fix(email): make the "Move to" context menu work across accounts

Moving a message to a folder in another account (own ↔ delegated/shared) via the
"Move to" context menu was a no-op — the handlers always issued a single-account
Email/set, which can't move between JMAP accounts. Drag-and-drop already routed
these correctly; the context menu never did.

Add moveToMailboxCrossAware: it detects a cross-account destination (own and
shared mailboxes both carry accountId) and routes through the drag-and-drop
crossAccountMoveEmails pipeline, else falls back to the single-account move.

Fix the pipeline for delegated folders too: a client can't stage a blob in a
delegated account (Blob/upload → blobNotFound), so importing into a shared folder
failed. When one client reaches both accounts, use a server-side JMAP Email/copy
(+ destroy original) instead of blob copy+import; the blob path is kept only for
separate cross-server login accounts. Adds client.copyEmailAcrossAccounts.

Unit tests for the dispatch; the two 08-shared-moves specs are un-pinned. Full
docker integration suite green (37 passed).

stores/email-store.ts

@@ -161,6 +161,14 @@ interface EmailStore {
   deleteEmail: (client: IJMAPClient, emailId: string, forceDelete?: boolean) => Promise<void>;
   markAsRead: (client: IJMAPClient, emailId: string, read: boolean) => Promise<void>;
   moveToMailbox: (client: IJMAPClient, emailId: string, mailboxId: string) => Promise<void>;
+  /**
+   * Move a single email, routing across the account boundary when the
+   * destination folder is owned by a different JMAP account (a delegated/shared
+   * mailbox, or a different connected account) — the "Move to" context-menu
+   * equivalent of what drag-and-drop already does. Falls back to the plain
+   * single-account `moveToMailbox` when source and destination share an account.
+   */
+  moveToMailboxCrossAware: (client: IJMAPClient, emailId: string, mailboxId: string) => Promise<void>;
   moveEmailsToMailbox: (client: IJMAPClient, emailIds: string[], mailboxId: string) => Promise<void>;
   moveThreadToMailbox: (client: IJMAPClient, emailId: string, mailboxId: string) => Promise<void>;
   /**
@@ -424,6 +432,23 @@ function resolveEmailActionContext(
   };
 }
 
+/**
+ * Local account id ("user@host") whose connected client owns `mailbox`.
+ * `mailbox.accountId` is the JMAP server's opaque id; map it back to a local
+ * client id, falling back to the viewing/active account — a delegated/shared
+ * folder has no separately-connected client, it's reached through the viewer's.
+ * Mirrors resolveDestAccountId in use-mailbox-drop.ts.
+ */
+function resolveDestLocalAccountId(mailbox: Mailbox): string | null {
+  const jmapId = mailbox.accountId;
+  if (jmapId) {
+    for (const [localId, client] of useAuthStore.getState().getAllConnectedClients()) {
+      if (client.getAccountId() === jmapId) return localId;
+    }
+  }
+  return useEmailStore.getState().viewingAccountId ?? useAuthStore.getState().activeAccountId;
+}
+
 /**
  * Builds the `UnifiedAccountClient[]` list used by every unified fan-out
  * action (browse, load-more, search). Each entry has a JMAP client plus a
@@ -1595,6 +1620,54 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
     }
   },
 
+  moveToMailboxCrossAware: async (client, emailId, destinationMailboxId) => {
+    const state = get();
+    const email = state.emails.find((e) => e.id === emailId);
+    if (!email) return;
+
+    const { mailboxes } = resolveEmailActionContext(email, client);
+    const find = (id: string) =>
+      mailboxes.find((mb) => mb.id === id) ?? state.mailboxes.find((mb) => mb.id === id);
+    const destMailbox = find(destinationMailboxId);
+    // A context-menu move acts on the visible list, so the source folder is the
+    // one currently open.
+    const sourceMailbox = find(state.selectedMailbox ?? '');
+
+    // Cross-account when the two folders live in different JMAP accounts (both
+    // own and shared mailboxes carry accountId, so this catches own↔shared too).
+    const isCrossAccount =
+      !!destMailbox &&
+      !!sourceMailbox?.accountId &&
+      !!destMailbox.accountId &&
+      sourceMailbox.accountId !== destMailbox.accountId;
+
+    if (!isCrossAccount) {
+      await get().moveToMailbox(client, emailId, destinationMailboxId);
+      return;
+    }
+
+    const destAccountId = resolveDestLocalAccountId(destMailbox!);
+    const sourceAccountId =
+      email.accountId ?? state.viewingAccountId ?? useAuthStore.getState().activeAccountId;
+    if (!destAccountId || !sourceAccountId) {
+      // Can't resolve the local endpoints — fall back rather than drop the mail.
+      await get().moveToMailbox(client, emailId, destinationMailboxId);
+      return;
+    }
+
+    // JMAP has no cross-account move: copy the raw message into the destination
+    // account's mailbox, then delete the original (crossAccountMoveEmails). The
+    // *Jmap* overrides target the owner account when a shared folder is reached
+    // through another user's client.
+    await get().crossAccountMoveEmails(
+      new Map([[sourceAccountId, [emailId]]]),
+      destAccountId,
+      destMailbox!.originalId ?? destMailbox!.id,
+      destMailbox!.isShared ? destMailbox!.accountId : undefined,
+      sourceMailbox?.isShared ? sourceMailbox.accountId : undefined,
+    );
+  },
+
   moveToMailbox: async (client, emailId, destinationMailboxId) => {
     try {
       const email = get().emails.find(e => e.id === emailId);
@@ -1763,9 +1836,23 @@ export const useEmailStore = create<EmailStore>((set, get) => ({
         // the source clean in the happy path.
         const results = await Promise.allSettled(
           emailIds.map(async (emailId) => {
-            // When the source is a delegated/shared mailbox, the email,
-            // its blob, and the destroy all live in the owner's JMAP
-            // account, not the source client's primary one.
+            // Delegated/shared folders: one client reaches both accounts, so a
+            // server-side Email/copy moves the message. A client can't stage a
+            // blob in a *delegated* account (blobNotFound), so the blob
+            // copy+import path below is only valid across separate login
+            // clients/servers.
+            if (sourceClient === destClient) {
+              await sourceClient.copyEmailAcrossAccounts(
+                emailId,
+                sourceJmapAccountId ?? sourceClient.getAccountId(),
+                destJmapAccountId ?? destClient.getAccountId(),
+                destMailboxId,
+              );
+              return emailId;
+            }
+            // Separate clients (cross-server multi-account): the email, its
+            // blob, and the destroy all live in the owner's JMAP account, not
+            // the source client's primary one.
             const full = await sourceClient.getEmail(emailId, sourceJmapAccountId);
             if (!full?.blobId) {
               throw new Error('Source email has no raw blob to copy');