Anthropic Max OAuth fails: token exchange 404s because Anthropic now blocks the claude-cli/ User-Agent

#48534 Fixed P1 comp/agent

Anthropic Max OAuth fails: token exchange 404s because Anthropic now blocks the claude-cli/ User-Agent

The built-in Anthropic OAuth token exchange fails with HTTP 404 because Anthropic now blocks any request carrying a claude-cli/ User-Agent prefix regardless of version, confirmed by testing multiple User-Agent strings.