fix(attachments): route all viewer blob fetches for cross-account messages

Extend the cross-account blob routing beyond download/preview to every blob
fetch in the message viewer, so a message opened from a different account in the
unified / All-Mail view renders and exports correctly instead of 404ing against
the active account:

- inline cid: images, drag-to-desktop, attachment thumbnails, the "download all"
  zip bundle, and the S/MIME / TNEF / embedded-rfc822 blob reads now use a
  resolved blobClient (getClientForAccount(sourceClientAccountId)) and the owner
  blobAccountId (sourceAccountId), computed once from the open message's source;
- fetchBlobAsObjectUrl / fetchBlobArrayBuffer / fetchBlob calls pass the
  accountId (the client methods gained the param in the previous commit);
- non-cross-account behaviour is unchanged (blobClient === active client).

Extends 10-attachments with an inline-image case (verified to fall back to the
placeholder without the routing). The SMTP helper can now send multipart/related
inline images.

integration/README.md

@@ -112,10 +112,12 @@ because the UI behaviour is currently incomplete. Worth a look:
   "Move to" submenu offers the shared folder, but clicking it is a no-op.
   Shared ⇆ shared (same owner) moves work. Pinned with `test.fail` in
   `08-shared-moves`.
-- **Cross-account attachments (fixed).** Blobs are account-scoped, so viewing/
-  downloading an attachment on an All-Mail message from another account 404'd
-  against the active account. The download/preview path now routes to the
-  message's owning client + accountId (`10-attachments`).
+- **Cross-account attachments & inline images (fixed).** Blobs are account-
+  scoped, so viewing/downloading/previewing an attachment, rendering an inline
+  `cid:` image, dragging out, and the bundle/S-MIME/TNEF/embedded-message
+  fetches on an All-Mail message from another account 404'd against the active
+  account. Every viewer blob fetch now routes to the message's owning client +
+  accountId (`10-attachments` covers download + inline image).
 
 ## How the tests work
 

integration/tests/10-attachments.spec.ts

@@ -74,4 +74,38 @@ test.describe('Cross-account attachments', () => {
     for await (const c of stream) chunks.push(c as Buffer);
     expect(Buffer.concat(chunks).toString()).toContain(ATT.content);
   });
+
+  test('an inline image on another account\'s All-Mail message renders', async ({ page }) => {
+    const subject = `IT inline ${Date.now()}`;
+    // 1x1 PNG referenced from the HTML body via cid.
+    const png = 'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==';
+    await sendMail({
+      from: bob.email, authPass: bob.password, to: bob.email, subject, body: '',
+      inlineImage: { cid: 'inlinepic', contentType: 'image/png', base64: png, html: '<p>see below</p><img src="cid:inlinepic" alt="pic" width="1" height="1" />' },
+    });
+
+    await seedSettings(page, {
+      enableUnifiedMailbox: true,
+      enableCrossAllView: true,
+      unifiedCrossAccount: true,
+      includeGroupInUnified: true,
+    });
+
+    await login(page, alice);
+    await addAccount(page, bob);
+    await switchAccount(page, alice.email);
+    await forceSync(page);
+
+    await openFolder(page, { name: '__cross_all__' });
+    await forceSync(page);
+    await expectEmailVisible(page, subject);
+    await emailItem(page, subject).first().click();
+
+    // The inline cid: image resolves to a blob URL fetched from bob's account.
+    // Pre-fix the fetch 404s and it falls back to the data:image/gif placeholder.
+    const img = page.frameLocator('iframe[title="Email content"]').locator('img').first();
+    await expect
+      .poll(async () => (await img.getAttribute('src').catch(() => '')) ?? '', { timeout: 15000 })
+      .toMatch(/^blob:/);
+  });
 });

integration/tests/helpers/smtp.ts

@@ -26,6 +26,11 @@ interface SendOptions {
   headers?: Record<string, string>;
   /** Optional single attachment (sent as multipart/mixed, base64). */
   attachment?: { filename: string; contentType: string; content: string };
+  /**
+   * Optional inline image referenced by the HTML body via `cid:<cid>`. Sent as
+   * multipart/related; `base64` is the pre-encoded image payload.
+   */
+  inlineImage?: { cid: string; contentType: string; base64: string; html: string };
 }
 
 class SmtpError extends Error {}
@@ -116,7 +121,26 @@ export async function sendMail(opts: SendOptions): Promise<void> {
     };
 
     let mime: string;
-    if (opts.attachment) {
+    if (opts.inlineImage) {
+      const boundary = 'itrelated_boundary_0001';
+      headers['MIME-Version'] = '1.0';
+      headers['Content-Type'] = `multipart/related; boundary="${boundary}"`;
+      const b64 = opts.inlineImage.base64.replace(/(.{76})/g, '$1\r\n');
+      mime = [
+        `--${boundary}`,
+        'Content-Type: text/html; charset=utf-8',
+        '',
+        crlf(opts.inlineImage.html),
+        `--${boundary}`,
+        `Content-Type: ${opts.inlineImage.contentType}`,
+        `Content-ID: <${opts.inlineImage.cid}>`,
+        'Content-Disposition: inline',
+        'Content-Transfer-Encoding: base64',
+        '',
+        b64,
+        `--${boundary}--`,
+      ].join('\r\n');
+    } else if (opts.attachment) {
       const boundary = 'itmixed_boundary_0001';
       headers['MIME-Version'] = '1.0';
       headers['Content-Type'] = `multipart/mixed; boundary="${boundary}"`;