fix(vmbc): restore metadata-reserved root locals

Author: fffonion

src/vmbc.rs

@@ -322,6 +322,26 @@ pub fn decode_program(bytes: &[u8]) -> Result<Program, WireError> {
     program.function_regions = function_regions;
     program.root_callable_bindings = root_callable_bindings;
     program.exported_callables = exported_callables;
+    let type_map_local_count = program
+        .type_map
+        .as_ref()
+        .map_or(0, |type_map| type_map.local_types.len());
+    let callable_local_count = program
+        .root_callable_bindings
+        .iter()
+        .map(|binding| binding.local_slot as usize + 1)
+        .chain(
+            program
+                .exported_callables
+                .iter()
+                .map(|exported| exported.local_slot as usize + 1),
+        )
+        .max()
+        .unwrap_or(0);
+    program.local_count = program
+        .local_count
+        .max(type_map_local_count)
+        .max(callable_local_count);
     Ok(program)
 }
 

tests/wire/wire_tests.rs

@@ -65,6 +65,25 @@ fn wire_roundtrip_preserves_constants_and_code() {
     assert_eq!(decoded.type_map, program.type_map);
 }
 
+#[test]
+fn wire_roundtrip_recovers_locals_reserved_by_type_metadata() {
+    let local_count = 8;
+    let program = Program::new(Vec::new(), vec![vm::OpCode::Ret as u8])
+        .with_local_count(local_count)
+        .with_type_map(TypeMap {
+            strict_types: true,
+            local_types: vec![ValueType::Unknown; local_count],
+            local_schemas: vec![None; local_count],
+            callable_slots: vec![false; local_count],
+            optional_slots: vec![false; local_count],
+            operand_types: HashMap::new(),
+        });
+
+    let encoded = encode_program(&program).expect("encode reserved locals");
+    let decoded = decode_program(&encoded).expect("decode reserved locals");
+    assert_eq!(decoded.local_count, local_count);
+}
+
 #[test]
 fn decode_rejects_invalid_magic_version_and_truncation() {
     let program = Program::new(vec![Value::Int(7)], vec![0x01]);