diff --git a/.changeset/frowny-paths-hear.md b/.changeset/frowny-paths-hear.md
new file mode 100644
index 000000000000..6d5a5f8f1f94
--- /dev/null
+++ b/.changeset/frowny-paths-hear.md
@@ -0,0 +1,11 @@
+---
+"@fluidframework/datastore": minor
+"@fluidframework/test-runtime-utils": minor
+"__section": legacy
+---
+
+Deprecate submitMessage on FluidDataStoreRuntime and MockFluidDataStoreRuntime
+
+Implementing `FluidDataStoreRuntime.submitMessage` is not required per `IFluidDataStoreChannel` and is now deprecated on `FluidDataStoreRuntime` and corresponding `MockFluidDataStoreRuntime`.
+
+See [issue #24406](https://github.com/microsoft/FluidFramework/issues/24406) for details and alternatives.
diff --git a/packages/common/core-interfaces/src/messages.ts b/packages/common/core-interfaces/src/messages.ts
index 92d7d2ad9360..25bb38b735ec 100644
--- a/packages/common/core-interfaces/src/messages.ts
+++ b/packages/common/core-interfaces/src/messages.ts
@@ -29,7 +29,6 @@ export interface ISignalEnvelope {
 	 */
 	contents: {
 		type: string;
-		// eslint-disable-next-line @typescript-eslint/no-explicit-any
-		content: any;
+		content: unknown;
 	};
 }
diff --git a/packages/framework/attributor/src/runtimeAttributorDataStoreChannel.ts b/packages/framework/attributor/src/runtimeAttributorDataStoreChannel.ts
index 594b10e6cf55..076f1edec81d 100644
--- a/packages/framework/attributor/src/runtimeAttributorDataStoreChannel.ts
+++ b/packages/framework/attributor/src/runtimeAttributorDataStoreChannel.ts
@@ -186,7 +186,7 @@ export class RuntimeAttributorDataStoreChannel
 	/**
 	 * {@inheritdoc IFluidDataStoreChannel.reSubmit}
 	 */
-	public reSubmit(type: string, content: unknown, localOpMetadata: unknown): void {
+	public reSubmit(): void {
 		// Should not resubmit anything from the attributor as the attributor does not send ops yet.
 		throw new Error("Should not resubmit anything from the attributor");
 	}
diff --git a/packages/runtime/container-runtime/src/channelCollection.ts b/packages/runtime/container-runtime/src/channelCollection.ts
index 01255683c30c..ef883430a756 100644
--- a/packages/runtime/container-runtime/src/channelCollection.ts
+++ b/packages/runtime/container-runtime/src/channelCollection.ts
@@ -11,7 +11,10 @@ import {
 	IResponse,
 	ITelemetryBaseLogger,
 } from "@fluidframework/core-interfaces";
-import type { IFluidHandleInternal } from "@fluidframework/core-interfaces/internal";
+import type {
+	IFluidHandleInternal,
+	ISignalEnvelope,
+} from "@fluidframework/core-interfaces/internal";
 import { assert, Lazy, LazyPromise } from "@fluidframework/core-utils/internal";
 import { FluidObjectHandle } from "@fluidframework/datastore/internal";
 import type { ISnapshot } from "@fluidframework/driver-definitions/internal";
@@ -24,6 +27,12 @@ import {
 	getSnapshotTree,
 	isInstanceOfISnapshot,
 } from "@fluidframework/driver-utils/internal";
+import type {
+	FluidDataStoreMessage,
+	IRuntimeMessagesContent,
+	InboundAttachMessage,
+	IRuntimeMessageCollection,
+} from "@fluidframework/runtime-definitions/internal";
 import {
 	ISummaryTreeWithStats,
 	ITelemetryContext,
@@ -43,9 +52,6 @@ import {
 	channelsTreeName,
 	IInboundSignalMessage,
 	gcDataBlobKey,
-	type IRuntimeMessagesContent,
-	type InboundAttachMessage,
-	type IRuntimeMessageCollection,
 } from "@fluidframework/runtime-definitions/internal";
 import {
 	GCDataBuilder,
@@ -98,6 +104,11 @@ import {
 import { DataStoreContexts } from "./dataStoreContexts.js";
 import { FluidDataStoreRegistry } from "./dataStoreRegistry.js";
 import { GCNodeType, IGCNodeUpdatedProps, urlToGCNodePath } from "./gc/index.js";
+import type {
+	ContainerRuntimeAliasMessage,
+	ContainerRuntimeDataStoreOpMessage,
+	OutboundContainerRuntimeAttachMessage,
+} from "./messageTypes.js";
 import { ContainerMessageType, LocalContainerRuntimeMessage } from "./messageTypes.js";
 import { StorageServiceWithAttachBlobs } from "./storageServiceWithAttachBlobs.js";
 import {
@@ -115,15 +126,47 @@ export const AllowTombstoneRequestHeaderKey = "allowTombstone"; // Belongs in th
 
 type PendingAliasResolve = (success: boolean) => void;
 
-interface FluidDataStoreMessage {
-	content: unknown;
-	type: string;
+/**
+ * Envelope for signals not intended for the container.
+ *
+ * @privateRemarks
+ * `clientBroadcastSignalSequenceNumber` might be added to the envelope by the container runtime.
+ * But it should not be provided to start with.
+ *
+ * @internal
+ */
+export type AddressedSignalEnvelope = IEnvelope<ISignalEnvelope["contents"]>;
+
+/**
+ * Kin of {@link @fluidframework/runtime-definitions#IFluidParentContext} with alternate
+ * submitMessage and submitSignal methods.
+ *
+ * @internal
+ * @privateRemarks Exposed per ChannelCollection testing and API extractor request
+ */
+export interface IFluidRootParentContext
+	extends Omit<IFluidParentContext, "submitMessage" | "submitSignal"> {
+	readonly submitMessage: (
+		containerRuntimeMessage:
+			| ContainerRuntimeDataStoreOpMessage
+			| OutboundContainerRuntimeAttachMessage
+			| ContainerRuntimeAliasMessage,
+		localOpMetadata: unknown,
+	) => void;
+	readonly submitSignal: (envelope: AddressedSignalEnvelope, targetClientId?: string) => void;
 }
 
+type SubmitKeys = "submitMessage" | "submitSignal";
+
 /**
- * Creates a shallow wrapper of {@link IFluidParentContext}. The wrapper can then have its methods overwritten as needed
+ * Creates a shallow wrapper of {@link IFluidParentContext} or
+ * {@link IFluidRootParentContext} with `submitMessage` and `submitSignal`
+ * methods replaced with the provided overrides.
  */
-export function wrapContext(context: IFluidParentContext): IFluidParentContext {
+export function formParentContext<T extends IFluidParentContext | IFluidRootParentContext>(
+	context: Omit<IFluidParentContext & IFluidRootParentContext, SubmitKeys>,
+	overrides: Pick<T, SubmitKeys>,
+): Omit<IFluidParentContext & IFluidRootParentContext, SubmitKeys> & Pick<T, SubmitKeys> {
 	return {
 		get IFluidDataStoreRegistry() {
 			return context.IFluidDataStoreRegistry;
@@ -162,12 +205,8 @@ export function wrapContext(context: IFluidParentContext): IFluidParentContext {
 		getAudience: (...args) => {
 			return context.getAudience(...args);
 		},
-		submitMessage: (...args) => {
-			return context.submitMessage(...args);
-		},
-		submitSignal: (...args) => {
-			return context.submitSignal(...args);
-		},
+		submitMessage: overrides.submitMessage.bind(overrides),
+		submitSignal: overrides.submitSignal,
 		makeLocallyVisible: (...args) => {
 			return context.makeLocallyVisible(...args);
 		},
@@ -194,38 +233,32 @@ export function wrapContext(context: IFluidParentContext): IFluidParentContext {
  * The wrapper will have the submit methods overwritten with the appropriate id as the destination address.
  *
  * @param id - the id of the channel
- * @param parentContext - the {@link IFluidParentContext} to wrap
+ * @param parentContext - the {@link IFluidRootParentContext} to wrap
  * @returns A wrapped {@link IFluidParentContext}
  */
 function wrapContextForInnerChannel(
 	id: string,
-	parentContext: IFluidParentContext,
+	parentContext: IFluidRootParentContext,
 ): IFluidParentContext {
-	const context = wrapContext(parentContext);
-
-	context.submitMessage = (type: string, content: unknown, localOpMetadata: unknown) => {
-		const fluidDataStoreContent: FluidDataStoreMessage = {
-			content,
-			type,
-		};
-		const envelope: IEnvelope = {
-			address: id,
-			contents: fluidDataStoreContent,
-		};
-		parentContext.submitMessage(
-			ContainerMessageType.FluidDataStoreOp,
-			envelope,
-			localOpMetadata,
-		);
-	};
-
-	context.submitSignal = (type: string, contents: unknown, targetClientId?: string) => {
-		const envelope: IEnvelope = {
-			address: id,
-			contents,
-		};
-		parentContext.submitSignal(type, envelope, targetClientId);
-	};
+	const context = formParentContext<IFluidParentContext>(parentContext, {
+		submitMessage: (type: string, content: unknown, localOpMetadata: unknown) => {
+			const fluidDataStoreContent: FluidDataStoreMessage = {
+				content,
+				type,
+			};
+			const envelope = {
+				address: id,
+				contents: fluidDataStoreContent,
+			};
+			parentContext.submitMessage(
+				{ type: ContainerMessageType.FluidDataStoreOp, contents: envelope },
+				localOpMetadata,
+			);
+		},
+		submitSignal: (type: string, content: unknown, targetClientId?: string) => {
+			parentContext.submitSignal({ address: id, contents: { type, content } }, targetClientId);
+		},
+	});
 
 	return context;
 }
@@ -242,7 +275,9 @@ export function getLocalDataStoreType(localDataStore: LocalFluidDataStoreContext
  * but eventually could be hosted on any channel once we formalize the channel api boundary.
  * @internal
  */
-export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
+export class ChannelCollection
+	implements Omit<IFluidDataStoreChannel, "entryPoint" | "reSubmit" | "rollback">, IDisposable
+{
 	// Stores tracked by the Domain
 	private readonly pendingAttach = new Map<string, IAttachMessage>();
 	// 0.24 back-compat attachingBeforeSummary
@@ -253,8 +288,6 @@ export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
 	// eslint-disable-next-line unicorn/consistent-function-scoping -- Property is defined once; no need to extract inner lambda
 	private readonly disposeOnce = new Lazy<void>(() => this.contexts.dispose());
 
-	public readonly entryPoint: IFluidHandleInternal<FluidObject>;
-
 	public readonly containerLoadStats: {
 		// number of dataStores during loadContainer
 		readonly containerLoadDataStoreCount: number;
@@ -272,20 +305,14 @@ export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
 
 	constructor(
 		protected readonly baseSnapshot: ISnapshotTree | ISnapshot | undefined,
-		public readonly parentContext: IFluidParentContext,
+		public readonly parentContext: IFluidRootParentContext,
 		baseLogger: ITelemetryBaseLogger,
 		private readonly gcNodeUpdated: (props: IGCNodeUpdatedProps) => void,
 		private readonly isDataStoreDeleted: (nodePath: string) => boolean,
 		private readonly aliasMap: Map<string, string>,
-		provideEntryPoint: (runtime: ChannelCollection) => Promise<FluidObject>,
 	) {
 		this.mc = createChildMonitoringContext({ logger: baseLogger });
 		this.contexts = new DataStoreContexts(baseLogger);
-		this.entryPoint = new FluidObjectHandle<FluidObject>(
-			new LazyPromise(async () => provideEntryPoint(this)),
-			"",
-			this.parentContext.IFluidHandleContext,
-		);
 		this.aliasedDataStores = new Set(aliasMap.values());
 
 		// Extract stores stored inside the snapshot
@@ -585,7 +612,10 @@ export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
 	protected submitAttachChannelOp(localContext: LocalFluidDataStoreContext): void {
 		const message = this.generateAttachMessage(localContext);
 		this.pendingAttach.set(localContext.id, message);
-		this.parentContext.submitMessage(ContainerMessageType.Attach, message, undefined);
+		this.parentContext.submitMessage(
+			{ type: ContainerMessageType.Attach, contents: message },
+			undefined,
+		);
 		this.attachOpFiredForDataStore.add(localContext.id);
 	}
 
@@ -690,24 +720,32 @@ export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
 	}
 	public readonly dispose = (): void => this.disposeOnce.value;
 
-	public reSubmit(type: string, content: unknown, localOpMetadata: unknown): void {
-		switch (type) {
+	public readonly reSubmitContainerMessage = (
+		message:
+			| ContainerRuntimeDataStoreOpMessage
+			| OutboundContainerRuntimeAttachMessage
+			| ContainerRuntimeAliasMessage,
+		localOpMetadata: unknown,
+	): void => {
+		switch (message.type) {
 			case ContainerMessageType.Attach:
 			case ContainerMessageType.Alias: {
-				this.parentContext.submitMessage(type, content, localOpMetadata);
+				this.parentContext.submitMessage(message, localOpMetadata);
 				return;
 			}
 			case ContainerMessageType.FluidDataStoreOp: {
-				return this.reSubmitChannelOp(type, content, localOpMetadata);
+				return this.resubmitDataStoreOp(message.contents, localOpMetadata);
 			}
 			default: {
 				assert(false, 0x907 /* unknown op type */);
 			}
 		}
-	}
+	};
 
-	protected reSubmitChannelOp(type: string, content: unknown, localOpMetadata: unknown): void {
-		const envelope = content as IEnvelope;
+	protected readonly resubmitDataStoreOp = (
+		envelope: IEnvelope<FluidDataStoreMessage>,
+		localOpMetadata: unknown,
+	): void => {
 		const context = this.contexts.get(envelope.address);
 		// If the data store has been deleted, log an error and throw an error. If there are local changes for a
 		// deleted data store, it can otherwise lead to inconsistent state when compared to other clients.
@@ -720,13 +758,13 @@ export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
 			});
 		}
 		assert(!!context, 0x160 /* "There should be a store context for the op" */);
-		const innerContents = envelope.contents as FluidDataStoreMessage;
-		context.reSubmit(innerContents.type, innerContents.content, localOpMetadata);
-	}
+		context.reSubmit(envelope.contents, localOpMetadata);
+	};
 
-	public rollback(type: string, content: unknown, localOpMetadata: unknown): void {
-		assert(type === ContainerMessageType.FluidDataStoreOp, 0x8e8 /* type */);
-		const envelope = content as IEnvelope;
+	public readonly rollbackDataStoreOp = (
+		envelope: IEnvelope<FluidDataStoreMessage>,
+		localOpMetadata: unknown,
+	): void => {
 		const context = this.contexts.get(envelope.address);
 		// If the data store has been deleted, log an error and throw an error. If there are local changes for a
 		// deleted data store, it can otherwise lead to inconsistent state when compared to other clients.
@@ -739,9 +777,8 @@ export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
 			});
 		}
 		assert(!!context, 0x2e8 /* "There should be a store context for the op" */);
-		const innerContents = envelope.contents as FluidDataStoreMessage;
-		context.rollback(innerContents.type, innerContents.content, localOpMetadata);
-	}
+		context.rollback(envelope.contents, localOpMetadata);
+	};
 
 	public async applyStashedOp(content: unknown): Promise<unknown> {
 		const opContents = content as LocalContainerRuntimeMessage;
@@ -875,7 +912,7 @@ export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
 		 * like merge tree or shared tree can process ops more efficiently when they are bunched together.
 		 */
 		for (const { contents, ...restOfMessagesContent } of messagesContent) {
-			const contentsEnvelope = contents as IEnvelope;
+			const contentsEnvelope = contents as IEnvelope<FluidDataStoreMessage>;
 			const address = contentsEnvelope.address;
 			const context = this.contexts.get(address);
 
@@ -902,8 +939,7 @@ export class ChannelCollection implements IFluidDataStoreChannel, IDisposable {
 				);
 			}
 
-			const { type: contextType, content: contextContents } =
-				contentsEnvelope.contents as FluidDataStoreMessage;
+			const { type: contextType, content: contextContents } = contentsEnvelope.contents;
 			// If the address or type of the message changes while processing the message, send the current bunch.
 			if (
 				currentMessageState?.address !== address ||
@@ -1592,11 +1628,100 @@ export function detectOutboundReferences(
 	}
 }
 
+// =====================================================================
+// The code below here is for experimentation (and one test) only.
+
+/**
+ * @privateRemarks This class is only used for experimentation/testing.
+ * @internal
+ */
+export class ComposableChannelCollection
+	extends ChannelCollection
+	implements IFluidDataStoreChannel
+{
+	public readonly entryPoint: IFluidHandleInternal<FluidObject>;
+
+	public constructor(
+		baseSnapshot: ISnapshotTree | ISnapshot | undefined,
+		parentContext: IFluidParentContext,
+		baseLogger: ITelemetryBaseLogger,
+		gcNodeUpdated: (props: IGCNodeUpdatedProps) => void,
+		isDataStoreDeleted: (nodePath: string) => boolean,
+		aliasMap: Map<string, string>,
+		provideEntryPoint: (runtime: ComposableChannelCollection) => Promise<FluidObject>,
+	) {
+		super(
+			baseSnapshot,
+			/* [root] parentContext */
+			formParentContext<IFluidRootParentContext>(parentContext, {
+				submitMessage: (
+					containerRuntimeMessage:
+						| ContainerRuntimeDataStoreOpMessage
+						| OutboundContainerRuntimeAttachMessage
+						| ContainerRuntimeAliasMessage,
+					localOpMetadata: unknown,
+				): void => {
+					// Note that here our message format is reconfigured.
+					// While `ContainerRuntime*Message`s use `contents`
+					// as `FluidDataStoreMessage`s the content is
+					// stored in `content`.
+					parentContext.submitMessage(
+						containerRuntimeMessage.type,
+						containerRuntimeMessage.contents,
+						localOpMetadata,
+					);
+				},
+				submitSignal: (envelope: AddressedSignalEnvelope, targetClientId?: string): void => {
+					parentContext.submitSignal(
+						envelope.contents.type,
+						{
+							address: envelope.address,
+							contents: envelope.contents.content,
+						} satisfies IEnvelope<unknown>,
+						targetClientId,
+					);
+				},
+			}),
+			baseLogger,
+			gcNodeUpdated,
+			isDataStoreDeleted,
+			aliasMap,
+		);
+		this.entryPoint = new FluidObjectHandle<FluidObject>(
+			new LazyPromise(async () => provideEntryPoint(this)),
+			"",
+			this.parentContext.IFluidHandleContext,
+		);
+	}
+
+	public reSubmit(type: string, content: unknown, localOpMetadata: unknown): void {
+		// If the cast is incorrect and type is not one of the three supported,
+		// reSubmitContainerMessage will assert.
+		// eslint-disable-next-line @typescript-eslint/consistent-type-assertions -- Need to force conversion
+		const message = {
+			type,
+			contents: content,
+		} as
+			| ContainerRuntimeDataStoreOpMessage
+			| OutboundContainerRuntimeAttachMessage
+			| ContainerRuntimeAliasMessage;
+		this.reSubmitContainerMessage(message, localOpMetadata);
+	}
+
+	public rollback(type: string, content: unknown, localOpMetadata: unknown): void {
+		assert(type === ContainerMessageType.FluidDataStoreOp, 0x8e8 /* type */);
+		this.rollbackDataStoreOp(content as IEnvelope<FluidDataStoreMessage>, localOpMetadata);
+	}
+}
+
 /**
+ * @privateRemarks This factory is only used for experimentation/testing.
+ *
  * @internal
  */
-export class ChannelCollectionFactory<T extends ChannelCollection = ChannelCollection>
-	implements IFluidDataStoreFactory
+export class ChannelCollectionFactory<
+	T extends ComposableChannelCollection = ComposableChannelCollection,
+> implements IFluidDataStoreFactory
 {
 	public readonly type = "ChannelCollectionChannel";
 
@@ -1608,7 +1733,9 @@ export class ChannelCollectionFactory<T extends ChannelCollection = ChannelColle
 		private readonly provideEntryPoint: (
 			runtime: IFluidDataStoreChannel,
 		) => Promise<FluidObject>,
-		private readonly ctor: (...args: ConstructorParameters<typeof ChannelCollection>) => T,
+		private readonly ctor: (
+			...args: ConstructorParameters<typeof ComposableChannelCollection>
+		) => T,
 	) {
 		this.IFluidDataStoreRegistry = new FluidDataStoreRegistry(registryEntries);
 	}
@@ -1623,10 +1750,10 @@ export class ChannelCollectionFactory<T extends ChannelCollection = ChannelColle
 	): Promise<IFluidDataStoreChannel> {
 		const runtime = this.ctor(
 			context.baseSnapshot,
-			context, // parentContext
+			/* parentContext */ context,
 			context.baseLogger,
-			() => {}, // gcNodeUpdated
-			(_nodePath: string) => false, // isDataStoreDeleted
+			/* gcNodeUpdated */ () => {},
+			/* isDataStoreDeleted */ (_nodePath: string) => false,
 			new Map(), // aliasMap
 			this.provideEntryPoint,
 		);
diff --git a/packages/runtime/container-runtime/src/containerRuntime.ts b/packages/runtime/container-runtime/src/containerRuntime.ts
index 412895d71695..f3b7452d9882 100644
--- a/packages/runtime/container-runtime/src/containerRuntime.ts
+++ b/packages/runtime/container-runtime/src/containerRuntime.ts
@@ -90,7 +90,6 @@ import type {
 	IInboundSignalMessage,
 	IRuntimeMessagesContent,
 	ISummarizerNodeWithGC,
-	IFluidParentContext,
 } from "@fluidframework/runtime-definitions/internal";
 import {
 	FlushMode,
@@ -147,10 +146,11 @@ import {
 	loadBlobManagerLoadInfo,
 	type IBlobManagerLoadInfo,
 } from "./blobManager/index.js";
+import type { AddressedSignalEnvelope, IFluidRootParentContext } from "./channelCollection.js";
 import {
 	ChannelCollection,
 	getSummaryForDatastores,
-	wrapContext,
+	formParentContext,
 } from "./channelCollection.js";
 import {
 	defaultCompatibilityMode,
@@ -181,11 +181,14 @@ import {
 import { InboundBatchAggregator } from "./inboundBatchAggregator.js";
 import {
 	ContainerMessageType,
+	type ContainerRuntimeAliasMessage,
+	type ContainerRuntimeDataStoreOpMessage,
 	type ContainerRuntimeDocumentSchemaMessage,
 	ContainerRuntimeGCMessage,
 	type ContainerRuntimeIdAllocationMessage,
 	type InboundSequencedContainerRuntimeMessage,
 	type LocalContainerRuntimeMessage,
+	type OutboundContainerRuntimeAttachMessage,
 	type UnknownContainerRuntimeMessage,
 } from "./messageTypes.js";
 import { ISavedOpMetadata } from "./metadata.js";
@@ -708,11 +711,11 @@ export class ContainerRuntime
 	extends TypedEventEmitter<IContainerRuntimeEvents>
 	implements
 		IContainerRuntime,
+		Omit<IFluidRootParentContext, "submitSignal">,
 		IRuntime,
 		IGarbageCollectionRuntime,
 		ISummarizerRuntime,
 		ISummarizerInternalsProvider,
-		IFluidParentContext,
 		IProvideFluidHandleContext,
 		IProvideLayerCompatDetails
 {
@@ -1096,7 +1099,9 @@ export class ContainerRuntime
 		referenceSequenceNumber?: number,
 	) => number;
 	/**
-	 * Do not call directly - use submitAddressesSignal
+	 * Do not call without first calling
+	 * signalTelemetryManager.applyTrackingToBroadcastSignalEnvelope
+	 * when targetClientId is undefined.
 	 */
 	private readonly submitSignalFn: (content: ISignalEnvelope, targetClientId?: string) => void;
 	public readonly disposeFn: (error?: ICriticalContainerError) => void;
@@ -1692,26 +1697,29 @@ export class ContainerRuntime
 			async () => this.garbageCollector.getBaseGCDetails(),
 		);
 
-		const parentContext = wrapContext(this);
+		const parentContext = formParentContext<IFluidRootParentContext>(this, {
+			submitMessage: this.submitMessage.bind(this),
+
+			// Due to a mismatch between different layers in terms of
+			// what is the interface of passing signals, we need the
+			// downstream stores to wrap the signal.
+			submitSignal: (envelope: AddressedSignalEnvelope, targetClientId?: string): void => {
+				// verifyNotClosed is called in FluidDataStoreContext, which is *the* expected caller.
+				assert(
+					!envelope.address.startsWith("/"),
+					"Addresses beginning with '/' are reserved for container use",
+				);
+				if (targetClientId === undefined) {
+					this.signalTelemetryManager.applyTrackingToBroadcastSignalEnvelope(envelope);
+				}
+				this.submitSignalFn(envelope, targetClientId);
+			},
+		});
 
 		if (snapshotWithContents !== undefined) {
 			this.isSnapshotInstanceOfISnapshot = true;
 		}
 
-		// Due to a mismatch between different layers in terms of
-		// what is the interface of passing signals, we need the
-		// downstream stores to wrap the signal.
-		parentContext.submitSignal = (type: string, content: unknown, targetClientId?: string) => {
-			// Future: Can the `content` argument type be IEnvelope?
-			// verifyNotClosed is called in FluidDataStoreContext, which is *the* expected caller.
-			const envelope1 = content as IEnvelope;
-			const envelope2 = createNewSignalEnvelope(envelope1.address, type, envelope1.contents);
-			if (targetClientId === undefined) {
-				this.signalTelemetryManager.applyTrackingToBroadcastSignalEnvelope(envelope2);
-			}
-			this.submitSignalFn(envelope2, targetClientId);
-		};
-
 		let snapshot: ISnapshot | ISnapshotTree | undefined = getSummaryForDatastores(
 			baseSnapshot,
 			metadata,
@@ -1734,7 +1742,6 @@ export class ContainerRuntime
 				}),
 			(path: string) => this.garbageCollector.isNodeDeleted(path),
 			new Map<string, string>(dataStoreAliasMap),
-			async (runtime: ChannelCollection) => provideEntryPoint,
 		);
 
 		this.blobManager = new BlobManager({
@@ -4213,17 +4220,13 @@ export class ContainerRuntime
 	}
 
 	public submitMessage(
-		type:
-			| ContainerMessageType.FluidDataStoreOp
-			| ContainerMessageType.Alias
-			| ContainerMessageType.Attach,
-		// TODO: better typing
-		// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types, @typescript-eslint/no-explicit-any
-		contents: any,
+		containerRuntimeMessage:
+			| ContainerRuntimeDataStoreOpMessage
+			| OutboundContainerRuntimeAttachMessage
+			| ContainerRuntimeAliasMessage,
 		localOpMetadata: unknown = undefined,
 	): void {
-		// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
-		this.submit({ type, contents }, localOpMetadata);
+		this.submit(containerRuntimeMessage, localOpMetadata);
 	}
 
 	public async uploadBlob(
@@ -4461,7 +4464,7 @@ export class ContainerRuntime
 			case ContainerMessageType.Alias: {
 				// For Operations, call resubmitDataStoreOp which will find the right store
 				// and trigger resubmission on it.
-				this.channelCollection.reSubmit(message.type, message.contents, localOpMetadata);
+				this.channelCollection.reSubmitContainerMessage(message, localOpMetadata);
 				break;
 			}
 			case ContainerMessageType.IdAllocation: {
@@ -4506,7 +4509,7 @@ export class ContainerRuntime
 			case ContainerMessageType.FluidDataStoreOp: {
 				// For operations, call rollbackDataStoreOp which will find the right store
 				// and trigger rollback on it.
-				this.channelCollection.rollback(type, contents, localOpMetadata);
+				this.channelCollection.rollbackDataStoreOp(contents, localOpMetadata);
 				break;
 			}
 			default: {
@@ -4755,7 +4758,7 @@ export class ContainerRuntime
 	}
 }
 
-export function createNewSignalEnvelope(
+function createNewSignalEnvelope(
 	address: string | undefined,
 	type: string,
 	content: unknown,
diff --git a/packages/runtime/container-runtime/src/dataStore.ts b/packages/runtime/container-runtime/src/dataStore.ts
index a02c45cae9ee..5c1ca321fcb7 100644
--- a/packages/runtime/container-runtime/src/dataStore.ts
+++ b/packages/runtime/container-runtime/src/dataStore.ts
@@ -24,6 +24,7 @@ import { ContainerMessageType } from "./messageTypes.js";
 /**
  * Interface for an op to be used for assigning an
  * alias to a datastore
+ * @internal
  */
 export interface IDataStoreAliasMessage {
 	/**
@@ -140,7 +141,10 @@ class DataStore implements IDataStore {
 		}
 
 		const aliased = await this.ackBasedPromise<boolean>((resolve) => {
-			this.parentContext.submitMessage(ContainerMessageType.Alias, message, resolve);
+			this.parentContext.submitMessage(
+				{ type: ContainerMessageType.Alias, contents: message },
+				resolve,
+			);
 		})
 			.catch((error) => {
 				this.logger.sendErrorEvent(
diff --git a/packages/runtime/container-runtime/src/dataStoreContext.ts b/packages/runtime/container-runtime/src/dataStoreContext.ts
index 0d92b7a379ed..8e7d296ed6a4 100644
--- a/packages/runtime/container-runtime/src/dataStoreContext.ts
+++ b/packages/runtime/container-runtime/src/dataStoreContext.ts
@@ -33,7 +33,8 @@ import {
 	readAndParse,
 } from "@fluidframework/driver-utils/internal";
 import type { IIdCompressor } from "@fluidframework/id-compressor";
-import {
+import type {
+	FluidDataStoreMessage,
 	ISummaryTreeWithStats,
 	ITelemetryContext,
 	IGarbageCollectionData,
@@ -53,12 +54,12 @@ import {
 	ISummarizeResult,
 	ISummarizerNodeWithGC,
 	SummarizeInternalFn,
-	channelsTreeName,
 	IInboundSignalMessage,
-	type IPendingMessagesState,
-	type IRuntimeMessageCollection,
-	type IFluidDataStoreFactory,
+	IPendingMessagesState,
+	IRuntimeMessageCollection,
+	IFluidDataStoreFactory,
 } from "@fluidframework/runtime-definitions/internal";
+import { channelsTreeName } from "@fluidframework/runtime-definitions/internal";
 import {
 	addBlobToSummary,
 	isSnapshotFetchRequiredForLoadingGroupId,
@@ -956,19 +957,19 @@ export abstract class FluidDataStoreContext
 		return {};
 	}
 
-	public reSubmit(type: string, contents: unknown, localOpMetadata: unknown): void {
+	public reSubmit(message: FluidDataStoreMessage, localOpMetadata: unknown): void {
 		assert(!!this.channel, 0x14b /* "Channel must exist when resubmitting ops" */);
-		this.channel.reSubmit(type, contents, localOpMetadata);
+		this.channel.reSubmit(message.type, message.content, localOpMetadata);
 	}
 
-	public rollback(type: string, contents: unknown, localOpMetadata: unknown): void {
+	public rollback(message: FluidDataStoreMessage, localOpMetadata: unknown): void {
 		if (!this.channel) {
 			throw new Error("Channel must exist when rolling back ops");
 		}
 		if (!this.channel.rollback) {
 			throw new Error("Channel doesn't support rollback");
 		}
-		this.channel.rollback(type, contents, localOpMetadata);
+		this.channel.rollback(message.type, message.content, localOpMetadata);
 	}
 
 	public async applyStashedOp(contents: unknown): Promise<unknown> {
diff --git a/packages/runtime/container-runtime/src/index.ts b/packages/runtime/container-runtime/src/index.ts
index a7a5a7e2bf4b..56586dc5aa18 100644
--- a/packages/runtime/container-runtime/src/index.ts
+++ b/packages/runtime/container-runtime/src/index.ts
@@ -20,12 +20,19 @@ export {
 export { CompressionAlgorithms, disabledCompressionConfig } from "./compressionDefinitions.js";
 export {
 	ContainerMessageType,
+	ContainerRuntimeAliasMessage,
+	ContainerRuntimeDataStoreOpMessage,
+	InternalUtilityTypes,
+	OutboundContainerRuntimeAttachMessage,
 	UnknownContainerRuntimeMessage,
 } from "./messageTypes.js";
 export { IBlobManagerLoadInfo } from "./blobManager/index.js";
+export type { IDataStoreAliasMessage } from "./dataStore.js";
 export { FluidDataStoreRegistry } from "./dataStoreRegistry.js";
 export {
 	detectOutboundReferences,
+	type AddressedSignalEnvelope,
+	type IFluidRootParentContext,
 	ChannelCollectionFactory,
 	AllowTombstoneRequestHeaderKey,
 } from "./channelCollection.js";
@@ -107,7 +114,7 @@ export {
 	DefaultSummaryConfiguration,
 } from "./summary/index.js";
 export { IChunkedOp, unpackRuntimeMessage } from "./opLifecycle/index.js";
-export { ChannelCollection } from "./channelCollection.js";
+export { ChannelCollection, ComposableChannelCollection } from "./channelCollection.js";
 export {
 	IFluidDataStoreContextInternal,
 	ISnapshotDetails,
diff --git a/packages/runtime/container-runtime/src/messageTypes.ts b/packages/runtime/container-runtime/src/messageTypes.ts
index 755f00a5d494..53fd30c5174e 100644
--- a/packages/runtime/container-runtime/src/messageTypes.ts
+++ b/packages/runtime/container-runtime/src/messageTypes.ts
@@ -5,7 +5,8 @@
 
 import { ISequencedDocumentMessage } from "@fluidframework/driver-definitions/internal";
 import type { IdCreationRange } from "@fluidframework/id-compressor/internal";
-import {
+import type {
+	FluidDataStoreMessage,
 	IAttachMessage,
 	IEnvelope,
 	InboundAttachMessage,
@@ -59,63 +60,88 @@ export enum ContainerMessageType {
 }
 
 /**
- * The unpacked runtime message / details to be handled or dispatched by the ContainerRuntime.
- * Message type are differentiated via a `type` string and contain different contents depending on their type.
- *
- * IMPORTANT: when creating one to be serialized, set the properties in the order they appear here.
- * This way stringified values can be compared.
+ * @internal
  */
-interface TypedContainerRuntimeMessage<TType extends ContainerMessageType, TContents> {
-	/**
-	 * Type of the op, within the ContainerRuntime's domain
-	 */
-	type: TType;
+// eslint-disable-next-line @typescript-eslint/no-namespace
+export namespace InternalUtilityTypes {
 	/**
-	 * Domain-specific contents, interpreted according to the type
+	 * The unpacked runtime message / details to be handled or dispatched by the ContainerRuntime.
+	 * Message type are differentiated via a `type` string and contain different contents depending on their type.
+	 *
+	 * IMPORTANT: when creating one to be serialized, set the properties in the order they appear here.
+	 * This way stringified values can be compared.
 	 */
-	contents: TContents;
+	export interface TypedContainerRuntimeMessage<
+		TType extends ContainerMessageType,
+		TContents,
+	> {
+		/**
+		 * Type of the op, within the ContainerRuntime's domain
+		 */
+		type: TType;
+		/**
+		 * Domain-specific contents, interpreted according to the type
+		 */
+		contents: TContents;
+	}
 }
 
-export type ContainerRuntimeDataStoreOpMessage = TypedContainerRuntimeMessage<
-	ContainerMessageType.FluidDataStoreOp,
-	IEnvelope
->;
-export type InboundContainerRuntimeAttachMessage = TypedContainerRuntimeMessage<
-	ContainerMessageType.Attach,
-	InboundAttachMessage
->;
-export type OutboundContainerRuntimeAttachMessage = TypedContainerRuntimeMessage<
-	ContainerMessageType.Attach,
-	IAttachMessage
->;
-export type ContainerRuntimeChunkedOpMessage = TypedContainerRuntimeMessage<
-	ContainerMessageType.ChunkedOp,
-	IChunkedOp
->;
-export type ContainerRuntimeBlobAttachMessage = TypedContainerRuntimeMessage<
-	ContainerMessageType.BlobAttach,
-	undefined
->;
-export type ContainerRuntimeRejoinMessage = TypedContainerRuntimeMessage<
+/**
+ * @internal
+ */
+export type ContainerRuntimeDataStoreOpMessage =
+	InternalUtilityTypes.TypedContainerRuntimeMessage<
+		ContainerMessageType.FluidDataStoreOp,
+		IEnvelope<FluidDataStoreMessage>
+	>;
+export type InboundContainerRuntimeAttachMessage =
+	InternalUtilityTypes.TypedContainerRuntimeMessage<
+		ContainerMessageType.Attach,
+		InboundAttachMessage
+	>;
+/**
+ * @internal
+ */
+export type OutboundContainerRuntimeAttachMessage =
+	InternalUtilityTypes.TypedContainerRuntimeMessage<
+		ContainerMessageType.Attach,
+		IAttachMessage
+	>;
+export type ContainerRuntimeChunkedOpMessage =
+	InternalUtilityTypes.TypedContainerRuntimeMessage<
+		ContainerMessageType.ChunkedOp,
+		IChunkedOp
+	>;
+export type ContainerRuntimeBlobAttachMessage =
+	InternalUtilityTypes.TypedContainerRuntimeMessage<
+		ContainerMessageType.BlobAttach,
+		undefined
+	>;
+export type ContainerRuntimeRejoinMessage = InternalUtilityTypes.TypedContainerRuntimeMessage<
 	ContainerMessageType.Rejoin,
 	undefined
 >;
-export type ContainerRuntimeAliasMessage = TypedContainerRuntimeMessage<
+/**
+ * @internal
+ */
+export type ContainerRuntimeAliasMessage = InternalUtilityTypes.TypedContainerRuntimeMessage<
 	ContainerMessageType.Alias,
 	IDataStoreAliasMessage
 >;
-export type ContainerRuntimeIdAllocationMessage = TypedContainerRuntimeMessage<
-	ContainerMessageType.IdAllocation,
-	IdCreationRange
->;
-export type ContainerRuntimeGCMessage = TypedContainerRuntimeMessage<
+export type ContainerRuntimeIdAllocationMessage =
+	InternalUtilityTypes.TypedContainerRuntimeMessage<
+		ContainerMessageType.IdAllocation,
+		IdCreationRange
+	>;
+export type ContainerRuntimeGCMessage = InternalUtilityTypes.TypedContainerRuntimeMessage<
 	ContainerMessageType.GC,
 	GarbageCollectionMessage
 >;
-export type ContainerRuntimeDocumentSchemaMessage = TypedContainerRuntimeMessage<
-	ContainerMessageType.DocumentSchemaChange,
-	IDocumentSchemaChangeMessage
->;
+export type ContainerRuntimeDocumentSchemaMessage =
+	InternalUtilityTypes.TypedContainerRuntimeMessage<
+		ContainerMessageType.DocumentSchemaChange,
+		IDocumentSchemaChangeMessage
+	>;
 
 /**
  * Represents an unrecognized TypedContainerRuntimeMessage, e.g. a message from a future version of the container runtime.
@@ -136,7 +162,7 @@ export interface UnknownContainerRuntimeMessage {
 }
 
 /**
- * A {@link TypedContainerRuntimeMessage} that is received from the server and will be processed by the container runtime.
+ * A {@link InternalUtilityTypes.TypedContainerRuntimeMessage} that is received from the server and will be processed by the container runtime.
  */
 export type InboundContainerRuntimeMessage =
 	| ContainerRuntimeDataStoreOpMessage
@@ -152,7 +178,7 @@ export type InboundContainerRuntimeMessage =
 	| UnknownContainerRuntimeMessage;
 
 /**
- * A {@link TypedContainerRuntimeMessage} that has been generated by the container runtime, eventually to be sent to the ordering service.
+ * A {@link InternalUtilityTypes.TypedContainerRuntimeMessage} that has been generated by the container runtime, eventually to be sent to the ordering service.
  * These are messages generated by the local runtime, before the outbox's op virtualization step.
  */
 export type LocalContainerRuntimeMessage =
diff --git a/packages/runtime/container-runtime/src/test/containerRuntime.spec.ts b/packages/runtime/container-runtime/src/test/containerRuntime.spec.ts
index 5440c7626125..5ce340644fa2 100644
--- a/packages/runtime/container-runtime/src/test/containerRuntime.spec.ts
+++ b/packages/runtime/container-runtime/src/test/containerRuntime.spec.ts
@@ -41,20 +41,22 @@ import {
 	type IDocumentAttributes,
 	SummaryType,
 } from "@fluidframework/driver-definitions/internal";
-import {
+import type {
+	FluidDataStoreMessage,
 	ISummaryTreeWithStats,
 	FluidDataStoreRegistryEntry,
-	FlushMode,
-	FlushModeExperimental,
 	IFluidDataStoreContext,
 	IFluidDataStoreFactory,
 	IFluidDataStoreRegistry,
 	NamedFluidDataStoreRegistryEntries,
-	type IRuntimeMessageCollection,
-	type ISequencedMessageEnvelope,
-	type IEnvelope,
-	type ITelemetryContext,
-	type ISummarizeInternalResult,
+	IRuntimeMessageCollection,
+	ISequencedMessageEnvelope,
+	ITelemetryContext,
+	ISummarizeInternalResult,
+} from "@fluidframework/runtime-definitions/internal";
+import {
+	FlushMode,
+	FlushModeExperimental,
 } from "@fluidframework/runtime-definitions/internal";
 import {
 	IFluidErrorBase,
@@ -102,17 +104,24 @@ import {
 	type IRefreshSummaryAckOptions,
 } from "../summary/index.js";
 
+const testDataStoreMessage = {
+	type: "op",
+	content: { address: "test-address", contents: "test-contents" },
+} satisfies FluidDataStoreMessage;
+
 function submitDataStoreOp(
 	runtime: Pick<ContainerRuntime, "submitMessage">,
 	id: string,
-	contents: unknown,
+	contents: FluidDataStoreMessage,
 	localOpMetadata?: unknown,
-) {
+): void {
 	runtime.submitMessage(
-		ContainerMessageType.FluidDataStoreOp,
 		{
-			address: id,
-			contents,
+			type: ContainerMessageType.FluidDataStoreOp,
+			contents: {
+				address: id,
+				contents,
+			},
 		},
 		localOpMetadata,
 	);
@@ -122,7 +131,7 @@ const changeConnectionState = (
 	runtime: Omit<ContainerRuntime, "submit">,
 	connected: boolean,
 	clientId: string,
-) => {
+): void => {
 	const audience = runtime.getAudience() as MockAudience;
 	audience.setCurrentClientId(clientId);
 
@@ -155,19 +164,12 @@ function isSignalEnvelope(obj: unknown): obj is ISignalEnvelope {
 }
 
 function defineResubmitAndSetConnectionState(containerRuntime: ContainerRuntime): void {
-	// eslint-disable-next-line @typescript-eslint/consistent-type-assertions, @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access -- Modifying private property
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access -- Modifying private property
 	(containerRuntime as any).channelCollection = {
 		setConnectionState: (_connected: boolean, _clientId?: string) => {},
 		// Pass data store op right back to ContainerRuntime
-		reSubmit: (type: string, envelope: IEnvelope, localOpMetadata: unknown) => {
-			submitDataStoreOp(
-				containerRuntime,
-				envelope.address,
-				envelope.contents,
-				localOpMetadata,
-			);
-		},
-	} as ChannelCollection;
+		reSubmitContainerMessage: containerRuntime.submitMessage.bind(containerRuntime),
+	} satisfies Partial<ChannelCollection>;
 }
 
 describe("Runtime", () => {
@@ -357,7 +359,7 @@ describe("Runtime", () => {
 				changeConnectionState(containerRuntime, false, mockClientId);
 
 				// Not connected, so nothing is submitted on flush - just queued in PendingStateManager
-				submitDataStoreOp(containerRuntime, "1", "test", { emptyBatch: true });
+				submitDataStoreOp(containerRuntime, "1", testDataStoreMessage, { emptyBatch: true });
 				// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
 				(containerRuntime as any).flush();
 				changeConnectionState(containerRuntime, true, mockClientId);
@@ -402,11 +404,11 @@ describe("Runtime", () => {
 					changeConnectionState(containerRuntime, false, mockClientId);
 
 					// Not connected, so nothing is submitted on flush - just queued in PendingStateManager
-					submitDataStoreOp(containerRuntime, "1", "test");
+					submitDataStoreOp(containerRuntime, "1", testDataStoreMessage);
 					// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
 					(containerRuntime as any).flush();
 
-					submitDataStoreOp(containerRuntime, "2", "test");
+					submitDataStoreOp(containerRuntime, "2", testDataStoreMessage);
 					changeConnectionState(containerRuntime, true, mockClientId);
 					// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
 					(containerRuntime as any).flush();
@@ -417,7 +419,7 @@ describe("Runtime", () => {
 					// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
 					assert.strictEqual(submittedOps[1].contents.address, "2");
 
-					function batchIdMatchesUnsentFormat(batchId?: string) {
+					function batchIdMatchesUnsentFormat(batchId?: string): boolean {
 						return (
 							batchId !== undefined &&
 							batchId.length === "00000000-0000-0000-0000-000000000000_[-1]".length &&
@@ -483,7 +485,7 @@ describe("Runtime", () => {
 					});
 
 					// Submit the first message
-					submitDataStoreOp(containerRuntime, "1", "testMessage1");
+					submitDataStoreOp(containerRuntime, "1", testDataStoreMessage);
 					assert.strictEqual(submittedOps.length, 0, "No ops submitted yet");
 
 					// Bump lastSequenceNumber and trigger the "op" event artificially to simulate processing a non-runtime op
@@ -507,7 +509,10 @@ describe("Runtime", () => {
 
 					// Submit the second message
 					// When [skipSafetyFlushDuringProcessStack: TRUE], this will trigger a flush via Outbox.maybeFlushPartialBatch
-					submitDataStoreOp(containerRuntime, "2", "testMessage2");
+					submitDataStoreOp(containerRuntime, "2", {
+						type: "op",
+						content: { address: "test-address", contents: "test-contents2" },
+					});
 					assert.equal(
 						submittedOps.length,
 						1,
@@ -699,9 +704,9 @@ describe("Runtime", () => {
 
 					it("Batching property set properly", () => {
 						containerRuntime.orderSequentially(() => {
-							submitDataStoreOp(containerRuntime, "1", "test");
-							submitDataStoreOp(containerRuntime, "2", "test");
-							submitDataStoreOp(containerRuntime, "3", "test");
+							submitDataStoreOp(containerRuntime, "1", testDataStoreMessage);
+							submitDataStoreOp(containerRuntime, "2", testDataStoreMessage);
+							submitDataStoreOp(containerRuntime, "3", testDataStoreMessage);
 						});
 						// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
 						(containerRuntime as any).flush();
@@ -732,17 +737,17 @@ describe("Runtime", () => {
 						changeConnectionState(containerRuntime, false, fakeClientId);
 
 						containerRuntime.orderSequentially(() => {
-							submitDataStoreOp(containerRuntime, "1", "test");
-							submitDataStoreOp(containerRuntime, "2", "test");
-							submitDataStoreOp(containerRuntime, "3", "test");
+							submitDataStoreOp(containerRuntime, "1", testDataStoreMessage);
+							submitDataStoreOp(containerRuntime, "2", testDataStoreMessage);
+							submitDataStoreOp(containerRuntime, "3", testDataStoreMessage);
 						});
 						// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
 						(containerRuntime as any).flush();
 
 						containerRuntime.orderSequentially(() => {
-							submitDataStoreOp(containerRuntime, "4", "test");
-							submitDataStoreOp(containerRuntime, "5", "test");
-							submitDataStoreOp(containerRuntime, "6", "test");
+							submitDataStoreOp(containerRuntime, "4", testDataStoreMessage);
+							submitDataStoreOp(containerRuntime, "5", testDataStoreMessage);
+							submitDataStoreOp(containerRuntime, "6", testDataStoreMessage);
 						});
 						// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
 						(containerRuntime as any).flush();
@@ -1291,14 +1296,7 @@ describe("Runtime", () => {
 				patched.channelCollection = {
 					setConnectionState: (_connected: boolean, _clientId?: string) => {},
 					// Pass data store op right back to ContainerRuntime
-					reSubmit: (type: string, envelope: IEnvelope, localOpMetadata: unknown) => {
-						submitDataStoreOp(
-							containerRuntime,
-							envelope.address,
-							envelope.contents,
-							localOpMetadata,
-						);
-					},
+					reSubmitContainerMessage: containerRuntime.submitMessage.bind(containerRuntime),
 				} satisfies Partial<ChannelCollection>;
 
 				return patched;
@@ -1309,14 +1307,14 @@ describe("Runtime", () => {
 
 				changeConnectionState(patchedContainerRuntime, false, mockClientId);
 
-				submitDataStoreOp(patchedContainerRuntime, "1", "test");
-				submitDataStoreOp(patchedContainerRuntime, "2", "test");
+				submitDataStoreOp(patchedContainerRuntime, "1", testDataStoreMessage);
+				submitDataStoreOp(patchedContainerRuntime, "2", testDataStoreMessage);
 				patchedContainerRuntime.submit({
 					// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-assignment
 					type: "FUTURE_TYPE" as any,
 					contents: "3",
 				});
-				submitDataStoreOp(patchedContainerRuntime, "4", "test");
+				submitDataStoreOp(patchedContainerRuntime, "4", testDataStoreMessage);
 
 				assert.strictEqual(
 					submittedOps.length,
@@ -1516,7 +1514,10 @@ describe("Runtime", () => {
 
 			it("modifying op content after submit does not reflect in PendingStateManager", () => {
 				const content = { prop1: 1 };
-				submitDataStoreOp(containerRuntime, "1", content);
+				submitDataStoreOp(containerRuntime, "1", {
+					type: "op",
+					content: { address: "test", contents: content },
+				});
 				// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access, @typescript-eslint/no-unsafe-call
 				(containerRuntime as any).flush();
 
@@ -1530,7 +1531,8 @@ describe("Runtime", () => {
 					// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
 					JSON.parse(state?.pendingStates?.[0].content).contents.contents,
 					{
-						prop1: 1,
+						type: "op",
+						content: { address: "test", contents: { prop1: 1 } },
 					},
 					"content of pending local message has changed",
 				);
@@ -1791,7 +1793,10 @@ describe("Runtime", () => {
 
 			it("summary fails before generate if there are pending ops", async () => {
 				// Submit an op and yield for it to be flushed from outbox to pending state manager.
-				submitDataStoreOp(containerRuntime, "fakeId", "fakeContents");
+				submitDataStoreOp(containerRuntime, "fakeId", {
+					type: "op",
+					content: { address: "fakeAddress", contents: "fakeContents" },
+				});
 				await yieldEventLoop();
 
 				const summarizeResultP = containerRuntime.submitSummary({
@@ -1824,7 +1829,10 @@ describe("Runtime", () => {
 					const boundFn = fn.bind(containerRuntime);
 					return async (...args: unknown[]) => {
 						// Submit an op and yield for it to be flushed from outbox to pending state manager.
-						submitDataStoreOp(containerRuntime, "fakeId", "fakeContents");
+						submitDataStoreOp(containerRuntime, "fakeId", {
+							type: "op",
+							content: { address: "fakeAddress", contents: "fakeContents" },
+						});
 						await yieldEventLoop();
 
 						return boundFn(...args);
@@ -3088,7 +3096,7 @@ describe("Runtime", () => {
 
 				// Submit op so message is queued in PendingStateManager
 				// This is needed to increase reconnect count
-				submitDataStoreOp(containerRuntime, "1", "test");
+				submitDataStoreOp(containerRuntime, "1", testDataStoreMessage);
 
 				// Disconnect + Reconnect
 				changeConnectionState(containerRuntime, false, mockClientId);
@@ -3140,7 +3148,7 @@ describe("Runtime", () => {
 				// so that message is queued in PendingStateManager and reconnect count is increased.
 				defineResubmitAndSetConnectionState(containerRuntime);
 				// Send and process an initial signal to prime the system.
-				submitDataStoreOp(containerRuntime, "1", "test");
+				submitDataStoreOp(containerRuntime, "1", testDataStoreMessage);
 				sendSignals(1); // 1st signal (#1)
 				processSubmittedSignals(1);
 
diff --git a/packages/runtime/container-runtime/src/test/dataStoreContext.spec.ts b/packages/runtime/container-runtime/src/test/dataStoreContext.spec.ts
index 91e03300db7f..c3a156acbf59 100644
--- a/packages/runtime/container-runtime/src/test/dataStoreContext.spec.ts
+++ b/packages/runtime/container-runtime/src/test/dataStoreContext.spec.ts
@@ -15,6 +15,7 @@ import {
 } from "@fluidframework/core-interfaces";
 import { IFluidHandleContext } from "@fluidframework/core-interfaces/internal";
 import { LazyPromise } from "@fluidframework/core-utils/internal";
+import type { LocalFluidDataStoreRuntimeMessage } from "@fluidframework/datastore/internal";
 import { DataStoreMessageType, FluidObjectHandle } from "@fluidframework/datastore/internal";
 import { ISummaryBlob, SummaryType } from "@fluidframework/driver-definitions";
 import {
@@ -22,10 +23,9 @@ import {
 	IBlob,
 	ISnapshotTree,
 } from "@fluidframework/driver-definitions/internal";
-import {
+import type {
 	IGarbageCollectionData,
 	CreateChildSummarizerNodeFn,
-	CreateSummarizerNodeSource,
 	IFluidDataStoreChannel,
 	IFluidDataStoreContext,
 	IFluidDataStoreFactory,
@@ -33,8 +33,11 @@ import {
 	IFluidParentContext,
 	IGarbageCollectionDetailsBase,
 	SummarizeInternalFn,
+	IContainerRuntimeBase,
+} from "@fluidframework/runtime-definitions/internal";
+import {
+	CreateSummarizerNodeSource,
 	channelsTreeName,
-	type IContainerRuntimeBase,
 } from "@fluidframework/runtime-definitions/internal";
 import {
 	GCDataBuilder,
@@ -376,11 +379,14 @@ describe("Data Store Context Tests", () => {
 				});
 				await localDataStoreContext.realize();
 
-				localDataStoreContext.submitMessage(
-					DataStoreMessageType.ChannelOp,
-					"summarizer message",
-					{},
-				);
+				const message = {
+					type: DataStoreMessageType.ChannelOp,
+					content: {
+						address: "address",
+						contents: "summarizer message",
+					},
+				} satisfies LocalFluidDataStoreRuntimeMessage;
+				localDataStoreContext.submitMessage(message.type, message.content, {});
 
 				const expectedEvents = [
 					{
@@ -417,11 +423,14 @@ describe("Data Store Context Tests", () => {
 
 				let eventCount = 0;
 				for (let i = 0; i < 15; i++) {
-					localDataStoreContext.submitMessage(
-						DataStoreMessageType.ChannelOp,
-						`summarizer message ${i}`,
-						{},
-					);
+					const message = {
+						type: DataStoreMessageType.ChannelOp,
+						content: {
+							address: "address",
+							contents: `summarizer message ${i}`,
+						},
+					} satisfies LocalFluidDataStoreRuntimeMessage;
+					localDataStoreContext.submitMessage(message.type, message.content, {});
 				}
 				for (const event of mockLogger.events) {
 					if (
diff --git a/packages/runtime/container-runtime/src/test/opLifecycle/opDecompressor.spec.ts b/packages/runtime/container-runtime/src/test/opLifecycle/opDecompressor.spec.ts
index 561b0487235c..596cfe2dd36c 100644
--- a/packages/runtime/container-runtime/src/test/opLifecycle/opDecompressor.spec.ts
+++ b/packages/runtime/container-runtime/src/test/opLifecycle/opDecompressor.spec.ts
@@ -7,7 +7,10 @@ import { strict as assert } from "node:assert";
 
 import { IsoBuffer } from "@fluid-internal/client-utils";
 import { ISequencedDocumentMessage } from "@fluidframework/driver-definitions/internal";
-import type { IEnvelope } from "@fluidframework/runtime-definitions/internal";
+import type {
+	FluidDataStoreMessage,
+	IEnvelope,
+} from "@fluidframework/runtime-definitions/internal";
 import { MockLogger } from "@fluidframework/telemetry-utils/internal";
 import { compress } from "lz4js";
 
@@ -28,7 +31,7 @@ function generateCompressedBatchMessage(length: number): ISequencedDocumentMessa
 		// Actual Op and contents aren't important. Values are not realistic.
 		batch.push({
 			type: ContainerMessageType.FluidDataStoreOp,
-			contents: `value${i}` as unknown as IEnvelope,
+			contents: `value${i}` as unknown as IEnvelope<FluidDataStoreMessage>,
 		});
 	}
 
diff --git a/packages/runtime/container-runtime/src/test/opLifecycle/opSerialization.spec.ts b/packages/runtime/container-runtime/src/test/opLifecycle/opSerialization.spec.ts
index 3d6ae8d50f1d..2cb66b9cc10a 100644
--- a/packages/runtime/container-runtime/src/test/opLifecycle/opSerialization.spec.ts
+++ b/packages/runtime/container-runtime/src/test/opLifecycle/opSerialization.spec.ts
@@ -64,7 +64,10 @@ describe("opSerialization", () => {
 
 			const op: LocalContainerRuntimeMessage = {
 				type: ContainerMessageType.FluidDataStoreOp,
-				contents: { address: "123", contents: { hereIsAHandle: mockHandle } },
+				contents: {
+					address: "123",
+					contents: { type: "op", content: { address: "test", contents: mockHandle } },
+				},
 			};
 
 			const serialized = serializeOp(op);
@@ -86,7 +89,11 @@ describe("opSerialization", () => {
 				contents: {
 					address: "123",
 					contents: {
-						alreadyEncodedHandle: encodeHandleForSerialization(new MockHandle({})),
+						type: "op",
+						content: {
+							address: "test",
+							contents: encodeHandleForSerialization(new MockHandle({})),
+						},
 					},
 				},
 			};
diff --git a/packages/runtime/datastore/api-report/datastore.legacy.alpha.api.md b/packages/runtime/datastore/api-report/datastore.legacy.alpha.api.md
index 0ccee30275df..ef96d997f8d6 100644
--- a/packages/runtime/datastore/api-report/datastore.legacy.alpha.api.md
+++ b/packages/runtime/datastore/api-report/datastore.legacy.alpha.api.md
@@ -79,7 +79,7 @@ export class FluidDataStoreRuntime extends TypedEventEmitter<IFluidDataStoreRunt
     // (undocumented)
     resolveHandle(request: IRequest): Promise<IResponse>;
     reSubmit(type: DataStoreMessageType, content: any, localOpMetadata: unknown): void;
-    rollback?(type: DataStoreMessageType, content: any, localOpMetadata: unknown): void;
+    rollback(type: DataStoreMessageType, content: any, localOpMetadata: unknown): void;
     // (undocumented)
     get rootRoutingContext(): this;
     // (undocumented)
@@ -88,7 +88,7 @@ export class FluidDataStoreRuntime extends TypedEventEmitter<IFluidDataStoreRunt
     setAttachState(attachState: AttachState.Attaching | AttachState.Attached): void;
     // (undocumented)
     setConnectionState(connected: boolean, clientId?: string): void;
-    // (undocumented)
+    // @deprecated (undocumented)
     submitMessage(type: DataStoreMessageType, content: any, localOpMetadata: unknown): void;
     submitSignal(type: string, content: unknown, targetClientId?: string): void;
     summarize(fullTree?: boolean, trackState?: boolean, telemetryContext?: ITelemetryContext): Promise<ISummaryTreeWithStats>;
diff --git a/packages/runtime/datastore/package.json b/packages/runtime/datastore/package.json
index 94fc59092489..487d78fd629c 100644
--- a/packages/runtime/datastore/package.json
+++ b/packages/runtime/datastore/package.json
@@ -158,7 +158,11 @@
 		"typescript": "~5.4.5"
 	},
 	"typeValidation": {
-		"broken": {},
+		"broken": {
+			"Class_FluidDataStoreRuntime": {
+				"forwardCompat": false
+			}
+		},
 		"entrypoint": "legacy"
 	}
 }
diff --git a/packages/runtime/datastore/src/dataStoreRuntime.ts b/packages/runtime/datastore/src/dataStoreRuntime.ts
index 290c5dabc384..ab478dc34fd8 100644
--- a/packages/runtime/datastore/src/dataStoreRuntime.ts
+++ b/packages/runtime/datastore/src/dataStoreRuntime.ts
@@ -112,6 +112,16 @@ export enum DataStoreMessageType {
 	ChannelOp = "op",
 }
 
+/**
+ * Outgoing {@link FluidDataStoreRuntime} message structures.
+ * @internal
+ *
+ * @privateRemarks The types here are required to satisfy {@link @fluidframework/runtime-definitions#FluidDataStoreMessage} interface.
+ */
+export type LocalFluidDataStoreRuntimeMessage =
+	| { type: DataStoreMessageType.ChannelOp; content: IEnvelope }
+	| { type: DataStoreMessageType.Attach; content: IAttachMessage };
+
 /**
  * @legacy
  * @alpha
@@ -1047,8 +1057,12 @@ export class FluidDataStoreRuntime
 		}
 	}
 
+	/**
+	 * @deprecated No implementation required and will be removed in 2.50.
+	 */
 	public submitMessage(type: DataStoreMessageType, content: any, localOpMetadata: unknown) {
-		this.submit(type, content, localOpMetadata);
+		this.verifyNotClosed();
+		this.submit({ type, content }, localOpMetadata);
 	}
 
 	/**
@@ -1110,7 +1124,7 @@ export class FluidDataStoreRuntime
 			type: channel.attributes.type,
 		};
 		this.pendingAttach.add(channel.id);
-		this.submit(DataStoreMessageType.Attach, message);
+		this.submit({ type: DataStoreMessageType.Attach, content: message });
 
 		const context = this.contexts.get(channel.id) as LocalChannelContextBase;
 		context.makeVisible();
@@ -1118,16 +1132,15 @@ export class FluidDataStoreRuntime
 
 	private submitChannelOp(address: string, contents: any, localOpMetadata: unknown) {
 		const envelope: IEnvelope = { address, contents };
-		this.submit(DataStoreMessageType.ChannelOp, envelope, localOpMetadata);
+		this.verifyNotClosed();
+		this.submit({ type: DataStoreMessageType.ChannelOp, content: envelope }, localOpMetadata);
 	}
 
 	private submit(
-		type: DataStoreMessageType,
-		content: any,
+		message: LocalFluidDataStoreRuntimeMessage,
 		localOpMetadata: unknown = undefined,
 	): void {
-		this.verifyNotClosed();
-		this.dataStoreContext.submitMessage(type, content, localOpMetadata);
+		this.dataStoreContext.submitMessage(message.type, message.content, localOpMetadata);
 	}
 
 	/**
@@ -1136,6 +1149,11 @@ export class FluidDataStoreRuntime
 	 * This typically happens when we reconnect and there are unacked messages.
 	 * @param content - The content of the original message.
 	 * @param localOpMetadata - The local metadata associated with the original message.
+	 *
+	 * @privateRemarks
+	 * `type` parameter's type of `DataStoreMessageType` is a covariance exception
+	 * over `string` that `IFluidDataStoreChannel` specifies. (`unreachableCase`
+	 * might be reachable over time without better typing in this area.)
 	 */
 	public reSubmit(type: DataStoreMessageType, content: any, localOpMetadata: unknown) {
 		this.verifyNotClosed();
@@ -1151,7 +1169,7 @@ export class FluidDataStoreRuntime
 			}
 			case DataStoreMessageType.Attach:
 				// For Attach messages, just submit them again.
-				this.submit(type, content, localOpMetadata);
+				this.submit({ type, content }, localOpMetadata);
 				break;
 			default:
 				unreachableCase(type);
@@ -1162,8 +1180,12 @@ export class FluidDataStoreRuntime
 	 * Revert a local op.
 	 * @param content - The content of the original message.
 	 * @param localOpMetadata - The local metadata associated with the original message.
+	 *
+	 * @privateRemarks
+	 * `type` parameter's type of `DataStoreMessageType` is a covariance exception
+	 * over `string` that `IFluidDataStoreChannel` specifies.
 	 */
-	public rollback?(type: DataStoreMessageType, content: any, localOpMetadata: unknown) {
+	public rollback(type: DataStoreMessageType, content: any, localOpMetadata: unknown) {
 		this.verifyNotClosed();
 
 		switch (type) {
diff --git a/packages/runtime/datastore/src/index.ts b/packages/runtime/datastore/src/index.ts
index efafb3267415..1cf3506b5000 100644
--- a/packages/runtime/datastore/src/index.ts
+++ b/packages/runtime/datastore/src/index.ts
@@ -8,6 +8,7 @@ export {
 	DataStoreMessageType,
 	FluidDataStoreRuntime,
 	ISharedObjectRegistry,
+	type LocalFluidDataStoreRuntimeMessage,
 	mixinRequestHandler,
 	mixinSummaryHandler,
 } from "./dataStoreRuntime.js";
diff --git a/packages/runtime/datastore/src/test/types/validateDatastorePrevious.generated.ts b/packages/runtime/datastore/src/test/types/validateDatastorePrevious.generated.ts
index bab8d7182452..5fe3440cb5cc 100644
--- a/packages/runtime/datastore/src/test/types/validateDatastorePrevious.generated.ts
+++ b/packages/runtime/datastore/src/test/types/validateDatastorePrevious.generated.ts
@@ -22,6 +22,7 @@ declare type MakeUnusedImportErrorsGoAway<T> = TypeOnly<T> | MinimalType<T> | Fu
  * typeValidation.broken:
  * "Class_FluidDataStoreRuntime": {"forwardCompat": false}
  */
+// @ts-expect-error compatibility expected to be broken
 declare type old_as_current_for_Class_FluidDataStoreRuntime = requireAssignableTo<TypeOnly<old.FluidDataStoreRuntime>, TypeOnly<current.FluidDataStoreRuntime>>
 
 /*
diff --git a/packages/runtime/runtime-definitions/api-report/runtime-definitions.legacy.alpha.api.md b/packages/runtime/runtime-definitions/api-report/runtime-definitions.legacy.alpha.api.md
index d497b1a40dff..be8eb164b332 100644
--- a/packages/runtime/runtime-definitions/api-report/runtime-definitions.legacy.alpha.api.md
+++ b/packages/runtime/runtime-definitions/api-report/runtime-definitions.legacy.alpha.api.md
@@ -108,9 +108,9 @@ export interface IDataStore {
 }
 
 // @alpha
-export interface IEnvelope {
+export interface IEnvelope<TContents = any> {
     address: string;
-    contents: any;
+    contents: TContents;
 }
 
 // @alpha
@@ -133,11 +133,11 @@ export interface IFluidDataStoreChannel extends IDisposable {
     processSignal(message: IInboundSignalMessage, local: boolean): void;
     // (undocumented)
     request(request: IRequest): Promise<IResponse>;
-    reSubmit(type: string, content: any, localOpMetadata: unknown): any;
+    reSubmit(type: string, content: any, localOpMetadata: unknown): void;
     rollback?(type: string, content: any, localOpMetadata: unknown): void;
     // (undocumented)
     setAttachState(attachState: AttachState.Attaching | AttachState.Attached): void;
-    setConnectionState(connected: boolean, clientId?: string): any;
+    setConnectionState(connected: boolean, clientId?: string): void;
     summarize(fullTree?: boolean, trackState?: boolean, telemetryContext?: ITelemetryContext): Promise<ISummaryTreeWithStats>;
     updateUsedRoutes(usedRoutes: string[]): void;
 }
diff --git a/packages/runtime/runtime-definitions/src/dataStoreContext.ts b/packages/runtime/runtime-definitions/src/dataStoreContext.ts
index 5530e9d02f94..11546c0f835b 100644
--- a/packages/runtime/runtime-definitions/src/dataStoreContext.ts
+++ b/packages/runtime/runtime-definitions/src/dataStoreContext.ts
@@ -368,7 +368,7 @@ export interface IFluidDataStoreChannel extends IDisposable {
 	 * @param clientId - ID of the client. It's old ID when in disconnected state and
 	 * it's new client ID when we are connecting or connected.
 	 */
-	setConnectionState(connected: boolean, clientId?: string);
+	setConnectionState(connected: boolean, clientId?: string): void;
 
 	/**
 	 * Ask the DDS to resubmit a message. This could be because we reconnected and this message was not acked.
@@ -377,7 +377,7 @@ export interface IFluidDataStoreChannel extends IDisposable {
 	 * @param localOpMetadata - The local metadata associated with the original message.
 	 */
 	// eslint-disable-next-line @typescript-eslint/no-explicit-any -- TODO (#28746): breaking change
-	reSubmit(type: string, content: any, localOpMetadata: unknown);
+	reSubmit(type: string, content: any, localOpMetadata: unknown): void;
 
 	// eslint-disable-next-line @typescript-eslint/no-explicit-any -- TODO (#28746): breaking change
 	applyStashedOp(content: any): Promise<unknown>;
diff --git a/packages/runtime/runtime-definitions/src/index.ts b/packages/runtime/runtime-definitions/src/index.ts
index 14178798eaa6..988865e34759 100644
--- a/packages/runtime/runtime-definitions/src/index.ts
+++ b/packages/runtime/runtime-definitions/src/index.ts
@@ -45,6 +45,7 @@ export {
 	gcTreeKey,
 } from "./garbageCollectionDefinitions.js";
 export type {
+	FluidDataStoreMessage,
 	IAttachMessage,
 	IEnvelope,
 	IInboundSignalMessage,
diff --git a/packages/runtime/runtime-definitions/src/protocol.ts b/packages/runtime/runtime-definitions/src/protocol.ts
index 762aaf02c2a5..84553ec05d7f 100644
--- a/packages/runtime/runtime-definitions/src/protocol.ts
+++ b/packages/runtime/runtime-definitions/src/protocol.ts
@@ -14,7 +14,8 @@ import type {
  * @legacy
  * @alpha
  */
-export interface IEnvelope {
+// eslint-disable-next-line @typescript-eslint/no-explicit-any -- TODO (#28746): breaking change
+export interface IEnvelope<TContents = any> {
 	/**
 	 * The target for the envelope
 	 */
@@ -23,8 +24,7 @@ export interface IEnvelope {
 	/**
 	 * The contents of the envelope
 	 */
-	// eslint-disable-next-line @typescript-eslint/no-explicit-any -- TODO (#28746): breaking change
-	contents: any;
+	contents: TContents;
 }
 
 /**
@@ -126,3 +126,24 @@ export interface IRuntimeMessageCollection {
 	 */
 	readonly messagesContent: readonly IRuntimeMessagesContent[];
 }
+
+/**
+ * Outgoing {@link IFluidDataStoreChannel} message structures.
+ * @internal
+ *
+ * @privateRemarks
+ * Future use opportunity:
+ * - Change {@link IFluidDataStoreChannel} and {@link IFluidParentContext},
+ * to have a generic specifying `T extends FluidDataStoreMessage` and uses
+ * `T["type"]` and `T["content"]` to qualify message related methods,
+ * preferably where `submitMessage`, `reSubmit`, and `rollback` have
+ * overloads to ensure callers pair values correctly.
+ * - A further improvement would be to reshape `submitMessage`, `reSubmit`,
+ * and `rollback` to accept `T` as `message` parameter instead of `type`
+ * and `content` parameters that are hard to convince TypeScript must be
+ * paired in implementations.
+ */
+export interface FluidDataStoreMessage {
+	type: string;
+	content: unknown;
+}
diff --git a/packages/runtime/test-runtime-utils/api-report/test-runtime-utils.legacy.alpha.api.md b/packages/runtime/test-runtime-utils/api-report/test-runtime-utils.legacy.alpha.api.md
index d2e38472f9b5..e699c307dde6 100644
--- a/packages/runtime/test-runtime-utils/api-report/test-runtime-utils.legacy.alpha.api.md
+++ b/packages/runtime/test-runtime-utils/api-report/test-runtime-utils.legacy.alpha.api.md
@@ -360,9 +360,9 @@ export class MockFluidDataStoreContext implements IFluidDataStoreContext {
     // (undocumented)
     storage: IDocumentStorageService;
     // (undocumented)
-    submitMessage(type: string, content: any, localOpMetadata: unknown): void;
+    submitMessage(): void;
     // (undocumented)
-    submitSignal(type: string, content: any): void;
+    submitSignal(): void;
     // (undocumented)
     uploadBlob(blob: ArrayBufferLike): Promise<IFluidHandleInternal<ArrayBufferLike>>;
 }
@@ -485,10 +485,10 @@ export class MockFluidDataStoreRuntime extends EventEmitter implements IFluidDat
     setAttachState(attachState: AttachState.Attaching | AttachState.Attached): void;
     // (undocumented)
     setConnectionState(connected: boolean, clientId?: string): void;
-    // (undocumented)
+    // @deprecated (undocumented)
     submitMessage(type: MessageType, content: any): null;
     // (undocumented)
-    submitSignal(type: string, content: any): null;
+    submitSignal: IFluidDataStoreRuntime["submitSignal"];
     // (undocumented)
     summarize(fullTree?: boolean, trackState?: boolean): Promise<ISummaryTreeWithStats>;
     // (undocumented)
diff --git a/packages/runtime/test-runtime-utils/src/mocks.ts b/packages/runtime/test-runtime-utils/src/mocks.ts
index 15636ce00a6a..3f9f95bd3589 100644
--- a/packages/runtime/test-runtime-utils/src/mocks.ts
+++ b/packages/runtime/test-runtime-utils/src/mocks.ts
@@ -990,6 +990,9 @@ export class MockFluidDataStoreRuntime
 		return null;
 	}
 
+	/**
+	 * @deprecated No implementation required and will be removed in 2.50.
+	 */
 	public submitMessage(type: MessageType, content: any) {
 		return null;
 	}
@@ -1010,9 +1013,7 @@ export class MockFluidDataStoreRuntime
 		return this.containerRuntime.dirty();
 	}
 
-	public submitSignal(type: string, content: any) {
-		return null;
-	}
+	public submitSignal: IFluidDataStoreRuntime["submitSignal"] = () => null;
 
 	public processMessages(messageCollection: IRuntimeMessageCollection) {
 		if (this.disposed) {
diff --git a/packages/runtime/test-runtime-utils/src/mocksDataStoreContext.ts b/packages/runtime/test-runtime-utils/src/mocksDataStoreContext.ts
index 33126e144086..898b1bb5f540 100644
--- a/packages/runtime/test-runtime-utils/src/mocksDataStoreContext.ts
+++ b/packages/runtime/test-runtime-utils/src/mocksDataStoreContext.ts
@@ -109,11 +109,11 @@ export class MockFluidDataStoreContext implements IFluidDataStoreContext {
 		return undefined as any as IAudience;
 	}
 
-	public submitMessage(type: string, content: any, localOpMetadata: unknown): void {
+	public submitMessage(): void {
 		throw new Error("Method not implemented.");
 	}
 
-	public submitSignal(type: string, content: any): void {
+	public submitSignal(): void {
 		throw new Error("Method not implemented.");
 	}
 
diff --git a/packages/test/local-server-tests/src/test/opsOnReconnect.spec.ts b/packages/test/local-server-tests/src/test/opsOnReconnect.spec.ts
index 441a846d0cbd..8eb58fdb2b74 100644
--- a/packages/test/local-server-tests/src/test/opsOnReconnect.spec.ts
+++ b/packages/test/local-server-tests/src/test/opsOnReconnect.spec.ts
@@ -24,7 +24,11 @@ import {
 	LocalResolver,
 } from "@fluidframework/local-driver/internal";
 import { SharedDirectory, type ISharedMap, SharedMap } from "@fluidframework/map/internal";
-import { FlushMode, IEnvelope } from "@fluidframework/runtime-definitions/internal";
+import {
+	type FluidDataStoreMessage,
+	FlushMode,
+	IEnvelope,
+} from "@fluidframework/runtime-definitions/internal";
 import { SharedString } from "@fluidframework/sequence/internal";
 import {
 	ILocalDeltaConnectionServer,
@@ -135,19 +139,20 @@ describe("Ops on Reconnect", () => {
 			"op",
 			(message: ISequencedDocumentMessage) => {
 				if (message.type === ContainerMessageType.FluidDataStoreOp) {
-					const envelope = message.contents as IEnvelope;
-					const address = envelope.contents.content.address;
-					const content = envelope.contents.content.contents;
+					const envelope = message.contents as IEnvelope<FluidDataStoreMessage>;
+					// explicitly using `any` even if IEnvelope default is later changed to unknown.
+					// eslint-disable-next-line @typescript-eslint/no-unnecessary-type-arguments
+					const { address, contents } = envelope.contents.content as IEnvelope<any>;
 					const batch = (message.metadata as { batch?: unknown } | undefined)?.batch;
 					let value1: string | number;
 					let value2: string;
 					// Add special handling for SharedString. SharedMap and SharedDirectory content structure is same.
 					if (address === stringId) {
-						value1 = content.pos1;
-						value2 = content.seg;
+						value1 = contents.pos1;
+						value2 = contents.seg;
 					} else {
-						value1 = content.key;
-						value2 = content.value.value;
+						value1 = contents.key;
+						value2 = contents.value.value;
 					}
 					receivedValues.push([value1, value2, batch]);
 				}
diff --git a/packages/test/test-end-to-end-tests/src/test/dataStoresNested.spec.ts b/packages/test/test-end-to-end-tests/src/test/dataStoresNested.spec.ts
index b4fcb8e66937..8dfb25a66d76 100644
--- a/packages/test/test-end-to-end-tests/src/test/dataStoresNested.spec.ts
+++ b/packages/test/test-end-to-end-tests/src/test/dataStoresNested.spec.ts
@@ -8,7 +8,7 @@ import { describeCompat } from "@fluid-private/test-version-utils";
 import { IContainer, IHostLoader } from "@fluidframework/container-definitions/internal";
 import { Loader } from "@fluidframework/container-loader/internal";
 import {
-	ChannelCollection,
+	ComposableChannelCollection,
 	ChannelCollectionFactory,
 	ISummarizer,
 	SummaryCollection,
@@ -66,8 +66,8 @@ describeCompat("Nested DataStores", "NoCompat", (getTestObjectProvider, apis) =>
 	const dataStoreFactory = new ChannelCollectionFactory(
 		[[testObjectFactory.type, Promise.resolve(testObjectFactory)]],
 		async (runtime: IFluidDataStoreChannel) => runtime,
-		(...args: ConstructorParameters<typeof ChannelCollection>) =>
-			new ChannelCollection(...args),
+		(...args: ConstructorParameters<typeof ComposableChannelCollection>) =>
+			new ComposableChannelCollection(...args),
 	);
 
 	const runtimeFactory = new ContainerRuntimeFactoryWithDefaultDataStore({