fix: preserve skip_tts flag when frames pass through LLM services (simple fix)

[jamsea]

Problem

When sending an LLMTextFrame with skip_tts=True through an LLMSwitcher (or any LLM service), the frame exits with skip_tts=False. This happens because the LLMService.push_frame() override unconditionally sets frame.skip_tts = self._skip_tts, overwriting any value already set on the frame.

This bug was introduced in commit 16f57be72cec9f718ab1d42df258baac82b39f96.

Solution

This PR implements a simple, minimal fix: only set skip_tts=True when self._skip_tts is True, rather than unconditionally overwriting the value:

if isinstance(frame, (LLMTextFrame, LLMFullResponseStartFrame, LLMFullResponseEndFrame)):
    if self._skip_tts:
        frame.skip_tts = True

How it works

Frame's skip_tts	Service's _skip_tts	Result
False (default)	False (default)	False (unchanged)
False (default)	True	True (set by service)
True (explicit)	False (default)	True (preserved) ✅
True (explicit)	True	True (unchanged)

Trade-offs

This fix still modifies frames after creation, which isn't ideal for Pipecat's architecture. However, it's a minimal change that fixes the bug without requiring updates to all LLM service implementations.

Alternative: Architectural Fix

For a more architecturally pure solution that sets skip_tts at frame creation time (no frame mutation), see #3160. That approach:

• Makes skip_tts an init parameter on frames
• Updates all LLM services to pass skip_tts=self._get_skip_tts() when creating frames
• Removes the push_frame() override entirely

Choose this PR for a quick fix, or #3160 for a cleaner long-term solution.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/pipecat/services/llm_service.py	0.00%	2 Missing :warning:

Files with missing lines	Coverage Δ
src/pipecat/services/llm_service.py	38.88% <0.00%> (-0.20%)	:arrow_down:

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[aconchillo]

Closing. This was merged in #3168