fix(startup): 密钥警告改读真实生效的 key 集合

启动时那条「gateway_keys is EMPTY — without a key every request is rejected」
读的是 legacy 的 cfg.GatewayKeys 段，而鉴权实际用 cfg.Keys（core.ListKeys）。
seedKeys 首次启动把 gateway_keys 搬进 keys[] 之后，YAML 里那个列表就不再
被鉴权使用。于是在它被清空（例如轮换掉 starter key 之后）而 keys[] 仍有
7 把可用 key（含 admin）时，进程每次启动都谎报「所有请求都会被拒绝」。

实测：生产日志出现该警告，而同一个 key 请求 /v1/models 返回 200。

- main.go 改为检查 c.ListKeys()，文案改成不绑定字段名。
- 顺带删掉 gateway.New 的 gatewayKeys 参数：函数体从未使用它，
  只读 ListKeys()，留着会继续诱导人以为鉴权来自那个列表。

判据：e2e/TestStartupWarningReflectsRealKeysNotLegacyList —— 构造
「gateway_keys 空 + keys[] 有 key」的真实形态，先断言该 key 确实能鉴权，
再断言日志里不再出现那句谎报。变异验证：回退成 GatewayKeys() 即变红。

e2e/e2e_test.go

@@ -326,3 +326,144 @@ func statusOf(resp *http.Response) int {
 	}
 	return resp.StatusCode
 }
+
+// The startup warning about key configuration must describe the key set that
+// AUTH actually uses (cfg.Keys, via core.ListKeys), not the legacy
+// gateway_keys YAML list.
+//
+// It used to check GatewayKeys() only. seedKeys copies gateway_keys into keys[]
+// on first start and the YAML list stops being consulted, so once that list was
+// emptied — e.g. after rotating the starter key away — the process logged
+// "every request will be rejected" while seven working keys, one of them admin,
+// were in service. Observed in production: the warning appeared and that same
+// key returned HTTP 200 on /v1/models.
+//
+// The fixture reproduces exactly that shape: gateway_keys EMPTY, with the
+// working key present only in keys[].
+func TestStartupWarningReflectsRealKeysNotLegacyList(t *testing.T) {
+	up := newMockUpstream(t)
+	dir := t.TempDir()
+
+	// Seed a real install once so keys[] gets populated from gateway_keys, then
+	// rewrite the file to look like a rotated install: legacy list cleared, the
+	// seeded key still present in keys[].
+	path := writeConfig(t, dir, "127.0.0.1:0", map[string]*mockUpstream{"good": up})
+	bin := buildBinary(t)
+
+	// First run creates the sealed config with keys[] populated.
+	seedPort := freePort(t)
+	cfg1 := writeConfig(t, dir, "127.0.0.1:"+seedPort, map[string]*mockUpstream{"good": up})
+	g1 := startGateway(t, bin, "127.0.0.1:"+seedPort, cfg1)
+	g1.stop()
+
+	data, err := os.ReadFile(cfg1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(string(data), "keys:") {
+		t.Fatalf("first run did not populate keys[]:\n%s", data)
+	}
+
+	// Now clear the legacy gateway_keys list, keeping keys[] intact. The
+	// rewritten file may use different indentation, so match loosely.
+	cleared, n := clearGatewayKeys(string(data))
+	if n == 0 {
+		t.Fatalf("could not find a gateway_keys entry to clear in:\n%s", data)
+	}
+	if err := os.WriteFile(cfg1, []byte(cleared), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Start again and inspect the log. The config pins its listen address, so
+	// rewrite that field to the port we will actually poll.
+	port2 := freePort(t)
+	rehosted, ok := replaceListen(string(cleared), "127.0.0.1:"+port2)
+	if !ok {
+		t.Fatalf("could not rewrite listen in:\n%s", cleared)
+	}
+	cfg2 := filepath.Join(dir, "config2.yaml")
+	if err := os.WriteFile(cfg2, []byte(rehosted), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	g2 := startGateway(t, bin, "127.0.0.1:"+port2, cfg2)
+	defer g2.stop()
+
+	// Sanity: the key really does authenticate, so the warning would be a lie.
+	resp, _ := g2.do("GET", "/v1/models", "", true)
+	if resp == nil || resp.StatusCode != http.StatusOK {
+		t.Fatalf("key from keys[] did not authenticate (status %v); test fixture is wrong",
+			resp)
+	}
+
+	logs := g2.logString()
+	if strings.Contains(logs, "gateway_keys is EMPTY") {
+		t.Errorf("startup logged 'gateway_keys is EMPTY ... every request is rejected' while "+
+			"a working admin key was in service — the warning must read the authoritative "+
+			"key set (core.ListKeys), not the legacy YAML list.\nlog:\n%s", logs)
+	}
+	_ = path
+	_ = g1
+}
+
+func freePort(t *testing.T) string {
+	t.Helper()
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer l.Close()
+	_, port, _ := net.SplitHostPort(l.Addr().String())
+	return port
+}
+
+// stop terminates the gateway and waits, so its log buffer is complete.
+func (g *gatewayUnderTest) stop() {
+	if g == nil || g.cmd == nil || g.cmd.Process == nil {
+		return
+	}
+	_ = g.cmd.Process.Kill()
+	_, _ = g.cmd.Process.Wait()
+}
+
+// logString returns everything the gateway has written so far.
+func (g *gatewayUnderTest) logString() string { return g.log.String() }
+
+// clearGatewayKeys empties the gateway_keys list in a config, tolerating any
+// indentation the YAML writer chose. Returns the new text and how many entries
+// it removed.
+func clearGatewayKeys(src string) (string, int) {
+	lines := strings.Split(src, "\n")
+	var out []string
+	removed := 0
+	inList := false
+	for _, l := range lines {
+		trimmed := strings.TrimSpace(l)
+		if strings.HasPrefix(l, "gateway_keys:") {
+			out = append(out, "gateway_keys: []")
+			inList = true
+			removed++
+			continue
+		}
+		if inList {
+			if strings.HasPrefix(trimmed, "- ") {
+				removed++
+				continue
+			}
+			inList = false
+		}
+		out = append(out, l)
+	}
+	return strings.Join(out, "\n"), removed
+}
+
+// replaceListen rewrites the top-level listen: value.
+func replaceListen(src, addr string) (string, bool) {
+	lines := strings.Split(src, "\n")
+	for i, l := range lines {
+		if strings.HasPrefix(l, "listen:") {
+			lines[i] = "listen: " + addr
+			return strings.Join(lines, "\n"), true
+		}
+	}
+	return src, false
+}