CVE-2026-107727: Strawberry legacy graphql-ws retains naturally completed subscription slots

Strawberry’s legacy graphql-ws subscription handler can retain task and subscription bookkeeping after a one-shot subscription has naturally sent its complete message. When the application configures max_subscriptions_per_connection, the handler counts those completed operations in len(self.tasks). A client that uses distinct operation IDs can therefore reach the configured subscription limit even though the earlier subscriptions have already completed, causing subsequent legitimate subscriptions on the same persistent WebSocket connection to receive Subscription limit reached.

This is a conditional connection-level availability and resource-accounting issue. It requires explicit use of the legacy graphql-ws protocol, a persistent WebSocket connection, one-shot subscriptions that naturally complete, and a configured max_subscriptions_per_connection limit. It is not an unconditional issue in a default Strawberry installation and is distinct from the previously fixed single-connection infinite-subscription issue.