[Bug]:HarnessAgent subagent task_output may be interrupted by default tool execution timeout

**Describe the bug**

When `HarnessAgent` enables subagent orchestration, the `task_output` tool supports blocking up to 10 minutes via its `timeout` parameter. However, the default tool execution configuration (`ExecutionConfig.TOOL_DEFAULTS`) times out after 5 minutes.

As a result, a long-running `task_output(block=true, timeout=600000)` call may be interrupted by the framework-level tool timeout before the task output wait reaches its own maximum timeout.

**To Reproduce**

1. Create a `HarnessAgent` with subagents enabled and no custom `toolExecutionConfig`.
2. Spawn a background subagent task that takes longer than 5 minutes but less than 10 minutes.
3. Call `task_output` with `block=true` and `timeout=600000`.
4. Observe that the tool execution may fail after about 5 minutes.

Example error:

```text
Tool execution failed: Tool execution timeout after PT5M