FerroGate v2026.08.23.4 - Pi Agent Anthropic compatibility

Changes

• map standard Anthropic ephemeral cache markers to automatic-cache upstream semantics
• preserve strict refusal for explicit cache disable and one-hour retention when an upstream cannot honor them
• add regression coverage for Pi Agent-style cache markers and long-retention refusal

Validation

• release review found no blocking issues or leaked credentials
• gateway typecheck and Biome passed
• 3,234 gateway tests, 26 rate-limit tests, and 50 tenancy tests passed

Deployment scope

• FerroGate gateway only