@@ -22,6 +22,7 @@
 -   Notes: Stop the editor's undo from detaching a newly added note from its block, or bringing back the highlight of a resolved note ([#84079](https://github.com/WordPress/gutenberg/pull/84079)).
 -   Notes: Delete notes permanently when they can't be moved to the trash, instead of failing with an error ([#84102](https://github.com/WordPress/gutenberg/pull/84102)).
 -   Notes: Disable the note form field while a note or reply is being sent, instead of accepting text the save would not include ([#84083](https://github.com/WordPress/gutenberg/pull/84083)).
+-   Notes: Keep an unsent note or reply when selecting another block or thread, instead of discarding it.
 
 ### Internal
 
 
@@ -36,7 +36,7 @@ collab-sidebar/
 ## Component hierarchy
 
 ```
-NotesSidebarContainer (index.jsx)         - gates on post type support
+NotesSidebarContainer (index.jsx)         - gates on post type support, owns the unsent drafts Map
  └── NotesSidebar (index.jsx)             - owns sidebarRef + useNoteThreads + sidebar registration
       ├── AddNoteMenuItem                - slot fill in the block toolbar
       ├── NoteAvatarIndicator            - slot fill in the block toolbar (per-thread avatars)
@@ -56,6 +56,8 @@ NotesSidebarContainer (index.jsx)         - gates on post type support
 
 `Notes` is reused for both sidebar surfaces. The only visual difference is driven by `isFloating` (whether to layer threads over the canvas or stack them in a panel).
 
+Unsent note and reply text lives in a `Map` owned by `NotesSidebarContainer`, keyed by block client ID or note ID, so it survives the forms unmounting. It is a cache, not state: `useNoteDraft` reads it on mount and writes it on change, so typing doesn't re-render the sidebar. Slot fills don't inherit context, so `NotesSidebar` provides it inside each fill.
+
 ## Floating board
 
 Goal: in the floating sidebar, each unresolved note appears beside its associated block, tracks canvas scroll, and shifts up/down to avoid overlapping with neighbors - all without re-rendering threads as the canvas scrolls.
 
@@ -10,6 +10,7 @@ import { NoteCard } from './note-card';
 import { NoteForm } from './note-form';
 import { FloatingContainer } from './floating-container';
 import { focusNoteThread } from './utils';
+import { useNoteDraft } from './hooks';
 import { store as editorStore } from '../../store';
 import { unlock } from '../../lock-unlock';
 
@@ -21,6 +22,7 @@ export function AddNote( { clientId, onSubmit, sidebarRef, floating } ) {
 	const { selectNote } = unlock( useDispatch( editorStore ) );
 	const { getSelectedNote } = unlock( useSelect( editorStore ) );
 	const isSubmittingRef = useRef( false );
+	const { initialValue, setDraft, hasDraft } = useNoteDraft( clientId );
 
 	/*
 	 * Dismiss the form once focus leaves it. `useFocusOutside` keeps the form
@@ -47,13 +49,14 @@ export function AddNote( { clientId, onSubmit, sidebarRef, floating } ) {
 		 * clear it while this still owns the selection, or it would wipe out the
 		 * newly selected note.
 		 */
-		if ( getSelectedNote() === 'new' ) {
+		if ( getSelectedNote() === 'new' && ! hasDraft() ) {
 			toggleBlockSpotlight( clientId, false );
 			selectNote( undefined );
 		}
 	} );
 
 	const unselectNote = () => {
+		setDraft( '' );
 		selectNote( undefined );
 		blockElement?.focus();
 		toggleBlockSpotlight( clientId, false );
@@ -95,6 +98,8 @@ export function AddNote( { clientId, onSubmit, sidebarRef, floating } ) {
 						}
 					} }
 					onCancel={ unselectNote }
+					initialValue={ initialValue }
+					onChange={ setDraft }
 					labels={ {
 						input: __( 'New note' ),
 						placeholder: __( 'Add a note or @ mention' ),
 
@@ -1,6 +1,8 @@
 import { speak } from '@wordpress/a11y';
 import { __ } from '@wordpress/i18n';
 import {
+	createContext,
+	useContext,
 	useState,
 	useEffect,
 	useLayoutEffect,
@@ -36,6 +38,11 @@ import {
 
 const { cleanEmptyObject } = unlock( blockEditorPrivateApis );
 
+/**
+ * Unsent note drafts, keyed by block client ID for new notes and note ID for replies.
+ */
+export const NoteDraftsContext = createContext();
+
 export function useNoteThreads( postId ) {
 	const queryArgs = {
 		post: postId,
@@ -507,6 +514,26 @@ export function useNoteActions() {
 	return { onCreate, onEdit, onDelete };
 }
 
+/**
+ * Keeps a note form's unsent content, so it survives the form unmounting.
+ *
+ * @param {string|number} key The block client ID for a new note, or the note ID for a reply.
+ * @return {Object} The draft stored when the form mounted, its setter, and a check for a stored draft.
+ */
+export function useNoteDraft( key ) {
+	const drafts = useContext( NoteDraftsContext );
+	const [ initialValue ] = useState( () => drafts.get( key ) ?? '' );
+	const setDraft = ( content ) => {
+		if ( content ) {
+			drafts.set( key, content );
+		} else {
+			drafts.delete( key );
+		}
+	};
+	const hasDraft = () => drafts.has( key );
+	return { initialValue, setDraft, hasDraft };
+}
+
 /**
  * Keeps the selected note in step with the selected block, and focuses the
  * selected note's thread when the selection asks for it.
@@ -517,6 +544,7 @@ export function useNoteActions() {
  */
 export function useNoteSelection( { notes, sidebarRef } ) {
 	const registry = useRegistry();
+	const drafts = useContext( NoteDraftsContext );
 	const { selectNote } = unlock( useDispatch( editorStore ) );
 	const selectedBlockClientId = useSelect(
 		( select ) => select( blockEditorStore ).getSelectedBlockClientId(),
@@ -532,7 +560,6 @@ export function useNoteSelection( { notes, sidebarRef } ) {
 		};
 	}, [] );
 
-	// Select the block's primary note, or clear the selection if it has none.
 	const syncWithBlock = useEvent( ( clientId ) => {
 		const { getSelectedNote, isNoteFocused } = unlock(
 			registry.select( editorStore )
@@ -550,7 +577,8 @@ export function useNoteSelection( { notes, sidebarRef } ) {
 		if ( blockThreads.some( ( thread ) => thread.id === currentNoteId ) ) {
 			return;
 		}
-		selectNote( pickPrimaryNote( blockThreads )?.id );
+		const draftNoteId = drafts.has( clientId ) ? 'new' : undefined;
+		selectNote( pickPrimaryNote( blockThreads )?.id ?? draftNoteId );
 	} );
 
 	// Sync only on block transitions, so in-block changes (Escape, Cancel,
 
@@ -1,7 +1,7 @@
 import clsx from 'clsx';
 import { __ } from '@wordpress/i18n';
 import { useDispatch, useSelect } from '@wordpress/data';
-import { useRef } from '@wordpress/element';
+import { useRef, useState } from '@wordpress/element';
 import { useViewportMatch } from '@wordpress/compose';
 import { __experimentalUseSlot as useSlot } from '@wordpress/components';
 import { useShortcut } from '@wordpress/keyboard-shortcuts';
@@ -17,13 +17,13 @@ import { store as editorStore } from '../../store';
 import { AddNoteMenuItem } from './add-note-menu-item';
 import { NoteAvatarIndicator } from './note-indicator-toolbar';
 import { NoteHighlightStyles } from './note-highlight-styles';
-import { useNoteThreads } from './hooks';
+import { NoteDraftsContext, useNoteThreads } from './hooks';
 import { getNoteIdsFromMetadata, pickPrimaryNote } from './utils';
 import PostTypeSupportCheck from '../post-type-support-check';
 import { CanvasMargin } from '../visual-editor/canvas-margin';
 import { unlock } from '../../lock-unlock';
 
-function NotesSidebar( { postId } ) {
+function NotesSidebar( { postId, drafts } ) {
 	const { getActiveComplementaryArea } = useSelect( interfaceStore );
 	const { enableComplementaryArea } = useDispatch( interfaceStore );
 	const { toggleBlockSpotlight, selectBlock } = unlock(
@@ -185,7 +185,9 @@ function NotesSidebar( { postId } ) {
 					icon={ commentIcon }
 					closeLabel={ __( 'Close Notes' ) }
 				>
-					<Notes notes={ notes } sidebarRef={ sidebarRef } />
+					<NoteDraftsContext.Provider value={ drafts }>
+						<Notes notes={ notes } sidebarRef={ sidebarRef } />
+					</NoteDraftsContext.Provider>
 				</PluginSidebar>
 			) }
 			{ showFloatingNotes && (
@@ -197,11 +199,13 @@ function NotesSidebar( { postId } ) {
 							'is-minimized': notesDisplayMode === 'minimized',
 						} ) }
 					>
-						<Notes
-							notes={ unresolvedNotes }
-							sidebarRef={ sidebarRef }
-							isFloating
-						/>
+						<NoteDraftsContext.Provider value={ drafts }>
+							<Notes
+								notes={ unresolvedNotes }
+								sidebarRef={ sidebarRef }
+								isFloating
+							/>
+						</NoteDraftsContext.Provider>
 					</div>
 				</CanvasMargin.Fill>
 			) }
@@ -210,6 +214,7 @@ function NotesSidebar( { postId } ) {
 }
 
 export default function NotesSidebarContainer() {
+	const [ drafts ] = useState( () => new Map() );
 	const { postId, editorMode, revisionsMode } = useSelect( ( select ) => {
 		const { getCurrentPostId, getEditorMode, isRevisionsMode } = unlock(
 			select( editorStore )
@@ -232,7 +237,7 @@ export default function NotesSidebarContainer() {
 
 	return (
 		<PostTypeSupportCheck supportKeys="editor.notes">
-			<NotesSidebar postId={ postId } />
+			<NotesSidebar postId={ postId } drafts={ drafts } />
 		</PostTypeSupportCheck>
 	);
 }
@@ -18,6 +18,7 @@ import { Note } from './note';
 import { NoteCard } from './note-card';
 import { NoteForm } from './note-form';
 import { FloatingContainer } from './floating-container';
+import { useNoteDraft } from './hooks';
 import {
 	focusNoteThread,
 	getNoteExcerpt,
@@ -29,6 +30,7 @@ import { unlock } from '../../lock-unlock';
 const { useBlockElement } = unlock( blockEditorPrivateApis );
 
 function NoteReply( { note, onEditNote, onAddReply, onCancel } ) {
+	const { initialValue, setDraft } = useNoteDraft( note.id );
 	return (
 		<NoteCard role="treeitem">
 			<NoteForm
@@ -46,7 +48,12 @@ function NoteReply( { note, onEditNote, onAddReply, onCancel } ) {
 						parent: note.id,
 					} );
 				} }
-				onCancel={ onCancel }
+				onCancel={ ( event ) => {
+					setDraft( '' );
+					onCancel( event );
+				} }
+				initialValue={ initialValue }
+				onChange={ setDraft }
 				labels={ {
 					submit:
 						'approved' === note.status
@@ -218,6 +225,7 @@ export function NoteThread( {
 	if ( isFloating && note.id === 'new' ) {
 		return (
 			<AddNote
+				key={ note.blockClientId }
 				clientId={ note.blockClientId }
 				onSubmit={ onAddReply }
 				sidebarRef={ sidebarRef }
 
@@ -207,6 +207,7 @@ export function Notes( { notes, sidebarRef, isFloating = false } ) {
 		>
 			{ isAddingNote && (
 				<AddNote
+					key={ selectedBlockClientId }
 					clientId={ selectedBlockClientId }
 					onSubmit={ onAddReply }
 					sidebarRef={ sidebarRef }
Original file line number	Diff line number	Diff line change
`@@ -207,6 +207,7 @@ export function Notes( { notes, sidebarRef, isFloating = false } ) {`
`207`	`207`	`>`
`208`	`208`	`{ isAddingNote && (`
`209`	`209`	`<AddNote`
	`210`	`+ key={ selectedBlockClientId }`
`210`	`211`	`clientId={ selectedBlockClientId }`
`211`	`212`	`onSubmit={ onAddReply }`
`212`	`213`	`sidebarRef={ sidebarRef }`