def create_stt(self, agent_info: AgentInfo):
    return stt.FallbackAdapter([
        _build_sarvam_stt_instance(self, agent_info),
        _build_azure_stt_instance(self, agent_info),
    ])

def _build_sarvam_stt_instance(provider: STTProvider, agent_info: AgentInfo):
    stt_details: STTDetails = agent_info.config.stt_details
    return sarvam.STT(
        model=agent_info.model_values.stt.model or provider.get_config_value('sarvam', 'model', ),
        language=stt_details.language or provider.get_config_value('sarvam', 'language', ),
        mode=stt_details.mode,
        prompt=stt_details.prompt or provider.get_config_value('sarvam', 'prompt', ),
        high_vad_sensitivity=stt_details.high_vad_sensitivity or provider.get_config_value(
            'sarvam', 'high_vad_sensitivity', ),
        sample_rate=stt_details.sample_rate or provider.get_config_value('sarvam', 'sample_rate', 'int'),
        flush_signal=stt_details.flush_signal or provider.get_config_value('sarvam', 'flush_signal', ),
        input_audio_codec=stt_details.input_audio_codec or provider.get_config_value('sarvam', 'input_audio_codec', ),
    )

def _build_azure_stt_instance(provider: STTProvider, agent_info: AgentInfo) -> azure_stt_1_3x.STT:
    stt_details: STTDetails = agent_info.config.stt_details
    profanity_option = AzureSTTProvider.get_profanity_option(
        stt_details.profanity or provider.get_config_value('azure', 'profanity', ))

    languages = stt_details.languages
    if languages is None:
        languages = []
    single_language = stt_details.language
    combined_languages = [
        lang.strip()
        for lang in (languages + ([single_language] if single_language else []))
        if lang and lang.strip()
    ]

    return azure_stt_1_3x.STT(
        speech_key=stt_details.speech_key or provider.get_config_value('azure', 'speech_key_env', 'env'),
        speech_region=stt_details.speech_region or provider.get_config_value('azure', 'speech_region_env', 'env'),
        speech_auth_token=stt_details.speech_auth_token or provider.get_config_value('azure', 'speech_auth_token', ),
        sample_rate=stt_details.sample_rate or provider.get_config_value('azure', 'sample_rate', 'int'),
        num_channels=stt_details.num_channels or provider.get_config_value('azure', 'num_channels', 'int'),
        segmentation_silence_timeout_ms=stt_details.segmentation_silence_timeout_ms or provider.get_config_value(
            'azure', 'segmentation_silence_timeout_ms', 'int'),
        segmentation_max_time_ms=stt_details.segmentation_max_time_ms or provider.get_config_value(
            'azure', 'segmentation_max_time_ms', 'int'),
        segmentation_strategy=stt_details.segmentation_strategy or provider.get_config_value(
            'azure', 'segmentation_strategy', ),
        language=combined_languages,
        profanity=profanity_option,
    )

import logging
from typing import List

logger = logging.getLogger(__name__)

def _is_valid_language(lang: str) -> bool:
    # replace with real validation (e.g., check against supported ISO codes)
    return bool(lang and len(lang) >= 2)

def create_stt(self, agent_info: AgentInfo):
    stt_details = agent_info.config.stt_details
    stt_instances: List[BaseSTT] = []

    # Try Sarvam first
    try:
        lang = stt_details.language or self.get_config_value('sarvam', 'language')
        if not _is_valid_language(lang):
            raise ValueError(f"invalid sarvam language: {lang!r}")

        sarvam_instance = _build_sarvam_stt_instance(self, agent_info)
        stt_instances.append(sarvam_instance)
        logger.info("Sarvam STT initialized")
    except Exception as e:
        logger.exception("Sarvam STT init failed, will try fallback: %s", e)

    # Then Azure
    try:
        # Validate at least one language for Azure if required
        azure_langs = (stt_details.languages or []) + ([stt_details.language] if stt_details.language else [])
        if azure_langs and not all(_is_valid_language(l) for l in azure_langs):
            raise ValueError(f"invalid azure languages: {azure_langs!r}")

        azure_instance = _build_azure_stt_instance(self, agent_info)
        stt_instances.append(azure_instance)
        logger.info("Azure STT initialized")
    except Exception as e:
        logger.exception("Azure STT init failed: %s", e)

    if not stt_instances:
        # No valid STT providers — handle gracefully (do not let exception crash session)
        logger.error("No STT providers available after validation. Proceeding without STT.")
        return None  # or return a NoOp STT implementation

    # Create FallbackAdapter with only valid instances
    return stt.FallbackAdapter(stt_instances)

_is_valid_language