Specify full entrypoint name on crash

src/main/java/net/fabricmc/loader/api/entrypoint/EntrypointContainer.java

@@ -34,4 +34,9 @@ public interface EntrypointContainer<T> {
 	 * Returns the mod that provided this entrypoint.
 	 */
 	ModContainer getProvider();
+
+	/**
+	 * Returns a string representation of the entrypoint.
+	 */
+	String getEntrypointName();
 }

src/main/java/net/fabricmc/loader/impl/FabricLoaderImpl.java

@@ -386,7 +386,7 @@ public <T> void invokeEntrypoints(String key, Class<T> type, Consumer<? super T>
 				exception = ExceptionUtil.gatherExceptions(t,
 						exception,
 						exc -> new RuntimeException(String.format("Could not execute entrypoint stage '%s' due to errors, provided by '%s'!",
-								key, container.getProvider().getMetadata().getId()),
+								key, container.getEntrypointName()),
 								exc));
 			}
 		}

src/main/java/net/fabricmc/loader/impl/entrypoint/EntrypointContainerImpl.java

@@ -64,4 +64,9 @@ public synchronized T getEntrypoint() {
 	public ModContainer getProvider() {
 		return entry.getModContainer();
 	}
+
+	@Override
+	public String getEntrypointName() {
+		return entry.toString();
+	}
 }