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Query Admission Control Implementation Plan

Goal: Bound resource occupancy per stateless Query replica while preserving incremental Flight streaming and the metadata shielding invariant.

Architecture

Add immutable QueryLimits plus one process-local QueryAdmission semaphore. GetFlightInfo holds a permit while validating/planning. DoGet acquires another permit and moves it into a deadline-aware stream wrapper; completion, timeout, or client drop releases it. Request-size validation occurs before catalog or DataFusion work. CLI parses finite environment limits once at startup.

Delivery order

  1. RED: saturation plus stream-drop permit release.
  2. Implement limits, admission acquisition, and permit-owning Flight stream.
  3. RED: execution deadline and oversize SQL/ticket behavior; implement both.
  4. RED: CLI environment-value parsing; wire QueryServerConfig.
  5. Document defaults and gRPC failure semantics.
  6. Run spec lifecycle, strict clippy, LocalStack integration, and full gate; rebase, re-run, open PR, and merge.