fix: only invalidate cached token on auth rejection, not all disconnects
Narrow token invalidation to only fire when the server returns 401/403
(upgrade_failure), indicating the token or OAuth client is invalid.
Normal disconnects (server restart, network blip) no longer force an
unnecessary HTTP reauthentication.
sow-157
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>