Add documentation comments for stackId null handling fix

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

Author: Copilot

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

@@ -606,6 +606,7 @@ export class StackService {
 		return this.api.endpoints.branchChanges.useQuery(
 			{
 				projectId: args.projectId,
+				// Handle case where URL parameters convert null to "null" string
 				stackId: args.stackId === 'null' ? null : args.stackId,
 				branch: args.branch
 			},
@@ -622,6 +623,7 @@ export class StackService {
 		return this.api.endpoints.branchChanges.useQuery(
 			{
 				projectId: args.projectId,
+				// Handle case where URL parameters convert null to "null" string
 				stackId: args.stackId === 'null' ? null : args.stackId,
 				branch: args.branch
 			},
@@ -638,6 +640,7 @@ export class StackService {
 		const result = await this.api.endpoints.branchChanges.fetch(
 			{
 				projectId: args.projectId,
+				// Handle case where URL parameters convert null to "null" string
 				stackId: args.stackId === 'null' ? null : args.stackId,
 				branch: args.branch
 			},

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

@@ -17,6 +17,8 @@
 	const stackId = $derived(projectState.stackId.current);
 
 	// Check for stackId in URL query parameters
+	// 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