refactor(chat): centralize session persistence

tests/routes/chatSession.test.ts

@@ -1,5 +1,8 @@
 import { describe, expect, it } from "bun:test";
 
+import {
+  buildForkedSessionUiState,
+} from "../../src/routes/chat.js";
 import {
   buildPromptWithLearningContext,
   extractLatestFrontendTurn,
@@ -199,3 +202,79 @@ describe("extractLatestFrontendTurn", () => {
     });
   });
 });
+
+describe("buildForkedSessionUiState", () => {
+  it("copies truncated source messages and preserves tool artifacts", () => {
+    const forked = buildForkedSessionUiState(
+      {
+        messages: [
+          { role: "user", content: "画压力曲线" },
+          {
+            role: "assistant",
+            content: "已生成图表",
+            artifacts: [
+              {
+                id: "chart-1",
+                tool: "show_chart",
+                kind: "chart",
+                params: { chart_type: "line" },
+              },
+            ],
+          },
+          { role: "user", content: "继续分析" },
+        ],
+      },
+      {
+        keepMessageCount: 2,
+        targetSessionId: "forked-session",
+      },
+    );
+
+    expect(forked).toEqual({
+      sessionId: "forked-session",
+      isTitleManuallyEdited: false,
+      messages: [
+        { role: "user", content: "画压力曲线" },
+        {
+          role: "assistant",
+          content: "已生成图表",
+          artifacts: [
+            {
+              id: "chart-1",
+              tool: "show_chart",
+              kind: "chart",
+              params: { chart_type: "line" },
+            },
+          ],
+        },
+      ],
+    });
+  });
+
+  it("creates an empty branch state when source UI state is missing or keep count is zero", () => {
+    expect(
+      buildForkedSessionUiState(null, {
+        keepMessageCount: 3,
+        targetSessionId: "forked-without-source",
+      }),
+    ).toEqual({
+      sessionId: "forked-without-source",
+      isTitleManuallyEdited: false,
+      messages: [],
+    });
+
+    expect(
+      buildForkedSessionUiState(
+        { messages: [{ role: "user", content: "不保留" }] },
+        {
+          keepMessageCount: 0,
+          targetSessionId: "forked-empty",
+        },
+      ),
+    ).toEqual({
+      sessionId: "forked-empty",
+      isTitleManuallyEdited: false,
+      messages: [],
+    });
+  });
+});

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(