fix(tts): surface post-cold-start streaming_call failures instead of dropping the delta - #3621

AgentScope Version

2.0.12dev (main @ 4acacb9)

Description

CosyVoiceModel.push() (realtime mode) silently drops the current text delta when streaming_call raises after the cold-start latch is set (src/agentscope/tts/_dashscope/_cosyvoice_model.py:286-291): the except branch returns TTSResponse(content=None) based on a recovery promise ("keep the cold-start buffer and flag intact so the next push retries it") that only holds during the cold-start phase. Once the latch is set the buffer is empty, so the failed delta exists only in _accumulated_text and is never sent — the synthesized speech silently misses words, with no error or log (#3620).

The surrounding code consistently chooses otherwise: the not self._connected guard right above raises, and _synthesize_realtime retries and eventually raises. #3535 built the cold-start failure handling this comment refers to — the post-cold-start path is its remaining gap.

Changes — the except branch now distinguishes the two phases:

• cold-start flush failure (not self._cold_start_done): unchanged — keep the buffer and flag intact so the next push retries the whole buffered text (fix(tts): keep CosyVoice cold-start buffer when the send fails #3535 behavior preserved);
• post-cold-start failure: raise, consistent with the _connected guard above — the caller still holds the text and can retry, instead of the delta vanishing from the synthesized speech.

How to test

New case in the existing CosyVoicePushTest (tests/tts_dashscope_test.py):

• test_push_after_cold_start_raises_on_send_failure — fails on main (the push returns TTSResponse(content=None) and the delta vanishes), passes with this fix;
• the existing cold-start failure test (test_push_keeps_cold_start_buffer_on_send_failure) is untouched and still passes, pinning the fix(tts): keep CosyVoice cold-start buffer when the send fails #3535 behavior.

python -m pytest tests/tts_dashscope_test.py
# 73 passed.

Fixes #3620

Checklist

• An issue has been created for this PR
• I have read the CONTRIBUTING.md
• Docstrings are in Google style
• Related documentation has been updated (e.g. links, examples, etc.) in documentation repository
• Code is ready for review