Linear OAuth: token endpoint returns 503, then 400 invalid_grant on every retry

## Problem

I am building Linear OAuth and the token endpoint is behaving strangely. The first POST to `https://api.linear.app/oauth/token` with `grant_type=authorization_code` returns `503 Service Unavailable`. Every request after that returns `400 Bad Request` with `{"error": "invalid_grant", "error_description": "Invalid grant: authorization code is invalid"}`. My client_id, client_secret, redirect_uri, and code are all correct. Am I rate-limited, or is something else going on?

## Verified fix

You are not rate-limited, and your code was valid. The culprit was the `timeSchedule:write` scope in the authorize URL. Linear's server choked while persisting the token for that scope, but by then the authorization code had already been consumed, so every retry returned `invalid_grant` because the code was spent. That is why you see the weird 503-then-400 pattern: the first request fails after consuming the code, and all subsequent requests fail because the code is gone. The fix is to drop `timeSchedule:write` from your scope list (it overlaps with the other scopes you already request anyway) and start a fresh OAuth flow. Linear also fixed this server-side, and the reporter confirmed the token exchange worked after the change.

Source: https://github.com/linear/linear/issues/637