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/handlers/chatCore.js

@@ -356,7 +356,17 @@ export async function handleChatCore({ body, modelInfo, credentials, log, onCred
   // exception: it is decoded by the executor into OpenAI-compatible output.
   let providerResponseFormat = targetFormat;
   try {
-    const result = await executor.execute({ model, body: translatedBody, stream, credentials, signal: streamController.signal, log, proxyOptions });
+    const result = await executor.execute({
+      model,
+      body: translatedBody,
+      stream,
+      credentials,
+      providerSessionId: sessionSeed,
+      clientTool,
+      signal: streamController.signal,
+      log,
+      proxyOptions,
+    });
     providerResponse = result.response;
     providerUrl = result.url;
     providerHeaders = result.headers;
@@ -410,7 +420,17 @@ export async function handleChatCore({ body, modelInfo, credentials, log, onCred
           try { await onCredentialsRefreshed(newCredentials); } catch (e) { log?.warn?.("TOKEN", `onCredentialsRefreshed failed: ${e.message}`); }
         }
         try {
-          const retryResult = await executor.execute({ model, body: translatedBody, stream, credentials, signal: streamController.signal, log, proxyOptions });
+          const retryResult = await executor.execute({
+            model,
+            body: translatedBody,
+            stream,
+            credentials,
+            providerSessionId: sessionSeed,
+            clientTool,
+            signal: streamController.signal,
+            log,
+            proxyOptions,
+          });
           if (retryResult.response.ok) {
             providerResponse = retryResult.response;
             providerUrl = retryResult.url;