fix(opencode-go): send stable session header (#3800)

- add a dedicated OpenCode Go executor that always sends x-opencode-session
- preserve a valid caller-provided native OpenCode session header
- translate downstream Agent session IDs into opaque, stable, Agent-scoped IDs
- forward the original provider session seed and client tool on both initial and credential-refresh requests

open-sse/executors/opencode-go.js

@@ -0,0 +1,71 @@
+import crypto from "node:crypto";
+import { DefaultExecutor } from "./default.js";
+import { resolveSessionId } from "../utils/sessionManager.js";
+
+const SESSION_HEADER = "x-opencode-session";
+const SESSION_FIELD = "_opencodeGoSession";
+const MAX_SESSION_LENGTH = 256;
+
+function normalizeSession(value) {
+  if (typeof value !== "string") return null;
+  const normalized = value.trim();
+  if (!normalized || normalized.length > MAX_SESSION_LENGTH) return null;
+  return normalized;
+}
+
+function nativeSession(headers) {
+  if (!headers || typeof headers !== "object") return null;
+  for (const [key, value] of Object.entries(headers)) {
+    if (key.toLowerCase() === SESSION_HEADER) return normalizeSession(value);
+  }
+  return null;
+}
+
+function translatedSession(sessionId, clientTool) {
+  const digest = crypto
+    .createHash("sha256")
+    .update(`opencode-go\0${clientTool || "generic"}\0${sessionId}`)
+    .digest("hex")
+    .slice(0, 32);
+  return `ses_${digest}`;
+}
+
+export class OpenCodeGoExecutor extends DefaultExecutor {
+  constructor() {
+    super("opencode-go");
+  }
+
+  prepareRequestCredentials({ body, credentials, providerSessionId, clientTool } = {}) {
+    const sourceCredentials = credentials || {};
+    const native = nativeSession(sourceCredentials.rawHeaders);
+    const resolved = normalizeSession(providerSessionId) || resolveSessionId({
+      headers: sourceCredentials.rawHeaders,
+      body,
+      connectionId: sourceCredentials.connectionId,
+      scope: "opencode-go",
+    });
+
+    return {
+      ...sourceCredentials,
+      [SESSION_FIELD]: native || translatedSession(resolved, clientTool),
+    };
+  }
+
+  async execute(args) {
+    const credentials = this.prepareRequestCredentials(args);
+    return super.execute({ ...args, credentials });
+  }
+
+  buildHeaders(credentials, stream = true, url, model) {
+    const headers = super.buildHeaders(credentials || {}, stream, url, model);
+    const prepared = credentials?.[SESSION_FIELD];
+    if (prepared) {
+      headers[SESSION_HEADER] = prepared;
+      return headers;
+    }
+
+    const fallback = this.prepareRequestCredentials({ credentials });
+    headers[SESSION_HEADER] = fallback[SESSION_FIELD];
+    return headers;
+  }
+}