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.

open-sse/executors/opencode.js

@@ -1,11 +1,13 @@
 import crypto from "crypto";
 import { BaseExecutor } from "./base.js";
 import { PROVIDERS } from "../config/providers.js";
+import { getThinkingLevels } from "../providers/thinkingLevels.js";
 import { injectReasoningContent } from "../utils/reasoningContentInjector.js";
 import { resolveSessionId } from "../utils/sessionManager.js";
 
 const OPENCODE_UA = "opencode";
-const MESSAGES_MODELS = new Set();
+// Models served by /zen/v1/responses; every other model stays on /chat/completions.
+const RESPONSES_MODELS = new Set(["muse-spark-1.2-contributor-free"]);
 
 function generateRequestId() {
   return `msg_${crypto.randomUUID().replace(/-/g, "")}`;
@@ -15,19 +17,47 @@ function generateSessionId() {
   return `ses_${crypto.randomUUID().replace(/-/g, "")}`;
 }
 
-// Normalize any resolved id into opencode's ses_ format (stable per-conversation)
-function toOpencodeSession(id) {
-  const stripped = String(id || "").replace(/^ses_/, "").replace(/-/g, "");
-  return stripped ? `ses_${stripped}` : null;
+// Strip the thinking suffix "model(level)" so registry lookups hit the base id.
+function baseModelId(model) {
+  return String(model || "").replace(/\([^()]+\)\s*$/, "").trim();
+}
+
+function isResponsesModel(model) {
+  return RESPONSES_MODELS.has(baseModelId(model));
 }
 
 function resolveOpencodeSession(body, credentials) {
-  return toOpencodeSession(resolveSessionId({
-    headers: credentials?.rawHeaders,
+  const headers = credentials?.rawHeaders || {};
+  return resolveSessionId({
+    headers,
     body,
     connectionId: credentials?.connectionId,
     scope: "opencode",
-  }));
+    generate: generateSessionId,
+  });
+}
+
+function normalizeOpencodeReasoning(model, body) {
+  const current = body.reasoning;
+  const currentReasoning = current && typeof current === "object" && !Array.isArray(current)
+    ? current
+    : null;
+  const requestedEffort = typeof body.reasoning_effort === "string"
+    ? body.reasoning_effort
+    : currentReasoning?.effort;
+  if (typeof requestedEffort !== "string") return;
+
+  const cleanModel = baseModelId(model || body.model);
+  const supportedLevels = getThinkingLevels("opencode", cleanModel);
+  let effort = requestedEffort.toLowerCase().trim();
+  if ((effort === "max" || effort === "ultra") && supportedLevels?.length && !supportedLevels.includes(effort)) {
+    if (effort === "ultra" && supportedLevels.includes("max")) effort = "max";
+    else if (supportedLevels.includes("xhigh")) effort = "xhigh";
+  }
+
+  body.reasoning = { ...currentReasoning, effort };
+  if (!body.reasoning.summary) body.reasoning.summary = "auto";
+  delete body.reasoning_effort;
 }
 
 export class OpenCodeExecutor extends BaseExecutor {
@@ -38,13 +68,24 @@ export class OpenCodeExecutor extends BaseExecutor {
 
   transformRequest(model, body, stream, credentials) {
     this._currentSessionId = resolveOpencodeSession(body, credentials);
+    if (isResponsesModel(model)) {
+      // Responses API names the output cap max_output_tokens and takes thinking
+      // as reasoning:{effort,summary} — normalize the Chat fields at this boundary.
+      if (body.max_output_tokens === undefined) {
+        if (body.max_completion_tokens !== undefined) body.max_output_tokens = body.max_completion_tokens;
+        else if (body.max_tokens !== undefined) body.max_output_tokens = body.max_tokens;
+      }
+      delete body.max_tokens;
+      delete body.max_completion_tokens;
+      normalizeOpencodeReasoning(model, body);
+    }
     return injectReasoningContent({ provider: this.provider, model, body });
   }
 
   buildUrl(model) {
     const base = this.config.baseUrl;
-    return MESSAGES_MODELS.has(model)
-      ? `${base}/zen/v1/messages`
+    return isResponsesModel(model)
+      ? `${base}/zen/v1/responses`
       : `${base}/zen/v1/chat/completions`;
   }