test: Add MIR VM PoC tests for TypeOp and WeakRef instructions

- Add comprehensive tests for TypeOp (Check/Cast) instructions
- Add tests for WeakRef creation and upgrade behavior
- Add tests for legacy TypeCheck/Cast instruction compatibility
- Verify VM execution with new MIR instructions

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

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

src/tests/mir_vm_poc.rs

@@ -0,0 +1,100 @@
+//! PoC tests for MIR unified ops and VM execution
+
+#[cfg(test)]
+mod tests {
+    use crate::backend::vm::VM;
+    use crate::mir::{MirModule, MirFunction, FunctionSignature};
+    use crate::mir::{BasicBlockId, MirInstruction, ConstValue, EffectMask, Effect, MirType};
+
+    fn make_main() -> MirFunction {
+        let sig = FunctionSignature {
+            name: "main".to_string(),
+            params: vec![],
+            return_type: MirType::Void,
+            effects: EffectMask::PURE,
+        };
+        MirFunction::new(sig, BasicBlockId::new(0))
+    }
+
+    #[test]
+    fn vm_exec_typeop_check_and_cast() {
+        let mut func = make_main();
+        let bb = func.entry_block;
+
+        let v0 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: v0, value: ConstValue::Integer(42) });
+
+        let v1 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::TypeOp { dst: v1, op: crate::mir::TypeOpKind::Check, value: v0, ty: MirType::Integer });
+
+        // Print result (should be true)
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Print { value: v1, effects: EffectMask::IO });
+
+        // Cast (no-op for PoC semantics)
+        let v2 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::TypeOp { dst: v2, op: crate::mir::TypeOpKind::Cast, value: v0, ty: MirType::Integer });
+
+        // Return void
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Return { value: None });
+
+        let mut module = MirModule::new("test".to_string());
+        module.add_function(func);
+
+        let mut vm = VM::new();
+        let _ = vm.execute_module(&module).expect("VM should execute module");
+    }
+
+    #[test]
+    fn vm_exec_legacy_typecheck_cast() {
+        let mut func = make_main();
+        let bb = func.entry_block;
+
+        let v0 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: v0, value: ConstValue::Integer(7) });
+
+        let v1 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::TypeCheck { dst: v1, value: v0, expected_type: "IntegerBox".to_string() });
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Print { value: v1, effects: EffectMask::IO });
+
+        let v2 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Cast { dst: v2, value: v0, target_type: MirType::Integer });
+
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Return { value: None });
+
+        let mut module = MirModule::new("test".to_string());
+        module.add_function(func);
+
+        let mut vm = VM::new();
+        let _ = vm.execute_module(&module).expect("VM should execute module");
+    }
+
+    #[test]
+    fn vm_exec_unified_weakref_and_barrier() {
+        let mut func = make_main();
+        let bb = func.entry_block;
+
+        let v0 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: v0, value: ConstValue::Integer(1) });
+
+        let v1 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::WeakRef { dst: v1, op: crate::mir::WeakRefOp::New, value: v0 });
+
+        let v2 = func.next_value_id();
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::WeakRef { dst: v2, op: crate::mir::WeakRefOp::Load, value: v1 });
+
+        // Optional barriers (no-op semantics)
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Barrier { op: crate::mir::BarrierOp::Read, ptr: v2 });
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Barrier { op: crate::mir::BarrierOp::Write, ptr: v2 });
+
+        // Print loaded value
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Print { value: v2, effects: EffectMask::IO });
+
+        func.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Return { value: None });
+
+        let mut module = MirModule::new("test".to_string());
+        module.add_function(func);
+
+        let mut vm = VM::new();
+        let _ = vm.execute_module(&module).expect("VM should execute module");
+    }
+}

src/tests/mod.rs

@@ -1 +1,2 @@
-pub mod box_tests;
+pub mod box_tests;
+pub mod mir_vm_poc;