路で emit_toplevel_phis() を呼ぶためのラッパー。
+struct ToplevelOps<'a>(&'a mut MirBuilder);
+
+impl<'a> PhiBuilderOps for ToplevelOps<'a> {
+    fn new_value(&mut self) -> ValueId {
+        self.0.next_value_id()
+    }
+
+    fn emit_phi(
+        &mut self,
+        block: BasicBlockId,
+        dst: ValueId,
+        inputs: Vec<(BasicBlockId, ValueId)>,
+    ) -> Result<(), String> {
+        // merge ブロックの先頭に PHI を挿入
+        if let (Some(func), Some(_cur_bb)) = (self.0.current_function.as_mut(), self.0.current_block)
+        {
+            crate::mir::ssot::cf_common::insert_phi_at_head_spanned(
+                func,
+                block,
+                dst,
+                inputs,
+                self.0.current_span,
+            );
+        } else {
+            self.0.emit_instruction(MirInstruction::Phi { dst, inputs })?;
+        }
+        Ok(())
+    }
+
+    fn update_var(&mut self, name: String, value: ValueId) {
+        self.0.variable_map.insert(name, value);
+    }
+
+    fn get_block_predecessors(&self, block: BasicBlockId) -> Vec<BasicBlockId> {
+        if let Some(ref func) = self.0.current_function {
+            func.blocks
+                .get(&block)
+                .map(|bb| bb.predecessors.iter().copied().collect())
+                .unwrap_or_default()
+        } else {
+            Vec::new()
+        }
+    }
+
+    fn emit_void(&mut self) -> ValueId {
+        let void_id = self.0.next_value_id();
+        let _ = self.0.emit_instruction(MirInstruction::Const {
+            dst: void_id,
+            value: ConstValue::Void,
+        });
+        void_id
+    }
+
+    fn set_current_block(&mut self, block: BasicBlockId) -> Result<(), String> {
+        self.0.current_block = Some(block);
+        Ok(())
+    }
+
+    fn block_exists(&self, block: BasicBlockId) -> bool {
+        if let Some(ref func) = self.0.current_function {
+            func.blocks.contains_key(&block)
+        } else {
+            false
+        }
+    }
+}
 
 impl MirBuilder {
     /// Lower an if/else using a structured IfForm (header→then/else→merge).
@@ -178,15 +251,37 @@ impl MirBuilder {
                             );
                         }
 
-                        // 本番経路が有効な場合のみ success = true
+                        // Phase 61-4-F: 本番経路 - emit_toplevel_phis でPHI生成
                         if joinir_toplevel {
-                            joinir_success = true;
-                            // TODO: Phase 61-4-E 本番経路のPHI生成
-                            // 現時点では dry-run 的動作（フォールバック経路を使用）
+                            // IfShape 構築
+                            let if_shape = IfShape {
+                                cond_block: pre_branch_bb,
+                                then_block,
+                                else_block: Some(else_block),
+                                merge_block,
+                            };
+
+                            // PHI 生成
+                            let phi_count = {
+                                let mut ops = ToplevelOps(self);
+                                crate::mir::loop_builder::IfInLoopPhiEmitter::emit_toplevel_phis(
+                                    &phi_spec,
+                                    &pre_if_var_map,
+                                    &then_var_map_end,
+                                    else_var_map_end_opt.as_ref(),
+                                    &mut ops,
+                                    &if_shape,
+                                )?
+                            };
+
                             if joinir_dryrun {
-                                eprintln!("[Phase 61-4] ⚠️ Production path not yet implemented, using fallback");
+                                eprintln!(
+                                    "[Phase 61-4] ✅ Production path: {} PHIs generated via JoinIR",
+                                    phi_count
+                                );
                             }
-                            joinir_success = false; // フォールバック使用
+
+                            joinir_success = true;
                         }
                     }
                     None => {

src/mir/join_ir/lowering/mod.rs

@@ -157,6 +157,7 @@ pub fn try_lower_if_to_joinir(
         func.signature.name.starts_with("IfSelectTest.") ||
         func.signature.name.starts_with("IfSelectLocalTest.") || // Phase 33-10 test
         func.signature.name.starts_with("IfMergeTest.") ||
+        func.signature.name.starts_with("IfToplevelTest.") || // Phase 61-4: loop-outside if test
         func.signature.name.starts_with("Stage1JsonScannerTestBox.") || // Phase 33-5 test
 
         // Stage-1 rollout (env-controlled)