Allow SingleAgentVoiceWorkflow to receive Runner context #4635

Please read this first

• Have you read the docs? Yes.
• Have you searched for related issues and PRs? Yes.

Related: #819 documented this limitation and was later closed after the reporter worked around it by creating a custom VoiceWorkflowBase implementation. I could not find an existing PR that adds context support to SingleAgentVoiceWorkflow itself.

Describe the feature

SingleAgentVoiceWorkflow is the convenience path for a single-agent voice workflow, but its internal call is currently fixed to:

Runner.run_streamed(self._current_agent, self._input_history)

That means an agent that relies on normal Runner context cannot use the convenience workflow directly. Context-dependent instructions, tools, handoffs, and is_enabled predicates require users to copy the workflow implementation into a custom subclass just to pass context=....

A narrow API addition would be to accept an optional keyword-only context when constructing SingleAgentVoiceWorkflow and forward that same context to each internal Runner.run_streamed() call.

For example:

context = UserContext(user_id="user-123")
workflow = SingleAgentVoiceWorkflow(agent, context=context)
pipeline = VoicePipeline(workflow=workflow)

Desired semantics

1. Existing SingleAgentVoiceWorkflow(agent) and SingleAgentVoiceWorkflow(agent, callbacks) calls remain unchanged.
2. context= is optional and keyword-only.
3. The supplied context is forwarded to every streamed Runner turn, including later turns after the workflow updates its input history/current agent.
4. Context behavior remains the normal Runner behavior; the voice layer does not introduce a separate context wrapper or lifecycle.
5. Custom VoiceWorkflowBase implementations remain the supported path for broader per-turn Runner customization.

Non-goals

• no change to VoicePipeline.run() arguments;
• no new voice-specific context abstraction;
• no automatic copying or serialization of application context;
• no broader RunConfig, session, or conversation-state API in this change.

This keeps the convenience workflow useful for context-dependent agents without expanding the voice pipeline contract.