StreamingResponseAggregator fails to yield final non-partial event on tool calls, causing agent termination.

[TimKerre]

Bug Report

Describe the bug
In StreamingResponseAggregator, the logic responsible for closing a stream fails to yield a final non-partial event when a tool call is made. This happens because the Gemini API often sends a final chunk without a candidates array. The aggregator sees the empty array and returns early, causing the llm_agent.js loop to detect an unexpected partial event and terminate the agent execution prematurely.

To Reproduce
Steps to reproduce the behavior:

1. Use @google/adk version 1.0.0.
2. Configure an agent with any functional tool (e.g., a local math function or an MCP server).
3. Send a prompt that triggers that tool.
4. The agent logs: "The last event is partial, which is not expected." and stops before executing the tool.

Expected behavior
The StreamingResponseAggregator.close() method should return a finalized event with partial: false and the complete accumulated partsSequence, even if the final chunk lacks a candidates array. This allows the agent loop to continue and execute the tool.

Screenshots
N/A

Desktop (please complete the following information):

• OS: [macOS]
• TS version/environment: Node.js v22
• ADK version: 1.0.0