fix: improve cancellation test to wait for tool execution before cancelling

Co-authored-by: SteveSandersonMS <1101362+SteveSandersonMS@users.noreply.github.com>

Author: Copilot

dotnet/test/SessionTests.cs

@@ -408,16 +408,23 @@ public async Task SendAndWait_Throws_OperationCanceledException_When_Token_Cance
     {
         var session = await Client.CreateSessionAsync();
 
+        // Set up wait for tool execution to start BEFORE sending
+        var toolStartTask = TestHelper.GetNextEventOfTypeAsync<ToolExecutionStartEvent>(session);
+
         using var cts = new CancellationTokenSource();
 
-        // Cancel before any response can arrive
+        // Start SendAndWaitAsync - don't await it yet
         var sendTask = session.SendAndWaitAsync(
-            new MessageOptions { Prompt = "Run 'sleep 2 && echo done'" },
+            new MessageOptions { Prompt = "run the shell command 'sleep 10' (note this works on both bash and PowerShell)" },
             cancellationToken: cts.Token);
 
+        // Wait for the tool to begin executing before cancelling
+        await toolStartTask;
+
+        // Cancel the token
         cts.Cancel();
 
-        await Assert.ThrowsAsync<OperationCanceledException>(() => sendTask);
+        await Assert.ThrowsAnyAsync<OperationCanceledException>(() => sendTask);
     }
 
     [Fact]

test/snapshots/session/sendandwait_throws_operationcanceledexception_when_token_cancelled.yaml

@@ -0,0 +1,24 @@
+models:
+  - claude-sonnet-4.5
+conversations:
+  - messages:
+      - role: system
+        content: ${system}
+      - role: user
+        content: run the shell command 'sleep 10' (note this works on both bash and PowerShell)
+      - role: assistant
+        content: I'll run the sleep command for 10 seconds.
+      - role: assistant
+        tool_calls:
+          - id: toolcall_0
+            type: function
+            function:
+              name: report_intent
+              arguments: '{"intent":"Running sleep command"}'
+      - role: assistant
+        tool_calls:
+          - id: toolcall_1
+            type: function
+            function:
+              name: ${shell}
+              arguments: '{"command":"sleep 10","description":"Run sleep 10 command","mode":"sync","initial_wait":15}'