fix(flows): stop after final preprocessing responses

[sylvesterkaczmarek]

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Link to Issue or Description of Change

• Closes Auth/confirmation resume ignores skip_summarization on re-executed tool response #4472

Auth and tool-confirmation resume processors can re-execute a paused tool during request preprocessing. When that tool response sets skip_summarization, the response is already final, but _run_one_step_async continued into another model call. The unwanted model response then replaced the tool response as the last event.

This change records whether preprocessing emitted a final response and returns after preprocessing completes. Non-final preprocessing events continue through the normal model path.

Testing Plan

• Added a regression test that yields a resumed function response with skip_summarization=True and fails if the model is called.
• Ran pytest -q tests/unittests/flows/llm_flows/test_base_llm_flow.py tests/unittests/flows/llm_flows/test_request_confirmation.py tests/unittests/auth/test_auth_preprocessor.py.
• Result: 129 passed.
• Ran all pre-commit hooks on the changed files.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my code.
• I have added a test that proves the fix.
• New and existing relevant unit tests pass locally.
• Formatting, linting, and repository compliance checks pass.