FerroGate v2026.08.23.3 - Anthropic Messages compatibility

Changes

• preserve the Anthropic Messages response contract when a provider uses the OpenAI Responses upstream protocol
• compose Responses-to-Chat and Chat-to-Anthropic stream normalization for Claude Code and Anthropic SDK clients
• reject invalid successful Responses payloads instead of returning an empty Anthropic message
• add buffered and streaming protocol and billing regression coverage

Validation

• gateway typecheck passed
• Biome checks passed
• 3,232 gateway tests passed
• 26 rate-limit harness tests passed
• 50 tenancy harness tests passed

Deployment scope

• FerroGate gateway only