Tool sessions

The MCP handler correlates calls into tool sessions so Cedar policies can reason about prior tool use and policy hit counts (server/utils/mcp-authz.ts, buildSessionEntity).

External session id resolution (server/routes/mcp/[...].ts) prefers, in order: vendor headers (x-claude-code-session-id, mcp-session-id, openai-conversation-id, x-mcp-session-id), optional JSON-RPC metadata, otherwise a short deterministic fingerprint from client IP, User-Agent, and proxy key (so unrelated tenants do not share a synthetic id). Values are sanitized before echoing in response headers.

Idle sessions are expired on a timer and on startup (see server/plugins/init.ts and the inactivity env documented there).