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/index.js

@@ -10,6 +10,7 @@ import { CodexExecutor } from "./codex.js";
 import { CursorExecutor } from "./cursor.js";
 import { VertexExecutor } from "./vertex.js";
 import { OpenCodeExecutor } from "./opencode.js";
+import { OpenCodeGoExecutor } from "./opencode-go.js";
 import { GrokWebExecutor } from "./grok-web.js";
 import { GrokCliExecutor } from "./grok-cli.js";
 import { PerplexityWebExecutor } from "./perplexity-web.js";
@@ -40,6 +41,7 @@ const executors = {
   vertex: new VertexExecutor("vertex"),
   "vertex-partner": new VertexExecutor("vertex-partner"),
   opencode: new OpenCodeExecutor(),
+  "opencode-go": new OpenCodeGoExecutor(),
   "grok-web": new GrokWebExecutor(),
   "grok-cli": new GrokCliExecutor(),
   gcli: new GrokCliExecutor(), // Alias
@@ -84,6 +86,7 @@ export { CursorExecutor } from "./cursor.js";
 export { VertexExecutor } from "./vertex.js";
 export { DefaultExecutor } from "./default.js";
 export { OpenCodeExecutor } from "./opencode.js";
+export { OpenCodeGoExecutor } from "./opencode-go.js";
 export { GrokWebExecutor } from "./grok-web.js";
 export { GrokCliExecutor } from "./grok-cli.js";
 export { PerplexityWebExecutor } from "./perplexity-web.js";