fix(presence): Do Not Disturb is real "busy" presence and keeps your status (#283)

DND was sent as presence unavailable with the literal status text
"dnd": it replaced your status, and other clients showed "dnd". Where
the server supports MSC3026 (busy_presence), DND now sends presence
org.matrix.msc3026.busy and leaves the status alone (Synapse keeps
busy across /sync set_presence=online). Busy renders as red "Do Not
Disturb" with the real status line; the legacy unavailable + "dnd"
encoding is still recognised and still used on servers without it.
Status saves / clears no longer downgrade busy. The SDK rejects
non-spec presences, so busy goes through a direct authed PUT.

Fixes #283

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/utils/presenceWrite.ts

@@ -1,4 +1,5 @@
-import { MatrixClient, MatrixError } from 'matrix-js-sdk';
+import { MatrixClient, MatrixError, IPresenceOpts, Method } from 'matrix-js-sdk';
+import { BUSY_PRESENCE } from './busyPresence';
 
 /**
  * Synapse rate-limits `PUT /presence/{user}/status` to ONE request per 10 s per
@@ -10,7 +11,29 @@ import { MatrixClient, MatrixError } from 'matrix-js-sdk';
  * and `PresenceDeduper` lets the heartbeat skip writes that would not change
  * anything, so it stops spending the budget in the first place.
  */
-export type PresenceWrite = { presence: 'online' | 'offline' | 'unavailable'; status_msg?: string };
+export type PresenceWrite = {
+  // [Gitea #283] or MSC3026 busy (Do Not Disturb)
+  presence: 'online' | 'offline' | 'unavailable' | typeof BUSY_PRESENCE;
+  status_msg?: string;
+};
+
+/**
+ * `mx.setPresence` for a PresenceWrite. The SDK refuses anything but the three
+ * spec presences ("Bad presence value"), so MSC3026 busy (#283) goes straight
+ * to the same endpoint.
+ */
+export const writePresence = async (
+  mx: Pick<MatrixClient, 'setPresence'> & Partial<Pick<MatrixClient, 'getSafeUserId' | 'http'>>,
+  write: PresenceWrite,
+): Promise<void> => {
+  if (write.presence !== BUSY_PRESENCE) {
+    await mx.setPresence(write as IPresenceOpts);
+    return;
+  }
+  if (!mx.getSafeUserId || !mx.http) throw new Error('busy presence needs a full MatrixClient');
+  const path = `/presence/${encodeURIComponent(mx.getSafeUserId())}/status`;
+  await mx.http.authedRequest(Method.Put, path, undefined, write);
+};
 
 const sleep = (ms: number) =>
   new Promise<void>((r) => {
@@ -28,7 +51,7 @@ export async function setPresenceWithRetry(
   for (;;) {
     try {
       // eslint-disable-next-line no-await-in-loop
-      await mx.setPresence(write);
+      await writePresence(mx, write);
       return;
     } catch (e) {
       if (!(e instanceof MatrixError) || e.httpStatus !== 429) throw e;