Fix stackId null handling in frontend API calls

- Fix URL parameter parsing converting null to "null" string
- Update branchChanges methods to convert "null" string to null
- Update type signatures to accept string | null for stackId
- Update mock backend validation to accept null stackId values

Co-authored-by: Byron <[email protected]>

Author: Copilot

apps/desktop/cypress/e2e/support/mock/changes.ts

@@ -147,7 +147,7 @@ export function isGetCommitChangesParams(args: unknown): args is GetCommitChange
 
 export type GetBranchChangesParams = {
 	projectId: string;
-	stackId?: string;
+	stackId?: string | null;
 	branch: string;
 };
 
@@ -157,7 +157,7 @@ export function isGetBranchChangesParams(args: unknown): args is GetBranchChange
 		args !== null &&
 		'projectId' in args &&
 		typeof args['projectId'] === 'string' &&
-		(typeof (args as any).stackId === 'string' || (args as any).stackId === undefined) &&
+		(typeof (args as any).stackId === 'string' || (args as any).stackId === undefined || (args as any).stackId === null) &&
 		'branch' in args &&
 		typeof args['branch'] === 'string'
 	);

apps/desktop/src/lib/stacks/stackService.svelte.ts

@@ -602,11 +602,12 @@ export class StackService {
 	 * If the branch is part of a stack and if the stackId is provided, this will include only the changes up to the next branch in the stack.
 	 * Otherwise, if stackId is not provided, this will include all changes as compared to the target branch
 	 */
-	branchChanges(args: { projectId: string; stackId?: string; branch: BranchRef }) {
+	branchChanges(args: { projectId: string; stackId?: string | null; branch: BranchRef }) {
 		return this.api.endpoints.branchChanges.useQuery(
 			{
 				projectId: args.projectId,
-				stackId: args.stackId,
+				// Handle case where URL parameters convert null to "null" string
+				stackId: args.stackId === 'null' ? null : args.stackId,
 				branch: args.branch
 			},
 			{
@@ -618,11 +619,12 @@ export class StackService {
 		);
 	}
 
-	branchChange(args: { projectId: string; stackId?: string; branch: BranchRef; path: string }) {
+	branchChange(args: { projectId: string; stackId?: string | null; branch: BranchRef; path: string }) {
 		return this.api.endpoints.branchChanges.useQuery(
 			{
 				projectId: args.projectId,
-				stackId: args.stackId,
+				// Handle case where URL parameters convert null to "null" string
+				stackId: args.stackId === 'null' ? null : args.stackId,
 				branch: args.branch
 			},
 			{ transform: (result) => changesSelectors.selectById(result.changes, args.path) }
@@ -631,14 +633,15 @@ export class StackService {
 
 	async branchChangesByPaths(args: {
 		projectId: string;
-		stackId?: string;
+		stackId?: string | null;
 		branch: BranchRef;
 		paths: string[];
 	}) {
 		const result = await this.api.endpoints.branchChanges.fetch(
 			{
 				projectId: args.projectId,
-				stackId: args.stackId,
+				// Handle case where URL parameters convert null to "null" string
+				stackId: args.stackId === 'null' ? null : args.stackId,
 				branch: args.branch
 			},
 			{ transform: (result) => selectChangesByPaths(result.changes, args.paths) }
@@ -1185,7 +1188,7 @@ function injectEndpoints(api: ClientState['backendApi'], uiState: UiState) {
 			}),
 			branchChanges: build.query<
 				{ changes: EntityState<TreeChange, string>; stats: TreeStats },
-				{ projectId: string; stackId?: string; branch: BranchRef }
+				{ projectId: string; stackId?: string | null; branch: BranchRef }
 			>({
 				extraOptions: { command: 'changes_in_branch' },
 				query: (args) => args,

apps/desktop/src/routes/[projectId]/workspace/+page.svelte

@@ -17,7 +17,13 @@
 	const stackId = $derived(projectState.stackId.current);
 
 	// Check for stackId in URL query parameters
-	const urlStackId = $derived(page.url.searchParams.get('stackId'));
+	// Note: URLSearchParams.get() returns strings, so "null" becomes the string "null"
+	// We need to convert it back to actual null for proper API handling
+	const urlStackId = $derived((() => {
+		const param = page.url.searchParams.get('stackId');
+		// Convert string "null" back to actual null
+		return param === 'null' ? null : param;
+	})());
 	let scrollToStackId = $state<string | undefined>(undefined);
 
 	const firstStackResult = $derived(stackService.stackAt(projectId, 0));
@@ -29,7 +35,7 @@
 	});
 
 	$effect(() => {
-		if (urlStackId) {
+		if (urlStackId !== null) {
 			projectState.stackId.set(urlStackId);
 			scrollToStackId = urlStackId;
 		} else if (stackId === undefined && firstStack) {