refactor(chat): centralize session persistence

tests/routes/chatUiState.test.ts

@@ -1,10 +1,45 @@
 import { describe, expect, it } from "bun:test";
 
 import {
+  appendBackendToolArtifact,
   cancelBackendTodos,
   upsertBackendQuestion,
 } from "../../src/routes/chatUiState.js";
 
+describe("appendBackendToolArtifact", () => {
+  it("persists show_chart tool calls as chart artifacts", () => {
+    const artifacts = appendBackendToolArtifact([], {
+      session_id: "session-1",
+      tool: "show_chart",
+      reason: "测试折线图渲染",
+      params: {
+        title: "压力曲线",
+        chart_type: "line",
+        x_data: ["00:00", "01:00"],
+        series: [{ name: "P-101", data: [0.42, 0.41] }],
+      },
+    }) as Array<Record<string, unknown>>;
+
+    expect(artifacts).toHaveLength(1);
+    expect(artifacts[0]).toMatchObject({
+      tool: "show_chart",
+      kind: "chart",
+      title: "压力曲线",
+      description: "测试折线图渲染",
+      params: {
+        chart_type: "line",
+        x_data: ["00:00", "01:00"],
+        series: [{ name: "P-101", data: [0.42, 0.41] }],
+      },
+    });
+    expect(artifacts[0]).toEqual(
+      expect.objectContaining({
+        id: expect.stringMatching(/^show_chart-/),
+      }),
+    );
+  });
+});
+
 describe("upsertBackendQuestion", () => {
   it("replaces a tool-call placeholder with the actionable question request", () => {
     const questions = upsertBackendQuestion(