fix(opencode): normalize Muse Free tool choice

OpenCode Free returns HTTP 400 for muse-spark-1.3-contributor-free when tool_choice is non-auto. Declare forceAutoToolChoiceModels quirk and normalize explicit tool_choice to auto.

open-sse/executors/opencode.js

@@ -411,6 +411,11 @@ export class OpenCodeExecutor extends BaseExecutor {
   transformRequest(model, body, stream, credentials) {
     if (body && typeof body === "object" && model && !body.model) body.model = model;
     if (isResponsesModel(model || body?.model) && body && typeof body === "object") {
+      // ponytail: chỉ model đã xác nhận auto-only; mở allowlist khi có bằng chứng.
+      if ("tool_choice" in body && body.tool_choice !== "auto"
+        && this.config.quirks?.forceAutoToolChoiceModels?.includes(baseModelId(model))) {
+        body.tool_choice = "auto";
+      }
       const normalized = normalizeResponsesInput(body.input);
       if (normalized) body.input = normalized;
       if (!Array.isArray(body.input) || body.input.length === 0) {

open-sse/providers/registry/opencode.js

@@ -18,6 +18,9 @@ export default {
       "x-opencode-client": "desktop",
     },
     noAuth: true,
+    quirks: {
+      forceAutoToolChoiceModels: ["muse-spark-1.3-contributor-free"],
+    },
   },
   models: [
     // Endpoint formats differ per model, so declare non-chat models explicitly.