fix(github): hold monthly-exhausted accounts until reset

Lock GitHub Copilot connections account-wide until 00:00 UTC on the
first of next month when the upstream 402 response indicates the
monthly additional-usage-limit was hit, instead of only cooling down
the requested model for 120s. Other GitHub 402 responses keep the
existing model-scoped cooldown.

src/sse/services/auth.js

@@ -8,6 +8,15 @@ import * as log from "../utils/logger.js";
 // Mutex to prevent race conditions during account selection
 let selectionMutex = Promise.resolve();
 
+const GITHUB_MONTHLY_USAGE_LIMIT = "you've reached your additional usage limit for your plan";
+
+function githubMonthlyResetMs(status, errorText, provider) {
+  if (resolveProviderId(provider) !== "github" || Number(status) !== 402) return null;
+  if (!String(errorText || "").toLowerCase().includes(GITHUB_MONTHLY_USAGE_LIMIT)) return null;
+  const now = new Date();
+  return Date.UTC(now.getUTCFullYear(), now.getUTCMonth() + 1, 1);
+}
+
 /**
  * Get provider credentials from localDb
  * Filters out unavailable accounts and returns the selected account based on strategy
@@ -213,9 +222,16 @@ export async function markAccountUnavailable(connectionId, status, errorText, pr
   const conn = connections.find(c => c.id === connectionId);
   const backoffLevel = conn?.backoffLevel || 0;
 
+  // GitHub premium-request exhaustion is account-wide until the next UTC month.
+  const githubResetAtMs = githubMonthlyResetMs(status, errorText, provider);
+
   // Provider-specific precise cooldown (e.g. codex usage_limit_reached resets_at) overrides backoff
   let shouldFallback, cooldownMs, newBackoffLevel;
-  if (resetsAtMs && resetsAtMs > Date.now()) {
+  if (githubResetAtMs) {
+    shouldFallback = true;
+    cooldownMs = githubResetAtMs - Date.now();
+    newBackoffLevel = 0;
+  } else if (resetsAtMs && resetsAtMs > Date.now()) {
     shouldFallback = true;
     cooldownMs = Math.min(resetsAtMs - Date.now(), MAX_RATE_LIMIT_COOLDOWN_MS);
     newBackoffLevel = 0;
@@ -225,7 +241,7 @@ export async function markAccountUnavailable(connectionId, status, errorText, pr
   if (!shouldFallback) return { shouldFallback: false, cooldownMs: 0 };
 
   const reason = typeof errorText === "string" ? errorText.slice(0, 100) : "Provider error";
-  const lockUpdate = buildModelLockUpdate(model, cooldownMs);
+  const lockUpdate = buildModelLockUpdate(githubResetAtMs ? null : model, cooldownMs);
 
   await updateProviderConnection(connectionId, {
     ...lockUpdate,

tests/unit/github-monthly-usage-lock.test.js

@@ -0,0 +1,86 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const dbMocks = vi.hoisted(() => ({
+  getProviderConnections: vi.fn(),
+  updateProviderConnection: vi.fn(),
+}));
+
+vi.mock("@/lib/localDb", () => dbMocks);
+vi.mock("@/lib/network/connectionProxy", () => ({
+  pickProxyPoolId: vi.fn(),
+  resolveConnectionProxyConfig: vi.fn(),
+}));
+vi.mock("@/shared/constants/providers.js", () => ({
+  FREE_PROVIDERS: {},
+  resolveProviderId: (provider) => provider,
+}));
+vi.mock("@/sse/utils/logger.js", () => ({ debug: vi.fn(), info: vi.fn(), warn: vi.fn() }));
+
+const { markAccountUnavailable } = await import("../../src/sse/services/auth.js");
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  dbMocks.getProviderConnections.mockResolvedValue([{
+    id: "github-a",
+    provider: "github",
+    name: "github-a",
+    backoffLevel: 4,
+  }]);
+});
+
+describe("GitHub monthly usage exhaustion", () => {
+  it("locks the whole account until the next UTC month", async () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-08-04T19:30:00.000Z"));
+
+    try {
+      await markAccountUnavailable(
+        "github-a",
+        402,
+        "You've reached your additional usage limit for your plan. Go to GitHub settings for details.",
+        "github",
+        "claude-fable-5",
+      );
+
+      expect(dbMocks.updateProviderConnection).toHaveBeenCalledWith(
+        "github-a",
+        expect.objectContaining({
+          modelLock___all: "2026-09-01T00:00:00.000Z",
+          testStatus: "unavailable",
+          errorCode: 402,
+          backoffLevel: 0,
+        }),
+      );
+      expect(dbMocks.updateProviderConnection.mock.calls[0][1])
+        .not.toHaveProperty("modelLock_claude-fable-5");
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+
+  it("keeps unrelated GitHub 402 errors model-scoped", async () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date("2026-08-04T19:30:00.000Z"));
+
+    try {
+      await markAccountUnavailable(
+        "github-a",
+        402,
+        "Payment required",
+        "github",
+        "claude-fable-5",
+      );
+
+      expect(dbMocks.updateProviderConnection).toHaveBeenCalledWith(
+        "github-a",
+        expect.objectContaining({
+          "modelLock_claude-fable-5": "2026-08-04T19:32:00.000Z",
+        }),
+      );
+      expect(dbMocks.updateProviderConnection.mock.calls[0][1])
+        .not.toHaveProperty("modelLock___all");
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+});