Scheduling: fair bounded admission for interactive, write and background work #176

Problem

Query, write, proof and subscription workloads need bounded admission without starving final subscription state or writers under sustained load.

Evidence

Source: 5c1f313379a5cb2995a43a66ddba0b5cc9798b7f (inspected 2026-10-03). These are source findings; the acceptance scenarios below still need implementation and execution.

• src/protocol/handler.rs:2280: Ordinary execution acquires the shared query semaphore.
• src/protocol/handler.rs:4135: Session execution also acquires the shared semaphore.

Acceptance criteria

• Reuse one admission policy with configurable measured lane sizes, bounded queues and deadlines; avoid a new global evaluator lock.
• Saturate each workload class and demonstrate bounded waits, background progress, no writer starvation and no lost final subscription state.
• Return honest overload/timeout errors and release counters on cancellation or disconnect.
• Run mixed cheap queries, writes, refreshes and proofs through Performance: baseline and mandatory pre-PR regression pipeline #163.

Delivery

Plan item: E02. R3 - Streaming SDK subscriptions.

Dependencies / related work: #173, #175.

Contributes to #132; completing this slice alone does not close the broader issue.