Bug: openai-completions mapStopReason does not handle finish_reason "error"

[machinekoder]

Bug

mapStopReason() in packages/ai/src/providers/openai-completions.ts does not handle the "error" finish reason. When an OpenAI-compatible proxy (e.g. GitHub Copilot) returns finish_reason: "error", the function falls into the default case and throws:

Error: Unhandled stop reason: error

This aborts the entire agent turn — tool calls emitted by the model are logged but never executed, and no tool result is returned to the model. The session becomes unrecoverable.

Affected code

packages/ai/src/providers/openai-completions.ts — mapStopReason():

function mapStopReason(reason: ChatCompletionChunk.Choice["finish_reason"]): StopReason {
    if (reason === null) return "stop";
    switch (reason) {
        case "stop":           return "stop";
        case "length":         return "length";
        case "function_call":
        case "tool_calls":     return "toolUse";
        case "content_filter": return "error";
        default: {
            const _exhaustive: never = reason;
            throw new Error(`Unhandled stop reason: ${_exhaustive}`);
            //                                       ^^^ receives "error"
        }
    }
}

Reproduction

1. Use openai-completions provider with github-copilot pointing at gemini-3-flash-preview
2. Send a multi-turn conversation with tool calls
3. Occasionally Gemini returns finish_reason: "error" (likely mapping from MALFORMED_FUNCTION_CALL or a transient issue)
4. The agent crashes with Unhandled stop reason: error

Observed in two separate OpenClaw agent sessions (@mariozechner/pi-ai v0.52.12).

Suggested fix

Add case "error" to the switch — same pattern the Google and Anthropic providers already use:

case "content_filter":
case "error":
    return "error";

The google-shared.ts and anthropic.ts providers both correctly map their respective error finish reasons to "error". The openai-completions provider is the only one missing this case.