Hosted rooms' instance IDs name their owner: <owner>-<2100000000+n>

The client takes a room's owner from the instance ID's first part; with 2100000000 there, the owner
couldn't decorate their hosted room (putting furniture on went to their home room instead).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/api/test/decorations.test.ts

@@ -119,7 +119,7 @@ test("only the room's owner decorates it; contents are checked", async () => {
   const put = (contents: unknown, instance = room) => call(owner, "PUT", `/api/v1/decorations/${instance}`, { contents });
   for (const bad of ["502", "0502-3", "502-0", "502-3-4", "x-1", "1234567890123-1"])
     expect((await put([item], bad)).status).toBe(400);
-  expect((await put([item], "2100000000-5")).json.error).toBe("hosted_room");
+  expect((await put([item], "12345-2100000005")).json.error).toBe("hosted_room");
   expect((await put([[7, "AAAAAAAAAA", ""]])).status).toBe(400);
   expect((await put([[7, 12345, ""]])).status).toBe(400);
   expect((await put([[-1, "aaaaaaaaaa", ""]])).status).toBe(400);
@@ -157,7 +157,7 @@ test("viewers see the products they may, with a hash of what they see", async ()
   // Unknown rooms have nothing.
   expect((await call(undefined, "GET", "/api/v1/decorations/601-9")).json).toEqual({ instance: "601-9", contents: [], hash: hash([]) });
   expect((await call(undefined, "GET", "/api/v1/decorations/601-x")).status).toBe(400);
-  expect((await call(undefined, "GET", "/api/v1/decorations/2100000000-1")).status).toBe(400);
+  expect((await call(undefined, "GET", "/api/v1/decorations/12345-2100000001")).status).toBe(400);
 
   const put = await call(owner, "PUT", `/api/v1/decorations/${room}`, { contents: [g, a, r] });
   expect(put.status).toBe(200);

apps/api/test/hosted.test.ts

@@ -133,7 +133,7 @@ test("rooms are made, listed, changed and closed by their owners", async () => {
   expect(made.status).toBe(201);
   const n = made.json.room.n;
   expect(made.json.room).toMatchObject({
-    instanceId: `2100000000-${n}`,
+    instanceId: `302-${2_100_000_000 + n}`,
     chatId: 2_100_000_000 + n,
     name: "The Lounge",
     description: "A quiet place.",