test(v2): skip stale_detection_misses_content_only_out_of_band_mutation under Miri

Author: abishekk92

lang-v2/tests/borsh_exit_semantics.rs

@@ -107,6 +107,15 @@ fn exit_writes_modified_in_memory_state_to_guard() {
 // (pre-mutation state) and clobbers the external change.
 
 #[test]
+// Simulates out-of-band data mutation while `BorshAccount` holds a live
+// `RefMut<[u8]>` from `try_borrow_mut`. The real-world scenario (SVM host
+// writes during a CPI) happens outside Rust's aliasing model — no Rust
+// code performs the concurrent write — so Tree Borrows has no way to
+// represent it. The Rust-side simulation is inherently UB and Miri
+// correctly rejects it. Covered under regular `cargo test`.
+#[cfg_attr(miri, ignore = "simulates external mutation by violating Rust's \
+    exclusive-borrow invariant — inexpressible under Tree Borrows; covered \
+    under cargo test")]
 fn stale_detection_misses_content_only_out_of_band_mutation() {
     let mut buf = AccountBuffer::<256>::new();
     setup_counter_buf(&mut buf, 42);