Merge strategy: keep local Claude customizations (ours), accept all other upstream changes. Claude constants.go retains: - DefaultCLIVersion = 2.1.88 - Enhanced beta headers (9 new betas) - ModelSupports1M() function - GetOAuthBetaHeader() function - GetAPIKeyBetaHeader() function - ApplyFingerprintOverrides() function Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>