feat(ai-router): test an endpoint before saving it, and re-point a live lane

Two gaps left by the AI Router feature: a profile could be saved without ever
being reachable, and a lane's router could only be chosen at creation.

**POST /api/ai-routers/test** answers the question saving cannot. It sends one
Anthropic-style message capped at a single output token to `<baseUrl>/v1/messages`
with a 15s timeout — the wire shape a claude lane's eight env keys point at, so
what is tested is what will actually run. A router that answers is a 200 here
whatever it replies: `{ ok, status, message }` carries the router's own words,
and `status` is null when nothing answered at all. Only bad input is a 4xx.

The stored key is only ever sent to the endpoint it was stored against. A blank
`apiKey` falls back to the key of the profile named by `name`, but only while
the submitted `baseUrl` still equals the saved one — so testing a retyped
endpoint needs a retyped key (`EBADKEY`). Without that rule this route would be
a way to make the server POST a saved API key to any URL a browser names.

Network failures report `error.cause`, not `error.message`: node's fetch reports
every transport failure as the same useless "fetch failed" and hides the part
the user can act on (ECONNREFUSED, ENOTFOUND, a TLS error) one level down.

**The lane card carries an AI Router select.** The Add-lane modal was the only
place a router was chosen, and a lane outlives its creation. Switching goes
through `POST /api/lanes/:id/router/apply` — never a lane PATCH — because the
DB column and the lane's own config on disk may only move together. A failed
apply puts the select back rather than leaving the card claiming a router the
lane did not get. Hidden when `native` is the only profile: a select with one
option is a control that cannot do anything.

Adds `Lane.router_profile` to the client type (the payload already carried it).

server/__tests__/ai-routers.test.js

@@ -188,3 +188,86 @@ describe("ai-routers — a corrupt file is skipped, never fatal", () => {
     assert.ok(!items.some((i) => i.name === "broken"));
   });
 });
+
+describe("ai-routers — testRouter", () => {
+  const realFetch = global.fetch;
+  after(() => {
+    global.fetch = realFetch;
+  });
+
+  /** Capture the one request testRouter makes, and answer it however asked. */
+  function stubFetch(answer) {
+    const calls = [];
+    global.fetch = async (url, init) => {
+      calls.push({ url, init });
+      if (answer instanceof Error) throw answer;
+      return answer;
+    };
+    return calls;
+  }
+
+  const ok = () => ({ ok: true, status: 200, statusText: "OK", text: async () => "{}" });
+
+  it("posts one capped message to the endpoint's /v1/messages", async () => {
+    const calls = stubFetch(ok());
+    const result = await routers.testRouter(nineRouter());
+    assert.equal(result.ok, true);
+    assert.equal(calls.length, 1);
+    assert.equal(calls[0].url, "http://localhost:20128/v1/v1/messages");
+    const body = JSON.parse(calls[0].init.body);
+    assert.equal(body.max_tokens, 1);
+    assert.equal(body.model, "Highest");
+    assert.equal(calls[0].init.headers["x-api-key"], "sk-secret-value");
+  });
+
+  it("reports a router that answered with an error rather than throwing", async () => {
+    stubFetch({ ok: false, status: 401, statusText: "Unauthorized", text: async () => "bad key" });
+    const result = await routers.testRouter(nineRouter());
+    assert.deepEqual(result, { ok: false, status: 401, message: "bad key" });
+  });
+
+  it("reports an endpoint that never answered", async () => {
+    // The shape node's own fetch throws: a useless outer message wrapping the
+    // one thing the user can act on.
+    stubFetch(
+      Object.assign(new Error("fetch failed"), {
+        cause: new Error("connect ECONNREFUSED 127.0.0.1:20199"),
+      })
+    );
+    const result = await routers.testRouter(nineRouter());
+    assert.equal(result.ok, false);
+    assert.equal(result.status, null);
+    assert.match(result.message, /ECONNREFUSED/);
+  });
+
+  it("falls back to the stored key for the endpoint it was stored against", async () => {
+    const created = routers.createRouter(nineRouter());
+    const calls = stubFetch(ok());
+    await routers.testRouter({
+      name: created.name,
+      baseUrl: "http://localhost:20128/v1",
+      model: "Highest",
+    });
+    assert.equal(calls[0].init.headers["x-api-key"], "sk-secret-value");
+  });
+
+  it("never sends the stored key to a different endpoint", async () => {
+    const created = routers.createRouter(nineRouter());
+    const calls = stubFetch(ok());
+    await assert.rejects(
+      routers.testRouter({
+        name: created.name,
+        baseUrl: "https://attacker.example/v1",
+        model: "Highest",
+      }),
+      { code: "EBADKEY" }
+    );
+    assert.equal(calls.length, 0);
+  });
+
+  it("refuses a base URL that is not http(s)", async () => {
+    await assert.rejects(routers.testRouter(nineRouter({ baseUrl: "file:///etc/passwd" })), {
+      code: "EBADURL",
+    });
+  });
+});

server/lib/ai-routers.js

@@ -21,6 +21,11 @@
  * native" is the same single write path as "switch to a router". It cannot be
  * edited, removed, or shadowed by a saved profile.
  *
+ * `testRouter` is the one thing here that talks to the network: the smallest
+ * real request a claude lane would make, so "saved" and "actually works" stop
+ * being the same claim. It is deliberately NOT a generic proxy — see the note
+ * on its stored-key fallback.
+ *
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -307,12 +312,93 @@ function removeRouter(name) {
   return { removed: name };
 }
 
+/** How long a connection test waits before calling the endpoint dead. */
+const TEST_TIMEOUT_MS = 15_000;
+
+/** Enough of a failing router's own words to be actionable, not enough to flood. */
+const TEST_BODY_MAX = 300;
+
+/**
+ * Probe a router endpoint with the smallest real request a claude lane makes:
+ * one Anthropic-style message capped at a single output token.
+ *
+ * Deliberately the CLAUDE wire shape and not Codex's `responses` one. A profile
+ * is not tool-specific, so a test has to pick; `/v1/messages` is what a claude
+ * lane's eight env keys point at, and it is the path a router has to serve for
+ * this feature to work at all.
+ *
+ * **The stored key is only ever sent to the endpoint it was stored against.**
+ * A blank `apiKey` falls back to the saved profile named by `name` — but only
+ * when the submitted `baseUrl` still matches the saved one. Without that check
+ * this route would be a way to make the server POST a saved API key to any URL
+ * a browser names, which is exactly the leak `listRouters` exists to prevent.
+ *
+ * A router that answers is a success even when it answers with an error: the
+ * outcome is reported (`ok`, `status`, `message`), never thrown. Only bad INPUT
+ * throws.
+ *
+ * @param {{name?:string, baseUrl:string, apiKey?:string, model:string}} input
+ * @returns {Promise<{ok:boolean, status:number|null, message:string}>}
+ */
+async function testRouter(input = {}) {
+  const baseUrl = normalizeBaseUrl(input.baseUrl);
+  const model = normalizeModel(input.model);
+
+  let apiKey = typeof input.apiKey === "string" ? input.apiKey.trim() : "";
+  if (!apiKey && input.name) {
+    const stored = readRouter(input.name);
+    if (stored && normalizeBaseUrl(stored.baseUrl || "") === baseUrl) apiKey = stored.apiKey || "";
+  }
+  if (!apiKey) throw err("EBADKEY", "enter the API key to test this endpoint");
+
+  let res;
+  try {
+    res = await fetch(`${baseUrl}/v1/messages`, {
+      method: "POST",
+      headers: {
+        "content-type": "application/json",
+        // Both, because routers disagree on which one they read, and it is the
+        // same key going to the same endpoint either way.
+        "x-api-key": apiKey,
+        authorization: `Bearer ${apiKey}`,
+        "anthropic-version": "2023-06-01",
+      },
+      body: JSON.stringify({
+        model,
+        max_tokens: 1,
+        messages: [{ role: "user", content: "ping" }],
+      }),
+      signal: AbortSignal.timeout(TEST_TIMEOUT_MS),
+    });
+  } catch (e) {
+    // Unreachable, DNS failure, TLS refusal, timeout — a real answer about the
+    // endpoint, so it is a result and not a 500.
+    //
+    // `cause` first: node's fetch reports every transport failure as the same
+    // useless "fetch failed", and hides the part the user can act on
+    // (ECONNREFUSED, ENOTFOUND, a TLS error) one level down.
+    return {
+      ok: false,
+      status: null,
+      message: e.name === "TimeoutError" ? "timed out" : (e.cause && e.cause.message) || e.message,
+    };
+  }
+
+  const body = await res.text().catch(() => "");
+  return {
+    ok: res.ok,
+    status: res.status,
+    message: res.ok ? model : body.slice(0, TEST_BODY_MAX) || res.statusText,
+  };
+}
+
 module.exports = {
   listRouters,
   getRouter,
   createRouter,
   updateRouter,
   removeRouter,
+  testRouter,
   MODEL_SLOTS,
   BUILTIN_NAME,
   NATIVE,

server/routes/ai-routers.js

@@ -27,6 +27,7 @@ const { sameOriginGuard } = require("../lib/same-origin");
 const router = express.Router();
 
 const ERR_TO_STATUS = {
+  EBADKEY: 400,
   EBADNAME: 400,
   EBADLABEL: 400,
   EBADURL: 400,
@@ -59,6 +60,22 @@ router.post("/", sameOriginGuard, (req, res) => {
   }
 });
 
+// POST /api/ai-routers/test — does this endpoint + key + model actually answer?
+// Body: `{ baseUrl, model, apiKey?, name? }`. Registered before `/:name` for
+// clarity; no collision today, since `/:name` takes no POST.
+//
+// A reachable router is a 200 here whatever it replies — `{ ok:false, status }`
+// carries the router's own words, which is the whole point. Only bad input is
+// a 4xx. The response never echoes the key, including on the path where the
+// stored one was used (see `testRouter` on why that path is narrow).
+router.post("/test", sameOriginGuard, async (req, res) => {
+  try {
+    res.json(await routers.testRouter(req.body || {}));
+  } catch (e) {
+    return fail(res, e);
+  }
+});
+
 // PATCH /api/ai-routers/:name — same fields, all optional. An omitted `apiKey`
 // keeps the stored one; the edit form cannot show a key, so it cannot echo one.
 //