fix(agent): complete opencode warmup before serving

The previous fire-and-forget startup only created the SDK client, leaving the first chat to await project and tool initialization. Warm the real session/tool path and gate port listening on completion.

src/runtime/opencode.ts

@@ -64,6 +64,38 @@ export class OpencodeRuntimeAdapter {
     return requireData(response.data, "global.health");
   }
 
+  async warmup(): Promise<void> {
+    const client = await this.ensureClient();
+    const healthResponse = await client.global.health();
+    requireData(healthResponse.data, "global.health");
+
+    const sessionResponse = await client.session.create({
+      title: "tjwater-agent-warmup",
+    });
+    const session = requireData(sessionResponse.data, "session.create");
+
+    try {
+      const [provider, model] = config.OPENCODE_MODEL.split("/");
+      if (!provider || !model) {
+        throw new Error(
+          `invalid OPENCODE_MODEL; expected provider/model, received ${config.OPENCODE_MODEL}`,
+        );
+      }
+      const toolsResponse = await client.tool.list({ provider, model });
+      requireData(toolsResponse.data, "tool.list");
+    } finally {
+      await client.session.delete(
+        { sessionID: session.id },
+        { throwOnError: true },
+      ).catch((error) => {
+        logger.warn(
+          { err: error, sessionId: session.id },
+          "failed to remove opencode warmup session",
+        );
+      });
+    }
+  }
+
   async createSession(title?: string) {
     const client = await this.ensureClient();
     const response = await client.session.create({