fix(claude): retain configured model metadata before a turn

Rebuilding an idle session cleared its observed model and published null despite retaining an explicit model in its configuration. Fall back to that configuration until the next turn supplies an observed model.

packages/server/src/server/agent/providers/claude/agent.runtime-info.test.ts

@@ -0,0 +1,48 @@
+import pino from "pino";
+import { describe, expect, test } from "vitest";
+
+import { ClaudeAgentClient } from "./agent.js";
+
+describe("Claude runtime info before a turn", () => {
+  const client = new ClaudeAgentClient({ logger: pino({ level: "silent" }) });
+
+  test("reports the explicitly configured model before the first turn", async () => {
+    const session = await client.createSession({
+      provider: "claude",
+      cwd: process.cwd(),
+      model: "claude-haiku-5-5",
+    });
+    try {
+      expect(await session.getRuntimeInfo()).toMatchObject({ model: "claude-haiku-5-5" });
+    } finally {
+      await session.close();
+    }
+  });
+
+  test("reports the persisted configured model after rebuilding an idle session", async () => {
+    const session = await client.resumeSession({
+      provider: "claude",
+      sessionId: "runtime-model-before-turn",
+      metadata: { cwd: process.cwd(), model: "claude-haiku-5-5" },
+    });
+    try {
+      expect(await session.getRuntimeInfo()).toMatchObject({
+        sessionId: "runtime-model-before-turn",
+        model: "claude-haiku-5-5",
+      });
+      expect((await session.getRuntimeInfo()).model).toBe("claude-haiku-5-5");
+      expect((await session.getRuntimeInfo()).extra?.runtimeModel).toBeUndefined();
+    } finally {
+      await session.close();
+    }
+  });
+
+  test("leaves the model unknown when Claude will choose its default", async () => {
+    const session = await client.createSession({ provider: "claude", cwd: process.cwd() });
+    try {
+      expect((await session.getRuntimeInfo()).model).toBeNull();
+    } finally {
+      await session.close();
+    }
+  });
+});

packages/server/src/server/agent/providers/claude/agent.ts

@@ -2460,7 +2460,7 @@ class ClaudeAgentSession implements AgentSession {
     const info: AgentRuntimeInfo = {
       provider: "claude",
       sessionId: this.claudeSessionId,
-      model: this.lastOptionsModel,
+      model: this.lastOptionsModel ?? this.config.model ?? null,
       modeId: this.currentMode ?? null,
       ...(this.lastRuntimeModel
         ? {