Update globals/args persistence handling as per gert

lib/client-api/src/new/ArgsStore.ts

@@ -19,8 +19,13 @@ export class ArgsStore {
   }
 
   updateFromPersisted(story: Story<any>, persisted: Args) {
+    // NOTE: we use `combineArgs` here rather than `combineParameters` because changes to arg
+    // array values are persisted in the URL as sparse arrays, and we have to take that into
+    // account when overriding the initialArgs (e.g. we patch [,'changed'] over ['initial', 'val'])
     this.argsByStoryId[story.id] = combineArgs(
       this.argsByStoryId[story.id],
+      // Use the argType to ensure we aren't persisting the wrong type of value to the type.
+      // For instance you could try and set a string-valued arg to a number by changing the URL
       mapArgsToTypes(persisted, story.argTypes)
     );
   }

lib/client-api/src/new/GlobalsStore.ts

@@ -39,7 +39,8 @@ export class GlobalsStore {
       if (this.allowedGlobalNames.has(key)) acc[key] = value;
       return acc;
     }, {} as Globals);
-    // TODO(Gert) -- why do we use combineParameters here?
+    // Note that unlike args, we do not have the same type information for globals to allow us
+    // to type check them here, so we just set them naively
     this.globals = combineParameters(this.globals, allowedUrlGlobals);
   }