diff --git a/smocore/body/body.cpp b/smocore/body/body.cpp
index 6c7e2f4..a583dcb 100644
--- a/smocore/body/body.cpp
+++ b/smocore/body/body.cpp
@@ -64,21 +64,8 @@ BodyViralPostingInvoker<void> Body::initializeCReq()
 			<< '\n';
 	}
 
-	sscl::MultiOperationResultSet attachResults = co_await
-		device::DeviceManager::getInstance()
-			.attachAllUnattachedDevicesFromCmdlineCReq();
-	std::cout << "Mrntt: attached "
-		<< attachResults.nSucceeded << " of " << attachResults.nTotal
-		<< " sense devices." << "\n";
-
-	if (attachResults.nTotal > 0 && attachResults.nSucceeded == 0)
-	{
-		throw std::runtime_error(
-			std::string(__func__)
-			+ ": Failed to attach any of "
-			+ std::to_string(attachResults.nTotal)
-			+ " requested sense devices");
-	}
+	co_await device::DeviceManager::getInstance()
+		.attachAllUnattachedDevicesFromCmdlineCReq();
 
 	co_return;
 }
@@ -102,21 +89,8 @@ BodyViralPostingInvoker<void> Body::finalizeCReq()
 	}
 
 	std::cout << "Mrntt: About to detach all sense devices." << "\n";
-	sscl::MultiOperationResultSet detachResults = co_await
-		device::DeviceManager::getInstance().detachAllAttachedDeviceRolesCReq();
-
-	if (detachResults.nFailed > 0)
-	{
-		std::cerr << "Mrntt: Failed to detach "
-			<< detachResults.nFailed << " of " << detachResults.nTotal
-			<< " sense devices." << "\n";
-	}
-	else
-	{
-		std::cout << "Mrntt: Successfully detached "
-			<< detachResults.nSucceeded << " of " << detachResults.nTotal
-			<< " sense devices." << "\n";
-	}
+	co_await device::DeviceManager::getInstance()
+		.detachAllAttachedDeviceRolesCReq();
 
 	std::cout << "Mrntt: About to finalize all stim buff api libs." << "\n";
 	co_await stim_buff::StimBuffApiManager::getInstance()
diff --git a/smocore/deviceManager/deviceManager.cpp b/smocore/deviceManager/deviceManager.cpp
index ec35557..44d19dd 100644
--- a/smocore/deviceManager/deviceManager.cpp
+++ b/smocore/deviceManager/deviceManager.cpp
@@ -16,6 +16,7 @@
 #include <mind.h>
 #include <spinscale/co/postTarget.h>
 #include <spinscale/co/group.h>
+#include <spinscale/asynchronousLoop.h>
 
 namespace smo {
 namespace device {
@@ -43,6 +44,28 @@ std::shared_ptr<sscl::ComponentThread> threadForDeviceOp(
 	return mind::globalMind->body.thread;
 }
 
+void throwIfStimBuffAttachFailed(
+	const stim_buff::StimBuffDeviceOpResult &result,
+	const char *callerFn)
+{
+	if (result.success) { return; }
+
+	throw std::runtime_error(
+		std::string(callerFn) + ": attach failed for "
+		+ result.deviceSpec->stringify());
+}
+
+void throwIfStimBuffDetachFailed(
+	const stim_buff::StimBuffDeviceOpResult &result,
+	const char *callerFn)
+{
+	if (result.success) { return; }
+
+	throw std::runtime_error(
+		std::string(callerFn) + ": detach failed for "
+		+ result.deviceSpec->stringify());
+}
+
 } // namespace
 
 DeviceManager::~DeviceManager()
@@ -60,38 +83,30 @@ const std::string DeviceManager::stringifyDeviceSpecs(void)
 	return oss.str();
 }
 
-mrntt::MrnttViralPostingInvoker<stim_buff::StimBuffDeviceOpResult>
+mrntt::MrnttViralPostingInvoker<void>
 DeviceManager::attachStimBuffDeviceCReq(
 	const std::shared_ptr<DeviceAttachmentSpec>& spec)
 {
 	assertMarionetteThread();
 
 	auto &sbam = stim_buff::StimBuffApiManager::getInstance();
-	auto libOpt = sbam.getStimBuffApiLibByApiName(spec->stimBuffApi);
-	if (!libOpt)
-	{
-		std::cerr << "attachStimBuffDeviceCReq: No library found for API '"
-			<< spec->stimBuffApi << "'" << std::endl;
-		co_return stim_buff::StimBuffDeviceOpResult{false, spec};
-	}
-
-	auto &lib = *libOpt.value();
+	auto &lib = sbam.getStimBuffApiLibByApiName(spec->stimBuffApi);
 
 	if (lib.isBeingDestroyed.load())
 	{
-		std::cerr << std::string(__func__) + ": Library is being destroyed"
-			<< " for API '" << spec->stimBuffApi << "'. Bailing out.\n";
-		co_return stim_buff::StimBuffDeviceOpResult{false, spec};
+		throw std::runtime_error(
+			std::string(__func__) + ": Library is being destroyed"
+			+ " for API '" + spec->stimBuffApi + "'");
 	}
 
 	if (!lib.stimBuffApiDesc.sal_mgmt_libOps.attachDeviceCReq)
 	{
-		std::cerr << std::string(__func__) + ": attachDeviceCReq() is NULL "
-			"for library '" << lib.libraryPath << "'"
-			<< std::endl;
-		co_return stim_buff::StimBuffDeviceOpResult{false, spec};
+		throw std::runtime_error(
+			std::string(__func__) + ": attachDeviceCReq() is NULL "
+			"for library '" + lib.libraryPath + "'");
 	}
 
+	/* FIXME Locking here  makes no sense. */
 	sscl::co::CoQutex::ReleaseHandle sbamGuard =
 		co_await sbam.s.lock.getAcquireInvocationAndSuspensionPolicy();
 	sscl::co::CoQutex::ReleaseHandle libGuard =
@@ -119,43 +134,38 @@ DeviceManager::attachStimBuffDeviceCReq(
 			<< spec->deviceIdentifier << " to body thread" << "\n";
 	}
 
-	co_return co_await lib.stimBuffApiDesc.sal_mgmt_libOps.attachDeviceCReq(
-		sscl::co::ExplicitPostTarget{targetThread->getIoContext()},
-		spec, targetThread);
+	stim_buff::StimBuffDeviceOpResult result =
+		co_await lib.stimBuffApiDesc.sal_mgmt_libOps.attachDeviceCReq(
+			sscl::co::ExplicitPostTarget{targetThread->getIoContext()},
+			spec, targetThread);
+	throwIfStimBuffAttachFailed(result, __func__);
+	co_return;
 }
 
-mrntt::MrnttViralPostingInvoker<stim_buff::StimBuffDeviceOpResult>
+mrntt::MrnttViralPostingInvoker<void>
 DeviceManager::detachStimBuffDeviceCReq(
 	const std::shared_ptr<DeviceAttachmentSpec>& spec)
 {
 	assertMarionetteThread();
 
 	auto &sbam = stim_buff::StimBuffApiManager::getInstance();
-	auto libOpt = sbam.getStimBuffApiLibByApiName(spec->stimBuffApi);
-	if (!libOpt)
-	{
-		std::cerr << "detachStimBuffDeviceCReq: No library found for API '"
-			<< spec->stimBuffApi << "'" << std::endl;
-		co_return stim_buff::StimBuffDeviceOpResult{false, spec};
-	}
-
-	auto &lib = *libOpt.value();
+	auto &lib = sbam.getStimBuffApiLibByApiName(spec->stimBuffApi);
 
 	if (lib.isBeingDestroyed.load())
 	{
-		std::cerr << std::string(__func__) + ": Library is being destroyed"
-			<< " for API '" << spec->stimBuffApi << "'. Bailing out.\n";
-		co_return stim_buff::StimBuffDeviceOpResult{false, spec};
+		throw std::runtime_error(
+			std::string(__func__) + ": Library is being destroyed"
+			+ " for API '" + spec->stimBuffApi + "'");
 	}
 
 	if (!lib.stimBuffApiDesc.sal_mgmt_libOps.detachDeviceCReq)
 	{
-		std::cerr << std::string(__func__) + ": detachDeviceCReq() is NULL "
-			"for library '" << lib.libraryPath << "'"
-			<< std::endl;
-		co_return stim_buff::StimBuffDeviceOpResult{false, spec};
+		throw std::runtime_error(
+			std::string(__func__) + ": detachDeviceCReq() is NULL "
+			"for library '" + lib.libraryPath + "'");
 	}
 
+	/* FIXME Locking here  makes no sense. */
 	sscl::co::CoQutex::ReleaseHandle sbamGuard =
 		co_await sbam.s.lock.getAcquireInvocationAndSuspensionPolicy();
 	sscl::co::CoQutex::ReleaseHandle libGuard =
@@ -165,12 +175,15 @@ DeviceManager::detachStimBuffDeviceCReq(
 	std::shared_ptr<sscl::ComponentThread> targetThread =
 		threadForDeviceOp(*spec);
 
-	co_return co_await lib.stimBuffApiDesc.sal_mgmt_libOps.detachDeviceCReq(
-		sscl::co::ExplicitPostTarget{targetThread->getIoContext()},
-		spec);
+	stim_buff::StimBuffDeviceOpResult result =
+		co_await lib.stimBuffApiDesc.sal_mgmt_libOps.detachDeviceCReq(
+			sscl::co::ExplicitPostTarget{targetThread->getIoContext()},
+			spec);
+	throwIfStimBuffDetachFailed(result, __func__);
+	co_return;
 }
 
-mrntt::MrnttViralPostingInvoker<DeviceManager::DeviceAttachmentIndResult>
+mrntt::MrnttViralPostingInvoker<std::shared_ptr<DeviceRole>>
 DeviceManager::newDeviceAttachmentSpecIndCReq(
 	const DeviceAttachmentSpec &spec)
 {
@@ -242,36 +255,29 @@ DeviceManager::newDeviceAttachmentSpecIndCReq(
 				", deviceExists=" + std::to_string(deviceExists));
 		}
 
-		// Already attached, return success
-		co_return DeviceAttachmentIndResult{
-			true, existingDeviceRole, specPtr};
+		co_return existingDeviceRole;
 	}
 
-	stim_buff::StimBuffDeviceOpResult attachResult =
-		co_await attachStimBuffDeviceCReq(specPtr);
+	dmGuard.release();
 
-	if (!attachResult.success)
-	{
-		std::cerr << __func__ << ": Attach failed for device spec "
-			<< attachResult.deviceSpec->stringify() << std::endl;
-		co_return DeviceAttachmentIndResult{
-			false, nullptr, attachResult.deviceSpec};
-	}
+	/*	FIXME:
+	 * We should add an unlocked flag to at/detachStimBuffDeviceCReq()
+	 * so we can call it with the devmgr lock held.
+	 */
+	co_await attachStimBuffDeviceCReq(specPtr);
 
-	try {
-		// Create DeviceRole and add it to both DeviceManager's and Device's collections
-		auto deviceRole = std::make_shared<DeviceRole>(*device, specPtr);
-		device->deviceRoles.push_back(deviceRole);
-		dm.s.rsrc.attachedDeviceRoles.push_back(deviceRole);
+	sscl::co::CoQutex::ReleaseHandle dmGuardAfterAttach =
+		co_await dm.s.lock.getAcquireInvocationAndSuspensionPolicy();
+	(void)dmGuardAfterAttach;
 
-		co_return DeviceAttachmentIndResult{true, deviceRole, specPtr};
-	} catch (const std::exception&) {
-		// Attach failed, return error
-		co_return DeviceAttachmentIndResult{false, nullptr, specPtr};
-	}
+	auto deviceRole = std::make_shared<DeviceRole>(*device, specPtr);
+	device->deviceRoles.push_back(deviceRole);
+	dm.s.rsrc.attachedDeviceRoles.push_back(deviceRole);
+
+	co_return deviceRole;
 }
 
-mrntt::MrnttViralPostingInvoker<DeviceManager::DeviceAttachmentIndResult>
+mrntt::MrnttViralPostingInvoker<void>
 DeviceManager::removeDeviceAttachmentSpecCReq(
 	const DeviceAttachmentSpec &spec)
 {
@@ -294,95 +300,92 @@ DeviceManager::removeDeviceAttachmentSpecCReq(
 
 	if (!specPtr)
 	{
-		// Spec not found, return failure
-		co_return DeviceAttachmentIndResult{false, nullptr, nullptr};
+		throw std::runtime_error(
+			std::string(__func__) + ": Device attachment spec not found: "
+			+ spec.stringify());
 	}
 
-	// Call detachStimBuffDeviceCReq first - only clean up metadata if this succeeds
-	stim_buff::StimBuffDeviceOpResult detachResult =
-		co_await detachStimBuffDeviceCReq(specPtr);
+	dmGuard.release();
 
-	if (!detachResult.success)
+	/*	FIXME:
+	 * We should add an unlocked flag to at/detachStimBuffDeviceCReq()
+	 * so we can call it with the devmgr lock held.
+	 */
+	 co_await detachStimBuffDeviceCReq(specPtr);
+
+	sscl::co::CoQutex::ReleaseHandle dmGuardAfterDetach =
+		co_await dm.s.lock.getAcquireInvocationAndSuspensionPolicy();
+	(void)dmGuardAfterDetach;
+
+	// Find the DeviceRole in attachedDeviceRoles
+	auto deviceRoleIt = std::find_if(
+		dm.s.rsrc.attachedDeviceRoles.begin(),
+		dm.s.rsrc.attachedDeviceRoles.end(),
+		[&specPtr](const std::shared_ptr<DeviceRole> &role) {
+			return *role->deviceAttachmentSpec == *specPtr;
+		}
+	);
+
+	if (deviceRoleIt == dm.s.rsrc.attachedDeviceRoles.end())
 	{
-		// Detach failed, metadata remains intact
-		co_return DeviceAttachmentIndResult{
-			false, nullptr, detachResult.deviceSpec};
+		throw std::runtime_error(
+			std::string(__func__) + ": DeviceRole not found for spec (race "
+			"condition)?: "
+			+ specPtr->stringify() + ", deviceRoles="
+			+ std::to_string(dm.s.rsrc.attachedDeviceRoles.size()));
 	}
 
-	// Detach succeeded, now find and clean up metadata
-	try {
-		// Find the DeviceRole in attachedDeviceRoles
-		auto deviceRoleIt = std::find_if(
-			dm.s.rsrc.attachedDeviceRoles.begin(),
-			dm.s.rsrc.attachedDeviceRoles.end(),
-			[&specPtr](const std::shared_ptr<DeviceRole> &role) {
-				return *role->deviceAttachmentSpec == *specPtr;
-			}
-		);
+	auto deviceRole = *deviceRoleIt;
+	auto& device = deviceRole->parentDevice;
 
-		if (deviceRoleIt == dm.s.rsrc.attachedDeviceRoles.end())
-		{
-			// DeviceRole not found, return failure
-			co_return DeviceAttachmentIndResult{
-				false, nullptr, detachResult.deviceSpec};
-		}
+	// Remove DeviceRole from DeviceManager's collection
+	dm.s.rsrc.attachedDeviceRoles.erase(deviceRoleIt);
 
-		auto deviceRole = *deviceRoleIt;
-		auto& device = deviceRole->parentDevice;
-
-		// Remove DeviceRole from DeviceManager's collection
-		dm.s.rsrc.attachedDeviceRoles.erase(deviceRoleIt);
-
-		// Remove DeviceRole from Device's collection
-		auto deviceRoleIt2 = std::find(
-			device.deviceRoles.begin(),
-			device.deviceRoles.end(),
-			deviceRole);
-		if (deviceRoleIt2 != device.deviceRoles.end())
-		{
-			device.deviceRoles.erase(deviceRoleIt2);
-		}
-
-		// Remove DeviceAttachmentSpec from deviceAttachmentSpecs collection
-		auto specIt = std::find_if(
-			dm.s.rsrc.deviceAttachmentSpecs.begin(),
-			dm.s.rsrc.deviceAttachmentSpecs.end(),
-			[&specPtr](
-				const std::shared_ptr<DeviceAttachmentSpec> &existingSpec)
-			{
-				return *existingSpec == *specPtr;
-			}
-		);
-
-		if (specIt != dm.s.rsrc.deviceAttachmentSpecs.end())
-		{
-			dm.s.rsrc.deviceAttachmentSpecs.erase(specIt);
-		}
-
-		co_return DeviceAttachmentIndResult{
-			true, deviceRole, detachResult.deviceSpec};
-	} catch (const std::exception&) {
-		// Cleanup failed, return error
-		co_return DeviceAttachmentIndResult{
-			false, nullptr, detachResult.deviceSpec};
+	// Remove DeviceRole from Device's collection
+	auto deviceRoleIt2 = std::find(
+		device.deviceRoles.begin(),
+		device.deviceRoles.end(),
+		deviceRole);
+	if (deviceRoleIt2 != device.deviceRoles.end())
+	{
+		device.deviceRoles.erase(deviceRoleIt2);
 	}
+
+	// Remove DeviceAttachmentSpec from deviceAttachmentSpecs collection
+	auto specIt = std::find_if(
+		dm.s.rsrc.deviceAttachmentSpecs.begin(),
+		dm.s.rsrc.deviceAttachmentSpecs.end(),
+		[&specPtr](
+			const std::shared_ptr<DeviceAttachmentSpec> &existingSpec)
+		{
+			return *existingSpec == *specPtr;
+		}
+	);
+
+	if (specIt != dm.s.rsrc.deviceAttachmentSpecs.end())
+	{
+		dm.s.rsrc.deviceAttachmentSpecs.erase(specIt);
+	}
+
+	co_return;
 }
 
-mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSet>
+mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSetWithException>
 DeviceManager::attachAllUnattachedDevicesFromCReq(
 	const std::shared_ptr<std::vector<DeviceAttachmentSpec>> &specs)
 {
 	assertMarionetteThread();
 
-	if (specs->empty()) {
-		co_return sscl::MultiOperationResultSet{};
+	const unsigned int nTotal = static_cast<unsigned int>(specs->size());
+	if (nTotal == 0) {
+		co_return sscl::MultiOperationResultSetWithException{};
 	}
 
 	sscl::co::Group group;
 	std::vector<
-		mrntt::MrnttViralPostingInvoker<DeviceManager::DeviceAttachmentIndResult>>
+		mrntt::MrnttViralPostingInvoker<std::shared_ptr<DeviceRole>>>
 		invokers;
-	invokers.reserve(specs->size());
+	invokers.reserve(nTotal);
 
 	for (const auto &spec : *specs)
 	{
@@ -390,32 +393,32 @@ DeviceManager::attachAllUnattachedDevicesFromCReq(
 		group.add(invokers.back());
 	}
 
-	co_await group.getAwaitAllSettlementsInvoker();
-	group.checkForAndReThrowGroupExceptions();
+	const std::vector<sscl::co::Group::SettlementDescriptor> &settlements =
+		co_await group.getAwaitAllSettlementsInvoker();
 
 	unsigned int nSucceeded = 0;
 	unsigned int nFailed = 0;
-	for (auto &invoker : invokers)
+	using SettlementType = sscl::co::Group::SettlementDescriptor::TypeE;
+	for (const auto &desc : settlements)
 	{
-		if (invoker.completedReturnValues().myReturnValue.success) {
-			nSucceeded++;
-		} else {
+		if (desc.type == SettlementType::EXCEPTION_THROWN) {
 			nFailed++;
+		} else {
+			nSucceeded++;
 		}
 	}
 
-	if (OptionParser::getOptions().verbose)
-	{
-		std::cout << __func__ << ": " << nSucceeded
-			<< " devices attached, "
-			<< nFailed << " devices failed\n";
+	std::exception_ptr memberFailureException = nullptr;
+	if (nFailed > 0) {
+		memberFailureException = group.captureAggregatedGroupExceptions();
 	}
 
-	co_return sscl::MultiOperationResultSet(
-		static_cast<unsigned int>(specs->size()), nSucceeded, nFailed);
+	co_return sscl::MultiOperationResultSetWithException(
+		sscl::MultiOperationResultSet(nTotal, nSucceeded, nFailed),
+		memberFailureException);
 }
 
-mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSet>
+mrntt::MrnttViralPostingInvoker<void>
 DeviceManager::attachAllUnattachedDevicesFromKnownListCReq()
 {
 	assertMarionetteThread();
@@ -447,39 +450,91 @@ DeviceManager::attachAllUnattachedDevicesFromKnownListCReq()
 
 	dmGuard.release();
 
-	co_return co_await attachAllUnattachedDevicesFromCReq(unattachedSpecs);
+	const sscl::MultiOperationResultSetWithException batchResult =
+		co_await attachAllUnattachedDevicesFromCReq(unattachedSpecs);
+
+	if (batchResult.results.nSucceeded > 0)
+	{
+		std::cout << "DeviceReattacher: Successfully reattached "
+			<< batchResult.results.nSucceeded << " of "
+			<< batchResult.results.nTotal
+			<< " devices" << std::endl;
+	}
+
+	if (batchResult.hasMemberFailure())
+	{
+		try {
+			std::rethrow_exception(batchResult.memberFailureException);
+		} catch (const std::exception &e) {
+			std::cerr << __func__ << ": " << e.what() << std::endl;
+		}
+	}
+
+	co_return;
 }
 
-mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSet>
+mrntt::MrnttViralPostingInvoker<void>
 DeviceManager::attachAllUnattachedDevicesFromCmdlineCReq()
 {
 	auto specs = std::make_shared<std::vector<DeviceAttachmentSpec>>(
 		getInstance().s.rsrc.commandLineDASpecs);
 
-	co_return co_await attachAllUnattachedDevicesFromCReq(specs);
+	const sscl::MultiOperationResultSetWithException batchResult =
+		co_await attachAllUnattachedDevicesFromCReq(specs);
+
+	std::cout << "Mrntt: attached "
+		<< batchResult.results.nSucceeded << " of "
+		<< batchResult.results.nTotal
+		<< " sense devices." << "\n";
+
+	if (batchResult.results.nTotal > 0
+		&& batchResult.results.nSucceeded == 0)
+	{
+		std::string message =
+			std::string(__func__)
+			+ ": Startup policy requires at least one cmdline sense device "
+			"to attach successfully; 0 of "
+			+ std::to_string(batchResult.results.nTotal)
+			+ " requested sense devices attached — aborting startup.";
+
+		if (batchResult.hasMemberFailure())
+		{
+			try {
+				std::rethrow_exception(batchResult.memberFailureException);
+			} catch (const std::exception &e) {
+				message += "\n";
+				message += e.what();
+			} catch (...) {
+				message += "\n<unknown exception type>";
+			}
+		}
+
+		throw std::runtime_error(message);
+	}
+
+	co_return;
 }
 
-mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSet>
+mrntt::MrnttViralPostingInvoker<void>
 DeviceManager::detachAllAttachedDeviceRolesCReq()
 {
 	assertMarionetteThread();
 
 	std::vector<std::shared_ptr<DeviceAttachmentSpec>> specsToDetach;
 	specsToDetach.reserve(getInstance().s.rsrc.attachedDeviceRoles.size());
-	for (const auto& deviceRole : getInstance().s.rsrc.attachedDeviceRoles)
-	{
+	for (const auto& deviceRole : getInstance().s.rsrc.attachedDeviceRoles) {
 		specsToDetach.push_back(deviceRole->deviceAttachmentSpec);
 	}
 
-	if (specsToDetach.empty()) {
-		co_return sscl::MultiOperationResultSet{};
+	sscl::AsynchronousLoop loop(
+		static_cast<unsigned int>(specsToDetach.size()));
+	if (loop.nTotalIsZero()) {
+		co_return;
 	}
 
 	sscl::co::Group group;
-	std::vector<
-		mrntt::MrnttViralPostingInvoker<stim_buff::StimBuffDeviceOpResult>>
-		invokers;
-	invokers.reserve(specsToDetach.size());
+	std::vector<mrntt::MrnttViralPostingInvoker<void>> invokers;
+	invokers.reserve(loop.nTotal);
 
 	for (const auto &spec : specsToDetach)
 	{
@@ -487,20 +542,39 @@ DeviceManager::detachAllAttachedDeviceRolesCReq()
 		group.add(invokers.back());
 	}
 
-	co_await group.getAwaitAllSettlementsInvoker();
-	group.checkForAndReThrowGroupExceptions();
+	const std::vector<sscl::co::Group::SettlementDescriptor> &settlements =
+		co_await group.getAwaitAllSettlementsInvoker();
 
-	unsigned int nSucceeded = 0;
-	unsigned int nFailed = 0;
-	for (auto &invoker : invokers)
+	using SettlementType = sscl::co::Group::SettlementDescriptor::TypeE;
+	for (const auto &desc : settlements)
 	{
-		if (invoker.completedReturnValues().myReturnValue.success) {
-			nSucceeded++;
-		} else {
-			nFailed++;
+		loop.incrementSuccessOrFailureDueTo(
+			desc.type != SettlementType::EXCEPTION_THROWN);
+	}
+
+	if (loop.nFailed.load() > 0)
+	{
+		try {
+			group.checkForAndReThrowGroupExceptions();
+		} catch (const std::exception &e) {
+			std::cerr << __func__ << ": " << e.what() << std::endl;
 		}
 	}
 
+	const unsigned int nSucceeded = loop.nSucceeded.load();
+	const unsigned int nFailed = loop.nFailed.load();
+
+	if (nFailed > 0)
+	{
+		std::cerr << "Mrntt: Failed to detach "
+			<< nFailed << " of " << loop.nTotal << " sense devices." << "\n";
+	}
+	else
+	{
+		std::cout << "Mrntt: Successfully detached "
+			<< nSucceeded << " of " << loop.nTotal << " sense devices." << "\n";
+	}
+
 	if (OptionParser::getOptions().verbose)
 	{
 		std::cout << __func__ << ": " << nSucceeded
@@ -508,9 +582,7 @@ DeviceManager::detachAllAttachedDeviceRolesCReq()
 			<< nFailed << " devices failed\n";
 	}
 
-	co_return sscl::MultiOperationResultSet(
-		static_cast<unsigned int>(specsToDetach.size()),
-		nSucceeded, nFailed);
+	co_return;
 }
 
 void DeviceManager::initializeDeviceReattacher()
diff --git a/smocore/deviceManager/deviceReattacher.cpp b/smocore/deviceManager/deviceReattacher.cpp
index f2cde88..549e83f 100644
--- a/smocore/deviceManager/deviceReattacher.cpp
+++ b/smocore/deviceManager/deviceReattacher.cpp
@@ -6,6 +6,7 @@
 #include <deviceManager/deviceReattacher.h>
 #include <deviceManager/deviceManager.h>
 #include <marionette/marionetteThread.h>
+#include <spinscale/co/nonViralCompletion.h>
 
 namespace smo {
 namespace device {
@@ -20,29 +21,25 @@ DeviceReattacher::DeviceReattacher(
 	DeviceManager& parent, std::shared_ptr<sscl::ComponentThread> ioThread)
 : parent(parent), ioThread(ioThread), timer(ioThread->getIoContext())
 {
+	/**	EXPLANATION:
+	 * The thread on which DeviceReattacher runs is whichever thread executes
+	 * the io_context that owns deadline_timer. Timer async_wait handlers
+	 * (onTimeout, holdReattachCReq, reattachKnownListCReq) are dispatched on
+	 * that thread. ioThread selects that io_context here; start() only arms
+	 * the timer on it.
+	 */
 }
 
-mrntt::MrnttNonViralPostingInvoker DeviceReattacher::reattachKnownListCReq(
-	[[maybe_unused]] sscl::co::ExplicitPostTarget postTarget,
+mrntt::MrnttNonViralNonPostingInvoker DeviceReattacher::reattachKnownListCReq(
 	[[maybe_unused]] std::exception_ptr &exceptionPtr,
 	[[maybe_unused]] std::function<void()> callback)
 {
 	/**	EXPLANATION:
-	 * DeviceManager attach APIs require the marionette thread; postTarget
-	 * selects where this coroutine runs (mrntt io_context). Completion still
-	 * posts back to the mrntt timer thread via callerIoContext.
+	 * Non-posting: invoked from holdReattachCReq on the timer callback thread
+	 * (see ctor). Nested DeviceManager attach APIs still post to MRNTT as
+	 * needed via their own viral posting invokers.
 	 */
-	(void)postTarget;
-
-	sscl::MultiOperationResultSet results = co_await
-		parent.attachAllUnattachedDevicesFromKnownListCReq();
-	if (results.nTotal > 0)
-	{
-		std::cout << "DeviceReattacher: Successfully reattached "
-			<< results.nSucceeded << " of " << results.nTotal
-			<< " devices" << std::endl;
-	}
-
+	co_await parent.attachAllUnattachedDevicesFromKnownListCReq();
 	co_return;
 }
 
@@ -92,10 +89,20 @@ void DeviceReattacher::holdReattachCReq()
 
 	reattachCReqInvoker.reset();
 	reattachCReqInvoker.emplace(reattachKnownListCReq(
-		sscl::co::ExplicitPostTarget{ioThread->getIoContext()},
 		reattachLifetimeExceptionPtr,
 		[this]()
 		{
+			sscl::co::NonViralCompletion nvc(reattachLifetimeExceptionPtr);
+			if (nvc.hasException())
+			{
+				try {
+					nvc.checkAndRethrowException();
+				} catch (const std::exception &e) {
+					std::cerr << "DeviceReattacher: " << e.what()
+						<< std::endl;
+				}
+			}
+
 			sscl::SpinLock::Guard guard(deviceReattacherCanceler.s.lock);
 			reattachOpInFlight = false;
 		}));
diff --git a/smocore/include/deviceManager/deviceManager.h b/smocore/include/deviceManager/deviceManager.h
index fb89ae1..b289194 100644
--- a/smocore/include/deviceManager/deviceManager.h
+++ b/smocore/include/deviceManager/deviceManager.h
@@ -13,8 +13,8 @@
 #include <deviceManager/deviceRole.h>
 #include <deviceManager/deviceReattacher.h>
 #include <marionette/marionetteThread.h>
-#include <spinscale/co/coQutex.h>
 #include <spinscale/multiOperationResultSet.h>
+#include <spinscale/co/coQutex.h>
 #include <spinscale/sharedResourceGroup.h>
 
 namespace smo {
@@ -25,13 +25,6 @@ class DeviceReattacher;
 class DeviceManager
 {
 public:
-	struct DeviceAttachmentIndResult
-	{
-		bool success = false;
-		std::shared_ptr<DeviceRole> deviceRole;
-		std::shared_ptr<DeviceAttachmentSpec> deviceSpec;
-	};
-
 	static DeviceManager& getInstance()
 	{
 		static DeviceManager instance;
@@ -52,31 +45,27 @@ public:
 
 	static const std::string stringifyDeviceSpecs(void);
 
-	mrntt::MrnttViralPostingInvoker<DeviceAttachmentIndResult>
+	mrntt::MrnttViralPostingInvoker<std::shared_ptr<DeviceRole>>
 	newDeviceAttachmentSpecIndCReq(const DeviceAttachmentSpec &spec);
 
-	mrntt::MrnttViralPostingInvoker<DeviceAttachmentIndResult>
+	mrntt::MrnttViralPostingInvoker<void>
 	removeDeviceAttachmentSpecCReq(const DeviceAttachmentSpec &spec);
 
-	mrntt::MrnttViralPostingInvoker<stim_buff::StimBuffDeviceOpResult>
+	mrntt::MrnttViralPostingInvoker<void>
 	attachStimBuffDeviceCReq(
 		const std::shared_ptr<DeviceAttachmentSpec>& spec);
 
-	mrntt::MrnttViralPostingInvoker<stim_buff::StimBuffDeviceOpResult>
+	mrntt::MrnttViralPostingInvoker<void>
 	detachStimBuffDeviceCReq(
 		const std::shared_ptr<DeviceAttachmentSpec>& spec);
 
-	mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSet>
-	attachAllUnattachedDevicesFromCReq(
-		const std::shared_ptr<std::vector<DeviceAttachmentSpec>> &specs);
-
-	mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSet>
+	mrntt::MrnttViralPostingInvoker<void>
 	attachAllUnattachedDevicesFromKnownListCReq();
 
-	mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSet>
+	mrntt::MrnttViralPostingInvoker<void>
 	attachAllUnattachedDevicesFromCmdlineCReq();
 
-	mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSet>
+	mrntt::MrnttViralPostingInvoker<void>
 	detachAllAttachedDeviceRolesCReq();
 
 private:
@@ -88,6 +77,10 @@ private:
 	DeviceManager(const DeviceManager&) = delete;
 	DeviceManager& operator=(const DeviceManager&) = delete;
 
+	mrntt::MrnttViralPostingInvoker<sscl::MultiOperationResultSetWithException>
+	attachAllUnattachedDevicesFromCReq(
+		const std::shared_ptr<std::vector<DeviceAttachmentSpec>> &specs);
+
 public:
 	struct Resources
 	{
diff --git a/smocore/include/deviceManager/deviceReattacher.h b/smocore/include/deviceManager/deviceReattacher.h
index 93babca..7ebc8ed 100644
--- a/smocore/include/deviceManager/deviceReattacher.h
+++ b/smocore/include/deviceManager/deviceReattacher.h
@@ -9,7 +9,6 @@
 #include <optional>
 #include <boost/asio/deadline_timer.hpp>
 #include <marionette/marionetteThread.h>
-#include <spinscale/multiOperationResultSet.h>
 #include <spinscale/syncCancelerForAsyncWork.h>
 
 namespace smo {
@@ -37,17 +36,17 @@ private:
 	void onTimeout(const boost::system::error_code& error);
 	void holdReattachCReq();
 
-	mrntt::MrnttNonViralPostingInvoker reattachKnownListCReq(
-		sscl::co::ExplicitPostTarget postTarget,
+	mrntt::MrnttNonViralNonPostingInvoker reattachKnownListCReq(
 		std::exception_ptr &exceptionPtr,
 		std::function<void()> callback);
 
 	DeviceManager &parent;
+	// io_context thread for timer and non-posting reattach shell (see ctor).
 	std::shared_ptr<sscl::ComponentThread> ioThread;
 	sscl::SyncCancelerForAsyncWork deviceReattacherCanceler;
 	boost::asio::deadline_timer timer;
 	std::exception_ptr reattachLifetimeExceptionPtr;
-	std::optional<mrntt::MrnttNonViralPostingInvoker> reattachCReqInvoker;
+	std::optional<mrntt::MrnttNonViralNonPostingInvoker> reattachCReqInvoker;
 	bool reattachOpInFlight = false;
 	std::chrono::steady_clock::time_point lastReattachReqTimestamp{};
 };
diff --git a/smocore/include/marionette/marionetteThread.h b/smocore/include/marionette/marionetteThread.h
index 109dfce..c6c8315 100644
--- a/smocore/include/marionette/marionetteThread.h
+++ b/smocore/include/marionette/marionetteThread.h
@@ -20,6 +20,9 @@ using MrnttPostingPromise =
 using MrnttNonViralPostingInvoker =
 	sscl::co::NonViralPostingInvoker<MrnttPostingPromise>;
 
+using MrnttNonViralNonPostingInvoker =
+	sscl::co::NonViralNonPostingInvoker;
+
 template <typename T>
 using MrnttViralPostingInvoker =
 	sscl::co::ViralPostingInvoker<MrnttPostingPromise, T>;
diff --git a/smocore/include/stimBuffApis/stimBuffApiManager.h b/smocore/include/stimBuffApis/stimBuffApiManager.h
index 61f45e7..b4b52d2 100644
--- a/smocore/include/stimBuffApis/stimBuffApiManager.h
+++ b/smocore/include/stimBuffApis/stimBuffApiManager.h
@@ -41,8 +41,9 @@ public:
 
 	std::optional<std::shared_ptr<StimBuffApiLib>> getStimBuffApiLib(
 		const std::string& libraryPath);
-	std::optional<std::shared_ptr<StimBuffApiLib>> getStimBuffApiLibByApiName(
+	std::optional<std::shared_ptr<StimBuffApiLib>> findStimBuffApiLibByApiName(
 		const std::string& apiName);
+	StimBuffApiLib &getStimBuffApiLibByApiName(const std::string& apiName);
 	void unloadStimBuffApiLib(const std::string& libraryPath);
 
 	void loadAllStimBuffApiLibsFromOptions(
diff --git a/smocore/stimBuffApis/stimBuffApiManager.cpp b/smocore/stimBuffApis/stimBuffApiManager.cpp
index c35cad4..f1b3343 100644
--- a/smocore/stimBuffApis/stimBuffApiManager.cpp
+++ b/smocore/stimBuffApis/stimBuffApiManager.cpp
@@ -230,7 +230,7 @@ StimBuffApiManager::getStimBuffApiLib(const std::string& libraryPath)
 }
 
 std::optional<std::shared_ptr<StimBuffApiLib>>
-StimBuffApiManager::getStimBuffApiLibByApiName(const std::string& apiName)
+StimBuffApiManager::findStimBuffApiLibByApiName(const std::string& apiName)
 {
     auto &libs = getInstance().s.rsrc.stimBuffApiLibs;
     auto it = std::find_if(libs.begin(), libs.end(),
@@ -243,6 +243,19 @@ StimBuffApiManager::getStimBuffApiLibByApiName(const std::string& apiName)
     return std::nullopt;
 }
 
+StimBuffApiLib &StimBuffApiManager::getStimBuffApiLibByApiName(
+	const std::string& apiName)
+{
+	auto libOpt = findStimBuffApiLibByApiName(apiName);
+	if (!libOpt)
+	{
+		throw std::runtime_error(
+			std::string(__func__) + ": No library for API '" + apiName + "'");
+	}
+
+	return *libOpt.value();
+}
+
 void StimBuffApiManager::unloadStimBuffApiLib(const std::string& libraryPath)
 {
     auto &libs = getInstance().s.rsrc.stimBuffApiLibs;