aisdk(): parallel tool results become separate tool messages, which breaks Gemini

Finding: In an external report against openai/openai-agents-js, the aisdk() adapter from @openai/agents-extensions (reported on 0.17.2, with the same code said to remain in 0.19.0) converts each function_call_result item into its own role 'tool' message. With Gemini 3.x through @ai-sdk/google-vertex 5.0.84 (@ai-sdk/google 4.0.72, ai 7, Node.js 24), the follow-up request reportedly fails whenever the model makes two or more parallel tool calls in one turn (https://github.com/openai/openai-agents-js/issues/2048). This is an external report; KFA has not reproduced it. Reported mechanism: the reporter says the AI SDK itself puts all tool results of one step into a single tool message. They say @ai-sdk/google maps each tool message to a separate user content, while Gemini requires the function response parts for a turn to be in one content and to match the number of function call parts. The issue paraphrases the resulting error as a function-response-count mismatch; no verbatim error text is supplied. The reporter also says Anthropic and Amazon Bedrock providers merge consecutive messages themselves, so the problem does not appear there. These are the reporter's claims; no maintainer has confirmed the cause in the supplied data (zero comments, comment fetch unavailable). Reproduction as reported: an Agent with a single get_weather tool, parallelToolCalls: true, model aisdk(vertex('gemini-3.1-pro-preview')), asked for the weather in two cities. The first model call returns two function calls and the follow-up request fails. The reporter says this is consistent whenever 2+ tool calls occur in one turn. Status: the issue is open. The only remedy in the sources is the reporter's proposed diff, which they say has run as a local patch in production for several months. It appends the new tool-result part to the previous message when that message is a role 'tool' message with array content, instead of pushing a new one (https://github.com/openai/openai-agents-js/issues/2048). No merged fix commit or released fix is cited, so fix status is unknown/not merged. The reporter notes each tool-result part keeps its own providerOptions, and suggests the provider-executed tool-result branch may need the same merge but has not tested it. Practical reading: if you use aisdk() with Gemini (direct or Vertex) and see follow-up failures only when parallel tool calls occur, this report is a candidate explanation. A temporary check is to see whether the failure disappears with a single tool call per turn; this is inference, not a source-stated test. Treat the patch as unreviewed third-party code, not a verified repair.