feat(opencode-go): add muse-spark-1.3-contributor and fix parallel tool calls on Responses paths (#3819)

- Add muse-spark-1.3-contributor as responses-only model on OpenCode Go with dedicated executor
- Key Responses→chat streaming tool calls by item_id to prevent parallel tool calls merging into index 0
- Standardize tool coercions and call_id clamping in Responses API translation

open-sse/translator/formats/responsesApi.js

@@ -23,6 +23,46 @@ export function normalizeResponsesInput(input) {
   return null;
 }
 
+// Strict Responses upstreams reject overlong call_ids with InputValidationError (#393).
+export const MAX_RESPONSES_CALL_ID_LEN = 64;
+
+export function clampResponsesCallId(id) {
+  if (typeof id !== "string" || !id) return `call_${Date.now()}`;
+  return id.length > MAX_RESPONSES_CALL_ID_LEN ? id.substring(0, MAX_RESPONSES_CALL_ID_LEN) : id;
+}
+
+// Single-stringify: objects → JSON once; valid JSON strings pass through untouched;
+// anything else (partial fragments, empty) falls back to "{}" instead of
+// double-encoding and tripping upstream InputValidationError.
+export function coerceResponsesArguments(value) {
+  if (value === undefined || value === null || value === "") return "{}";
+  if (typeof value !== "string") {
+    try {
+      return JSON.stringify(value);
+    } catch {
+      return "{}";
+    }
+  }
+  try {
+    JSON.parse(value);
+    return value;
+  } catch {
+    return "{}";
+  }
+}
+
+// function_call_output.output must be a string — never null/object.
+export function coerceResponsesOutput(value) {
+  if (typeof value === "string") return value;
+  if (value === undefined || value === null) return "";
+  if (Array.isArray(value)) return value.map((c) => c?.text ?? JSON.stringify(c)).join("");
+  try {
+    return JSON.stringify(value);
+  } catch {
+    return String(value);
+  }
+}
+
 /**
  * Convert OpenAI Responses API format to standard chat completions format
  * Responses API uses: { input: [...], instructions: "..." }