fix: verify caller_program_id in program output

test_program_methods/guest/src/bin/malicious_caller_program_id.rs

@@ -0,0 +1,34 @@
+use nssa_core::program::{
+    AccountPostState, DEFAULT_PROGRAM_ID, ProgramInput, ProgramOutput, read_nssa_inputs,
+};
+
+type Instruction = ();
+
+fn main() {
+    let (
+        ProgramInput {
+            self_program_id,
+            caller_program_id: _, // ignore the actual caller
+            pre_states,
+            instruction: (),
+        },
+        instruction_words,
+    ) = read_nssa_inputs::<Instruction>();
+
+    let post_states = pre_states
+        .iter()
+        .map(|a| AccountPostState::new(a.account.clone()))
+        .collect();
+
+    // Deliberately output wrong caller_program_id.
+    // A real caller_program_id is None for a top-level call, so we spoof Some(DEFAULT_PROGRAM_ID)
+    // to simulate a program claiming it was invoked by another program when it was not.
+    ProgramOutput::new(
+        self_program_id,
+        Some(DEFAULT_PROGRAM_ID), // WRONG: should be None for a top-level call
+        instruction_words,
+        pre_states,
+        post_states,
+    )
+    .write();
+}