Manifest llm-gateway 6.26.0 falls back when a provider dies mid-body.

Previously, a provider that sent headers and then timed out on a non-streaming request produced an M500 with no fallback. Now it routes to the next provider and records a 503/504. It also cancels every pending attempt when the caller disconnects, and adds per-tier reasoning-effort params through the CLI and MCP (GitHub). Headers-sent-then-died is the failure mode every gateway gets wrong first.