feat(container-runtime): add groupedOpCount to grouped batch metadata

.changeset/grouped-batch-op-count.md

@@ -0,0 +1,14 @@
+---
+"@fluidframework/container-runtime": minor
+"__section": feature
+---
+Add groupedOpCount to grouped batch metadata
+
+A new `groupedOpCount` field on the metadata of grouped batch envelope messages exposes the number of inner ops in the batch. This lets wire-level consumers record batch sizes in telemetry without parsing the grouped batch contents.
+
+The field is set on:
+- The single envelope produced by grouping a batch (`OpGroupingManager.groupBatch`).
+- The empty-grouped-batch placeholder used when a resubmitted batch becomes empty (`OpGroupingManager.createEmptyGroupedBatch`, value `0`).
+- The final chunk of a chunked grouped batch (`OpSplitter.splitSingletonBatchMessage`), so the count survives chunking.
+
+Compression preserves the metadata as-is, so compressed grouped batches carry the field through unchanged.

packages/runtime/container-runtime/src/metadata.ts

@@ -40,6 +40,11 @@ export interface IBatchMetadata {
 	 * Maybe set on first message of a batch, to the batchId generated when resubmitting (set/fixed on first resubmit)
 	 */
 	batchId?: BatchId;
+	/**
+	 * Set on the envelope of a grouped batch op to the number of inner ops it contains.
+	 * Exposed on the wire so consumers can record batch sizes in telemetry without parsing the grouped batch contents.
+	 */
+	groupedOpCount?: number;
 }
 
 /**

packages/runtime/container-runtime/src/opLifecycle/opGroupingManager.ts

@@ -100,7 +100,7 @@ export class OpGroupingManager {
 		const serializedOp = JSON.stringify(emptyGroupedBatch);
 
 		const placeholderMessage: LocalEmptyBatchPlaceholder = {
-			metadata: { batchId: resubmittingBatchId },
+			metadata: { batchId: resubmittingBatchId, groupedOpCount: 0 },
 			localOpMetadata: { emptyBatch: true },
 			referenceSequenceNumber,
 			runtimeOp: emptyGroupedBatch,
@@ -169,7 +169,7 @@ export class OpGroupingManager {
 			...batch,
 			messages: [
 				{
-					metadata: { batchId: groupedBatchId },
+					metadata: { batchId: groupedBatchId, groupedOpCount: batch.messages.length },
 					referenceSequenceNumber: batch.messages[0].referenceSequenceNumber,
 					contents: serializedContent,
 				},

packages/runtime/container-runtime/src/opLifecycle/opSplitter.ts

@@ -172,11 +172,16 @@ export class OpSplitter {
 		}
 
 		// The last chunk will be part of the new batch and needs to
-		// preserve the batch metadata of the original batch
+		// preserve the batch metadata of the original batch.
+		// groupedOpCount is surfaced here so wire-level telemetry can read it once
+		// per chunked grouped batch (mirroring where the batch flag is preserved).
+		const rawGroupedOpCount = firstMessage.metadata?.groupedOpCount;
+		const groupedOpCount =
+			typeof rawGroupedOpCount === "number" ? rawGroupedOpCount : undefined;
 		const lastChunk = chunkToBatchMessage(
 			chunks[chunks.length - 1],
 			batch.referenceSequenceNumber,
-			{ batch: firstMessage.metadata?.batch },
+			{ batch: firstMessage.metadata?.batch, groupedOpCount },
 		);
 
 		this.logger.sendPerformanceEvent({

packages/runtime/container-runtime/src/test/opLifecycle/OpGroupingManager.spec.ts

@@ -74,7 +74,7 @@ describe("OpGroupingManager", () => {
 				{
 					contents:
 						'{"type":"groupedBatch","contents":[{"contents":0},{"contents":0},{"contents":0},{"contents":0},{"contents":0}]}',
-					metadata: { batchId: undefined },
+					metadata: { batchId: undefined, groupedOpCount: 5 },
 					referenceSequenceNumber: 0,
 				},
 			]);
@@ -90,6 +90,7 @@ describe("OpGroupingManager", () => {
 			).groupBatch(createBatch(5, false, false, batchId));
 			assert.strictEqual(result.messages.length, 1);
 			assert.strictEqual(result.messages[0].metadata?.batchId, batchId);
+			assert.strictEqual(result.messages[0].metadata?.groupedOpCount, 5);
 		});
 
 		it("empty grouped batching disabled", () => {
@@ -111,7 +112,7 @@ describe("OpGroupingManager", () => {
 			const batchId = "batchId";
 			const expectedOutboundMessage: OutboundBatchMessage = {
 				contents: '{"type":"groupedBatch","contents":[]}',
-				metadata: { batchId },
+				metadata: { batchId, groupedOpCount: 0 },
 				localOpMetadata: { emptyBatch: true },
 				referenceSequenceNumber: 0,
 				runtimeOp: undefined,
@@ -128,7 +129,7 @@ describe("OpGroupingManager", () => {
 
 			const expectedPlaceholderMessage: LocalEmptyBatchPlaceholder = {
 				runtimeOp: emptyGroupedBatch,
-				metadata: { batchId },
+				metadata: { batchId, groupedOpCount: 0 },
 				localOpMetadata: { emptyBatch: true },
 				referenceSequenceNumber: 0,
 			};