diff --git a/rampart/attacks/_xpia.py b/rampart/attacks/_xpia.py
index d7746365..245f33c7 100644
--- a/rampart/attacks/_xpia.py
+++ b/rampart/attacks/_xpia.py
@@ -160,13 +160,28 @@ async def _activate_handles_async(
     ) -> None:
         """Activate all injection handles and wait for readiness.
 
+        Handle ``__aenter__`` runs concurrently via ``asyncio.gather`` with
+        ``return_exceptions=True`` so a failing sibling does not cancel
+        others mid-entry.  That lets successful handles finish
+        ``enter_async_context`` and register ``__aexit__`` cleanup before
+        the first error is re-raised.  ``TaskGroup`` would cancel remaining
+        entries and could orphan remote payloads that were created but not
+        yet registered on the exit stack.
+
         Args:
             stack (AsyncExitStack): The exit stack managing cleanup.
         """
-        for handle in self._handles:
-            await stack.enter_async_context(handle)
+        # Concurrent context entry (network uploads); non-cancelling so
+        # successful siblings still register cleanup on the exit stack.
+        results = await asyncio.gather(
+            *(stack.enter_async_context(handle) for handle in self._handles),
+            return_exceptions=True,
+        )
+        errors = [result for result in results if isinstance(result, BaseException)]
+        if errors:
+            raise errors[0]
 
-        # Concurrent: total = max of all wait times
+        # Concurrent readiness wait (indexing delays)
         async with asyncio.TaskGroup() as tg:
             for handle in self._handles:
                 tg.create_task(handle.wait_until_ready_async())
diff --git a/tests/unit/attacks/test_xpia.py b/tests/unit/attacks/test_xpia.py
index c932e327..96fbad66 100644
--- a/tests/unit/attacks/test_xpia.py
+++ b/tests/unit/attacks/test_xpia.py
@@ -3,6 +3,7 @@
 
 from __future__ import annotations
 
+import asyncio
 from unittest.mock import AsyncMock
 
 from rampart.attacks import Attacks
@@ -219,6 +220,49 @@ async def test_handle_activation_failure_async(self) -> None:
         assert result.status is SafetyStatus.ERROR
         assert "SharePoint 503" in result.summary
 
+    async def test_partial_activation_failure_still_cleans_up_siblings_async(
+        self,
+    ) -> None:
+        """A slow successful sibling must register cleanup even if another fails.
+
+        Concurrent activation uses gather(return_exceptions=True) so a
+        failing handle does not cancel siblings mid-__aenter__.
+        """
+        entered = asyncio.Event()
+
+        async def slow_success_aenter_async(
+            *_args: object,
+            **_kwargs: object,
+        ) -> AsyncMock:
+            entered.set()
+            await asyncio.sleep(0.05)
+            return slow
+
+        async def fast_fail_aenter_async(
+            *_args: object,
+            **_kwargs: object,
+        ) -> AsyncMock:
+            await entered.wait()
+            raise InfrastructureError("SharePoint 503")
+
+        slow = _mock_handle(surface_name="Exchange")
+        slow.__aenter__.side_effect = slow_success_aenter_async
+        failing = _mock_handle(surface_name="SharePoint")
+        failing.__aenter__.side_effect = fast_fail_aenter_async
+
+        result = await Attacks.xpia(
+            inject=[slow, failing],
+            trigger="Summarize Q3",
+            evaluator=_mock_evaluator(EvalOutcome.DETECTED),
+        ).execute_async(adapter=_adapter())
+
+        assert result.status is SafetyStatus.ERROR
+        assert "SharePoint 503" in result.summary
+        slow.__aenter__.assert_awaited_once()
+        failing.__aenter__.assert_awaited_once()
+        # Successful sibling registered on the exit stack and is cleaned up.
+        slow.__aexit__.assert_awaited_once()
+
     async def test_session_creation_failure_async(self) -> None:
         adapter = AsyncMock()
         adapter.create_session_async.side_effect = InfrastructureError(