Fix agent.test.ts test suite failures

[hughlv]

Fixed a test suite issue by updating the tools API mock logic in src/__tests__/agent.test.ts.

• Replaced old buildExecutorTool test expectations with captureSessionTool and sendToSessionTool matching updated dependencies.
• Added steps: [] to the mocked return value for generateText and mocked stepCountIs helper so that the tests execute properly.

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PR created automatically by Jules for task 9128546850376396753 started by @hughlv

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