make route prefixes have a single place where they are defined (#3624)

This is for maintainabilty of the paths. It's hard to track down all the
places where a route is being referenced. This helps unify them so that
it's easily searchable in the codebase. This came up during the readonly
room refactor and being able to find the way a particular route was
wired through the codebase.

### Change Type

<!-- ❗ Please select a 'Scope' label ❗️ -->

- [x] `sdk` — Changes the tldraw SDK
- [ ] `dotcom` — Changes the tldraw.com web app
- [ ] `docs` — Changes to the documentation, examples, or templates.
- [ ] `vs code` — Changes to the vscode plugin
- [ ] `internal` — Does not affect user-facing stuff

<!-- ❗ Please select a 'Type' label ❗️ -->

- [ ] `bugfix` — Bug fix
- [ ] `feature` — New feature
- [ ] `improvement` — Improving existing features
- [x] `chore` — Updating dependencies, other boring stuff
- [ ] `galaxy brain` — Architectural changes
- [ ] `tests` — Changes to any test code
- [ ] `tools` — Changes to infrastructure, CI, internal scripts,
debugging tools, etc.
- [ ] `dunno` — I don't know

packages/dotcom-shared/src/index.ts

@@ -1,4 +1,12 @@
-export { ROOM_OPEN_MODE, RoomOpenModeToPath, type RoomOpenMode } from './routes'
+export {
+	READ_ONLY_LEGACY_PREFIX,
+	READ_ONLY_PREFIX,
+	ROOM_OPEN_MODE,
+	ROOM_PREFIX,
+	RoomOpenModeToPath,
+	SNAPSHOT_PREFIX,
+	type RoomOpenMode,
+} from './routes'
 export type {
 	CreateRoomRequestBody,
 	CreateSnapshotRequestBody,

packages/dotcom-shared/src/routes.ts

@@ -6,9 +6,18 @@ export const ROOM_OPEN_MODE = {
 } as const
 export type RoomOpenMode = (typeof ROOM_OPEN_MODE)[keyof typeof ROOM_OPEN_MODE]
 
+/** @public */
+export const READ_ONLY_PREFIX = 'ro'
+/** @public */
+export const READ_ONLY_LEGACY_PREFIX = 'v'
+/** @public */
+export const ROOM_PREFIX = 'r'
+/** @public */
+export const SNAPSHOT_PREFIX = 's'
+
 /** @public */
 export const RoomOpenModeToPath: Record<RoomOpenMode, string> = {
-	[ROOM_OPEN_MODE.READ_ONLY]: 'ro',
-	[ROOM_OPEN_MODE.READ_ONLY_LEGACY]: 'v',
-	[ROOM_OPEN_MODE.READ_WRITE]: 'r',
+	[ROOM_OPEN_MODE.READ_ONLY]: READ_ONLY_PREFIX,
+	[ROOM_OPEN_MODE.READ_ONLY_LEGACY]: READ_ONLY_LEGACY_PREFIX,
+	[ROOM_OPEN_MODE.READ_WRITE]: ROOM_PREFIX,
 }