STTMuteFilter for function call does not work

[Regan17]

pipecat version

0.0.91

Python version

3.11

Operating System

Windows 11

Issue description

Problem Description

I'm trying to implement STTMuteFilter with FUNCTION_CALL strategy to mute user STT input during function execution, but it's not working as expected.

Configuration

I've configured STTMuteFilter as follows:

stt_mute_filter = STTMuteFilter(
    config=STTMuteConfig(
        strategies={
            STTMuteStrategy.FIRST_SPEECH,
            STTMuteStrategy.FUNCTION_CALL,
        }
    )
)

pipeline = Pipeline([
    transport.input(),
    stt_service,
    stt_mute_filter,
    context_aggregator.user(),
    llm,  # OpenAILLMService
    ...
])

In the logs you can check that it unmutes immediately when it mutes for a function call. Its working fine for FIRST_SPEECH though

Reproduction steps

I've configured STTMuteFilter as follows:

stt_mute_filter = STTMuteFilter(
    config=STTMuteConfig(
        strategies={
            STTMuteStrategy.FIRST_SPEECH,
            STTMuteStrategy.FUNCTION_CALL,
        }
    )
)

pipeline = Pipeline([
    transport.input(),
    stt_service,
    stt_mute_filter,
    context_aggregator.user(),
    llm,  # OpenAILLMService
    ...
])

### Expected behavior

According to the documentation, when `FUNCTION_CALL` strategy is enabled, `STTMuteFilter` should:
1. Mute STT when it receives `FunctionCallInProgressFrame`
2. Unmute STT when it receives `FunctionCallResultFrame`

### Actual behavior

Function muting is not happening. When functions are called:
- STT continues to process user input during function execution
- No muting occurs, leading to interruptions


### Logs

```shell
2025-10-31T14:44:12.441+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - > TranscriptLogger: MetricsFrame#17
2025-10-31T14:44:12.454+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - > TranscriptLogger: FunctionCallsStartedFrame#0
2025-10-31T14:44:12.459+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - > TranscriptLogger: MetricsFrame#18
2025-10-31T14:44:12.462+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - < STT Logger: FunctionCallsStartedFrame#1
**2025-10-31T14:44:12.464+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - STTMuteFilter muting
2025-10-31T14:44:12.466+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - STTMuteFilter unmuting**
2025-10-31T14:44:12.478+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - > TranscriptLogger: FunctionCallInProgressFrame#0
2025-10-31T14:44:12.481+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - > TranscriptLogger: FunctionCallResultFrame#0
2025-10-31T14:44:12.485+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - < STT Logger: FunctionCallInProgressFrame#1
2025-10-31T14:44:12.490+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - < STT Logger: STTMuteFrame#4
2025-10-31T14:44:12.492+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - < STT Logger: FunctionCallResultFrame#1
2025-10-31T14:44:12.492+0530 - DEBUG - CA9690e2f0fb1d4c5e24a348a8010900f2 - < STT Logger: STTMuteFrame#6