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.

tests/runtime/opencode.test.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it } from "bun:test";
 import { type OpencodeClient } from "@opencode-ai/sdk/v2";
 
+import { config } from "../../src/config.js";
 import { OpencodeRuntimeAdapter } from "../../src/runtime/opencode.js";
 
 const createRuntimeAdapter = (
@@ -85,3 +86,47 @@ describe("OpencodeRuntimeAdapter.ensureClient", () => {
     expect(attempts).toBe(2);
   });
 });
+
+describe("OpencodeRuntimeAdapter.warmup", () => {
+  it("initializes the project session and model tools before reporting ready", async () => {
+    const calls: string[] = [];
+    const client = {
+      global: {
+        health: async () => {
+          calls.push("health");
+          return { data: { healthy: true, version: "test" } };
+        },
+      },
+      session: {
+        create: async () => {
+          calls.push("session.create");
+          return { data: { id: "warmup-session" } };
+        },
+        delete: async ({ sessionID }: { sessionID: string }) => {
+          calls.push(`session.delete:${sessionID}`);
+          return { data: true };
+        },
+      },
+      tool: {
+        list: async (model: { provider: string; model: string }) => {
+          calls.push(`tool.list:${model.provider}/${model.model}`);
+          return { data: [] };
+        },
+      },
+    } as unknown as OpencodeClient;
+    const runtime = Object.assign(Object.create(OpencodeRuntimeAdapter.prototype), {
+      clientPromise: null,
+      closeServer: null,
+      ensureClient: async () => client,
+    }) as OpencodeRuntimeAdapter;
+
+    await runtime.warmup();
+
+    expect(calls).toEqual([
+      "health",
+      "session.create",
+      `tool.list:${config.OPENCODE_MODEL}`,
+      "session.delete:warmup-session",
+    ]);
+  });
+});