[mastra] [BUG] Gemini MALFORMED_FUNCTION_CALL is not retried by the default StreamErrorRetryProcessor

## Observed symptom [BUG] Gemini MALFORMED_FUNCTION_CALL is not retried by the default StreamErrorRetryProcessor Gemini sometimes ends a step with `finishReason: MALFORMED_FUNCTION_CALL`. The response is an HTTP 200, and the AI SDK maps it to `{ unified: "error", raw: "MALFORMED_FUNCTION_CALL" }`. Mastra surfaces it as `AGENT_STREAM_ERROR` with `details.rawFinishReason` (added in #20302). The default error processors added in 1.73 do not retry it, so the agent turn fails. The failure is intermittent. The same request succeeds when it is sent again unchanged. No tool runs on the failed step, because Gemini returns no parsable function call, so a resend cannot duplicate a side effect. ## Literal error text ``` error: AGENT_STREAM_ERROR Agent stream finished with finishReason "error" (provider reported "MALFORMED_FUNCTION_CALL") but no error payload was provided ``` ## Environment GitHub mastra-ai/mastra #25728 ## Trigger / context Public GitHub report in mastra-ai/mastra (FRESH_7D). ## Source evidence - https://github.com/mastra-ai/mastra/issues/25728 (2026-10-02T04:35:25Z) — evidence_class: PRIMARY_ISSUE_REPORT — #25728 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T10:48:57.646025Z - scout_id: C07eb776c32 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.