fix: preserve sessionKey for agent runs

src/commands/agent.test.ts

@@ -168,6 +168,45 @@ describe("agentCommand", () => {
     });
   });
 
+  it("keeps explicit sessionKey even when sessionId exists elsewhere", async () => {
+    await withTempHome(async (home) => {
+      const store = path.join(home, "sessions.json");
+      fs.mkdirSync(path.dirname(store), { recursive: true });
+      fs.writeFileSync(
+        store,
+        JSON.stringify(
+          {
+            "agent:main:main": {
+              sessionId: "sess-main",
+              updatedAt: Date.now(),
+            },
+          },
+          null,
+          2,
+        ),
+      );
+      mockConfig(home, store);
+
+      await agentCommand(
+        {
+          message: "hi",
+          sessionId: "sess-main",
+          sessionKey: "agent:main:subagent:abc",
+        },
+        runtime,
+      );
+
+      const callArgs = vi.mocked(runEmbeddedPiAgent).mock.calls.at(-1)?.[0];
+      expect(callArgs?.sessionKey).toBe("agent:main:subagent:abc");
+
+      const saved = JSON.parse(fs.readFileSync(store, "utf-8")) as Record<
+        string,
+        { sessionId?: string }
+      >;
+      expect(saved["agent:main:subagent:abc"]?.sessionId).toBe("sess-main");
+    });
+  });
+
   it("defaults thinking to low for reasoning-capable models", async () => {
     await withTempHome(async (home) => {
       const store = path.join(home, "sessions.json");