feat: add agent cost reporting

hub/test/unit/runner.test.ts

@@ -21,11 +21,12 @@ function assistantMessage(text: string) {
   };
 }
 
-function resultMessage(sessionId: string) {
+function resultMessage(sessionId: string, costUsd?: number) {
   return {
     type: "result",
     subtype: "success",
     session_id: sessionId,
+    ...(costUsd !== undefined ? { total_cost_usd: costUsd } : {}),
   };
 }
 
@@ -103,6 +104,22 @@ describe("runAgent", () => {
     expect(call?.options).not.toHaveProperty("resume");
   });
 
+  it("returns SDK-reported cost when present", async () => {
+    queryMock.mockReturnValue(messages(assistantMessage("ok"), resultMessage("sdk-session-1", 0.0042)));
+
+    const result = await runAgent({
+      prompt: "算一下成本",
+      model: undefined,
+      project: { projectId: "p", boundChatId: "c", workspaceDir: "/tmp/ws" },
+      systemPrompt: undefined,
+      runId: "run-1",
+      sessionId: "hub-session-1",
+      prisma: stubPrisma,
+    });
+
+    expect(result.costUsd).toBe(0.0042);
+  });
+
   it("passes provider env per run without mutating process env", async () => {
     delete process.env["CPH_TEST_PROVIDER_ENV_MUTATION"];
     queryMock.mockReturnValue(messages(assistantMessage("ok"), resultMessage("sdk-session-1")));