When the LLM returned zero text tokens (e.g. it was interrupted before producing
tokens or about to push tokens), push_aggregation() returned an empty string and
on_assistant_turn_stopped was never emitted. This left consumers waiting for an
event that would never arrive.
Now on_assistant_turn_stopped always fires, with an empty content string when
the LLM produced no text tokens.
Fixes#4292
Add tests for LLMRunFrame, LLMMessagesAppendFrame, LLMMessagesUpdateFrame,
and LLMMessagesTransformFrame sent upstream to LLMAssistantAggregator,
mirroring the existing LLMUserAggregator downstream tests. Add
frames_to_send_direction param to run_test helper to support this.
The previous approach required the caller to directly grab a reference to the context object, grab a "snapshot" of its messages *at that point in time*, transform the messages, and then push an `LLMMessagesUpdateFrame` with the transformed messages. This approach can lead to problems: what if there had already been a change to the context queued in the pipeline? The transformed messages would simply overwrite it without consideration.
Turn completion instructions were being injected as a system message in
the LLM context, which caused warning spam when system_instruction was
also set, did not persist across full context updates, and broke LLMs
that do not support consecutive system messages.
Instead, compose the turn completion instructions into the LLM service
system_instruction field. This is managed via _base_system_instruction
which stores the original value for restoration when turn completion is
disabled.
When filter_incomplete_user_turns is enabled and an LLMMessagesUpdateFrame
replaces the context via set_messages(), the turn completion instructions
system message was lost. This caused the LLM to stop emitting turn
completion markers. Re-inject the instructions after set_messages() to
fix this.
These frames were falling through to the else branch and being pushed
downstream, unlike TranscriptionFrame which is explicitly consumed.
This aligns with how the assistant aggregator already filters them.
Refactor TranscriptionUserTurnStopStrategy and TurnAnalyzerUserTurnStopStrategy
to use VADUserStoppedSpeakingFrame as the ground truth for when speech ended,
rather than triggering timeouts from transcription frames.
