mcp: abstract transport session storage

TASKS.md

@@ -2,19 +2,19 @@
 
 ## Current
 
-### `feat/runtime-rate-limiting-and-backpressure`
+### `feat/distributed-mcp-session-store`
 
 Status: in_progress
 
 DoD:
-- runtime rejects overload deterministically with stable error codes
-- unary, window, session, and async-job execution paths are concurrency-bounded
-- configuration is explicit and documented
-- admin-api and mcp-server use the configured runtime limits
+- transport sessions are stored behind a shared store abstraction
+- mcp-server no longer depends directly on process-local session storage implementation
+- in-memory session store remains available for tests and local fallback
+- follow-up slices can add a Postgres-backed transport session store without changing transport handlers
 
 ## Next
 
-- `feat/distributed-mcp-session-store`
+- `feat/runtime-rate-limiting-and-backpressure`
 
 ## Backlog