Collab Notes: Defer the full comments fetch behind preloaded count probes

lib/compat/wordpress-7.0/preload.php

@@ -57,3 +57,37 @@
 	return $paths;
 }
 add_filter( 'block_editor_rest_api_preload_paths', 'gutenberg_block_editor_preload_paths_root_fields' );
+
+/**
+ * Preload the notes-presence probes for the post editor.
+ *
+ * The collab notes feature drives sidebar visibility and the
+ * floating-sidebar auto-open from two count probes:
+ *   - total note count   (`status=all`)
+ *   - unresolved count   (`status=hold`)
+ * Each is a tiny list call (`per_page=1&_fields=id`) whose
+ * `X-WP-Total` header carries the count. Preloading them keeps the
+ * boot path cache-only — the full per-page comments fetch only fires
+ * when the total count is > 0.
+ *
+ * @param array                   $paths   REST API paths to preload.
+ * @param WP_Block_Editor_Context $context Current block editor context.
+ * @return array Filtered preload paths.
+ */
+function gutenberg_block_editor_preload_paths_notes_counts( $paths, $context ) {
+	if ( 'core/edit-post' !== $context->name || ! isset( $context->post ) ) {
+		return $paths;
+	}
+	$post_id = (int) $context->post->ID;
+	if ( ! $post_id ) {
+		return $paths;
+	}
+	$base = sprintf(
+		'/wp/v2/comments?context=edit&post=%d&type=note&per_page=1&_fields=id',
+		$post_id
+	);
+	$paths[] = $base . '&status=all';
+	$paths[] = $base . '&status=hold';
+	return $paths;
+}
+add_filter( 'block_editor_rest_api_preload_paths', 'gutenberg_block_editor_preload_paths_notes_counts', 10, 2 );

packages/edit-post/src/index.js

@@ -236,6 +236,26 @@ async function preloadResolutions( postType, postId ) {
 							postId
 						),
 						core.getAutosaves( postType, postId ),
+						// Collab notes presence probes — paired with the
+						// preload entries in `wordpress-7.0/preload.php`.
+						// The hook in `useNoteThreads` reads `totalItems`
+						// from these to drive the sidebar/floating gates
+						// without doing the full per-page comments fetch
+						// on every boot.
+						core.getEntityRecords( 'root', 'comment', {
+							post: postId,
+							type: 'note',
+							status: 'all',
+							per_page: 1,
+							_fields: 'id',
+						} ),
+						core.getEntityRecords( 'root', 'comment', {
+							post: postId,
+							type: 'note',
+							status: 'hold',
+							per_page: 1,
+							_fields: 'id',
+						} ),
 				  ]
 				: [] ),
 		] );

packages/editor/src/components/collab-sidebar/hooks.js

@@ -36,18 +36,54 @@ import {
 const { cleanEmptyObject } = unlock( blockEditorPrivateApis );
 
 export function useNoteThreads( postId ) {
+	const enabled = !! postId && typeof postId === 'number';
+
+	// Cheap presence probes: 1-record list calls whose response body is
+	// effectively empty but whose `X-WP-Total` header gives the exact
+	// count. The kickoff's PHP preload covers these (see
+	// `lib/compat/wordpress-7.0/preload.php`), so the boot path resolves
+	// them from cache. The counts then gate the heavier full fetch
+	// below.
+	const { totalItems: notesCount } = useEntityRecords(
+		'root',
+		'comment',
+		{
+			post: postId,
+			type: 'note',
+			status: 'all',
+			per_page: 1,
+			_fields: 'id',
+		},
+		{ enabled }
+	);
+	const { totalItems: unresolvedCount } = useEntityRecords(
+		'root',
+		'comment',
+		{
+			post: postId,
+			type: 'note',
+			status: 'hold',
+			per_page: 1,
+			_fields: 'id',
+		},
+		{ enabled }
+	);
+
 	const queryArgs = {
 		post: postId,
 		type: 'note',
 		status: 'all',
 		per_page: -1,
 	};
 
+	// Full fetch only when there's at least one note. Posts with no
+	// notes pay just the cached count probes; posts with notes pay the
+	// same fetch they pay today.
 	const { records: threads } = useEntityRecords(
 		'root',
 		'comment',
 		queryArgs,
-		{ enabled: !! postId && typeof postId === 'number' }
+		{ enabled: enabled && ( notesCount ?? 0 ) > 0 }
 	);
 
 	const { getBlockAttributes } = useSelect( blockEditorStore );
@@ -142,6 +178,8 @@ export function useNoteThreads( postId ) {
 	return {
 		notes,
 		unresolvedNotes,
+		hasNotes: ( notesCount ?? 0 ) > 0,
+		hasUnresolvedNotes: ( unresolvedCount ?? 0 ) > 0,
 	};
 }
 

packages/editor/src/components/collab-sidebar/index.js

@@ -67,15 +67,16 @@ function NotesSidebar( { postId } ) {
 		[]
 	);
 
-	const { notes, unresolvedNotes } = useNoteThreads( postId );
+	const { notes, unresolvedNotes, hasNotes, hasUnresolvedNotes } =
+		useNoteThreads( postId );
 
 	// Only enable the floating sidebar for large viewports.
 	const showFloatingSidebar = isLargeViewport;
 	// Fallback to "All notes" sidebar on smaller viewports.
-	const showAllNotesSidebar = notes.length > 0 || ! showFloatingSidebar;
+	const showAllNotesSidebar = hasNotes || ! showFloatingSidebar;
 	useEnableFloatingSidebar(
 		showFloatingSidebar &&
-			( unresolvedNotes.length > 0 || selectedNote !== undefined )
+			( hasUnresolvedNotes || selectedNote !== undefined )
 	);
 
 	async function focusNote( {