diff --git a/apps/meteor/app/slashcommand-asciiarts/client/gimme.ts b/apps/meteor/app/slashcommand-asciiarts/client/gimme.ts
index 7cd5edb6bb879..e91ce830cfb88 100644
--- a/apps/meteor/app/slashcommand-asciiarts/client/gimme.ts
+++ b/apps/meteor/app/slashcommand-asciiarts/client/gimme.ts
@@ -8,7 +8,7 @@ import { slashCommands } from '../../utils/client/slashCommand';
  */
 async function Gimme({ message, params }: SlashCommandCallbackParams<'gimme'>): Promise<void> {
 	const msg = message;
-	await sdk.call('sendMessage', { ...msg, msg: `༼ つ ◕_◕ ༽つ ${params}` });
+	await sdk.rest.post('/v1/chat.sendMessage', { message: { ...msg, msg: `༼ つ ◕_◕ ༽つ ${params}` } });
 }
 
 slashCommands.add({
diff --git a/apps/meteor/app/slashcommand-asciiarts/client/lenny.ts b/apps/meteor/app/slashcommand-asciiarts/client/lenny.ts
index 0e3cc55f6b867..4fb47b6941e78 100644
--- a/apps/meteor/app/slashcommand-asciiarts/client/lenny.ts
+++ b/apps/meteor/app/slashcommand-asciiarts/client/lenny.ts
@@ -9,7 +9,7 @@ import { slashCommands } from '../../utils/client/slashCommand';
 
 async function LennyFace({ message, params }: SlashCommandCallbackParams<'lenny'>): Promise<void> {
 	const msg = message;
-	await sdk.call('sendMessage', { ...msg, msg: `${params} ( ͡° ͜ʖ ͡°)` });
+	await sdk.rest.post('/v1/chat.sendMessage', { message: { ...msg, msg: `${params} ( ͡° ͜ʖ ͡°)` } });
 }
 
 slashCommands.add({
diff --git a/apps/meteor/app/slashcommand-asciiarts/client/shrug.ts b/apps/meteor/app/slashcommand-asciiarts/client/shrug.ts
index c4bdec8f1a8cf..8ad22a0fd380f 100644
--- a/apps/meteor/app/slashcommand-asciiarts/client/shrug.ts
+++ b/apps/meteor/app/slashcommand-asciiarts/client/shrug.ts
@@ -11,7 +11,7 @@ slashCommands.add({
 	command: 'shrug',
 	callback: async ({ message, params }: SlashCommandCallbackParams<'shrug'>): Promise<void> => {
 		const msg = message;
-		await sdk.call('sendMessage', { ...msg, msg: `${params} ¯\\\\_(ツ)_/¯` });
+		await sdk.rest.post('/v1/chat.sendMessage', { message: { ...msg, msg: `${params} ¯\\\\_(ツ)_/¯` } });
 	},
 	options: {
 		description: 'Slash_Shrug_Description',
diff --git a/apps/meteor/app/slashcommand-asciiarts/client/tableflip.ts b/apps/meteor/app/slashcommand-asciiarts/client/tableflip.ts
index 8820b81f7c4ae..f5383214c4bd2 100644
--- a/apps/meteor/app/slashcommand-asciiarts/client/tableflip.ts
+++ b/apps/meteor/app/slashcommand-asciiarts/client/tableflip.ts
@@ -11,7 +11,7 @@ slashCommands.add({
 	command: 'tableflip',
 	callback: async ({ message, params }: SlashCommandCallbackParams<'tableflip'>): Promise<void> => {
 		const msg = message;
-		await sdk.call('sendMessage', { ...msg, msg: `${params} (╯°□°）╯︵ ┻━┻` });
+		await sdk.rest.post('/v1/chat.sendMessage', { message: { ...msg, msg: `${params} (╯°□°）╯︵ ┻━┻` } });
 	},
 	options: {
 		description: 'Slash_Tableflip_Description',
diff --git a/apps/meteor/app/slashcommand-asciiarts/client/unflip.ts b/apps/meteor/app/slashcommand-asciiarts/client/unflip.ts
index 6c02fa196052c..eaf478ac79b39 100644
--- a/apps/meteor/app/slashcommand-asciiarts/client/unflip.ts
+++ b/apps/meteor/app/slashcommand-asciiarts/client/unflip.ts
@@ -11,7 +11,7 @@ slashCommands.add({
 	command: 'unflip',
 	callback: async ({ message, params }: SlashCommandCallbackParams<'unflip'>): Promise<void> => {
 		const msg = message;
-		await sdk.call('sendMessage', { ...msg, msg: `${params} ┬─┬ ノ( ゜-゜ノ)` });
+		await sdk.rest.post('/v1/chat.sendMessage', { message: { ...msg, msg: `${params} ┬─┬ ノ( ゜-゜ノ)` } });
 	},
 	options: {
 		description: 'Slash_TableUnflip_Description',
diff --git a/apps/meteor/app/utils/client/lib/RestApiClient.ts b/apps/meteor/app/utils/client/lib/RestApiClient.ts
index 7cdb81beb7835..2498ff07f4688 100644
--- a/apps/meteor/app/utils/client/lib/RestApiClient.ts
+++ b/apps/meteor/app/utils/client/lib/RestApiClient.ts
@@ -3,6 +3,7 @@ import { RestClient } from '@rocket.chat/api-client';
 
 import { invokeTwoFactorModal } from '../../../../client/lib/2fa/process2faReturn';
 import { baseURI } from '../../../../client/lib/baseURI';
+import { clearStoredCredentials } from '../../../../client/lib/sdk/ddpSdk';
 import { STORAGE_KEYS, getStoredItem } from '../../../../client/lib/sdk/storage';
 
 class RestApiClient extends RestClient {
@@ -37,11 +38,31 @@ APIClient.handleTwoFactorChallenge(invokeTwoFactorModal);
  * This middleware will throw the error object instead.
  * */
 
+/**
+ * A 401 means the request reached an authRequired route without a session the server recognizes.
+ * That is only evidence of an expired session when the request was an action the user just took:
+ * boot-time reads (OmnichannelProvider's livechat/config/routing, custom-sounds.list) fire before
+ * the session is established and answer 401 with the same message, and clearing on those logs out
+ * a session that is coming up. Restricting the wipe to mutations mirrors the DDP path this replaced
+ * — ddpOverREST only clears credentials for method calls, never for background fetches — so a
+ * session that dies while idle is noticed on the user's next write, exactly as before.
+ */
+const isMutation = (method: string): boolean => method === 'POST' || method === 'PUT' || method === 'DELETE';
+
 APIClient.use(async (request, next) => {
+	const [, method] = request;
+	const tokenAtSend = getStoredItem(STORAGE_KEYS.LOGIN_TOKEN);
+
 	try {
 		return await next(...request);
 	} catch (error) {
 		if (error instanceof Response) {
+			// Never 403 (authenticated but lacking permission) — that must not log the user out.
+			// The token comparison keeps a request that was in flight across a re-login from
+			// evicting the session it does not belong to.
+			if (error.status === 401 && isMutation(method) && tokenAtSend && tokenAtSend === getStoredItem(STORAGE_KEYS.LOGIN_TOKEN)) {
+				clearStoredCredentials();
+			}
 			const e = await error.json();
 			throw e;
 		}
diff --git a/apps/meteor/client/apps/gameCenter/GameCenterInvitePlayersModal.tsx b/apps/meteor/client/apps/gameCenter/GameCenterInvitePlayersModal.tsx
index 13da02330d6a3..01f5b36373c5c 100644
--- a/apps/meteor/client/apps/gameCenter/GameCenterInvitePlayersModal.tsx
+++ b/apps/meteor/client/apps/gameCenter/GameCenterInvitePlayersModal.tsx
@@ -10,7 +10,6 @@ import { sdk } from '../../../app/utils/client/lib/SDKClient';
 import UserAutoCompleteMultiple from '../../components/UserAutoCompleteMultiple';
 import { useOpenedRoom } from '../../lib/RoomManager';
 import { roomCoordinator } from '../../lib/rooms/roomCoordinator';
-import { callWithErrorHandling } from '../../lib/utils/callWithErrorHandling';
 
 type Username = Exclude<IUser['username'], undefined>;
 
@@ -35,10 +34,12 @@ const GameCenterInvitePlayersModal = ({ game, onClose }: IGameCenterInvitePlayer
 			roomCoordinator.openRouteLink(group.t, { rid: group._id, name: group.name });
 
 			if (openedRoom === group._id) {
-				await callWithErrorHandling('sendMessage', {
-					_id: Random.id(),
-					rid: group._id,
-					msg: t('Apps_Game_Center_Play_Game_Together', { name }),
+				await sdk.rest.post('/v1/chat.sendMessage', {
+					message: {
+						_id: Random.id(),
+						rid: group._id,
+						msg: t('Apps_Game_Center_Play_Game_Together', { name }),
+					},
 				});
 			}
 			onClose();
diff --git a/apps/meteor/client/components/message/toolbar/useReadReceiptsDetailsAction.tsx b/apps/meteor/client/components/message/toolbar/useReadReceiptsDetailsAction.tsx
index faaf1f3a9efed..d8230dd300a17 100644
--- a/apps/meteor/client/components/message/toolbar/useReadReceiptsDetailsAction.tsx
+++ b/apps/meteor/client/components/message/toolbar/useReadReceiptsDetailsAction.tsx
@@ -24,6 +24,7 @@ export const useReadReceiptsDetailsAction = (message: IMessage): MessageActionCo
 			setModal(
 				<ReadReceiptsModal
 					messageId={message._id}
+					rid={message.rid}
 					onClose={() => {
 						setModal(null);
 					}}
diff --git a/apps/meteor/client/hooks/notification/useNotification.ts b/apps/meteor/client/hooks/notification/useNotification.ts
index 0ef377703fcd6..88296e3334323 100644
--- a/apps/meteor/client/hooks/notification/useNotification.ts
+++ b/apps/meteor/client/hooks/notification/useNotification.ts
@@ -51,10 +51,12 @@ export const useNotification = () => {
 			n.addEventListener(
 				'reply',
 				({ response }) =>
-					void sdk.call('sendMessage', {
-						_id: Random.id(),
-						rid,
-						msg: response,
+					void sdk.rest.post('/v1/chat.sendMessage', {
+						message: {
+							_id: Random.id(),
+							rid,
+							msg: response,
+						},
 					}),
 			);
 		}
diff --git a/apps/meteor/client/lib/chats/flows/sendMessage.ts b/apps/meteor/client/lib/chats/flows/sendMessage.ts
index 69d2a079d16c9..7e02b49ede3e9 100644
--- a/apps/meteor/client/lib/chats/flows/sendMessage.ts
+++ b/apps/meteor/client/lib/chats/flows/sendMessage.ts
@@ -47,9 +47,13 @@ const process = async (chat: ChatAPI, message: IMessage, previewUrls?: string[],
 
 	chat.composer?.clear();
 	await runOptimisticSendMessage(message);
-	await sdk.call('sendMessage', message, previewUrls);
 
-	// after the request is complete we can go ahead and mark as sent
+	await sdk.rest.post('/v1/chat.sendMessage', { message, previewUrls });
+
+	// Clear the optimistic `temp` flag only if the messages stream hasn't already
+	// replaced the record. Overwriting with the server response can clobber stream
+	// updates that arrive first — e.g. read-receipt-driven `unread: false`, async
+	// URL/quote attachments, or E2EE decrypt — leading to stale UI state.
 	Messages.state.update(
 		(record) => record._id === message._id && record.temp === true,
 		({ temp: _, ...record }) => record,
@@ -107,8 +111,13 @@ export const sendMessage = async (
 		}
 
 		try {
-			await process(chat, message, previewUrls, isSlashCommandAllowed);
+			// Dismiss quoted messages optimistically — they are already baked into
+			// `message` by composeMessage above, so the composer preview must unmount
+			// regardless of whether the send request resolves. Keeping it coupled to a
+			// resolved request leaves the quote stuck in the composer when the REST call
+			// rejects even though the message was already broadcast over the stream.
 			chat.composer?.dismissAllQuotedMessages();
+			await process(chat, message, previewUrls, isSlashCommandAllowed);
 			await afterSendMessageCallback(message, message.rid);
 		} catch (error) {
 			dispatchToastMessage({ type: 'error', message: error });
diff --git a/apps/meteor/client/views/room/modals/ReadReceiptsModal/ReadReceiptsModal.tsx b/apps/meteor/client/views/room/modals/ReadReceiptsModal/ReadReceiptsModal.tsx
index 725bb44a1c4ae..9ef49032f045b 100644
--- a/apps/meteor/client/views/room/modals/ReadReceiptsModal/ReadReceiptsModal.tsx
+++ b/apps/meteor/client/views/room/modals/ReadReceiptsModal/ReadReceiptsModal.tsx
@@ -1,28 +1,44 @@
-import type { IMessage } from '@rocket.chat/core-typings';
+import type { IMessage, IRoom } from '@rocket.chat/core-typings';
 import { GenericModal, GenericModalSkeleton } from '@rocket.chat/ui-client';
-import { useMethod, useToastMessageDispatch } from '@rocket.chat/ui-contexts';
-import { useQuery } from '@tanstack/react-query';
+import { useEndpoint, useStream, useToastMessageDispatch } from '@rocket.chat/ui-contexts';
+import { useQuery, useQueryClient } from '@tanstack/react-query';
+import type { ReactElement } from 'react';
 import { useEffect } from 'react';
 import { useTranslation } from 'react-i18next';
 
 import ReadReceiptRow from './ReadReceiptRow';
+import { mapReadReceiptFromApi } from '../../../../lib/utils/mapReadReceiptFromApi';
 
-export type ReadReceiptsModalProps = {
+type ReadReceiptsModalProps = {
 	messageId: IMessage['_id'];
+	rid?: IRoom['_id'];
 	onClose: () => void;
 };
 
-const ReadReceiptsModal = ({ messageId, onClose }: ReadReceiptsModalProps) => {
+const readReceiptsQueryKey = (messageId: IMessage['_id']) => ['read-receipts', messageId] as const;
+
+const ReadReceiptsModal = ({ messageId, rid, onClose }: ReadReceiptsModalProps): ReactElement => {
 	const { t } = useTranslation();
 	const dispatchToastMessage = useToastMessageDispatch();
+	const queryClient = useQueryClient();
+	const subscribeToNotifyRoom = useStream('notify-room');
 
-	const getReadReceipts = useMethod('getReadReceipts');
+	const getReadReceipts = useEndpoint('GET', '/v1/chat.getMessageReadReceipts');
 
 	const readReceiptsResult = useQuery({
-		queryKey: ['read-receipts', messageId],
-		queryFn: () => getReadReceipts({ messageId }),
+		queryKey: readReceiptsQueryKey(messageId),
+		queryFn: async () => (await getReadReceipts({ messageId })).receipts.map(mapReadReceiptFromApi),
 	});
 
+	useEffect(() => {
+		if (!rid) {
+			return;
+		}
+		return subscribeToNotifyRoom(`${rid}/messagesRead`, () => {
+			queryClient.invalidateQueries({ queryKey: readReceiptsQueryKey(messageId) });
+		});
+	}, [rid, messageId, queryClient, subscribeToNotifyRoom]);
+
 	useEffect(() => {
 		if (readReceiptsResult.isError) {
 			dispatchToastMessage({ type: 'error', message: readReceiptsResult.error });
diff --git a/apps/meteor/ee/server/lib/message-read-receipt/ReadReceipt.ts b/apps/meteor/ee/server/lib/message-read-receipt/ReadReceipt.ts
index 23745f8773f0f..165acb5e6c12e 100644
--- a/apps/meteor/ee/server/lib/message-read-receipt/ReadReceipt.ts
+++ b/apps/meteor/ee/server/lib/message-read-receipt/ReadReceipt.ts
@@ -49,7 +49,7 @@ class ReadReceiptClass {
 			return;
 		}
 
-		void this.storeReadReceipts(
+		await this.storeReadReceipts(
 			() => {
 				return Messages.findVisibleUnreadMessagesByRoomAndDate(roomId, userLastSeen).toArray();
 			},
@@ -80,7 +80,7 @@ class ReadReceiptClass {
 			}
 		}
 
-		void this.storeReadReceipts(
+		await this.storeReadReceipts(
 			() => {
 				return Promise.resolve([message]);
 			},
@@ -101,7 +101,7 @@ class ReadReceiptClass {
 			return;
 		}
 
-		void this.storeReadReceipts(
+		await this.storeReadReceipts(
 			() => {
 				return Messages.findUnreadThreadMessagesByDate(message.rid, tmid, userId, userLastSeen).toArray();
 			},
diff --git a/apps/meteor/ee/server/meteor-methods/getReadReceipts.ts b/apps/meteor/ee/server/meteor-methods/getReadReceipts.ts
index e5054c92e0a63..e54d18f356937 100644
--- a/apps/meteor/ee/server/meteor-methods/getReadReceipts.ts
+++ b/apps/meteor/ee/server/meteor-methods/getReadReceipts.ts
@@ -6,6 +6,7 @@ import { check } from 'meteor/check';
 import { Meteor } from 'meteor/meteor';
 
 import { canAccessRoomIdAsync } from '../../../server/lib/authorization/canAccessRoom';
+import { methodDeprecationLogger } from '../../../server/lib/deprecationWarningLogger';
 import { ReadReceipt } from '../lib/message-read-receipt/ReadReceipt';
 
 declare module '@rocket.chat/ddp-client' {
@@ -37,6 +38,8 @@ export const getReadReceiptsFunction = async function (messageId: IMessage['_id'
 
 Meteor.methods<ServerMethods>({
 	async getReadReceipts({ messageId }) {
+		methodDeprecationLogger.method('getReadReceipts', '9.0.0', '/v1/chat.getMessageReadReceipts');
+
 		check(messageId, String);
 
 		const uid = Meteor.userId();
diff --git a/apps/meteor/server/api/validation/ajv.ts b/apps/meteor/server/api/validation/ajv.ts
index 10556de26582f..cd3678516abaa 100644
--- a/apps/meteor/server/api/validation/ajv.ts
+++ b/apps/meteor/server/api/validation/ajv.ts
@@ -10,6 +10,28 @@ if (components) {
 		(mad as Record<string, unknown>).additionalProperties = false;
 	}
 
+	// Lock down the catch-all "plain file" attachment branch. typia emits the
+	// FileAttachmentProps union as `(type: 'file') & (video | image | audio | base)`;
+	// the base branch only requires `type: 'file'`, so it also matches image/video/audio
+	// payloads. That makes the MessageAttachment oneOf ambiguous — a single image
+	// attachment satisfies both its specific branch and the base branch, violating
+	// oneOf's "exactly one" rule and failing response validation for any message with a
+	// file or quoted-file attachment. Reject unknown props on the base branch so only
+	// genuine plain-file attachments match it.
+	for (const key in components) {
+		if (!Object.prototype.hasOwnProperty.call(components, key)) {
+			continue;
+		}
+		const schema = components[key] as { properties?: Record<string, unknown> };
+		const props = schema?.properties;
+		const typeEnum = (props?.type as { enum?: unknown[] } | undefined)?.enum;
+		const isFileBranch = Array.isArray(typeEnum) && typeEnum.length === 1 && typeEnum[0] === 'file';
+		const hasMediaUrl = !!props && ('image_url' in props || 'video_url' in props || 'audio_url' in props);
+		if (isFileBranch && !hasMediaUrl) {
+			(schema as Record<string, unknown>).additionalProperties = false;
+		}
+	}
+
 	for (const key in components) {
 		if (Object.prototype.hasOwnProperty.call(components, key)) {
 			const uri = `#/components/schemas/${key}`;
diff --git a/apps/meteor/server/meteor-methods/messages/getThreadMessages.ts b/apps/meteor/server/meteor-methods/messages/getThreadMessages.ts
index e1b99ca9e940d..cce60acaf044b 100644
--- a/apps/meteor/server/meteor-methods/messages/getThreadMessages.ts
+++ b/apps/meteor/server/meteor-methods/messages/getThreadMessages.ts
@@ -5,6 +5,7 @@ import { Meteor } from 'meteor/meteor';
 
 import { canAccessRoomAsync } from '../../lib/authorization';
 import { callbacks } from '../../lib/callbacks';
+import { methodDeprecationLogger } from '../../lib/deprecationWarningLogger';
 import { readThread } from '../../lib/messaging/threads/functions';
 import { settings } from '../../settings';
 
@@ -19,6 +20,8 @@ const MAX_LIMIT = 100;
 
 Meteor.methods<ServerMethods>({
 	async getThreadMessages({ tmid, limit, skip }) {
+		methodDeprecationLogger.method('getThreadMessages', '9.0.0', '/v1/chat.getThreadMessages');
+
 		if ((limit ?? 0) > MAX_LIMIT) {
 			throw new Meteor.Error('error-not-allowed', `max limit: ${MAX_LIMIT}`, {
 				method: 'getThreadMessages',
diff --git a/apps/meteor/server/meteor-methods/messages/sendMessage.ts b/apps/meteor/server/meteor-methods/messages/sendMessage.ts
index 0fe3a238e4f5f..a408e92db0121 100644
--- a/apps/meteor/server/meteor-methods/messages/sendMessage.ts
+++ b/apps/meteor/server/meteor-methods/messages/sendMessage.ts
@@ -13,6 +13,7 @@ import { RateLimiterClass as RateLimiter } from '../../lib/RateLimiter';
 import { canSendMessageAsync } from '../../lib/authorization/canSendMessage';
 import { hasPermissionAsync } from '../../lib/authorization/hasPermission';
 import { applyAirGappedRestrictionsValidation } from '../../lib/cloud/license/airGappedRestrictionsWrapper';
+import { methodDeprecationLogger } from '../../lib/deprecationWarningLogger';
 import { i18n } from '../../lib/i18n';
 import { SystemLogger } from '../../lib/logger/system';
 import { sendMessage } from '../../lib/messages/sendMessage';
@@ -136,6 +137,8 @@ declare module '@rocket.chat/ddp-client' {
 
 Meteor.methods<ServerMethods>({
 	async sendMessage(message, previewUrls) {
+		methodDeprecationLogger.method('sendMessage', '9.0.0', '/v1/chat.sendMessage');
+
 		check(message, {
 			_id: Match.Maybe(String),
 			rid: Match.Maybe(String),