diff --git a/src/google/adk/agents/invocation_context.py b/src/google/adk/agents/invocation_context.py
index 7ec28187998..3037b7f2dfa 100644
--- a/src/google/adk/agents/invocation_context.py
+++ b/src/google/adk/agents/invocation_context.py
@@ -203,6 +203,19 @@ class InvocationContext(BaseModel):
   None for non-workflow agents.
   """
 
+  _consumed_tool_confirmation_ids: set[str] = PrivateAttr(default_factory=set)
+  _tool_confirmation_consume_lock: asyncio.Lock = PrivateAttr(
+      default_factory=asyncio.Lock
+  )
+
+  async def _consume_tool_confirmation(self, function_call_id: str) -> bool:
+    """Atomically claim a confirmation so it can only resume a tool once."""
+    async with self._tool_confirmation_consume_lock:
+      if function_call_id in self._consumed_tool_confirmation_ids:
+        return False
+      self._consumed_tool_confirmation_ids.add(function_call_id)
+      return True
+
   agent_states: dict[str, dict[str, Any]] = Field(default_factory=dict)
   """The state of the agent for this invocation."""
 
diff --git a/src/google/adk/flows/llm_flows/tools/_confirmation.py b/src/google/adk/flows/llm_flows/tools/_confirmation.py
index 1debe440044..4c56b604adb 100644
--- a/src/google/adk/flows/llm_flows/tools/_confirmation.py
+++ b/src/google/adk/flows/llm_flows/tools/_confirmation.py
@@ -293,20 +293,13 @@ async def run_async(
 
     # Step 2: Drop confirmations that have already been consumed.
     #
-    # This must happen BEFORE resolving targets. The processor re-runs on every
-    # LLM step of the invocation, and the approval stays the last user event for
-    # the rest of the turn, so a confirmation the previous step already acted on
-    # is seen again here. Re-validating consumed state is not just wasted work:
-    # the session and the toolset have moved on since the approval, so the
-    # strict checks in `_resolve_confirmation_targets` can now legitimately fail
-    # and abort the invocation.
+    # This must happen BEFORE resolving targets. Persisted event history is the
+    # durable source of truth when a later run rebuilds InvocationContext.
     confirmation_to_original_fc_id = _map_confirmation_to_original_fc_ids(
         events, set(confirmations_by_fc_id.keys())
     )
     responded_fc_ids: set[str] = set()
-    for event in reversed(events):
-      if event.author == "user":
-        break
+    for event in events:
       for function_response in event.get_function_responses():
         if function_response.id:
           responded_fc_ids.add(function_response.id)
@@ -356,6 +349,26 @@ async def run_async(
     if not tools_to_resume_with_confirmation:
       return
 
+    claimed_ids = {
+        function_call_id
+        for function_call_id in tools_to_resume_with_confirmation
+        if await invocation_context._consume_tool_confirmation(function_call_id)
+    }
+    if not claimed_ids:
+      return
+    tools_to_resume_with_confirmation = {
+        function_call_id: confirmation
+        for function_call_id, confirmation in (
+            tools_to_resume_with_confirmation.items()
+        )
+        if function_call_id in claimed_ids
+    }
+    tools_to_resume_with_args = {
+        function_call_id: function_call
+        for function_call_id, function_call in tools_to_resume_with_args.items()
+        if function_call_id in claimed_ids
+    }
+
     # Step 4: Re-execute the confirmed tools.
     from .. import functions
 
diff --git a/tests/unittests/flows/llm_flows/tools/test_confirmation.py b/tests/unittests/flows/llm_flows/tools/test_confirmation.py
index 16cab223363..b4c15c09844 100644
--- a/tests/unittests/flows/llm_flows/tools/test_confirmation.py
+++ b/tests/unittests/flows/llm_flows/tools/test_confirmation.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import asyncio
 from unittest.mock import create_autospec
 from unittest.mock import patch
 
@@ -40,6 +41,22 @@ def mock_tool(param1: str):
   return f"Mock tool result with {param1}"
 
 
+@pytest.mark.asyncio
+async def test_tool_confirmation_claim_is_atomic():
+  """Only one concurrent resume may claim a function call confirmation."""
+  agent = LlmAgent(name="test_agent")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+
+  claims = await asyncio.gather(
+      invocation_context._consume_tool_confirmation(MOCK_FUNCTION_CALL_ID),
+      invocation_context._consume_tool_confirmation(MOCK_FUNCTION_CALL_ID),
+  )
+
+  assert sorted(claims) == [False, True]
+
+
 @pytest.mark.asyncio
 async def test_request_confirmation_processor_no_events():
   """Test that the processor returns None when there are no events."""