Complete shared denied-permission snapshot

Add the optional post-denial model turn for the shared multi-client replay snapshot so SDKs that wait for the final assistant message can replay deterministically.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

test/snapshots/multi_client/one_client_rejects_permission_and_both_see_the_result.yaml

@@ -23,3 +23,30 @@ conversations:
             function:
               name: view
               arguments: '{"path":"${workdir}/protected.txt"}'
+  - messages:
+      - role: system
+        content: ${system}
+      - role: user
+        content: Edit protected.txt and replace 'protected' with 'hacked'.
+      - role: assistant
+        content: I'll help you edit protected.txt to replace 'protected' with 'hacked'. Let me first view the file and then make
+          the change.
+        tool_calls:
+          - id: toolcall_0
+            type: function
+            function:
+              name: report_intent
+              arguments: '{"intent":"Editing protected.txt file"}'
+          - id: toolcall_1
+            type: function
+            function:
+              name: view
+              arguments: '{"path":"${workdir}/protected.txt"}'
+      - role: tool
+        tool_call_id: toolcall_0
+        content: Intent logged
+      - role: tool
+        tool_call_id: toolcall_1
+        content: Permission denied and could not request permission from user
+      - role: assistant
+        content: I don't have permission to view or edit protected.txt, so I can't make that change.