Nursery: document syncAwaitAll's caller io_context requirement for LLMs

README.md

@@ -204,7 +204,8 @@ nursery.launch(
 
 nursery.requestCancelOnAll();
 nursery.closeAdmission();
-nursery.syncAwaitAllSettlements(ioContext);
+nursery.syncAwaitAllSettlements(
+	sscl::ComponentThread::getSelf()->getIoContext());
 ```
 
 Each slot owns a `SyncCancelerForAsyncWork`. `requestCancelOnAll()` only signals
@@ -213,6 +214,14 @@ completion callbacks run. Call `closeAdmission()` explicitly before
 `asyncAwaitAllSettlements()` or `syncAwaitAllSettlements()`; those APIs wait until
 all slots have retired naturally and throw if admission is still open.
 
+`syncAwaitAllSettlements()` runs a nested `io_context` loop on the **calling
+thread** (it blocks in `run_one()` until every slot has retired). Pass the
+caller thread's `io_context` — usually `ComponentThread::getSelf()->getIoContext()`
+— not some other thread's context. While the caller is blocked pumping another
+thread's queue, handlers posted to the caller's own `io_context` are abandoned
+and the drain can deadlock even when in-flight work has already completed on a
+different thread.
+
 `launch(factory, onSettledHook)` registers a non-null hook before `fillSlot()`.
 Omit the hook (default `nullptr`) when no settlement callback is needed.
 `Slot::Lease` is commit-required: an uncommitted lease removes its

include/spinscale/co/nonViralTaskNursery.h

@@ -45,9 +45,15 @@ struct MemberInvoker : MemberInvokerBase
  *	SyncCancelerForAsyncWork, and provides drain APIs.
  *
  *	Call closeAdmission() explicitly before asyncAwaitAllSettlements() or
- *	syncAwaitAllSettlements(). syncAwaitAllSettlements() caller must pass the
+ *	syncAwaitAllSettlements().
- *	io_context where non-viral posting completions will land, and must ensure
+ *
- *	that io_context is prepared to run (e.g. not left stopped without restart).
+ *	syncAwaitAllSettlements() runs a nested io_context loop on the calling
+ *	thread (AsynchronousBridge). Pass the calling thread's io_context —
+ *	typically
+ *	ComponentThread::getSelf()->getIoContext() — not another thread's
+ *	io_context. If the caller pumps a different thread's queue while blocked,
+ *	completions posted back to the caller's own io_context are never executed
+ *	and the drain can deadlock even after cooperative cancel.
  */
 class NonViralTaskNursery
 {
@@ -307,6 +313,9 @@ public:
 		}
 	}
 
+	/** Nested drain: blocks the calling thread in run_one() on @p ioContext until
+	 * all slots retire. @p ioContext must be the caller thread's io_context.
+	 */
 	void syncAwaitAllSettlements(boost::asio::io_context &ioContext)
 	{
 		if (admissionIsOpen())

include/spinscale/cps/asynchronousBridge.h

@@ -25,6 +25,10 @@ public:
 		boost::asio::post(io_context, []{});
 	}
 
+	/** Blocks the calling thread in run_one() on the bridge's io_context.
+	 * Used by syncAwaitAllSettlements(); that io_context must be the caller
+	 * thread's own queue so posted completions on the caller are not starved.
+	 */
 	void waitForAsyncOperationCompleteOrIoContextStopped(void)
 	{
 		for (;;)