fix(chat): recover session list from snapshots

tkmind-proxy.test.mjs

@@ -452,6 +452,134 @@ test('buildVisionPayload injects public standard image urls for page generation'
   assert.match(text, /不得改写图片里人物的年龄、性别、人数或主体关系/);
 });
 
+test('GET /sessions serves snapshot summaries when every upstream is unavailable', async () => {
+  let upstream;
+  try {
+    upstream = createServer((_req, res) => {
+      res.writeHead(503, { 'Content-Type': 'text/plain' });
+      res.end('temporarily unavailable');
+    });
+    const upstreamPort = await listen(upstream);
+    const proxy = createTkmindProxy({
+      apiTarget: `http://127.0.0.1:${upstreamPort}`,
+      apiSecret: 'test-secret',
+      userAuth: {
+        async listOwnedSessionIds() {
+          return new Set(['session-1']);
+        },
+        async getSessionOrigins() {
+          return new Map([['session-1', 'h5']]);
+        },
+      },
+      sessionSnapshotService: {
+        isEnabled() {
+          return true;
+        },
+        async get(sessionId) {
+          assert.equal(sessionId, 'session-1');
+          return {
+            session: {
+              id: sessionId,
+              name: 'Recovered session',
+              updated_at: '2026-07-27T00:00:00.000Z',
+            },
+            messages: [{ role: 'user', content: [{ type: 'text', text: 'hello' }] }],
+            meta: {
+              synced_msg_count: 1,
+              source_updated_at: '2026-07-27T00:00:00.000Z',
+            },
+          };
+        },
+      },
+    });
+
+    const req = {
+      currentUser: { id: 'user-1', username: 'john' },
+      query: {},
+    };
+    let payload;
+    const headers = new Map();
+    const res = {
+      statusCode: 200,
+      status(code) {
+        this.statusCode = code;
+        return this;
+      },
+      setHeader(name, value) {
+        headers.set(name, value);
+      },
+      json(value) {
+        payload = value;
+        return this;
+      },
+    };
+
+    await proxy.handlers['GET /sessions'][1](req, res);
+
+    assert.equal(res.statusCode, 200);
+    assert.equal(headers.get('X-TKMind-Degraded'), '1');
+    assert.equal(payload.sessions.length, 1);
+    assert.equal(payload.sessions[0].id, 'session-1');
+    assert.equal(payload.sessions[0].name, 'Recovered session');
+    assert.equal(payload.sessions[0].message_count, 1);
+  } finally {
+    await closeServer(upstream);
+  }
+});
+
+test('GET /sessions keeps the upstream error when no fallback session can be recovered', async () => {
+  let upstream;
+  try {
+    upstream = createServer((_req, res) => {
+      res.writeHead(503, { 'Content-Type': 'text/plain' });
+      res.end('temporarily unavailable');
+    });
+    const upstreamPort = await listen(upstream);
+    const proxy = createTkmindProxy({
+      apiTarget: `http://127.0.0.1:${upstreamPort}`,
+      apiSecret: 'test-secret',
+      userAuth: {
+        async listOwnedSessionIds() {
+          return new Set(['session-1']);
+        },
+      },
+      sessionSnapshotService: {
+        isEnabled() {
+          return true;
+        },
+        async get() {
+          return null;
+        },
+      },
+    });
+
+    const req = {
+      currentUser: { id: 'user-1', username: 'john' },
+      query: {},
+    };
+    let payload;
+    const res = {
+      statusCode: 200,
+      status(code) {
+        this.statusCode = code;
+        return this;
+      },
+      setHeader() {},
+      json(value) {
+        payload = value;
+        return this;
+      },
+    };
+
+    await proxy.handlers['GET /sessions'][1](req, res);
+
+    assert.equal(res.statusCode, 502);
+    assert.equal(payload.message, 'temporarily unavailable');
+  } finally {
+    await closeServer(upstream);
+  }
+});
+
 test('proxySessionEvents does not send JSON after SSE headers were sent', async () => {
   let upstream;