[SaladDay]

A Turn in waiting kept its OAC_EXECUTION_CONCURRENCY slot until the application answered. With the default of 4, four unanswered function calls stopped all hosted execution in Core, for every provider and Harness.

• The delivery loop reports whether its Turn waits for function results. The Session stays reserved (no other work runs on it), but the Worker counts only the remaining Sessions against the limit.
• A resumed Turn takes its slot back, so execution.slots_in_use can briefly exceed slots_total; documented in Core metrics (English and Chinese).
• Turn completions no longer rely on a buffer sized to the limit: more Turns than the limit can now be alive.

Test: TestWorkerWaitingTurnHoldsNoExecutionSlot — with concurrency 1, a waiting Turn no longer blocks another Session's Turn (fails on main with a read timeout).

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