feat(call): screenshare stays on the call bar in Firefox/Safari via the in-frame prompt (#43)

With a fork that reports `screensharePrompt` (element-call lotus-screenshare-
prompt), the call bar and status bar keep their screenshare button on every
engine. Where the click can't be delegated, starting asks the fork to show
"Share your screen?" inside the call frame (io.lotus.prompt_screenshare)
instead of our own confirm; its Share click starts the share. Stopping works
from the bar as before (no click needed in the frame). Chromium is unchanged.

- useScreenshareMode: hidden (older fork's corner button) | prompt | direct.
- The room's call policy is also pushed to the fork in prompt mode, so the
  prompt never opens where sharing is forbidden.
- Picture-in-picture: the "Return to call" overlay covers the frame; while
  the fork reports the prompt open it lets clicks through to it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/call-status/CallControl.tsx

@@ -7,7 +7,7 @@ import {
   CallEmbed,
   useCallControlState,
   useCallMicLevel,
-  useFrameScreenshare,
+  useScreenshareMode,
 } from '../../plugins/call';
 import { AsyncStatus, useAsyncCallback } from '../../hooks/useAsyncCallback';
 import { callEmbedAtom } from '../../state/callEmbed';
@@ -197,10 +197,16 @@ export function CallControl({
   // Keep a forbidden control visible while its track is still live (so the user
   // can stop it); otherwise hide it entirely.
   const showCamera = allowCamera || video;
-  // [Gitea #43] Hidden where EC shows its own screenshare button in the frame.
-  const frameScreenshare = useFrameScreenshare(callEmbed.control);
-  const showScreenshare = !frameScreenshare && (allowScreenshare || screenshare);
+  // [Gitea #43] Hidden where EC shows its own screenshare button in the frame;
+  // where the click can't be delegated, starting asks for the in-frame prompt.
+  const screenshareMode = useScreenshareMode(callEmbed.control);
+  const showScreenshare = screenshareMode !== 'hidden' && (allowScreenshare || screenshare);
   const [shareConfirm, setShareConfirm] = useState(false);
+  const handleScreenshareToggle = () => {
+    if (screenshare) callEmbed.control.toggleScreenshare();
+    else if (screenshareMode === 'prompt') callEmbed.control.promptScreenshare();
+    else setShareConfirm(true);
+  };
 
   const handleMicrophoneToggle = useCallback(
     () => callEmbed.control.toggleMicrophone(),
@@ -255,9 +261,7 @@ export function CallControl({
         {!compact && showScreenshare && (
           <ScreenShareButton
             enabled={screenshare}
-            onToggle={() =>
-              screenshare ? callEmbed.control.toggleScreenshare() : setShareConfirm(true)
-            }
+            onToggle={() => handleScreenshareToggle()}
             disabled={!callJoined}
           />
         )}

src/app/features/call/CallControls.tsx

@@ -33,7 +33,7 @@ import {
   CallEmbed,
   useCallControlState,
   useCallMicLevel,
-  useFrameScreenshare,
+  useScreenshareMode,
 } from '../../plugins/call';
 import { useSetting } from '../../state/hooks/settings';
 import { settingsAtom } from '../../state/settings';
@@ -112,9 +112,14 @@ export function CallControls({ callEmbed }: CallControlsProps) {
   // can stop it); otherwise hide it entirely.
   const showCamera = allowCamera || video;
   // [Gitea #43] Where EC shows its own screenshare button in the frame, ours
-  // is hidden (this engine can't start a share from the host); the
-  // screenshare-audio mute stays.
-  const frameScreenshare = useFrameScreenshare(callEmbed.control);
+  // is hidden (the screenshare-audio mute stays); where the click can't be
+  // delegated, starting asks for the fork's in-frame "Share your screen?".
+  const screenshareMode = useScreenshareMode(callEmbed.control);
+  const handleScreenshareToggle = () => {
+    if (screenshare) callEmbed.control.toggleScreenshare();
+    else if (screenshareMode === 'prompt') callEmbed.control.promptScreenshare();
+    else setShareConfirm(true);
+  };
   const showScreenshare = allowScreenshare || screenshare;
   const showVideoGroup = showCamera || showScreenshare || !!document.fullscreenEnabled;
   const handleOpenMenu: MouseEventHandler<HTMLButtonElement> = (evt) => {
@@ -225,12 +230,10 @@ export function CallControls({ callEmbed }: CallControlsProps) {
               {showCamera && <VideoButton enabled={video} onToggle={handleVideoToggle} />}
               {showScreenshare && (
                 <>
-                  {!frameScreenshare && (
+                  {screenshareMode !== 'hidden' && (
                     <ScreenShareButton
                       enabled={screenshare}
-                      onToggle={() =>
-                        screenshare ? callEmbed.control.toggleScreenshare() : setShareConfirm(true)
-                      }
+                      onToggle={() => handleScreenshareToggle()}
                     />
                   )}
                   {/* Mute-screenshare-audio sits directly next to the screenshare