fix: handle GitHub API rate limits in account age check

The GitHub account lookup uses unauthenticated requests (60 req/hr
per IP). Since this runs server-side in Convex, all users share the
same IP and quickly exhaust the rate limit, causing "GitHub account
lookup failed" errors during skill publish.

- Detect 403/429 responses and surface a clear rate-limit message
- Support optional GITHUB_TOKEN env var for authenticated requests
  (5,000 req/hr)

Fixes #155

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

convex/lib/githubAccount.test.ts

@@ -105,11 +105,80 @@ describe('requireGitHubAccountAge', () => {
       githubFetchedAt: 0,
     })
     const runMutation = vi.fn()
-    const fetchMock = vi.fn().mockResolvedValue({ ok: false })
+    const fetchMock = vi.fn().mockResolvedValue({ ok: false, status: 404 })
     vi.stubGlobal('fetch', fetchMock)
 
     await expect(
       requireGitHubAccountAge({ runQuery, runMutation } as never, 'users:1' as never),
     ).rejects.toThrow(/GitHub account lookup failed/i)
   })
+
+  it('throws rate-limit error on 403', async () => {
+    const runQuery = vi.fn().mockResolvedValue({
+      _id: 'users:1',
+      handle: 'steipete',
+      githubCreatedAt: undefined,
+      githubFetchedAt: 0,
+    })
+    const runMutation = vi.fn()
+    const fetchMock = vi.fn().mockResolvedValue({ ok: false, status: 403 })
+    vi.stubGlobal('fetch', fetchMock)
+
+    await expect(
+      requireGitHubAccountAge({ runQuery, runMutation } as never, 'users:1' as never),
+    ).rejects.toThrow(/rate limit exceeded/i)
+  })
+
+  it('throws rate-limit error on 429', async () => {
+    const runQuery = vi.fn().mockResolvedValue({
+      _id: 'users:1',
+      handle: 'steipete',
+      githubCreatedAt: undefined,
+      githubFetchedAt: 0,
+    })
+    const runMutation = vi.fn()
+    const fetchMock = vi.fn().mockResolvedValue({ ok: false, status: 429 })
+    vi.stubGlobal('fetch', fetchMock)
+
+    await expect(
+      requireGitHubAccountAge({ runQuery, runMutation } as never, 'users:1' as never),
+    ).rejects.toThrow(/rate limit exceeded/i)
+  })
+
+  it('includes Authorization header when GITHUB_TOKEN is set', async () => {
+    vi.useFakeTimers()
+    const now = new Date('2026-02-02T12:00:00Z')
+    vi.setSystemTime(now)
+
+    vi.stubEnv('GITHUB_TOKEN', 'ghp_test123')
+
+    const runQuery = vi.fn().mockResolvedValue({
+      _id: 'users:1',
+      handle: 'steipete',
+      githubCreatedAt: undefined,
+      githubFetchedAt: now.getTime() - 2 * ONE_DAY_MS,
+    })
+    const runMutation = vi.fn()
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({
+        created_at: '2020-01-01T00:00:00Z',
+      }),
+    })
+    vi.stubGlobal('fetch', fetchMock)
+
+    await requireGitHubAccountAge({ runQuery, runMutation } as never, 'users:1' as never)
+
+    expect(fetchMock).toHaveBeenCalledWith(
+      'https://api.github.com/users/steipete',
+      expect.objectContaining({
+        headers: {
+          'User-Agent': 'clawhub',
+          Authorization: 'Bearer ghp_test123',
+        },
+      }),
+    )
+
+    vi.useRealTimers()
+  })
 })

convex/lib/githubAccount.ts

@@ -24,10 +24,23 @@ export async function requireGitHubAccountAge(ctx: ActionCtx, userId: Id<'users'
   const stale = !createdAt || now - fetchedAt > FETCH_TTL_MS
 
   if (stale) {
+    const headers: Record<string, string> = { 'User-Agent': 'clawhub' }
+    const token = process.env.GITHUB_TOKEN
+    if (token) {
+      headers['Authorization'] = `Bearer ${token}`
+    }
+
     const response = await fetch(`${GITHUB_API}/users/${encodeURIComponent(handle)}`, {
-      headers: { 'User-Agent': 'clawhub' },
+      headers,
     })
-    if (!response.ok) throw new ConvexError('GitHub account lookup failed')
+    if (!response.ok) {
+      if (response.status === 403 || response.status === 429) {
+        throw new ConvexError(
+          'GitHub API rate limit exceeded — please try again in a few minutes',
+        )
+      }
+      throw new ConvexError('GitHub account lookup failed')
+    }
 
     const payload = (await response.json()) as GitHubUser
     const parsed = payload.created_at ? Date.parse(payload.created_at) : Number.NaN