diff --git a/crates/cognitive-shader-driver/src/attention_mask.rs b/crates/cognitive-shader-driver/src/attention_mask.rs
index 58f4c6d4..03373875 100644
--- a/crates/cognitive-shader-driver/src/attention_mask.rs
+++ b/crates/cognitive-shader-driver/src/attention_mask.rs
@@ -8,13 +8,12 @@
 //! `AttentionMaskSoA` is `!Send` by design (non-atomic interior mutation).
 //! Callers that need cross-thread access must wrap in `tokio::sync::Mutex`.
 //!
-//! # Registration
-//! This file is intentionally NOT registered in `lib.rs`. The main thread
-//! adds `pub mod attention_mask;` after the sprint-12 fleet completes.
+//! # MailboxId
+//! Imports the canonical `MailboxId` alias from
+//! `lance_graph_contract::collapse_gate` (also re-exported here for ergonomic
+//! `use cognitive_shader_driver::attention_mask::MailboxId` access).
 
-/// Re-export the canonical `MailboxId` alias so this module compiles
-/// standalone without an explicit `--extern` flag.
-pub type MailboxId = u32;
+pub use lance_graph_contract::collapse_gate::MailboxId;
 
 // ── SoA row ──────────────────────────────────────────────────────────────────
 
diff --git a/crates/cognitive-shader-driver/src/attention_mask_actor.rs b/crates/cognitive-shader-driver/src/attention_mask_actor.rs
index 14a540ff..8e2a7a8e 100644
--- a/crates/cognitive-shader-driver/src/attention_mask_actor.rs
+++ b/crates/cognitive-shader-driver/src/attention_mask_actor.rs
@@ -33,6 +33,25 @@ pub trait AttentionMaskBackend {
     fn is_active(&self, mailbox_id: MailboxId) -> bool;
 }
 
+/// Production-backend impl: wires the sibling `attention_mask::AttentionMaskSoA`
+/// into the actor without forcing downstream consumers to write a newtype
+/// (Rust orphan rules would block them — neither the trait nor the SoA is
+/// theirs). Per codex P2 review on PR #388.
+impl AttentionMaskBackend for crate::attention_mask::AttentionMaskSoA {
+    fn touch(&mut self, mailbox_id: MailboxId, w_slot: u8) -> bool {
+        crate::attention_mask::AttentionMaskSoA::touch(self, mailbox_id, w_slot)
+    }
+    fn evict_lru(&mut self) -> Option<MailboxId> {
+        crate::attention_mask::AttentionMaskSoA::evict_lru(self)
+    }
+    fn tick(&mut self) {
+        crate::attention_mask::AttentionMaskSoA::tick(self)
+    }
+    fn is_active(&self, mailbox_id: MailboxId) -> bool {
+        crate::attention_mask::AttentionMaskSoA::is_active(self, mailbox_id)
+    }
+}
+
 pub struct AttentionMaskActor<B: AttentionMaskBackend> {
     inner: B,
     pending_evictions: Vec<MailboxId>,