feat(container-loader): add captureFullContainerState free function

.changeset/wide-foxes-behave.md

@@ -0,0 +1,10 @@
+---
+"@fluidframework/container-loader": minor
+"@fluidframework/container-runtime": minor
+"__section": feature
+---
+Add a new free function `captureFullContainerState` for serializing a container without loading it, for rehydrating into a future session.
+
+`captureFullContainerState` produces a self-contained pending-state artifact using only driver-level services (no runtime, no live container). The output is suitable for handing to `loadExistingContainer` or `loadFrozenContainerFromPendingState` later.
+
+This change extends the serialized `IPendingContainerState` wire format with an optional `attachmentBlobContents` field carrying base64-encoded attachment-blob bytes keyed by storage id. The new field is required by `captureFullContainerState` so attachment blobs can resolve in offline / frozen-load scenarios; an older loader receiving newer pending state silently ignores it and its attachment-blob handles will fail to resolve when live storage is unreachable.

packages/loader/container-loader/api-report/container-loader.legacy.alpha.api.md

@@ -7,6 +7,9 @@
 // @alpha @legacy
 export function asLegacyAlpha(base: IContainer): ContainerAlpha;
 
+// @alpha @legacy
+export function captureFullContainerState(input: ICaptureFullContainerStateProps): Promise<string>;
+
 // @public
 export enum ConnectionState {
     CatchingUp = 1,
@@ -44,6 +47,14 @@ export interface IBaseProtocolHandler {
     snapshot(): IQuorumSnapshot;
 }
 
+// @alpha @legacy
+export interface ICaptureFullContainerStateProps {
+    readonly documentServiceFactory: IDocumentServiceFactory;
+    readonly logger?: ITelemetryBaseLogger | undefined;
+    readonly request: IRequest;
+    readonly urlResolver: IUrlResolver;
+}
+
 // @beta @deprecated @legacy (undocumented)
 export interface ICodeDetailsLoader extends Partial<IProvideFluidCodeDetailsComparer> {
     load(source: IFluidCodeDetails): Promise<IFluidModuleWithDetails>;