feat(opencode-go): muse-spark-1.2 and Responses tool fixes (#3820)

- Add muse-spark-1.2-contributor as responses-only model on OpenCode Go
- Normalize object tool schemas without properties in OpenCode Go executor
- Make fallback Responses call_ids unique across same-millisecond calls
- Make Responses output coercion fail-soft for circular and non-stringifiable values

tests/unit/responses-parallel-tool-calls.test.js

@@ -6,6 +6,7 @@
 import { describe, expect, it } from "vitest";
 import "../translator/registerAll.js";
 import { openaiResponsesToOpenAIResponse } from "../../open-sse/translator/response/openai-responses.js";
+import { clampResponsesCallId, coerceResponsesOutput, MAX_RESPONSES_CALL_ID_LEN } from "../../open-sse/translator/formats/responsesApi.js";
 import { initState, translateResponse } from "../../open-sse/translator/index.js";
 import { FORMATS } from "../../open-sse/translator/formats.js";
 
@@ -138,3 +139,27 @@ describe("responses → claude end-to-end keeps parallel tool_use blocks separat
     ]);
   });
 });
+
+describe("fallback call_ids stay unique within a batch", () => {
+  it("same-millisecond fallbacks never collide", () => {
+    const ids = new Set(Array.from({ length: 50 }, () => clampResponsesCallId(undefined)));
+    expect(ids.size).toBe(50);
+    for (const id of ids) {
+      expect(id.startsWith("call_")).toBe(true);
+      expect(id.length).toBeLessThanOrEqual(MAX_RESPONSES_CALL_ID_LEN);
+    }
+    expect(new Set([clampResponsesCallId(""), clampResponsesCallId(null)]).size).toBe(2);
+  });
+});
+
+describe("output coercion stays fail-soft on unstringifiable values", () => {
+  it("never throws on BigInt/circular array elements", () => {
+    const circular = {};
+    circular.self = circular;
+    const input = [1n, circular, { text: "ok" }];
+    expect(() => coerceResponsesOutput(input)).not.toThrow();
+    const out = coerceResponsesOutput(input);
+    expect(typeof out).toBe("string");
+    expect(out).toContain("ok");
+  });
+});