Prevent message queue from draining when tool approvals are pending

[KaranJagtiani]

When the agent completes a stream that ends with a tool call requiring approval, the chat interface incorrectly auto-drains queued messages even though it's still waiting for user action. This causes queued messages to interrupt the approval flow, breaking the conversation state and creating race conditions.

Scope

• UI (ui/src/components/chat/ChatInterface.tsx):
  • Modify the queue-draining useEffect (currently around line 614-627) to check if there are any pending approvals before draining the queue.
  • Add a condition that prevents auto-drain when approvableTools.length > 0.
  • Ensure the effect has access to approvableTools by positioning it after the approvableTools memoized value definition.
  • Update the dependency array to include approvableTools.length.
• The fix should preserve existing queue behavior: messages should still drain automatically once approvals are resolved and the stream completes.

Acceptance criteria

• Queued messages remain in the queue when the agent is waiting for tool approval.
• Once an approval is given and the subsequent agent response completes (with no remaining pending approvals), the queue resumes draining normally.
• The "Submit now" feature for queued messages continues to work during approval wait states.
• No regressions to existing queue functionality (FIFO ordering, removal, immediate submission).
• Attach a screen recording showing the new behavior to demonstrate the fix.

How to test manually

1. Run the Engine, MCP server, and UI locally (see respective README files).
2. Start a conversation that triggers a tool call requiring approval (e.g., "Delete the nginx deployment in the default namespace").
3. While the agent is responding, type and submit another message — it should enter the queue.
4. Wait for the tool approval prompt to appear.
5. Verify that the queued message remains in the queue and does not auto-submit.
6. Approve or deny the tool call.
7. Wait for the agent's response to complete.
8. Verify that the queued message now auto-drains and sends.