test(integration): draft handling and shared-folder moves

Add draft and shared-folder-move coverage (suite now 31 tests). Findings are
asserted server-side or pinned with test.fail where the UI is incomplete.

Drafts (07):
- multiple recipients (committed and typed-but-uncommitted) persist, and the
  draft reopens via the continue-draft button;
- a server-created draft (with $draft) shows the continue-draft button;
- a changed sender identity is saved to the draft on the server;
- KNOWN BUG (test.fail): reopening a draft resets the From selector to the
  default identity instead of the one the draft was saved with.

Shared-folder moves (08):
- shared -> shared (same owner) moves work in both directions (server-verified);
- KNOWN LIMITATION (test.fail): cross-account moves (own account <-> shared
  folder) don't relocate the message — the Move-to submenu offers the target
  but clicking it is a no-op.

Hooks added: composer From select + save-status, viewer edit-draft button,
context-menu "Move to" submenu + per-target testids (testId on
ContextMenuSubMenu). Helpers: JMAP identities/createDraft/sharing, composer
drive + move-via-submenu. README documents the findings.

integration/tests/helpers/jmap.ts

@@ -13,6 +13,7 @@ import { JMAP_URL } from './config';
 const CORE = 'urn:ietf:params:jmap:core';
 const MAIL = 'urn:ietf:params:jmap:mail';
 const PRINCIPALS = 'urn:ietf:params:jmap:principals';
+const SUBMISSION = 'urn:ietf:params:jmap:submission';
 
 /** Rights granted on a shared mailbox (JMAP ACL). */
 export const FULL_MAILBOX_RIGHTS = {
@@ -73,6 +74,29 @@ export class JmapClient {
     return res.json();
   }
 
+  /** All sending identities of this account. */
+  async identities(): Promise<Array<{ id: string; name: string; email: string }>> {
+    const r = await this.request([['Identity/get', { accountId: this.accountId }, '0']], [CORE, SUBMISSION]);
+    return r.methodResponses[0][1].list;
+  }
+
+  /**
+   * Ensure a second sending identity `name <email>` exists (idempotent by
+   * name). Returns its id. Used to make the composer's From selector appear so
+   * a changed sender can be exercised.
+   */
+  async ensureIdentity(name: string, email: string): Promise<string> {
+    const existing = (await this.identities()).find((i) => i.name === name);
+    if (existing) return existing.id;
+    const r = await this.request(
+      [['Identity/set', { accountId: this.accountId, create: { alt: { name, email, replyTo: null } } }, '0']],
+      [CORE, SUBMISSION],
+    );
+    const created = r.methodResponses[0][1].created?.alt;
+    if (!created) throw new Error(`Identity/set failed: ${JSON.stringify(r.methodResponses[0][1])}`);
+    return created.id;
+  }
+
   /** Resolve another user's principal id (needed as the key in `shareWith`). */
   async principalIdByEmail(email: string): Promise<string> {
     const r = await this.request(
@@ -194,6 +218,31 @@ export class JmapClient {
     return id;
   }
 
+  /** Create a draft message (with the $draft keyword) in the Drafts folder. */
+  async createDraft(subject: string, toEmail: string): Promise<string> {
+    const drafts = await this.mailboxByRole('drafts');
+    if (!drafts) throw new Error('No Drafts mailbox');
+    const r = await this.request([
+      ['Email/set', {
+        accountId: this.accountId,
+        create: {
+          d: {
+            mailboxIds: { [drafts.id]: true },
+            keywords: { $draft: true },
+            from: [{ email: this.email }],
+            to: [{ email: toEmail }],
+            subject,
+            bodyValues: { b: { value: 'server-created draft body' } },
+            textBody: [{ partId: 'b', type: 'text/plain' }],
+          },
+        },
+      }, '0'],
+    ]);
+    const created = r.methodResponses[0][1].created?.d;
+    if (!created) throw new Error(`createDraft failed: ${JSON.stringify(r.methodResponses[0][1])}`);
+    return created.id;
+  }
+
   /** Set or clear the $seen keyword on an email. */
   async setSeen(emailId: string, seen: boolean): Promise<void> {
     await this.request([
@@ -210,7 +259,7 @@ export class JmapClient {
       ['Email/get', {
         accountId: this.accountId,
         '#ids': { resultOf: '0', name: 'Email/query', path: '/ids' },
-        properties: ['id', 'subject', 'keywords', 'mailboxIds', 'from', 'preview'],
+        properties: ['id', 'subject', 'keywords', 'mailboxIds', 'from', 'to', 'preview'],
       }, '1'],
     ]);
     return r.methodResponses[1][1].list[0];