diff --git a/packages/types/src/common/index.ts b/packages/types/src/common/index.ts
index 317898d80..21158afe3 100644
--- a/packages/types/src/common/index.ts
+++ b/packages/types/src/common/index.ts
@@ -1,5 +1,6 @@
 export * from "./payments";
 export * from "./payment-messaging";
+export * from "./support-attachments";
 
 export interface BaseEntity {
   id: string;
diff --git a/packages/types/src/common/support-attachments.ts b/packages/types/src/common/support-attachments.ts
new file mode 100644
index 000000000..1f6a1b376
--- /dev/null
+++ b/packages/types/src/common/support-attachments.ts
@@ -0,0 +1,73 @@
+/**
+ * Rules shared by the freight and passenger support-chat attachment flows.
+ *
+ * The two chat backends are independent implementations (freight: TypeORM +
+ * polymorphic `FileRecord`; passenger: Prisma + `SupportAttachment`), but the
+ * *contract* a client codes against — what may be uploaded, how large, how the
+ * preview URL behaves — must not drift between them. Keep the limits here so
+ * both APIs validate identically and all four web apps can render one consistent
+ * "file too large / type not allowed" message.
+ */
+
+/** `FileRecord.resource` discriminator for freight chat attachments. */
+export const SUPPORT_ATTACHMENT_RESOURCE = "support_message";
+
+/** Per-file ceiling. Enforced server-side; the UI pre-checks to fail fast. */
+export const SUPPORT_ATTACHMENT_MAX_BYTES = 10 * 1024 * 1024;
+
+/** Max files on a single message. */
+export const SUPPORT_ATTACHMENT_MAX_PER_MESSAGE = 10;
+
+/**
+ * How long a minted preview URL stays valid. Long enough that an open thread
+ * doesn't rot mid-read, short enough that a leaked URL isn't a durable grant.
+ */
+export const SUPPORT_ATTACHMENT_URL_TTL_SECONDS = 60 * 60;
+
+/**
+ * Types accepted on a chat message.
+ *
+ * Deliberately NARROWER than `FilesService.ALLOWED_UPLOAD_MIME` (which also
+ * serves generated PDFs and scanned business documents at 25MB). Chat is
+ * user-to-user, so the blast radius of a bad file is another human clicking it.
+ *
+ * `image/svg+xml` is excluded on purpose and must stay excluded: an SVG is
+ * executable markup, and previewing one inline (`<img>` is safe, but an
+ * `<iframe>`/direct navigation is not) executes any script it carries under the
+ * serving origin. Nothing in chat needs vector uploads.
+ */
+export const SUPPORT_ATTACHMENT_ALLOWED_MIME: readonly string[] = [
+  // images (previewable inline)
+  "image/jpeg",
+  "image/png",
+  "image/webp",
+  "image/gif",
+  // documents
+  "application/pdf",
+  "application/msword",
+  "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+  "application/vnd.ms-excel",
+  "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+  "text/csv",
+  "text/plain",
+];
+
+/** Image subset — these are the ones worth rendering as a thumbnail. */
+export const SUPPORT_ATTACHMENT_IMAGE_MIME: readonly string[] = [
+  "image/jpeg",
+  "image/png",
+  "image/webp",
+  "image/gif",
+];
+
+export function isSupportAttachmentImage(mimeType: string): boolean {
+  return SUPPORT_ATTACHMENT_IMAGE_MIME.includes(mimeType);
+}
+
+export function isSupportAttachmentAllowed(mimeType: string): boolean {
+  return SUPPORT_ATTACHMENT_ALLOWED_MIME.includes(mimeType);
+}
+
+/** `accept` attribute for a file input / paste target. */
+export const SUPPORT_ATTACHMENT_ACCEPT =
+  SUPPORT_ATTACHMENT_ALLOWED_MIME.join(",");
diff --git a/packages/types/src/freight/support-chat.ts b/packages/types/src/freight/support-chat.ts
index 84b9a7262..6d7e69973 100644
--- a/packages/types/src/freight/support-chat.ts
+++ b/packages/types/src/freight/support-chat.ts
@@ -16,12 +16,37 @@
  * constants shared by the gateway (emitter) and both web apps (subscribers).
  */
 
+import { SUPPORT_ATTACHMENT_RESOURCE } from "../common/support-attachments";
+
 /** Who authored a message — the customer side or a backoffice agent. */
 export enum SupportAuthorRole {
   CUSTOMER = "CUSTOMER",
   AGENT = "AGENT",
 }
 
+/** `FileRecord.resource` value chat attachments are stored under. */
+export { SUPPORT_ATTACHMENT_RESOURCE };
+
+/** A file attached to a support message. */
+export interface SupportAttachmentDto {
+  /**
+   * FileRecord id. For an authenticated download use
+   * `GET /support/attachments/:id?download=1` — the generic `GET /files/:id`
+   * route deliberately refuses chat attachments (it has no ownership check).
+   */
+  id: string;
+  name: string;
+  mimeType: string;
+  /** Bytes. */
+  size: number;
+  /**
+   * Short-lived signed URL for inline preview (`<img src>`), minted per response.
+   * Expires — see SUPPORT_ATTACHMENT_URL_TTL_SECONDS. Clients must not persist it;
+   * refetch the thread to renew.
+   */
+  url: string;
+}
+
 /** A single chat message on the wire. */
 export interface SupportMessageDto {
   id: string;
@@ -30,7 +55,9 @@ export interface SupportMessageDto {
   authorRole: SupportAuthorRole;
   /** Display name of the author, resolved at send time (best-effort). */
   authorName?: string | null;
+  /** Empty string for attachment-only messages. */
   body: string;
+  attachments: SupportAttachmentDto[];
   createdAt: string;
 }
 
@@ -54,9 +81,17 @@ export interface SupportConversationDto {
   updatedAt: string;
 }
 
-/** Post a message. The portal omits the id; the thread is implied by the company. */
+/**
+ * Post a message. The portal omits the id; the thread is implied by the company.
+ *
+ * Attachments do not travel in this shape — a message carrying files is sent as
+ * `multipart/form-data` with a `body` field plus one or more `attachments` file
+ * parts, so the files are written with `resourceId = message.id` in the same
+ * request. There is no staging area and therefore no orphan-file GC to run.
+ */
 export interface SendSupportMessageDto {
-  body: string;
+  /** Optional only when the request carries at least one attachment. */
+  body?: string;
 }
 
 /** Agent opens a thread with a company that has none yet. */
@@ -81,6 +116,24 @@ export interface SupportConversationListResult {
   unreadCount: number;
 }
 
+/**
+ * A page of messages, walking **backwards** from newest.
+ *
+ * Chat pages by keyset, not by offset: an inbound message while an agent is
+ * scrolled back would shift every offset by one and duplicate/skip rows across
+ * pages. The cursor pins a fixed point in (createdAt, id), so concurrent inserts
+ * at the head can't disturb pages already read.
+ */
+export interface SupportMessageListResult {
+  /** Oldest-first *within the page*, so a page appends/prepends as a block. */
+  items: SupportMessageDto[];
+  /**
+   * Opaque cursor for the next (older) page; null when the thread's start has
+   * been reached. Pass back as `before`.
+   */
+  nextCursor: string | null;
+}
+
 /** Socket.io event names pushed server → client on the `support-chat` namespace. */
 export const SUPPORT_CHAT_WS_EVENTS = {
   /** A new message was added to a conversation the socket can see. */
diff --git a/packages/types/src/passenger/support-chat.ts b/packages/types/src/passenger/support-chat.ts
index 254b64e55..e6b7d1219 100644
--- a/packages/types/src/passenger/support-chat.ts
+++ b/packages/types/src/passenger/support-chat.ts
@@ -23,6 +23,33 @@ export enum PassengerSupportSender {
   AGENT = "AGENT",
 }
 
+/**
+ * A file attached to a passenger support message.
+ *
+ * Structurally identical to the freight `SupportAttachmentDto` — kept as its own
+ * declaration because the two namespaces are independently versioned and the
+ * backing stores differ (Prisma `SupportAttachment` here, polymorphic
+ * `FileRecord` in freight). The upload rules themselves are shared: see
+ * `SUPPORT_ATTACHMENT_*` in `common/support-attachments`.
+ */
+export interface PassengerSupportAttachmentDto {
+  id: string;
+  name: string;
+  mimeType: string;
+  /** Bytes. */
+  size: number;
+  /**
+   * Short-lived signed URL — serves both inline preview and download. Expires
+   * (see SUPPORT_ATTACHMENT_URL_TTL_SECONDS); clients must not persist it,
+   * refetch the thread to renew.
+   *
+   * There is no API-streamed alternative here, unlike freight: this app has no
+   * general file endpoint, so the signed URL is the only handle. It is minted
+   * only into responses the caller was already authorized to receive.
+   */
+  url: string;
+}
+
 /** A single chat message on the wire. */
 export interface PassengerSupportMessageDto {
   id: string;
@@ -30,7 +57,9 @@ export interface PassengerSupportMessageDto {
   sender: PassengerSupportSender;
   /** Display name of the author, best-effort. */
   authorName?: string | null;
+  /** Empty string for attachment-only messages. */
   text: string;
+  attachments: PassengerSupportAttachmentDto[];
   createdAt: string;
 }
 
@@ -74,15 +103,43 @@ export interface CreateGuestSupportConversationDto {
   initialMessage: string;
 }
 
-/** Post a message into an existing conversation. */
+/**
+ * Post a message into an existing conversation.
+ *
+ * As in freight, attachments travel as `multipart/form-data` (a `text` field
+ * plus `attachments` file parts) rather than as ids in this body, so files are
+ * persisted against the message that owns them in one request.
+ */
 export interface SendPassengerSupportMessageDto {
-  text: string;
+  /** Optional only when the request carries at least one attachment. */
+  text?: string;
 }
 
-/** The single device-scoped thread for the portal: conversation + its messages. */
+/**
+ * The single device-scoped thread for the portal: conversation + its newest page
+ * of messages.
+ *
+ * `messages` is the *first page only* (newest N, oldest-first within the page) —
+ * it is not the whole thread. Page backwards with `nextCursor` via the messages
+ * endpoint, exactly as the backoffice does.
+ */
 export interface PassengerSupportThreadDto {
   conversation: PassengerSupportConversationDto | null;
   messages: PassengerSupportMessageDto[];
+  /** Cursor for the next (older) page; null when the thread's start is loaded. */
+  nextCursor: string | null;
+}
+
+/**
+ * A page of messages, walking backwards from newest. Keyset — not offset — so a
+ * message arriving while the reader is scrolled back cannot shift or duplicate
+ * pages already fetched. See the freight twin for the full rationale.
+ */
+export interface PassengerSupportMessageListResult {
+  /** Oldest-first within the page. */
+  items: PassengerSupportMessageDto[];
+  /** Pass back as `before`; null at the start of the thread. */
+  nextCursor: string | null;
 }
 
 /** Paginated list envelope for the conversations list endpoints. */