fix(opencode): route Muse Spark through the Responses API

muse-spark-1.2-contributor-free returned HTTP 500 on /zen/v1/chat/completions.
The model is only served by /zen/v1/responses, so route it there via a per-model
targetFormat and normalize the Chat fields the Responses API rejects
(max_tokens -> max_output_tokens, reasoning_effort -> reasoning{effort,summary}),
clamping max/ultra down to the highest effort the model accepts (xhigh).

Routing stays per-model: the other free models (big-pickle, hy3-free, mimo,
nemotron, laguna) are not served by /responses and keep /chat/completions.

tests/unit/executor-const-guard.test.js

@@ -9,6 +9,7 @@ import { DEFAULT_MAX_TOKENS, DEFAULT_MIN_TOKENS } from "../../open-sse/config/ru
 import mimoFree from "../../open-sse/providers/registry/mimo-free.js";
 import opencode from "../../open-sse/providers/registry/opencode.js";
 import antigravity from "../../open-sse/providers/registry/antigravity.js";
+import { OpenCodeExecutor } from "../../open-sse/executors/opencode.js";
 
 describe("compat base URLs / version", () => {
   it("OPENAI_COMPAT_BASE", () => {
@@ -46,3 +47,36 @@ describe("antigravity retry (intentional change: 429=6, 503=3)", () => {
     expect(antigravity.transport.retry["503"].attempts).toBe(3);
   });
 });
+
+describe("OpenCode Free endpoint routing", () => {
+  const MUSE = "muse-spark-1.2-contributor-free";
+
+  it("declares the Responses format only on the Muse Spark model", () => {
+    expect(opencode.transport.format).toBeUndefined();
+    const muse = opencode.models.find((m) => m.id === MUSE);
+    expect(muse?.targetFormat).toBe("openai-responses");
+  });
+
+  it("routes Muse Spark to /responses and every other model to /chat/completions", () => {
+    const executor = new OpenCodeExecutor();
+    expect(executor.buildUrl(MUSE)).toBe("https://opencode.ai/zen/v1/responses");
+    expect(executor.buildUrl(`${MUSE}(xhigh)`)).toBe("https://opencode.ai/zen/v1/responses");
+    expect(executor.buildUrl("big-pickle")).toBe("https://opencode.ai/zen/v1/chat/completions");
+    expect(executor.buildUrl("hy3-free")).toBe("https://opencode.ai/zen/v1/chat/completions");
+  });
+
+  it("normalizes Chat token/thinking fields only for the Responses model", () => {
+    const executor = new OpenCodeExecutor();
+    const muse = { max_tokens: 4096, reasoning_effort: "high" };
+    executor.transformRequest(MUSE, muse, true, {});
+    expect(muse.max_output_tokens).toBe(4096);
+    expect(muse.max_tokens).toBeUndefined();
+    expect(muse.reasoning).toEqual({ effort: "high", summary: "auto" });
+
+    const chat = { max_tokens: 4096, reasoning_effort: "high" };
+    executor.transformRequest("big-pickle", chat, true, {});
+    expect(chat.max_tokens).toBe(4096);
+    expect(chat.max_output_tokens).toBeUndefined();
+    expect(chat.reasoning_effort).toBe("high");
+  });
+});

tests/unit/opencode-muse-spark-thinking.test.js

@@ -0,0 +1,94 @@
+import { describe, expect, it } from "vitest";
+import { getCapabilitiesForModel } from "../../open-sse/providers/capabilities.js";
+import { PROVIDER_MODELS } from "../../open-sse/config/providerModels.js";
+import { getThinkingLevels } from "../../open-sse/providers/thinkingLevels.js";
+import { FORMATS } from "../../open-sse/translator/formats.js";
+import { OpenCodeExecutor } from "../../open-sse/executors/opencode.js";
+import "../translator/registerAll.js";
+import { translateRequest } from "../../open-sse/translator/index.js";
+
+const MODEL = "muse-spark-1.2-contributor-free";
+const PROVIDER = "opencode";
+
+const input = [{
+  type: "message",
+  role: "user",
+  content: [{ type: "input_text", text: "Think, then answer: 2 + 2?" }],
+}];
+
+describe("OpenCode Free Muse Spark thinking", () => {
+  it("advertises reasoning and the requested model limits", () => {
+    expect(PROVIDER_MODELS.oc?.some((model) => model.id === MODEL)).toBe(true);
+    expect(getCapabilitiesForModel(PROVIDER, MODEL)).toMatchObject({
+      reasoning: true,
+      thinkingFormat: "openai",
+      contextWindow: 1048576,
+      maxOutput: 131072,
+    });
+    expect(getCapabilitiesForModel(PROVIDER, `oc/${MODEL}`)).toMatchObject({
+      reasoning: true,
+      contextWindow: 1048576,
+      maxOutput: 131072,
+    });
+    expect(getThinkingLevels(PROVIDER, MODEL)).toEqual([
+      "none",
+      "minimal",
+      "low",
+      "medium",
+      "high",
+      "xhigh",
+    ]);
+  });
+
+  it("clamps max to xhigh and emits the Responses reasoning shape", () => {
+    const body = {
+      input,
+      reasoning: { effort: "max" },
+      max_tokens: 131072,
+    };
+
+    const out = new OpenCodeExecutor().transformRequest(MODEL, body, true, {
+      connectionId: "opencode-muse-spark-test",
+    });
+
+    expect(out.reasoning).toEqual({ effort: "xhigh", summary: "auto" });
+    expect(out.reasoning_effort).toBeUndefined();
+    expect(out.max_output_tokens).toBe(131072);
+    expect(out.max_tokens).toBeUndefined();
+  });
+
+  it("leaves the other free models on Chat Completions", () => {
+    const executor = new OpenCodeExecutor();
+    const body = { messages: [{ role: "user", content: "hi" }], max_tokens: 1024 };
+    executor.transformRequest("big-pickle", body, true, {});
+    expect(executor.buildUrl("big-pickle")).toBe("https://opencode.ai/zen/v1/chat/completions");
+    expect(body.max_tokens).toBe(1024);
+    expect(body.max_output_tokens).toBeUndefined();
+  });
+
+  it("translates Chat Completions max thinking into a Responses request", () => {
+    const body = {
+      model: `oc/${MODEL}`,
+      messages: [{ role: "user", content: "Think, then answer: 2 + 2?" }],
+      reasoning_effort: "max",
+      max_tokens: 131072,
+    };
+
+    const translated = translateRequest(
+      FORMATS.OPENAI,
+      FORMATS.OPENAI_RESPONSES,
+      MODEL,
+      body,
+      true,
+      {},
+      PROVIDER,
+    );
+    const out = new OpenCodeExecutor().transformRequest(MODEL, translated, true, {
+      connectionId: "opencode-muse-spark-translation-test",
+    });
+
+    expect(out.reasoning).toEqual({ effort: "xhigh", summary: "auto" });
+    expect(out.max_output_tokens).toBe(131072);
+    expect(out.max_tokens).toBeUndefined();
+  });
+});