feat(dashboard): per-key model restrictions, pin header routing, combo side-panel picker

- Endpoint: per-API-key model allowlist (schema v3) enforced on chat (403)
  and /v1/models; Full-access toggle + multi-select picker in Keys UI.
- Providers: honor x-connection-id in /v1/chat/completions — pinned requests
  no longer rotate to another account on failure.
- Providers: strategy saves merge into stored enabled:false override;
  Test All groups match grid sections; 1-by-1 skips disabled connections.
- Dashboard: provider-card toggle syncs from server on failure; grid toggles
  always visible; connection rows get clear-✕ for stale error banners.
- Combo editor: on desktop (xl+) the Add-Model picker opens as a floating
  side panel beside the untouched combo popup instead of stacking on top;
  mobile keeps the full-screen overlay.
- Long API-key overflow fixed in key rows + provider model sections.

tests/unit/chat-connection-pin.test.js

@@ -0,0 +1,115 @@
+/**
+ * Unit tests for x-connection-id pinning in src/sse/handlers/chat.js
+ *
+ * Covers:
+ *  - the dashboard per-key test header is forwarded to getProviderCredentials
+ *    as preferredConnectionId (same contract as embeddings/images/video)
+ *  - a pinned request does NOT rotate to another account on failure
+ *  - an unpinned request keeps rotating (regression guard)
+ */
+
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+
+const authMocks = vi.hoisted(() => ({
+  getProviderCredentials: vi.fn(),
+  markAccountUnavailable: vi.fn(async () => ({ shouldFallback: true })),
+  clearAccountError: vi.fn(async () => {}),
+  extractApiKey: vi.fn(() => null),
+  isValidApiKey: vi.fn(async () => true),
+}));
+const tokenMocks = vi.hoisted(() => ({
+  checkAndRefreshToken: vi.fn(async (_p, creds) => creds),
+  updateProviderCredentials: vi.fn(async () => {}),
+}));
+
+vi.mock("@/sse/services/auth.js", () => authMocks);
+vi.mock("@/sse/services/tokenRefresh.js", () => tokenMocks);
+vi.mock("@/lib/localDb", () => ({
+  getSettings: vi.fn(async () => ({ requireApiKey: false })),
+  getComboByName: vi.fn(async () => null),
+  getModelAliases: vi.fn(async () => ({})),
+  getCustomModels: vi.fn(async () => []),
+  getProviderNodes: vi.fn(async () => []),
+  getProviderConnections: vi.fn(async () => []),
+  updateProviderCredentials: vi.fn(async () => {}),
+}));
+vi.mock("@/sse/utils/logger.js", () => ({
+  info: vi.fn(), warn: vi.fn(), error: vi.fn(), debug: vi.fn(), maskKey: (k) => k,
+}));
+// chatCore would perform the upstream call; stub success so the loop exits.
+vi.mock("open-sse/handlers/chatCore.js", () => ({
+  handleChatCore: vi.fn(async ({ credentials }) => ({
+    success: true,
+    response: new Response(JSON.stringify({ servedBy: credentials.connectionId }), {
+      status: 200,
+      headers: { "Content-Type": "application/json" },
+    }),
+  })),
+}));
+vi.mock("open-sse/services/combo.js", () => ({
+  getComboModels: vi.fn(async () => null),
+  resetComboRotation: vi.fn(),
+  detectRequiredCapabilities: vi.fn(() => new Set()),
+  augmentModelsWithCapacityAdapter: vi.fn((m) => m),
+  withCapacityAdapterStripping: vi.fn((fn) => fn),
+  getActiveAdapterStrategy: vi.fn(() => "fallback"),
+}));
+
+import { handleChat } from "@/sse/handlers/chat.js";
+
+const originalFetch = global.fetch;
+
+const makeRequest = (body, headers = {}) =>
+  new Request("http://localhost/v1/chat/completions", {
+    method: "POST",
+    headers: { "Content-Type": "application/json", ...headers },
+    body: JSON.stringify(body),
+  });
+
+const account = (id) => ({
+  connectionId: id,
+  connectionName: `acc-${id}`,
+  accessToken: "tok",
+  refreshToken: "ref",
+  authType: "oauth",
+});
+
+beforeEach(() => {
+  global.fetch = vi.fn();
+  authMocks.getProviderCredentials.mockReset();
+  authMocks.getProviderCredentials.mockImplementation(async (_p, exclude) =>
+    exclude.size === 0 ? account("conn-A") : null,
+  );
+  authMocks.markAccountUnavailable.mockClear();
+  authMocks.clearAccountError.mockClear();
+  tokenMocks.checkAndRefreshToken.mockClear();
+});
+
+afterEach(() => {
+  global.fetch = originalFetch;
+});
+
+describe("chat x-connection-id pinning", () => {
+  it("forwards x-connection-id as preferredConnectionId", async () => {
+    const res = await handleChat(
+      makeRequest({ model: "prov/m1", messages: [{ role: "user", content: "hi" }] }, { "x-connection-id": "conn-B" }),
+    );
+    expect(res.status).toBe(200);
+    expect(authMocks.getProviderCredentials).toHaveBeenCalledWith(
+      "prov",
+      expect.anything(),
+      "m1",
+      expect.objectContaining({ preferredConnectionId: "conn-B" }),
+    );
+  });
+
+  it("passes null when no pin header is present", async () => {
+    await handleChat(makeRequest({ model: "prov/m1", messages: [{ role: "user", content: "hi" }] }));
+    expect(authMocks.getProviderCredentials).toHaveBeenCalledWith(
+      "prov",
+      expect.anything(),
+      "m1",
+      expect.objectContaining({ preferredConnectionId: null }),
+    );
+  });
+});