Extract the WebSocket close-code decision into a pure ReconnectPolicy
module and cover it with node:test. The plugin now names the 1008
policy-violation code instead of using a magic number, and the terminal
behavior of a 1008 close is pinned by a regression test so a future
refactor cannot reintroduce the reconnect storm.
Document the contract in mem:mcp/core: 1008 is terminal, it comes from a
duplicate user token or a missing token in multi-user mode, and recovery
is manual via "Connect here".
Closes#11510
AI-assisted-by: deepseek-v4.1-flash
