fix: open files sent from Explorer's Send to and Open with in a compose window, leaving the main window where it is

components/mail/__tests__/compose-plugin-hooks.test.tsx

@@ -211,6 +211,17 @@ describe('a mail link from another program in the desktop app', () => {
     expect(screen.queryByText('stub composer')).not.toBeInTheDocument();
   });
 
+  it('files from Send to or Open with go to a compose window too, attached, and the main window shows no composer', async () => {
+    const { handOffDraft } = await import('@/lib/launch-handoff');
+    render(<MailApp />);
+    const file = new File(['pdf'], 'report.pdf', { type: 'application/pdf' });
+    act(() => { handOffDraft({ files: [file], fromOs: true }); });
+    await waitFor(() => expect(desktopWindows.handOver).toHaveBeenCalledTimes(1));
+    expect(desktopWindows.handOver).toHaveBeenCalledWith(expect.objectContaining({ mode: 'compose', initialFiles: [file] }));
+    await act(() => new Promise((r) => setTimeout(r, 50)));
+    expect(screen.queryByText('stub composer')).not.toBeInTheDocument();
+  });
+
   it('a link inside the app still opens here', async () => {
     render(<MailApp />);
     act(() => { requestInternalMailto('mailto:bob@example.com?subject=Hi'); });

components/mail/mail-app.tsx

@@ -1717,7 +1717,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
   // as Outlook and Thunderbird do, and the main window stays where it was. Plugins get
   // their say first. False when it has to open here instead.
   const openMailtoInWindow = useCallback(async (pending: DraftRequest): Promise<boolean> => {
-    if (!pending.fromOs || pending.initialFiles?.length || !hasDesktopWindows() || !popoutsAvailable()) return false;
+    if (!pending.fromOs || !hasDesktopWindows() || !popoutsAvailable()) return false;
     let prefill: ComposePrefill | null = null;
     if (emailHooks.onBeforeCompose.size > 0) {
       prefill = await runBeforeCompose(composeOptionsFor('compose', {
@@ -1735,6 +1735,8 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
       mode: 'compose',
       initialData: mailtoComposerDraft(pending, useSettingsStore.getState().plainTextMode),
       prefill: prefill && Object.keys(prefill).length > 0 ? prefill : null,
+      // Send to and Open with: the files go along (desktop-p2-6).
+      ...(pending.initialFiles?.length ? { initialFiles: pending.initialFiles } : {}),
     });
     return true;
   }, [identities, t]);
@@ -1857,6 +1859,7 @@ export function MailApp({ linkSegments: routeSegments }: MailAppProps = {}) {
         body: handoff.body ?? '',
         initialFiles: handoff.files,
         unedited: true,
+        ...(handoff.fromOs ? { fromOs: true } : {}),
       });
     };
 

components/popout/popout-compose-app.tsx

@@ -516,6 +516,7 @@ function PopoutComposer({ payload, handoffId, onReopen }: {
         replyTo={payload.replyTo}
         initialDraftText={payload.initialDraftText}
         initialData={payload.initialData}
+        initialFiles={payload.initialFiles ?? null}
         prefill={payload.prefill}
         sessionKey={sessionKey}
         sourceEmailId={payload.sourceEmailId ?? undefined}

lib/desktop/__tests__/os-commands.test.ts

@@ -132,6 +132,12 @@ describe('launches', () => {
     expect(takeHandoff('compose')?.files.map((file) => file.name)).toEqual(['a.pdf', 'b.png']);
   });
 
+  it('files sent from another program are marked so, for a compose window of their own, as a mail link', async () => {
+    const { takeHandoff } = await import('@/lib/launch-handoff');
+    await run({ type: 'files', reason: 'attach', failed: [], files: [{ name: 'a.pdf', data: text('a') }] });
+    expect(takeHandoff('compose')).toMatchObject({ fromOs: true });
+  });
+
   it('a file opened with the app asks: new message or Files, a new message first', async () => {
     const { takeHandoff } = await import('@/lib/launch-handoff');
     const { listenForFileChoices } = await import('@/lib/file-drop/choice');

lib/desktop/os-commands.ts

@@ -133,10 +133,13 @@ function handleFiles(command: Extract<DesktopOsCommand, { type: 'files' }>, env:
   const made = command.files.map(({ name, data }) => new File([new Uint8Array(data)], name));
   const failed = [...command.failed];
   if (command.reason === 'attach' && command.ask) {
-    // Opened with the app ("Open with"): the same choice as dropping it on the window.
+    // An older shell's "Open with": the same choice as dropping it on the window.
     requestFileChoice({ files: made, preferred: 'new-message' });
   } else if (command.reason === 'attach') {
-    if (made.length > 0) handOffDraft({ files: made });
+    // Send to and Open with: a compose window with the files, as a mail link gets, and the
+    // main window stays where it is. Signed out, the sign-in has to show.
+    if (!useAuthStore.getState().isAuthenticated) showWindow();
+    if (made.length > 0) handOffDraft({ files: made, fromOs: true });
   } else {
     for (const file of made) {
       const kind = kindForFile(file);

lib/launch-handoff.ts

@@ -42,6 +42,8 @@ export interface Handoff {
   /** New draft only. */
   subject?: string;
   body?: string;
+  /** From another program through the desktop app (Send to, Open with): a compose window of its own. */
+  fromOs?: boolean;
   createdAt: number;
 }
 
@@ -307,13 +309,14 @@ export function handOffFiles(files: File[], kind: HandoffKind): void {
 }
 
 /** Opens a new draft with this text and these files. Trusted: what came from outside was asked about first. */
-export function handOffDraft(draft: { subject?: string; body?: string; files?: File[] }): void {
+export function handOffDraft(draft: { subject?: string; body?: string; files?: File[]; fromOs?: boolean }): void {
   const subject = cleanMailtoSubject(draft.subject ?? '');
   const body = cleanMailtoBody(draft.body ?? '');
   enqueue({
     id: newId(),
     kind: 'compose',
     files: draft.files ?? [],
+    ...(draft.fromOs ? { fromOs: true } : {}),
     ...(subject ? { subject } : {}),
     ...(body ? { body } : {}),
     createdAt: Date.now(),

lib/popout/compose-handoff.ts

@@ -109,7 +109,9 @@ export function createComposeHandoff(): ComposeHandoff | null {
 /** Keeps the draft with this window, so a reload starts from it. */
 export function rememberComposePayload(handoffId: string, payload: ComposePopoutPayload): void {
   try {
-    sessionStorage.setItem(STORAGE_PREFIX + handoffId, JSON.stringify(payload));
+    // A File doesn't go into JSON: once attached, the draft holds it.
+    const { initialFiles: _files, ...kept } = payload;
+    sessionStorage.setItem(STORAGE_PREFIX + handoffId, JSON.stringify(kept));
   } catch {
     // Full or unavailable: a reload then starts from the saved draft's first state.
   }

lib/popout/compose-payload.ts

@@ -20,4 +20,9 @@ export interface ComposePopoutPayload {
   sourceEmailSource?: EmailWriteSource | null;
   /** The mailbox a new message was started from; picks the identity (see the composer's prop). */
   composeFromAccountEmail?: string;
+  /**
+   * Files to attach as it opens: Send to and Open with in the desktop app. They cross to the
+   * window as they are (BroadcastChannel clones a File) and aren't kept for a reload.
+   */
+  initialFiles?: File[];
 }