fix(plugins/sarvam): shorten TTS WS pool duration to 50s and refresh on get

[dvirarad]

Summary

Fixes #5681.

The Sarvam TTS plugin configures its WebSocket ConnectionPool with max_session_duration=3600 (1 hour) and mark_refreshed_on_get=False. Sarvam's server, however, closes idle WebSockets after 60 seconds, so the pool routinely hands out connections that are already dead, producing:

livekit.plugins.sarvam.log: Error in send task: Cannot write to closing transport
livekit.agents: failed to synthesize speech: Send task failed: Cannot write to closing transport, retrying in 0.1s

on nearly every turn after a conversation pause longer than 60 s, which translates to 2–6 seconds of silence per call.

Fix

Align the pool config with the other streaming-WS TTS plugins (Cartesia, Neuphonic, Murf, AsyncAI) that don't have this issue:

-    max_session_duration=3600,  # 1 hour
-    mark_refreshed_on_get=False,
+    # Sarvam's server closes the WebSocket after 60 s of inactivity, so the
+    # pool must recycle connections well before that threshold and treat each
+    # get() as a refresh.
+    max_session_duration=50,
+    mark_refreshed_on_get=True,

50s (instead of the 300s used by other plugins) keeps a safety margin below Sarvam's 60s idle cutoff. mark_refreshed_on_get=True ensures an actively used connection isn't recycled mid-conversation.

Out of scope (follow-up)

The issue also mentions Sarvam's {"type": "ping"} keepalive frame as the most robust long-term solution (similar to pipecat-ai/pipecat#3730). That's a larger change — happy to follow up with a dedicated PR adding a keepalive task if this minimal fix is accepted first.

Test plan

• Config matches the pattern used by Cartesia / Neuphonic / Murf / AsyncAI plugins in the same repo
• Sarvam-authenticated end-to-end test with a long-pause conversation — needs a Sarvam API key to run; if maintainers can run it I'd appreciate the confirmation, otherwise the analytical comparison with peer plugins is the strongest signal pre-merge

[devin-ai-integration]

✅ Devin Review: No Issues Found

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