[hhugo-gradium]

Summary

Smaller fixes in the Gradium STT stream, each its own commit.

• Interim transcripts carried one word instead of the partial utterance. Each text piece from the server was emitted as its own INTERIM_TRANSCRIPT. The agent treats an interim as the whole current partial: it replaces the previous one for live captions, and when the final transcript is late it becomes the user's turn text. One-word interims made captions flicker and could hand the LLM only the last word. The stream now emits the joined buffer of the current utterance, with the utterance's start time, on both interim and final events.

• vad_bucket=0 disabled end-of-turn detection. The option was tested for truthiness, so selecting bucket 0 (the 0.5 s horizon) meant no FINAL_TRANSCRIPT was ever emitted. Only None means disabled.

• No connect timeout. ws_connect ran under the shared aiohttp session's default of five minutes, so a hung handshake blocked the stream for minutes and conn_options.timeout was never applied. The connect is wrapped in asyncio.wait_for, and timeouts and handshake failures (401, 402, …) are mapped to APITimeoutError and APIStatusError so the base class retry rules apply instead of a raw aiohttp exception.

• update_options reconnected and lost the utterance in progress. Changing buffer_size_seconds set the reconnect event; the receive task was cancelled without finalizing, so the words buffered so far were dropped (live, an update mid-sentence lost the first half of the transcript). Nothing update_options changes is read by the live session, so the stream now keeps its socket, and the reconnect loop that only this path drove is gone; the base class already retries a failed session.

• Websocket lifecycle hardening, matching the Deepgram, AssemblyAI and Soniox plugins: a 30 s heartbeat so a dead socket is noticed, transport ERROR frames and failed audio writes surface as retryable connection errors instead of raw aiohttp exceptions, a text frame without start_s no longer corrupts the turn, and handshake failures of any kind map to the base class error types.

Testing

• tests/test_plugin_gradium_stt.py: nine tests on the fake socket from the previous PR, one per fix; each fails without its commit. 19 tests in the module.
• ruff, ruff format --check and mypy --strict clean on the plugin.
• Live against api.gradium.ai with the repository's 46 s speech sample: 122 interims, the longest 148 words, one final transcript.

Stacked on #7870

The diff includes its commits until it merges; the last three commits are this PR. The connect-timeout commit touches the same two lines of _connect_ws as #7815 (x-api-source), so whichever lands second needs a one-line rebase.

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