feat(lotus): io.lotus.screenshare_notice — window closed, no frames, sharing alone (#39)

Watches the local screenshare publication and tells the host, once per
share each: the MediaStreamTrack ended (window closed), it has been muted
(no frames — minimised/occluded window) for 15 s, or 30 min of sharing
with nobody else in the call. Detection only; the host renders the
notices. LiveKit already unpublishes an ended share, so nothing lingers.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/lotus/lotusScreenshareWatch.ts

@@ -0,0 +1,123 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import {
+  type LocalTrackPublication,
+  type Room as LivekitRoom,
+  RoomEvent,
+  Track,
+} from "livekit-client";
+
+import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
+import { widget } from "../widget";
+import { LotusWidgetActions } from "./lotusActions";
+import { lotusSendToHost } from "./lotusWidget";
+
+export type ScreenshareNoticeKind = "ended" | "no-frames" | "alone";
+
+/** A shared window minimised/occluded this long with no frames → tell the host. */
+export const NO_FRAMES_MS = 15_000;
+/** Sharing this long with nobody else in the call → one "still sharing?" nudge. */
+export const ALONE_MS = 30 * 60_000;
+const ALONE_CHECK_MS = 60_000;
+
+/**
+ * [lotus #39] Watch the local screenshare and tell the host about the two
+ * cases people miss: the share went black/ended (window closed or minimised)
+ * and a long share with nobody else in the call. Detection only — the host
+ * renders the notices. Each notice fires at most once per share.
+ */
+export function startLotusScreenshareWatch(
+  vm: CallViewModel,
+  now: () => number = () => Date.now(),
+): () => void {
+  if (!widget) return () => undefined;
+
+  const notify = (kind: ScreenshareNoticeKind): void => {
+    lotusSendToHost(LotusWidgetActions.ScreenshareNotice, { kind });
+  };
+
+  const perRoom = new Map<LivekitRoom, () => void>();
+
+  const attach = (room: LivekitRoom): void => {
+    let cleanupTrack: (() => void) | undefined;
+
+    const watchPublication = (pub: LocalTrackPublication): void => {
+      if (pub.source !== Track.Source.ScreenShare) return;
+      cleanupTrack?.();
+      const mst = pub.track?.mediaStreamTrack;
+      const startedAt = now();
+      let noFramesTimer: ReturnType<typeof setTimeout> | undefined;
+      let sentNoFrames = false;
+      let sentAlone = false;
+
+      const onEnded = (): void => notify("ended");
+      const onMute = (): void => {
+        if (sentNoFrames) return;
+        noFramesTimer = setTimeout(() => {
+          sentNoFrames = true;
+          notify("no-frames");
+        }, NO_FRAMES_MS);
+      };
+      const onUnmute = (): void => {
+        if (noFramesTimer !== undefined) clearTimeout(noFramesTimer);
+        noFramesTimer = undefined;
+      };
+      mst?.addEventListener("ended", onEnded);
+      mst?.addEventListener("mute", onMute);
+      mst?.addEventListener("unmute", onUnmute);
+
+      const aloneTimer = setInterval(() => {
+        if (sentAlone) return;
+        if (room.remoteParticipants.size > 0) return;
+        if (now() - startedAt < ALONE_MS) return;
+        sentAlone = true;
+        notify("alone");
+      }, ALONE_CHECK_MS);
+
+      cleanupTrack = (): void => {
+        mst?.removeEventListener("ended", onEnded);
+        mst?.removeEventListener("mute", onMute);
+        mst?.removeEventListener("unmute", onUnmute);
+        if (noFramesTimer !== undefined) clearTimeout(noFramesTimer);
+        clearInterval(aloneTimer);
+        cleanupTrack = undefined;
+      };
+    };
+
+    const onUnpublished = (pub: LocalTrackPublication): void => {
+      if (pub.source === Track.Source.ScreenShare) cleanupTrack?.();
+    };
+
+    room.on(RoomEvent.LocalTrackPublished, watchPublication);
+    room.on(RoomEvent.LocalTrackUnpublished, onUnpublished);
+    room.localParticipant.trackPublications.forEach(watchPublication);
+
+    perRoom.set(room, () => {
+      cleanupTrack?.();
+      room.off(RoomEvent.LocalTrackPublished, watchPublication);
+      room.off(RoomEvent.LocalTrackUnpublished, onUnpublished);
+    });
+  };
+
+  const sub = vm.allConnections$.subscribe((data) => {
+    const rooms = data.getConnections().map((c) => c.livekitRoom);
+    for (const [room, off] of perRoom) {
+      if (!rooms.includes(room)) {
+        off();
+        perRoom.delete(room);
+      }
+    }
+    for (const room of rooms) if (!perRoom.has(room)) attach(room);
+  });
+
+  return () => {
+    sub.unsubscribe();
+    for (const off of perRoom.values()) off();
+    perRoom.clear();
+  };
+}