dita_v2+adapters: phantom-position root-cause fixes (UV audit §8)

bingx_direct.submit_intent: (1) empty/orderId-less ack (VST offline-symbol
hole: code==0 + empty data) -> REJECTED, never fabricate fill from
target_size; (2) honor upstream u- client id (intent.metadata
promo_client_id/client_order_id) over self-minted p- id.
rust_backend: EXIT asset-mismatch guard both sync+async paths — EXIT for
asset X while slot holds Y -> NO_OPEN_POSITION/EXIT_ASSET_MISMATCH instead
of asset-blind close (THETA 76bbf8ee cross-slot contamination).
9 regression tests, mutation-RED verified (guard flip).

prod/clean_arch/dita_v2/rust_backend.py

@@ -761,6 +761,36 @@ class ExecutionKernel:
                     control=self.control,
                 )
 
+    def _exit_asset_mismatch_outcome(self, intent: KernelIntent) -> Optional[KernelOutcome]:
+        """UV-FIX 2026-07-11: an EXIT must name the asset its slot holds.
+
+        All UV promotion intents share slot 0. During the 2026-07-10/11
+        phantom-pair incident, an EXIT for asset X arriving while the slot
+        held asset Y was accepted asset-blind — closing Y's venue position
+        and orphaning Y's own later exit (NO_OPEN_POSITION). Reject the
+        mismatch at the kernel boundary instead.
+        """
+        if intent.action != KernelCommandType.EXIT:
+            return None
+        slot = self._get_slot(int(intent.slot_id))
+        open_asset = str(getattr(slot, "asset", "") or "")
+        if slot.is_open() and open_asset and open_asset != intent.asset:
+            return KernelOutcome(
+                accepted=False,
+                slot_id=int(intent.slot_id),
+                trade_id=intent.trade_id,
+                state=slot.fsm_state,
+                diagnostic_code=KernelDiagnosticCode.NO_OPEN_POSITION,
+                severity=KernelSeverity.WARNING,
+                details={
+                    "reason": "EXIT_ASSET_MISMATCH",
+                    "slot_asset": open_asset,
+                    "intent_asset": intent.asset,
+                    "intent_id": intent.intent_id,
+                },
+            )
+        return None
+
     def process_intent(self, intent: KernelIntent) -> KernelOutcome:
         self.zinc_plane.publish_intent(intent)
         if not (0 <= int(intent.slot_id) < self.max_slots):
@@ -795,6 +825,9 @@ class ExecutionKernel:
                     "asset": intent.asset,
                 },
             )
+        _mismatch = self._exit_asset_mismatch_outcome(intent)
+        if _mismatch is not None:
+            return _mismatch
         payload = _intent_to_payload(intent)
         result = _get_rust().process_intent(
             self._backend,
@@ -943,6 +976,9 @@ class ExecutionKernel:
                 details={"reason": "INVALID_INTENT", "field": name, "value": str(value),
                          "intent_id": intent.intent_id, "action": intent.action.value, "asset": intent.asset},
             )
+        _mismatch = self._exit_asset_mismatch_outcome(intent)
+        if _mismatch is not None:
+            return _mismatch
         # ── Rust FSM (sync, atomic, μs-fast — no await here) ─────────────────
         payload = _intent_to_payload(intent)
         result = _get_rust().process_intent(