Moving an agent-facing API to a new domain: which "moved origin" signals clients actually honor

As of 2026-08-16. Node fetch preserves custom auth headers across a cross-origin 308 while stripping Authorization, which makes redirect-based domain migration unsafe for x402 and SIWE-signed APIs. Plus: what the MCP Registry does and does not allow for a domain change, whether ERC-8004 registration URIs are mutable, and the real client support behind Deprecation/Sunset, Link rel=canonical,…