fix(local-server-stress-tests): defer containerObjectMap registration during staging mode (#26257)

## Summary
- Fix containerObjectMap registration during staging mode to prevent
rollback issues
- When a data store is created during staging mode and then discarded,
the containerObjectMap.set() was rolled back, but the data store still
existed locally
- When the data store was later attached by storing its handle in a DDS,
other clients couldn't find it

## Changes
- Defer containerObjectMap registration during staging mode by adding to
a pending list
- Flush pending registrations when staging mode exits (both commit and
discard)
- This ensures registration ops are never part of the staged batch and
can't be rolled back

## Test plan
- [x] All 200 local-server-stress-tests pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: anthony-murphy-agent <[email protected]>
Co-authored-by: anthony-murphy <[email protected]>
Co-authored-by: Claude Opus 4.5 <[email protected]>

Author: 3 people

packages/test/local-server-stress-tests/src/stressDataObject.ts

@@ -289,13 +289,33 @@ export class DefaultStressDataObject extends StressDataObject {
 		)) as any as ISharedMap;
 	}
 
-	public registerLocallyCreatedObject(obj: ContainerObjects): void {
+	/**
+	 * Objects created during staging mode that need to be registered in containerObjectMap
+	 * after staging mode exits. We defer the write to avoid it being rolled back on discard.
+	 */
+	private readonly _pendingContainerObjectRegistrations: ContainerObjects[] = [];
+
+	/**
+	 * Registers an object to the containerObjectMap if not already present.
+	 */
+	private registerToContainerObjectMap(obj: ContainerObjects): void {
 		if (obj.handle !== undefined) {
 			const handle = toFluidHandleInternal(obj.handle);
 			if (this.containerObjectMap.get(handle.absolutePath) === undefined) {
 				this.containerObjectMap.set(handle.absolutePath, { tag: obj.tag, type: obj.type });
 			}
 		}
+	}
+
+	public registerLocallyCreatedObject(obj: ContainerObjects): void {
+		if (obj.handle !== undefined) {
+			if (this.inStagingMode()) {
+				// Defer registration until staging mode exits to avoid rollback on discard
+				this._pendingContainerObjectRegistrations.push(obj);
+			} else {
+				this.registerToContainerObjectMap(obj);
+			}
+		}
 		this._locallyCreatedObjects.push(obj);
 	}
 
@@ -325,6 +345,13 @@ export class DefaultStressDataObject extends StressDataObject {
 			this.stageControls.discardChanges();
 		}
 		this.stageControls = undefined;
+
+		// Flush any pending containerObjectMap registrations that were deferred during staging mode.
+		// This happens after staging mode exits so the writes won't be rolled back.
+		for (const obj of this._pendingContainerObjectRegistrations) {
+			this.registerToContainerObjectMap(obj);
+		}
+		this._pendingContainerObjectRegistrations.length = 0;
 	}
 }