fix(common): isolate every event multicast across the codebase

[ottobolyos]

Summary

PR #185 introduced per-delegate isolation for the DeviceReceived event so a throwing subscriber no longer cuts off downstream handlers, with swallowed faults routed through InternalError. This PR closes the same bug class atomically across the entire codebase: the HTTP client surface (outer client and every sub-client), the HTTP server surface, both MQTT clients, the SHDR adapter and client, the device finder, and the agent / broker.

Changes

Shared helper

libraries/MTConnect.NET-Common/MulticastIsolation.cs — adds the MulticastIsolation static class with three Raise shapes:

• Raise<T>(this EventHandler<T>, object, T, EventHandler<Exception> = null) — extension method on EventHandler<T> events.
• Raise(this EventHandler, object, EventArgs, EventHandler<Exception> = null) — extension method on non-generic EventHandler events.
• Raise<TDelegate>(TDelegate, Action<TDelegate>, EventHandler<Exception> = null, object = null) where TDelegate : Delegate — static call for any custom delegate shape; the caller supplies the per-subscriber invocation lambda so no per-signature overload is required. Stays a static call because extension-method syntax does not compose cleanly with the where TDelegate : Delegate constraint at the call site.

All three shapes share the same contract: a throwing subscriber cannot starve later subscribers; subscriber faults are routed through the caller-supplied internalError sink, which is itself iterated per-delegate so a throwing fault reporter cannot starve later fault reporters; secondary faults from the internalError handler are terminal and swallowed.

Call sites for the typed overloads read as:

ObservationAdded.Raise(this, observation);
ConnectionError.Raise(this, ex, InternalError);

HTTP clients

libraries/MTConnect.NET-HTTP/Clients/MTConnectHttpClient.cs, MTConnectHttpProbeClient.cs, MTConnectHttpCurrentClient.cs, MTConnectHttpSampleClient.cs, MTConnectHttpAssetClient.cs, MTConnectHttpClientStream.cs — every ?.Invoke raise site replaced with the appropriate Raise extension-method call across the outer client and every sub-client.

MQTT clients

• libraries/MTConnect.NET-MQTT/Clients/MTConnectMqttClient.cs — 16 raise sites: ClientStarting, ClientStopping, ClientStarted, ClientStopped, ConnectionError, InternalError, DeviceReceived, ProbeReceived, ResponseReceived (×2), CurrentReceived, ObservationReceived (×2), SampleReceived, AssetsReceived, AssetReceived.
• libraries/MTConnect.NET-MQTT/Clients/MTConnectMqttExpandedClient.cs — 9 raise sites: ClientStarting, ClientStopping, ClientStarted, ClientStopped, ConnectionError, InternalError, ObservationReceived (×2), ConnectionStatusChanged (×2), DeviceReceived, AssetReceived.

SHDR adapter and client

• libraries/MTConnect.NET-SHDR/Adapters/ShdrAdapter.cs — 8 raise sites: AgentConnected, AgentDisconnected, PingReceived, PongSent, ConnectionError, LineSent (×2), SendError (×2).
• libraries/MTConnect.NET-SHDR/Shdr/ShdrClient.cs — 20 raise sites: Connected, PingSent (×2), ConnectionError (×2), Disconnected (×2), Listening, PongReceived, ProtocolReceived (×11).

Device finder

• libraries/MTConnect.NET-DeviceFinder/MTConnectDeviceFinder.cs — 8 raise sites: PingSent, PingReceived, SearchCompleted, PortOpened, PortClosed, ProbeSent, DeviceFound, ProbeSuccessful.
• libraries/MTConnect.NET-DeviceFinder/PingQueue.cs — 3 raise sites: PingSent, PingReceived, Completed.

These classes declare every event with a custom delegate shape (DeviceHandler, PingSentHandler, RequestStatusHandler, etc.); each site uses the generic-delegate MulticastIsolation.Raise(handler, invoke) static call with the per-subscriber invocation passed inline.

Agent and broker

• libraries/MTConnect.NET-Common/Agents/MTConnectAgent.cs — 15 raise sites total: the EventHandler<T> events DeviceAdded, ObservationReceived, ObservationAdded (×4), AssetAdded use the extension-method form; the custom-delegate validation events InvalidComponentAdded, InvalidCompositionAdded, InvalidDataItemAdded, InvalidObservationAdded (×3), InvalidDeviceAdded, InvalidAssetAdded (×2) use the generic-delegate static call.
• libraries/MTConnect.NET-Common/Agents/MTConnectAgentBroker.cs — 35 raise sites total: the EventHandler event StreamsResponseSent (×12) uses the extension-method form; the custom-delegate request / response events DevicesRequestReceived (×2), DevicesResponseSent (×2), StreamsRequestReceived (×12), AssetsRequestReceived, DeviceAssetsRequestReceived, AssetsResponseSent (×2), ErrorResponseSent (×2) use the generic-delegate static call.

HTTP server

• libraries/MTConnect.NET-HTTP/Servers/MTConnectHttpResponseHandler.cs — 5 raise sites: ClientConnected, ResponseSent, ClientDisconnected (×3), ClientException (×2).
• libraries/MTConnect.NET-HTTP/Servers/MTConnectHttpServerStream.cs — 5 raise sites: StreamStarted, HeartbeatReceived, DocumentReceived, StreamException, StreamStopped.

Test coverage

• tests/MTConnect.NET-Common-Tests/MulticastIsolationTests.cs — helper unit tests for all three shapes, including the generic-delegate path.
• tests/MTConnect.NET-Common-Tests/MqttClientMulticastIsolationTests.cs — helper contract tests for the delegate shapes used by both MQTT clients.
• tests/MTConnect.NET-Common-Tests/DeviceFinderMulticastIsolationTests.cs — helper contract tests for every custom-delegate shape declared on MTConnectDeviceFinder and PingQueue.
• tests/MTConnect.NET-Common-Tests/Agents/AgentMulticastIsolationTests.cs — helper contract tests for every event on MTConnectAgent and MTConnectAgentBroker, including the validation and request / response custom delegates.
• tests/MTConnect.NET-SHDR-Tests/ShdrMulticastIsolationTests.cs — helper contract tests for EventHandler<string>, EventHandler<AdapterEventArgs<string>>, EventHandler<AdapterEventArgs<Exception>>, and EventHandler<Exception> shapes.
• tests/MTConnect.NET-HTTP-Tests/Clients/MulticastIsolationTests.cs, NonGenericMulticastIsolationTests.cs, SubClientMulticastIsolationTests.cs — positive (multi-subscriber fan-out) and negative (InternalError-itself-throws) tests per raise site on the HTTP client surface.
• tests/MTConnect.NET-HTTP-Tests/Integration/DevicesAndDeviceReceivedIntegrationTests.cs — end-to-end test for the probe → Devices cache → DeviceReceived flow.
• tests/MTConnect.NET-HTTP-Tests/Servers/HttpServerMulticastIsolationTests.cs — helper contract tests for the HTTP server delegate shapes.

Verification

• dotnet build MTConnect.NET.sln — green (0 warnings, 0 errors).
• dotnet test MTConnect.NET.sln --filter "Category!=E2E&Category!=RequiresDocker&Category!=XsdLoadStrict" — green (4831 / 4831).
• dotnet test tests/MTConnect.NET-Common-Tests --filter "FullyQualifiedName~MulticastIsolation" — green (80 / 80).

[PatrickRitchie]

I'm wondering if it might be better to make the MulticastIsolation.Raise() method into an extension method. May also want to make the internalError parameter optional. This might make the usage a little cleaner. Let me know your thoughts.

Example:

public static void Raise<T>(this EventHandler<T> handler, object sender, T arg, EventHandler<Exception> internalError = null)

public static void Raise(this EventHandler handler, object sender, EventArgs arg, EventHandler<Exception> internalError = null)

Example Usage:

ObservationAdded.Raise(this, observation);

[ottobolyos]

Good call — extension-method syntax reads much cleaner at the call sites. Applied across the typed EventHandler and EventHandler<T> overloads and made internalError optional. The generic-delegate overload (the one that takes an Action<TDelegate> invocation lambda for custom delegate signatures) stays as a static call: extension-method syntax doesn't compose cleanly with a where TDelegate : Delegate constraint at the call site. Sites in MTConnectAgent, MTConnectAgentBroker, the HTTP and MQTT clients, the HTTP server stream, the SHDR adapter and client, and the multicast-isolation test suites now read as event.Raise(this, args) / event.Raise(this, args, InternalError).