The per-provider semaphore (e.g. `providers.ollama-cloud.maxConcurrency`) was acquired before `SessionManager.open` and released only after `driveSessionToYield` returned, so it bracketed the whole subagent lifecycle. Any spawn tree wider than `maxConcurrency` deadlocked: parents held every slot while waiting for children that were queued on the same cap — symptoms matched zero LLM requests and tokens=0/requests=0 cancellations.
Moved the bracket into a `StreamFn` wrapper. The wrapper acquires the slot just before each provider HTTP request and releases it the moment the response stream produces 'done'/'error', so a parent's slot is free between turns and child subagents can acquire while their parent's tool calls run. Wraps both the main agent and the advisor (both consume `settingsAwareStreamFn`).
Fixes#3749
The per-provider subagent limiter (providers.ollama-cloud.maxConcurrency)
created a fresh Semaphore whenever the configured limit changed, orphaning
in-flight slots on the old instance so a runtime or mixed limit value could
exceed the cap. getProviderSemaphore now always hands out one shared limiter
(Infinity when unlimited, so every run is still counted) and resizes it in
place. Semaphore.release() decrements before admitting, and the new
Semaphore.resize() raises the ceiling by admitting queued waiters while
lowering it drains in-flight holders without admitting past the new cap.
Refs #3464
Semaphore.acquire now accepts an AbortSignal so a queued waiter that is cancelled (parent task abort, wall-clock budget elapsing) removes itself from the wait queue instead of being resolved by the next release. The provider semaphore in runSubprocess passes the run's abortSignal through, preventing aborted ollama-cloud subagents from permanently draining the provider concurrency budget.
Fixes#3464
roboomp