Context Compress

REST door for MCP focus (alias compress_context). POST /context/focus is the canonical path (Jay SETTLED 2026-10-09 rename to Focus); /context/compress is kept as an alias on the same handler. (CONNECT request 2026-09-09: workers skip the MCP handshake). Same core, same caller binding (API key), same brief + fidelity + metrics body. Key-required, quota-free on the sell plane ("/context" in AUTH_PATHS is customer-tier here — see metering._admin_required). The caller's context profile is enforced BEFORE the model sees the text (coded LIM-CTX-002/003 → 400; over budget → withheld with a receipt on context_receipt, never an error).