feat(phase32): L-2.1 Stage-1 UsingResolver JoinIR integration + cleanup

Phase 32 L-2.1 complete implementation:

1. Stage-1 UsingResolver main line JoinIR connection
   - CFG-based LoopForm construction for resolve_for_source/5
   - LoopToJoinLowerer integration with handwritten fallback
   - JSON snapshot tests 6/6 PASS

2. JoinIR/VM Bridge improvements
   - Simplified join_ir_vm_bridge.rs dispatch logic
   - Enhanced json.rs serialization
   - PHI core boxes cleanup (local_scope_inspector, loop_exit_liveness, loop_var_classifier)

3. Stage-1 CLI enhancements
   - Extended args.rs, groups.rs, mod.rs for new options
   - Improved stage1_bridge module (args, env, mod)
   - Updated stage1_cli.hako

4. MIR builder cleanup
   - Simplified if_form.rs control flow
   - Removed dead code from loop_builder.rs
   - Enhanced phi_merge.rs

5. Runner module updates
   - json_v0_bridge/lowering.rs improvements
   - dispatch.rs, selfhost.rs, modes/vm.rs cleanup

6. Documentation updates
   - CURRENT_TASK.md, AGENTS.md
   - Various docs/ updates

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

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

src/backend/mir_interpreter/mod.rs

@@ -316,6 +316,25 @@ impl MirInterpreter {
         Ok(ret.to_nyash_box())
     }
 
+    /// Execute a specific function with explicit arguments (bypasses entry discovery).
+    pub fn execute_function_with_args(
+        &mut self,
+        module: &MirModule,
+        func_name: &str,
+        args: &[VMValue],
+    ) -> Result<VMValue, VMError> {
+        // Snapshot functions for call resolution
+        self.functions = module.functions.clone();
+
+        let func = self
+            .functions
+            .get(func_name)
+            .ok_or_else(|| VMError::InvalidInstruction(format!("function not found: {}", func_name)))?
+            .clone();
+
+        self.exec_function_inner(&func, Some(args))
+    }
+
     fn execute_function(&mut self, func: &MirFunction) -> Result<VMValue, VMError> {
         self.exec_function_inner(func, None)
     }