feat(joinir): L-2.2 Step-2 - Add Stage-B to VM bridge dispatch

Add Stage-B BodyExtractor and FuncScanner to JoinIR VM bridge dispatch:
- Import stageb_body and stageb_funcscanner lowering functions
- Add routing for StageBBodyExtractorBox.build_body_src/2
- Add routing for StageBFuncScannerBox.scan_all_boxes/1
- Add try_run_stageb_body() and try_run_stageb_funcscanner() (lowering verification only)

Also cleanup unused imports in funcscanner_trim.rs and stage1_using_resolver.rs

Note: Stage-B functions use lowering verification pattern (like Stage-1)
because ArrayBox/MapBox args are not yet supported in JoinValue.

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

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

src/mir/join_ir/lowering/funcscanner_trim.rs

@@ -48,8 +48,6 @@ use crate::mir::join_ir::{
     BinOpKind, CompareOp, ConstValue, JoinContId, JoinFuncId, JoinFunction, JoinInst, JoinModule,
     LoopExitShape, LoopHeaderShape, MirLikeInst,
 };
-use crate::mir::loop_form::LoopForm;
-use crate::mir::query::MirQuery;
 use crate::mir::ValueId;
 
 /// Phase 27.9: Toggle dispatcher for trim lowering

src/mir/join_ir/lowering/stage1_using_resolver.rs

@@ -47,8 +47,7 @@ use crate::mir::join_ir::lowering::common::{
 };
 use crate::mir::join_ir::lowering::value_id_ranges::stage1_using_resolver as vid;
 use crate::mir::join_ir::JoinModule;
-use crate::mir::loop_form::LoopForm;
-use crate::mir::query::{MirQuery, MirQueryBox};
+use crate::mir::query::MirQueryBox;
 
 /// Phase 27.12: Stage1UsingResolverBox.resolve_for_source の JoinIR lowering（public dispatcher）
 ///

src/mir/join_ir_vm_bridge_dispatch.rs

@@ -6,6 +6,8 @@
 //! 判定に差し替え可能な設計になっている。
 
 use crate::config::env::{joinir_experiment_enabled, joinir_vm_bridge_enabled};
+use crate::mir::join_ir::lowering::stageb_body::lower_stageb_body_to_joinir;
+use crate::mir::join_ir::lowering::stageb_funcscanner::lower_stageb_funcscanner_to_joinir;
 use crate::mir::join_ir::lowering::stage1_using_resolver::lower_stage1_usingresolver_to_joinir;
 use crate::mir::join_ir::{lower_funcscanner_trim_to_joinir, lower_skip_ws_to_joinir, JoinFuncId};
 use crate::mir::join_ir_ops::JoinValue;
@@ -78,6 +80,16 @@ pub fn try_run_joinir_vm_bridge(module: &MirModule, quiet_pipe: bool) -> bool {
         return try_run_stage1_usingresolver(module);
     }
 
+    // Stage-B BodyExtractor（まだ実行には対応せず、lowering 検証のみ）
+    if module.functions.contains_key("StageBBodyExtractorBox.build_body_src/2") {
+        return try_run_stageb_body(module);
+    }
+
+    // Stage-B FuncScanner（まだ実行には対応せず、lowering 検証のみ）
+    if module.functions.contains_key("StageBFuncScannerBox.scan_all_boxes/1") {
+        return try_run_stageb_funcscanner(module);
+    }
+
     false
 }
 
@@ -183,3 +195,61 @@ fn try_run_stage1_usingresolver(module: &MirModule) -> bool {
         }
     }
 }
+
+/// StageBBodyExtractorBox.build_body_src/2 用 JoinIR ブリッジ（検証のみ）
+///
+/// Note: ArrayBox/MapBox 引数がまだ JoinValue でサポートされていないため、
+/// lowering の検証のみ行い、実際の実行は通常 VM にフォールバックする。
+fn try_run_stageb_body(module: &MirModule) -> bool {
+    eprintln!(
+        "[joinir/vm_bridge] Attempting JoinIR path for StageBBodyExtractorBox.build_body_src"
+    );
+
+    match lower_stageb_body_to_joinir(module) {
+        Some(join_module) => {
+            eprintln!(
+                "[joinir/vm_bridge] ✅ Stage-B Body JoinIR module generated ({} functions)",
+                join_module.functions.len()
+            );
+            eprintln!(
+                "[joinir/vm_bridge] Note: ArrayBox/MapBox args not yet supported in JoinValue"
+            );
+            eprintln!("[joinir/vm_bridge] Falling back to normal VM path for actual execution");
+            false // 実行はまだサポートしていない
+        }
+        None => {
+            eprintln!("[joinir/vm_bridge] lower_stageb_body_to_joinir returned None");
+            eprintln!("[joinir/vm_bridge] Falling back to normal VM path");
+            false
+        }
+    }
+}
+
+/// StageBFuncScannerBox.scan_all_boxes/1 用 JoinIR ブリッジ（検証のみ）
+///
+/// Note: ArrayBox/MapBox 引数がまだ JoinValue でサポートされていないため、
+/// lowering の検証のみ行い、実際の実行は通常 VM にフォールバックする。
+fn try_run_stageb_funcscanner(module: &MirModule) -> bool {
+    eprintln!(
+        "[joinir/vm_bridge] Attempting JoinIR path for StageBFuncScannerBox.scan_all_boxes"
+    );
+
+    match lower_stageb_funcscanner_to_joinir(module) {
+        Some(join_module) => {
+            eprintln!(
+                "[joinir/vm_bridge] ✅ Stage-B FuncScanner JoinIR module generated ({} functions)",
+                join_module.functions.len()
+            );
+            eprintln!(
+                "[joinir/vm_bridge] Note: ArrayBox/MapBox args not yet supported in JoinValue"
+            );
+            eprintln!("[joinir/vm_bridge] Falling back to normal VM path for actual execution");
+            false // 実行はまだサポートしていない
+        }
+        None => {
+            eprintln!("[joinir/vm_bridge] lower_stageb_funcscanner_to_joinir returned None");
+            eprintln!("[joinir/vm_bridge] Falling back to normal VM path");
+            false
+        }
+    }
+}