diff --git a/packages/runtime/container-runtime/src/containerRuntime.ts b/packages/runtime/container-runtime/src/containerRuntime.ts
index 8c6e2edf457..1f851f72c4f 100644
--- a/packages/runtime/container-runtime/src/containerRuntime.ts
+++ b/packages/runtime/container-runtime/src/containerRuntime.ts
@@ -181,7 +181,7 @@ import {
 } from "./opLifecycle/index.js";
 import { pkgVersion } from "./packageVersion.js";
 import {
-	IPendingBatchMessage,
+	PendingMessageResubmitData,
 	IPendingLocalState,
 	PendingStateManager,
 } from "./pendingStateManager.js";
@@ -668,7 +668,7 @@ export const makeLegacySendBatchFn =
 	(batch: IBatch) => {
 		// Default to negative one to match Container.submitBatch behavior
 		let clientSequenceNumber: number = -1;
-		for (const message of batch.content) {
+		for (const message of batch.messages) {
 			clientSequenceNumber = submitFn(
 				MessageType.Operation,
 				// For back-compat (submitFn only works on deserialized content)
@@ -1549,10 +1549,6 @@ export class ContainerRuntime
 				clientId: () => this.clientId,
 				close: this.closeFn,
 				connected: () => this.connected,
-				reSubmit: (message: IPendingBatchMessage) => {
-					this.reSubmit(message);
-					this.flush();
-				},
 				reSubmitBatch: this.reSubmitBatch.bind(this),
 				isActiveConnection: () => this.innerDeltaManager.active,
 				isAttached: () => this.attachState !== AttachState.Detached,
@@ -2909,7 +2905,7 @@ export class ContainerRuntime
 			// Note: we are not touching any batches other than mainBatch here, for two reasons:
 			// 1. It would not help, as other batches are flushed independently from main batch.
 			// 2. There is no way to undo process of data store creation, blob creation, ID compressor ops, or other things tracked by other batches.
-			checkpoint = this.outbox.checkpoint().mainBatch;
+			checkpoint = this.outbox.getBatchCheckpoints().mainBatch;
 		}
 		try {
 			this._orderSequentiallyCalls++;
@@ -3052,7 +3048,7 @@ export class ContainerRuntime
 	}
 
 	/**
-	 * Are we in the middle of batching ops together?
+	 * Typically ops are batched and later flushed together, but in some cases we want to flush immediately.
 	 */
 	private currentlyBatching() {
 		return this.flushMode !== FlushMode.Immediate || this._orderSequentiallyCalls !== 0;
@@ -4032,7 +4028,9 @@ export class ContainerRuntime
 				this.outbox.submit(message);
 			}
 
-			if (!this.currentlyBatching()) {
+			// Note: Technically, the system "always" batches - if this case is true we'll just have a single-message batch.
+			const flushImmediatelyOnSubmit = !this.currentlyBatching();
+			if (flushImmediatelyOnSubmit) {
 				this.flush();
 			} else {
 				this.scheduleFlush();
@@ -4113,7 +4111,7 @@ export class ContainerRuntime
 		}
 	}
 
-	private reSubmitBatch(batch: IPendingBatchMessage[]) {
+	private reSubmitBatch(batch: PendingMessageResubmitData[]) {
 		this.orderSequentially(() => {
 			for (const message of batch) {
 				this.reSubmit(message);
@@ -4122,7 +4120,7 @@ export class ContainerRuntime
 		this.flush();
 	}
 
-	private reSubmit(message: IPendingBatchMessage) {
+	private reSubmit(message: PendingMessageResubmitData) {
 		// Need to parse from string for back-compat
 		const containerRuntimeMessage = this.parseLocalOpContent(message.content);
 		this.reSubmitCore(containerRuntimeMessage, message.localOpMetadata, message.opMetadata);
diff --git a/packages/runtime/container-runtime/src/metadata.ts b/packages/runtime/container-runtime/src/metadata.ts
index 7e7fca33946..7e451310c8f 100644
--- a/packages/runtime/container-runtime/src/metadata.ts
+++ b/packages/runtime/container-runtime/src/metadata.ts
@@ -3,6 +3,20 @@
  * Licensed under the MIT License.
  */
 
+/**
+ * Does the metadata object look like batch metadata?
+ */
+export function isBatchMetadata(metadata: any): metadata is IBatchMetadata {
+	return typeof metadata?.batch === "boolean";
+}
+
+/**
+ * Cast the given metadata object to IBatchMetadata if it is so, otherwise yield undefined
+ */
+export function asBatchMetadata(metadata: unknown): IBatchMetadata | undefined {
+	return isBatchMetadata(metadata) ? metadata : undefined;
+}
+
 /**
  * Batching makes assumptions about what might be on the metadata. This interface codifies those assumptions, but does not validate them.
  */
diff --git a/packages/runtime/container-runtime/src/opLifecycle/batchManager.ts b/packages/runtime/container-runtime/src/opLifecycle/batchManager.ts
index b05700e7baf..804e33965bd 100644
--- a/packages/runtime/container-runtime/src/opLifecycle/batchManager.ts
+++ b/packages/runtime/container-runtime/src/opLifecycle/batchManager.ts
@@ -99,7 +99,7 @@ export class BatchManager {
 
 	public popBatch(): IBatch {
 		const batch: IBatch = {
-			content: this.pendingBatch,
+			messages: this.pendingBatch,
 			contentSizeInBytes: this.batchContentSize,
 			referenceSequenceNumber: this.referenceSequenceNumber,
 			hasReentrantOps: this.hasReentrantOps,
@@ -134,13 +134,13 @@ export class BatchManager {
 }
 
 const addBatchMetadata = (batch: IBatch): IBatch => {
-	if (batch.content.length > 1) {
-		batch.content[0].metadata = {
-			...batch.content[0].metadata,
+	if (batch.messages.length > 1) {
+		batch.messages[0].metadata = {
+			...batch.messages[0].metadata,
 			batch: true,
 		};
-		batch.content[batch.content.length - 1].metadata = {
-			...batch.content[batch.content.length - 1].metadata,
+		batch.messages[batch.messages.length - 1].metadata = {
+			...batch.messages[batch.messages.length - 1].metadata,
 			batch: false,
 		};
 	}
@@ -157,7 +157,7 @@ const addBatchMetadata = (batch: IBatch): IBatch => {
  * @returns An estimate of the payload size in bytes which will be produced when the batch is sent over the wire
  */
 export const estimateSocketSize = (batch: IBatch): number => {
-	return batch.contentSizeInBytes + opOverhead * batch.content.length;
+	return batch.contentSizeInBytes + opOverhead * batch.messages.length;
 };
 
 export const sequenceNumbersMatch = (
diff --git a/packages/runtime/container-runtime/src/opLifecycle/definitions.ts b/packages/runtime/container-runtime/src/opLifecycle/definitions.ts
index 6898c9b8fe5..4556bfe9285 100644
--- a/packages/runtime/container-runtime/src/opLifecycle/definitions.ts
+++ b/packages/runtime/container-runtime/src/opLifecycle/definitions.ts
@@ -28,7 +28,7 @@ export interface IBatch<TMessages extends BatchMessage[] = BatchMessage[]> {
 	/**
 	 * All the messages in the batch
 	 */
-	readonly content: TMessages;
+	readonly messages: TMessages;
 	/**
 	 * The reference sequence number for the batch
 	 */
diff --git a/packages/runtime/container-runtime/src/opLifecycle/opCompressor.ts b/packages/runtime/container-runtime/src/opLifecycle/opCompressor.ts
index 5ab0ff1d8c9..6bf19bb5fc0 100644
--- a/packages/runtime/container-runtime/src/opLifecycle/opCompressor.ts
+++ b/packages/runtime/container-runtime/src/opLifecycle/opCompressor.ts
@@ -35,7 +35,7 @@ export class OpCompressor {
 	 */
 	public compressBatch(batch: IBatch): IBatch {
 		assert(
-			batch.contentSizeInBytes > 0 && batch.content.length > 0,
+			batch.contentSizeInBytes > 0 && batch.messages.length > 0,
 			0x5a4 /* Batch should not be empty */,
 		);
 
@@ -47,14 +47,14 @@ export class OpCompressor {
 
 		const messages: BatchMessage[] = [];
 		messages.push({
-			...batch.content[0],
+			...batch.messages[0],
 			contents: JSON.stringify({ packedContents: compressedContent }),
-			metadata: batch.content[0].metadata,
+			metadata: batch.messages[0].metadata,
 			compression: CompressionAlgorithms.lz4,
 		});
 
 		// Add empty placeholder messages to reserve the sequence numbers
-		for (const message of batch.content.slice(1)) {
+		for (const message of batch.messages.slice(1)) {
 			messages.push({
 				localOpMetadata: message.localOpMetadata,
 				metadata: message.metadata,
@@ -64,7 +64,7 @@ export class OpCompressor {
 
 		const compressedBatch: IBatch = {
 			contentSizeInBytes: compressedContent.length,
-			content: messages,
+			messages,
 			referenceSequenceNumber: batch.referenceSequenceNumber,
 		};
 
@@ -74,7 +74,7 @@ export class OpCompressor {
 				duration,
 				sizeBeforeCompression: batch.contentSizeInBytes,
 				sizeAfterCompression: compressedBatch.contentSizeInBytes,
-				opCount: compressedBatch.content.length,
+				opCount: compressedBatch.messages.length,
 				socketSize: estimateSocketSize(compressedBatch),
 			});
 		}
@@ -88,7 +88,7 @@ export class OpCompressor {
 	private serializeBatchContents(batch: IBatch): string {
 		try {
 			// Yields a valid JSON array, since each message.contents is already serialized to JSON
-			return `[${batch.content.map((message) => message.contents).join(",")}]`;
+			return `[${batch.messages.map(({ contents }) => contents).join(",")}]`;
 		} catch (e: any) {
 			if (e.message === "Invalid string length") {
 				// This is how JSON.stringify signals that
@@ -98,7 +98,7 @@ export class OpCompressor {
 					{
 						eventName: "BatchTooLarge",
 						size: batch.contentSizeInBytes,
-						length: batch.content.length,
+						length: batch.messages.length,
 					},
 					error,
 				);
diff --git a/packages/runtime/container-runtime/src/opLifecycle/opGroupingManager.ts b/packages/runtime/container-runtime/src/opLifecycle/opGroupingManager.ts
index b4f83e3b286..864917a182a 100644
--- a/packages/runtime/container-runtime/src/opLifecycle/opGroupingManager.ts
+++ b/packages/runtime/container-runtime/src/opLifecycle/opGroupingManager.ts
@@ -59,17 +59,17 @@ export class OpGroupingManager {
 	public groupBatch(batch: IBatch): IBatch<[BatchMessage]> {
 		assert(this.shouldGroup(batch), 0x946 /* cannot group the provided batch */);
 
-		if (batch.content.length >= 1000) {
+		if (batch.messages.length >= 1000) {
 			this.logger.sendTelemetryEvent({
 				eventName: "GroupLargeBatch",
-				length: batch.content.length,
+				length: batch.messages.length,
 				threshold: this.config.opCountThreshold,
 				reentrant: batch.hasReentrantOps,
-				referenceSequenceNumber: batch.content[0].referenceSequenceNumber,
+				referenceSequenceNumber: batch.messages[0].referenceSequenceNumber,
 			});
 		}
 
-		for (const message of batch.content) {
+		for (const message of batch.messages) {
 			if (message.metadata) {
 				const keys = Object.keys(message.metadata);
 				assert(keys.length < 2, 0x5dd /* cannot group ops with metadata */);
@@ -79,7 +79,7 @@ export class OpGroupingManager {
 
 		const serializedContent = JSON.stringify({
 			type: OpGroupingManager.groupedBatchOp,
-			contents: batch.content.map<IGroupedMessage>((message) => ({
+			contents: batch.messages.map<IGroupedMessage>((message) => ({
 				contents: message.contents === undefined ? undefined : JSON.parse(message.contents),
 				metadata: message.metadata,
 				compression: message.compression,
@@ -88,10 +88,10 @@ export class OpGroupingManager {
 
 		const groupedBatch: IBatch<[BatchMessage]> = {
 			...batch,
-			content: [
+			messages: [
 				{
 					metadata: undefined,
-					referenceSequenceNumber: batch.content[0].referenceSequenceNumber,
+					referenceSequenceNumber: batch.messages[0].referenceSequenceNumber,
 					contents: serializedContent,
 				},
 			],
@@ -118,7 +118,7 @@ export class OpGroupingManager {
 			// Grouped batching must be enabled
 			this.config.groupedBatchingEnabled &&
 			// The number of ops in the batch must surpass the configured threshold
-			batch.content.length >= this.config.opCountThreshold &&
+			batch.messages.length >= this.config.opCountThreshold &&
 			// Support for reentrant batches must be explicitly enabled
 			(this.config.reentrantBatchGroupingEnabled || batch.hasReentrantOps !== true)
 		);
diff --git a/packages/runtime/container-runtime/src/opLifecycle/opSplitter.ts b/packages/runtime/container-runtime/src/opLifecycle/opSplitter.ts
index 2b9ae72f228..766161ace86 100644
--- a/packages/runtime/container-runtime/src/opLifecycle/opSplitter.ts
+++ b/packages/runtime/container-runtime/src/opLifecycle/opSplitter.ts
@@ -121,7 +121,7 @@ export class OpSplitter {
 	public splitFirstBatchMessage(batch: IBatch): IBatch {
 		assert(this.isBatchChunkingEnabled, 0x513 /* Chunking needs to be enabled */);
 		assert(
-			batch.contentSizeInBytes > 0 && batch.content.length > 0,
+			batch.contentSizeInBytes > 0 && batch.messages.length > 0,
 			0x514 /* Batch needs to be non-empty */,
 		);
 		assert(
@@ -134,13 +134,13 @@ export class OpSplitter {
 			0x516 /* Chunk size needs to be smaller than the max batch size */,
 		);
 
-		const firstMessage = batch.content[0]; // we expect this to be the large compressed op, which needs to be split
+		const firstMessage = batch.messages[0]; // we expect this to be the large compressed op, which needs to be split
 		assert(
 			(firstMessage.contents?.length ?? 0) >= this.chunkSizeInBytes,
 			0x518 /* First message in the batch needs to be chunkable */,
 		);
 
-		const restOfMessages = batch.content.slice(1); // we expect these to be empty ops, created to reserve sequence numbers
+		const restOfMessages = batch.messages.slice(1); // we expect these to be empty ops, created to reserve sequence numbers
 		const socketSize = estimateSocketSize(batch);
 		const chunks = splitOp(
 			firstMessage,
@@ -171,7 +171,7 @@ export class OpSplitter {
 		this.logger.sendPerformanceEvent({
 			// Used to be "Chunked compressed batch"
 			eventName: "CompressedChunkedBatch",
-			length: batch.content.length,
+			length: batch.messages.length,
 			sizeInBytes: batch.contentSizeInBytes,
 			chunks: chunks.length,
 			chunkSizeInBytes: this.chunkSizeInBytes,
@@ -179,7 +179,7 @@ export class OpSplitter {
 		});
 
 		return {
-			content: [lastChunk, ...restOfMessages],
+			messages: [lastChunk, ...restOfMessages],
 			contentSizeInBytes: lastChunk.contents?.length ?? 0,
 			referenceSequenceNumber: batch.referenceSequenceNumber,
 		};
diff --git a/packages/runtime/container-runtime/src/opLifecycle/outbox.ts b/packages/runtime/container-runtime/src/opLifecycle/outbox.ts
index 76b78f6d49c..0b5cd292f06 100644
--- a/packages/runtime/container-runtime/src/opLifecycle/outbox.ts
+++ b/packages/runtime/container-runtime/src/opLifecycle/outbox.ts
@@ -15,7 +15,7 @@ import {
 } from "@fluidframework/telemetry-utils/internal";
 
 import { ICompressionRuntimeOptions } from "../containerRuntime.js";
-import { IPendingBatchMessage, PendingStateManager } from "../pendingStateManager.js";
+import { PendingMessageResubmitData, PendingStateManager } from "../pendingStateManager.js";
 
 import {
 	BatchManager,
@@ -48,7 +48,7 @@ export interface IOutboxParameters {
 	readonly logger: ITelemetryBaseLogger;
 	readonly groupingManager: OpGroupingManager;
 	readonly getCurrentSequenceNumbers: () => BatchSequenceNumbers;
-	readonly reSubmit: (message: IPendingBatchMessage) => void;
+	readonly reSubmit: (message: PendingMessageResubmitData) => void;
 	readonly opReentrancy: () => boolean;
 	readonly closeContainer: (error?: ICriticalContainerError) => void;
 }
@@ -87,6 +87,13 @@ export function getLongStack<T>(action: () => T, length: number = 50): T {
 	}
 }
 
+/**
+ * The Outbox collects messages submitted by the ContainerRuntime into a batch,
+ * and then flushes the batch when requested.
+ *
+ * @remarks There are actually multiple independent batches (some are for a specific message type),
+ * to support slight variation in semantics for each batch (e.g. support for rebasing or grouping).
+ */
 export class Outbox {
 	private readonly mc: MonitoringContext;
 	private readonly mainBatch: BatchManager;
@@ -269,7 +276,7 @@ export class Outbox {
 			clientSequenceNumber = this.sendBatch(processedBatch);
 		}
 
-		this.params.pendingStateManager.onFlushBatch(rawBatch.content, clientSequenceNumber);
+		this.params.pendingStateManager.onFlushBatch(rawBatch.messages, clientSequenceNumber);
 	}
 
 	/**
@@ -283,7 +290,7 @@ export class Outbox {
 		assert(batchManager.options.canRebase, 0x9a7 /* BatchManager does not support rebase */);
 
 		this.rebasing = true;
-		for (const message of rawBatch.content) {
+		for (const message of rawBatch.messages) {
 			this.params.reSubmit({
 				// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
 				content: message.contents!,
@@ -296,7 +303,7 @@ export class Outbox {
 			this.mc.logger.sendTelemetryEvent(
 				{
 					eventName: "BatchRebase",
-					length: rawBatch.content.length,
+					length: rawBatch.messages.length,
 					referenceSequenceNumber: rawBatch.referenceSequenceNumber,
 				},
 				new UsageError("BatchRebase"),
@@ -323,7 +330,7 @@ export class Outbox {
 	 */
 	private compressBatch(batch: IBatch): IBatch {
 		if (
-			batch.content.length === 0 ||
+			batch.messages.length === 0 ||
 			this.params.config.compressionOptions === undefined ||
 			this.params.config.compressionOptions.minimumBatchSizeInBytes >
 				batch.contentSizeInBytes ||
@@ -345,7 +352,7 @@ export class Outbox {
 			throw new GenericError("BatchTooLarge", /* error */ undefined, {
 				batchSize: batch.contentSizeInBytes,
 				compressedBatchSize: compressedBatch.contentSizeInBytes,
-				count: compressedBatch.content.length,
+				count: compressedBatch.messages.length,
 				limit: this.params.config.maxBatchSizeInBytes,
 				chunkingEnabled: this.params.splitter.isBatchChunkingEnabled,
 				compressionOptions: JSON.stringify(this.params.config.compressionOptions),
@@ -363,7 +370,7 @@ export class Outbox {
 	 * @returns the clientSequenceNumber of the start of the batch, or undefined if nothing was sent
 	 */
 	private sendBatch(batch: IBatch) {
-		const length = batch.content.length;
+		const length = batch.messages.length;
 		if (length === 0) {
 			return undefined; // Nothing submitted
 		}
@@ -372,7 +379,7 @@ export class Outbox {
 		if (socketSize >= this.params.config.maxBatchSizeInBytes) {
 			this.mc.logger.sendPerformanceEvent({
 				eventName: "LargeBatch",
-				length: batch.content.length,
+				length: batch.messages.length,
 				sizeInBytes: batch.contentSizeInBytes,
 				socketSize,
 			});
@@ -383,7 +390,7 @@ export class Outbox {
 			// Legacy path - supporting old loader versions. Can be removed only when LTS moves above
 			// version that has support for batches (submitBatchFn)
 			assert(
-				batch.content[0].compression === undefined,
+				batch.messages[0].compression === undefined,
 				0x5a6 /* Compression should not have happened if the loader does not support it */,
 			);
 
@@ -391,7 +398,7 @@ export class Outbox {
 		} else {
 			assert(batch.referenceSequenceNumber !== undefined, 0x58e /* Batch must not be empty */);
 			clientSequenceNumber = this.params.submitBatchFn(
-				batch.content.map((message) => ({
+				batch.messages.map<IBatchMessage>((message) => ({
 					contents: message.contents,
 					metadata: message.metadata,
 					compression: message.compression,
@@ -407,7 +414,10 @@ export class Outbox {
 		return clientSequenceNumber;
 	}
 
-	public checkpoint() {
+	/**
+	 * @returns A checkpoint object per batch that facilitates iterating over the batch messages when rolling back.
+	 */
+	public getBatchCheckpoints() {
 		// This variable is declared with a specific type so that we have a standard import of the IBatchCheckpoint type.
 		// When the type is inferred, the generated .d.ts uses a dynamic import which doesn't resolve.
 		const mainBatch: IBatchCheckpoint = this.mainBatch.checkpoint();
diff --git a/packages/runtime/container-runtime/src/opLifecycle/remoteMessageProcessor.ts b/packages/runtime/container-runtime/src/opLifecycle/remoteMessageProcessor.ts
index fc19b73c146..1a7e118779d 100644
--- a/packages/runtime/container-runtime/src/opLifecycle/remoteMessageProcessor.ts
+++ b/packages/runtime/container-runtime/src/opLifecycle/remoteMessageProcessor.ts
@@ -16,6 +16,7 @@ import {
 	type InboundSequencedContainerRuntimeMessageOrSystemMessage,
 	type InboundSequencedRecentlyAddedContainerRuntimeMessage,
 } from "../messageTypes.js";
+import { asBatchMetadata } from "../metadata.js";
 
 import { OpDecompressor } from "./opDecompressor.js";
 import { OpGroupingManager, isGroupedBatch } from "./opGroupingManager.js";
@@ -127,7 +128,7 @@ export class RemoteMessageProcessor {
 	 * the batch tracking info (this.batchStartCsn) based on whether we're still mid-batch.
 	 */
 	private getAndUpdateBatchStartCsn(message: ISequencedDocumentMessage): number {
-		const batchMetadataFlag = (message.metadata as { batch: boolean | undefined })?.batch;
+		const batchMetadataFlag = asBatchMetadata(message.metadata)?.batch;
 		if (this.batchStartCsn === undefined) {
 			// We are waiting for a new batch
 			assert(batchMetadataFlag !== false, "Unexpected batch end marker");
diff --git a/packages/runtime/container-runtime/src/pendingStateManager.ts b/packages/runtime/container-runtime/src/pendingStateManager.ts
index 0fe54af6c3d..085b9aef06c 100644
--- a/packages/runtime/container-runtime/src/pendingStateManager.ts
+++ b/packages/runtime/container-runtime/src/pendingStateManager.ts
@@ -16,7 +16,7 @@ import {
 import Deque from "double-ended-queue";
 
 import { InboundSequencedContainerRuntimeMessage } from "./messageTypes.js";
-import { IBatchMetadata } from "./metadata.js";
+import { asBatchMetadata, IBatchMetadata } from "./metadata.js";
 import type { BatchMessage } from "./opLifecycle/index.js";
 import { pkgVersion } from "./packageVersion.js";
 
@@ -41,19 +41,18 @@ export interface IPendingLocalState {
 	pendingStates: IPendingMessage[];
 }
 
-export interface IPendingBatchMessage {
-	content: string;
-	localOpMetadata: unknown;
-	opMetadata: Record<string, unknown> | undefined;
-}
+/** Info needed to replay/resubmit a pending message */
+export type PendingMessageResubmitData = Pick<
+	IPendingMessage,
+	"content" | "localOpMetadata" | "opMetadata"
+>;
 
 export interface IRuntimeStateHandler {
 	connected(): boolean;
 	clientId(): string | undefined;
 	close(error?: ICriticalContainerError): void;
 	applyStashedOp(content: string): Promise<unknown>;
-	reSubmit(message: IPendingBatchMessage): void;
-	reSubmitBatch(batch: IPendingBatchMessage[]): void;
+	reSubmitBatch(batch: PendingMessageResubmitData[]): void;
 	isActiveConnection: () => boolean;
 	isAttached: () => boolean;
 }
@@ -116,7 +115,8 @@ export class PendingStateManager implements IDisposable {
 	// the correct batch metadata.
 	private pendingBatchBeginMessage: ISequencedDocumentMessage | undefined;
 
-	private clientId: string | undefined;
+	/** Used to ensure we don't replay ops on the same connection twice */
+	private clientIdFromLastReplay: string | undefined;
 
 	/**
 	 * The pending messages count. Includes `pendingMessages` and `initialMessages` to keep in sync with
@@ -406,10 +406,10 @@ export class PendingStateManager implements IDisposable {
 
 		// This assert suggests we are about to send same ops twice, which will result in data loss.
 		assert(
-			this.clientId !== this.stateHandler.clientId(),
+			this.clientIdFromLastReplay !== this.stateHandler.clientId(),
 			0x173 /* "replayPendingStates called twice for same clientId!" */,
 		);
-		this.clientId = this.stateHandler.clientId();
+		this.clientIdFromLastReplay = this.stateHandler.clientId();
 
 		assert(
 			this.initialMessages.isEmpty(),
@@ -426,54 +426,58 @@ export class PendingStateManager implements IDisposable {
 			// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
 			let pendingMessage = this.pendingMessages.shift()!;
 			remainingPendingMessagesCount--;
-			assert(
-				pendingMessage.opMetadata?.batch !== false,
-				0x41b /* We cannot process batches in chunks */,
-			);
+
+			const batchMetadataFlag = asBatchMetadata(pendingMessage.opMetadata)?.batch;
+			assert(batchMetadataFlag !== false, 0x41b /* We cannot process batches in chunks */);
 
 			/**
-			 * We want to ensure grouped messages get processed in a batch.
+			 * We must preserve the distinct batches on resubmit.
 			 * Note: It is not possible for the PendingStateManager to receive a partially acked batch. It will
-			 * either receive the whole batch ack or nothing at all.
+			 * either receive the whole batch ack or nothing at all.  @see ScheduleManager for how this works.
 			 */
-			if (pendingMessage.opMetadata?.batch) {
-				assert(
-					remainingPendingMessagesCount > 0,
-					0x554 /* Last pending message cannot be a batch begin */,
-				);
-
-				const batch: IPendingBatchMessage[] = [];
-
-				// check is >= because batch end may be last pending message
-				while (remainingPendingMessagesCount >= 0) {
-					batch.push({
+			if (batchMetadataFlag === undefined) {
+				// Single-message batch
+				this.stateHandler.reSubmitBatch([
+					{
 						content: pendingMessage.content,
 						localOpMetadata: pendingMessage.localOpMetadata,
 						opMetadata: pendingMessage.opMetadata,
-					});
+					},
+				]);
+				continue;
+			}
+			// else: batchMetadataFlag === true  (It's a typical multi-message batch)
 
-					if (pendingMessage.opMetadata?.batch === false) {
-						break;
-					}
-					assert(remainingPendingMessagesCount > 0, 0x555 /* No batch end found */);
+			assert(
+				remainingPendingMessagesCount > 0,
+				0x554 /* Last pending message cannot be a batch begin */,
+			);
 
-					// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-					pendingMessage = this.pendingMessages.shift()!;
-					remainingPendingMessagesCount--;
-					assert(
-						pendingMessage.opMetadata?.batch !== true,
-						0x556 /* Batch start needs a corresponding batch end */,
-					);
-				}
+			const batch: PendingMessageResubmitData[] = [];
 
-				this.stateHandler.reSubmitBatch(batch);
-			} else {
-				this.stateHandler.reSubmit({
+			// check is >= because batch end may be last pending message
+			while (remainingPendingMessagesCount >= 0) {
+				batch.push({
 					content: pendingMessage.content,
 					localOpMetadata: pendingMessage.localOpMetadata,
 					opMetadata: pendingMessage.opMetadata,
 				});
+
+				if (pendingMessage.opMetadata?.batch === false) {
+					break;
+				}
+				assert(remainingPendingMessagesCount > 0, 0x555 /* No batch end found */);
+
+				// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+				pendingMessage = this.pendingMessages.shift()!;
+				remainingPendingMessagesCount--;
+				assert(
+					pendingMessage.opMetadata?.batch !== true,
+					0x556 /* Batch start needs a corresponding batch end */,
+				);
 			}
+
+			this.stateHandler.reSubmitBatch(batch);
 		}
 
 		// pending ops should no longer depend on previous sequenced local ops after resubmit
diff --git a/packages/runtime/container-runtime/src/test/opLifecycle/OpGroupingManager.spec.ts b/packages/runtime/container-runtime/src/test/opLifecycle/OpGroupingManager.spec.ts
index e8c435757a6..c2c4d7be55b 100644
--- a/packages/runtime/container-runtime/src/test/opLifecycle/OpGroupingManager.spec.ts
+++ b/packages/runtime/container-runtime/src/test/opLifecycle/OpGroupingManager.spec.ts
@@ -26,7 +26,7 @@ describe("OpGroupingManager", () => {
 		hasReentrantOps,
 	});
 	const messagesToBatch = (messages: BatchMessage[]): IBatch => ({
-		content: messages,
+		messages,
 		contentSizeInBytes: messages
 			.map((message) => JSON.stringify(message).length)
 			.reduce((a, b) => a + b),
@@ -99,8 +99,8 @@ describe("OpGroupingManager", () => {
 				},
 				mockLogger,
 			).groupBatch(createBatch(5));
-			assert.strictEqual(result.content.length, 1);
-			assert.deepStrictEqual(result.content, [
+			assert.strictEqual(result.messages.length, 1);
+			assert.deepStrictEqual(result.messages, [
 				{
 					contents:
 						'{"type":"groupedBatch","contents":[{"contents":0},{"contents":0},{"contents":0},{"contents":0},{"contents":0}]}',
diff --git a/packages/runtime/container-runtime/src/test/opLifecycle/batchManager.spec.ts b/packages/runtime/container-runtime/src/test/opLifecycle/batchManager.spec.ts
index 9be4e938f17..a46d033339e 100644
--- a/packages/runtime/container-runtime/src/test/opLifecycle/batchManager.spec.ts
+++ b/packages/runtime/container-runtime/src/test/opLifecycle/batchManager.spec.ts
@@ -56,9 +56,9 @@ describe("BatchManager", () => {
 		);
 
 		const batch = batchManager.popBatch();
-		assert.equal(batch.content[0].metadata?.batch, true);
-		assert.equal(batch.content[1].metadata?.batch, undefined);
-		assert.equal(batch.content[2].metadata?.batch, false);
+		assert.equal(batch.messages[0].metadata?.batch, true);
+		assert.equal(batch.messages[1].metadata?.batch, undefined);
+		assert.equal(batch.messages[2].metadata?.batch, false);
 
 		assert.equal(
 			batchManager.push(
@@ -68,7 +68,7 @@ describe("BatchManager", () => {
 			true,
 		);
 		const singleOpBatch = batchManager.popBatch();
-		assert.equal(singleOpBatch.content[0].metadata?.batch, undefined);
+		assert.equal(singleOpBatch.messages[0].metadata?.batch, undefined);
 	});
 
 	it("Batch content size is tracked correctly", () => {
diff --git a/packages/runtime/container-runtime/src/test/opLifecycle/opCompressor.spec.ts b/packages/runtime/container-runtime/src/test/opLifecycle/opCompressor.spec.ts
index 6bf26a5efd6..8ded4fc76ca 100644
--- a/packages/runtime/container-runtime/src/test/opLifecycle/opCompressor.spec.ts
+++ b/packages/runtime/container-runtime/src/test/opLifecycle/opCompressor.spec.ts
@@ -21,7 +21,7 @@ describe("OpCompressor", () => {
 	const createBatch = (length: number, messageSize: number) =>
 		messagesToBatch(new Array(length).fill(createMessage(generateStringOfSize(messageSize))));
 	const messagesToBatch = (messages: BatchMessage[]): IBatch => ({
-		content: messages,
+		messages,
 		contentSizeInBytes: messages
 			.map((message) => JSON.stringify(message).length)
 			.reduce((a, b) => a + b),
@@ -48,17 +48,17 @@ describe("OpCompressor", () => {
 			// large batch with small messages
 			createBatch(1000, 100 * 1024),
 		].forEach((batch) => {
-			it(`Batch of ${batch.content.length} ops of total size ${toMB(
+			it(`Batch of ${batch.messages.length} ops of total size ${toMB(
 				batch.contentSizeInBytes,
 			)} MB`, () => {
 				const compressedBatch = compressor.compressBatch(batch);
-				assert.strictEqual(compressedBatch.content.length, batch.content.length);
-				assert.strictEqual(compressedBatch.content[0].compression, "lz4");
-				assert.strictEqual(compressedBatch.content[0].metadata?.flag, true);
-				if (compressedBatch.content.length > 1) {
-					assert.strictEqual(compressedBatch.content[1].contents, undefined);
-					assert.strictEqual(compressedBatch.content[1].compression, undefined);
-					assert.strictEqual(compressedBatch.content[1].contents, undefined);
+				assert.strictEqual(compressedBatch.messages.length, batch.messages.length);
+				assert.strictEqual(compressedBatch.messages[0].compression, "lz4");
+				assert.strictEqual(compressedBatch.messages[0].metadata?.flag, true);
+				if (compressedBatch.messages.length > 1) {
+					assert.strictEqual(compressedBatch.messages[1].contents, undefined);
+					assert.strictEqual(compressedBatch.messages[1].compression, undefined);
+					assert.strictEqual(compressedBatch.messages[1].contents, undefined);
 				}
 			}).timeout(3000);
 		}));
@@ -70,7 +70,7 @@ describe("OpCompressor", () => {
 			// small batch with large messages
 			createBatch(6, 100 * 1024 * 1024),
 		].forEach((batch) => {
-			it(`Not compressing batch of ${batch.content.length} ops of total size ${toMB(
+			it(`Not compressing batch of ${batch.messages.length} ops of total size ${toMB(
 				batch.contentSizeInBytes,
 			)} MB`, () => {
 				assert.throws(() => compressor.compressBatch(batch));
@@ -78,7 +78,7 @@ describe("OpCompressor", () => {
 					{
 						eventName: "OpCompressor:BatchTooLarge",
 						category: "error",
-						length: batch.content.length,
+						length: batch.messages.length,
 						size: batch.contentSizeInBytes,
 					},
 				]);
diff --git a/packages/runtime/container-runtime/src/test/opLifecycle/opSplitter.spec.ts b/packages/runtime/container-runtime/src/test/opLifecycle/opSplitter.spec.ts
index 8d5cee7e2ef..015967a649c 100644
--- a/packages/runtime/container-runtime/src/test/opLifecycle/opSplitter.spec.ts
+++ b/packages/runtime/container-runtime/src/test/opLifecycle/opSplitter.spec.ts
@@ -239,7 +239,7 @@ describe("OpSplitter", () => {
 		// Empty batch
 		assert.throws(() =>
 			opSplitter.splitFirstBatchMessage({
-				content: [compressedMessage],
+				messages: [compressedMessage],
 				contentSizeInBytes: 0,
 				referenceSequenceNumber: 0,
 			}),
@@ -248,7 +248,7 @@ describe("OpSplitter", () => {
 		// Empty batch
 		assert.throws(() =>
 			opSplitter.splitFirstBatchMessage({
-				content: [],
+				messages: [],
 				contentSizeInBytes: 1,
 				referenceSequenceNumber: 0,
 			}),
@@ -257,7 +257,7 @@ describe("OpSplitter", () => {
 		// Batch is too small to be chunked
 		assert.throws(() =>
 			opSplitter.splitFirstBatchMessage({
-				content: [compressedMessage],
+				messages: [compressedMessage],
 				contentSizeInBytes: 1,
 				referenceSequenceNumber: 0,
 			}),
@@ -266,7 +266,7 @@ describe("OpSplitter", () => {
 		// Batch is not compressed
 		assert.throws(() =>
 			opSplitter.splitFirstBatchMessage({
-				content: [regularMessage],
+				messages: [regularMessage],
 				contentSizeInBytes: 3,
 				referenceSequenceNumber: 0,
 			}),
@@ -281,7 +281,7 @@ describe("OpSplitter", () => {
 				maxBatchSizeInBytes,
 				mockLogger,
 			).splitFirstBatchMessage({
-				content: [compressedMessage],
+				messages: [compressedMessage],
 				contentSizeInBytes: 3,
 				referenceSequenceNumber: 0,
 			}),
@@ -291,7 +291,7 @@ describe("OpSplitter", () => {
 		assert.throws(() =>
 			new OpSplitter([], undefined, 0, maxBatchSizeInBytes, mockLogger).splitFirstBatchMessage(
 				{
-					content: [compressedMessage],
+					messages: [compressedMessage],
 					contentSizeInBytes: 3,
 					referenceSequenceNumber: 0,
 				},
@@ -301,7 +301,7 @@ describe("OpSplitter", () => {
 		// Misconfigured op splitter
 		assert.throws(() =>
 			new OpSplitter([], mockSubmitBatchFn, 2, 1, mockLogger).splitFirstBatchMessage({
-				content: [compressedMessage],
+				messages: [compressedMessage],
 				contentSizeInBytes: 3,
 				referenceSequenceNumber: 0,
 			}),
@@ -316,7 +316,7 @@ describe("OpSplitter", () => {
 				maxBatchSizeInBytes,
 				mockLogger,
 			).splitFirstBatchMessage({
-				content: [compressedMessage],
+				messages: [compressedMessage],
 				contentSizeInBytes: 3,
 				referenceSequenceNumber: 0,
 			}),
@@ -340,7 +340,7 @@ describe("OpSplitter", () => {
 				const emptyMessage = generateChunkableOp(0);
 
 				const result = opSplitter.splitFirstBatchMessage({
-					content: [largeMessage, emptyMessage, emptyMessage, emptyMessage],
+					messages: [largeMessage, emptyMessage, emptyMessage, emptyMessage],
 					contentSizeInBytes: largeMessage.contents?.length ?? 0,
 					referenceSequenceNumber: 0,
 				});
@@ -352,12 +352,13 @@ describe("OpSplitter", () => {
 					assert.equal(batch.referenceSequenceNumber, 0);
 				}
 
-				assert.equal(result.content.length, 4);
-				const lastChunk = JSON.parse(result.content[0].contents!).contents as IChunkedOp;
+				assert.equal(result.messages.length, 4);
+				const lastChunk = JSON.parse(result.messages[0].contents!).contents as IChunkedOp;
 				assert.equal(lastChunk.chunkId, lastChunk.totalChunks);
-				assert.deepStrictEqual(result.content.slice(1), new Array(3).fill(emptyMessage));
+				assert.deepStrictEqual(result.messages.slice(1), new Array(3).fill(emptyMessage));
 				assert.equal(
-					!extraOp || JSON.parse(result.content[0].contents!).contents?.contents?.length === 0,
+					!extraOp ||
+						JSON.parse(result.messages[0].contents!).contents?.contents?.length === 0,
 					true,
 				);
 				assert.notEqual(result.contentSizeInBytes, largeMessage.contents?.length ?? 0);
@@ -375,7 +376,7 @@ describe("OpSplitter", () => {
 					mockLogger.matchEvents([
 						{
 							eventName: "OpSplitter:CompressedChunkedBatch",
-							length: result.content.length,
+							length: result.messages.length,
 							chunks: 100 / 20 + 1 + (extraOp ? 1 : 0),
 							chunkSizeInBytes: 20,
 						},
@@ -397,7 +398,7 @@ describe("OpSplitter", () => {
 				const largeMessage = generateChunkableOp(100);
 
 				const result = opSplitter.splitFirstBatchMessage({
-					content: [largeMessage],
+					messages: [largeMessage],
 					contentSizeInBytes: largeMessage.contents?.length ?? 0,
 					referenceSequenceNumber: 0,
 				});
@@ -409,12 +410,13 @@ describe("OpSplitter", () => {
 					assert.equal(batch.referenceSequenceNumber, 0);
 				}
 
-				assert.equal(result.content.length, 1);
+				assert.equal(result.messages.length, 1);
 				assert.notEqual(result.contentSizeInBytes, largeMessage.contents?.length ?? 0);
-				const lastChunk = JSON.parse(result.content[0].contents!).contents as IChunkedOp;
+				const lastChunk = JSON.parse(result.messages[0].contents!).contents as IChunkedOp;
 				assert.equal(lastChunk.chunkId, lastChunk.totalChunks);
 				assert.equal(
-					!extraOp || JSON.parse(result.content[0].contents!).contents?.contents?.length === 0,
+					!extraOp ||
+						JSON.parse(result.messages[0].contents!).contents?.contents?.length === 0,
 					true,
 				);
 				assert.notEqual(result.contentSizeInBytes, largeMessage.contents?.length ?? 0);
@@ -432,7 +434,7 @@ describe("OpSplitter", () => {
 					mockLogger.matchEvents([
 						{
 							eventName: "OpSplitter:CompressedChunkedBatch",
-							length: result.content.length,
+							length: result.messages.length,
 							chunks: 100 / 20 + 1 + (extraOp ? 1 : 0),
 							chunkSizeInBytes: 20,
 						},
diff --git a/packages/runtime/container-runtime/src/test/opLifecycle/outbox.spec.ts b/packages/runtime/container-runtime/src/test/opLifecycle/outbox.spec.ts
index 8610aa1c10e..b1d964c4327 100644
--- a/packages/runtime/container-runtime/src/test/opLifecycle/outbox.spec.ts
+++ b/packages/runtime/container-runtime/src/test/opLifecycle/outbox.spec.ts
@@ -35,7 +35,7 @@ import {
 	Outbox,
 } from "../../opLifecycle/index.js";
 import {
-	IPendingBatchMessage,
+	PendingMessageResubmitData,
 	PendingStateManager,
 	type IPendingMessage,
 } from "../../pendingStateManager.js";
@@ -174,7 +174,7 @@ describe("Outbox", () => {
 		return messages;
 	};
 	const toBatch = (messages: BatchMessage[]): IBatch => ({
-		content: addBatchMetadata(messages),
+		messages: addBatchMetadata(messages),
 		contentSizeInBytes: messages
 			.map((message) => message.contents?.length ?? 0)
 			.reduce((a, b) => a + b, 0),
@@ -228,7 +228,7 @@ describe("Outbox", () => {
 				mockLogger,
 			),
 			getCurrentSequenceNumbers: () => currentSeqNumbers,
-			reSubmit: (message: IPendingBatchMessage) => {
+			reSubmit: (message: PendingMessageResubmitData) => {
 				state.opsResubmitted++;
 			},
 			opReentrancy: () => state.isReentrant,
diff --git a/packages/runtime/container-runtime/src/test/opLifecycle/remoteMessageProcessor.spec.ts b/packages/runtime/container-runtime/src/test/opLifecycle/remoteMessageProcessor.spec.ts
index 5c3e618b83e..f945a722ba4 100644
--- a/packages/runtime/container-runtime/src/test/opLifecycle/remoteMessageProcessor.spec.ts
+++ b/packages/runtime/container-runtime/src/test/opLifecycle/remoteMessageProcessor.spec.ts
@@ -110,7 +110,7 @@ describe("RemoteMessageProcessor", () => {
 			let batch: IBatch = {
 				contentSizeInBytes: 1,
 				referenceSequenceNumber: Infinity,
-				content: [
+				messages: [
 					getOutboundMessage("a", true),
 					getOutboundMessage("b"),
 					getOutboundMessage("c"),
@@ -154,7 +154,7 @@ describe("RemoteMessageProcessor", () => {
 				}
 			}
 			let startSeqNum = outboundMessages.length + 1;
-			outboundMessages.push(...batch.content);
+			outboundMessages.push(...batch.messages);
 
 			const messageProcessor = getMessageProcessor();
 			const actual: ISequencedDocumentMessage[] = [];
diff --git a/packages/runtime/container-runtime/src/test/pendingStateManager.spec.ts b/packages/runtime/container-runtime/src/test/pendingStateManager.spec.ts
index ad5ffadbab7..0b5a17aefb5 100644
--- a/packages/runtime/container-runtime/src/test/pendingStateManager.spec.ts
+++ b/packages/runtime/container-runtime/src/test/pendingStateManager.spec.ts
@@ -140,7 +140,6 @@ describe("Pending State Manager", () => {
 					clientId: () => "oldClientId",
 					close: (error?: ICriticalContainerError) => (closeError = error),
 					connected: () => true,
-					reSubmit: () => {},
 					reSubmitBatch: () => {},
 					isActiveConnection: () => false,
 					isAttached: () => true,
@@ -361,7 +360,6 @@ describe("Pending State Manager", () => {
 					clientId: () => undefined,
 					close: () => {},
 					connected: () => true,
-					reSubmit: () => {},
 					reSubmitBatch: () => {},
 					isActiveConnection: () => false,
 					isAttached: () => true,
@@ -450,7 +448,6 @@ describe("Pending State Manager", () => {
 					clientId: () => undefined,
 					close: () => {},
 					connected: () => true,
-					reSubmit: () => {},
 					reSubmitBatch: () => {},
 					isActiveConnection: () => false,
 					isAttached: () => true,
@@ -583,7 +580,6 @@ describe("Pending State Manager", () => {
 					clientId: () => "123",
 					close: () => {},
 					connected: () => true,
-					reSubmit: () => {},
 					reSubmitBatch: () => {},
 					isActiveConnection: () => false,
 					isAttached: () => true,