Keep a pathless tab when it is dragged out

Dragging a tab out of its window closes it and reloads the document by
path in the new window. A tab opened from an embedded attachment has no
path, so the drag destroyed it and CreateEngineFromFile reported an
empty path.

Leave such a tab in its window.

crash: 2026-10-13-12-51-c0c4 (e0444247 len(path) == 0 at
CreateEngineFromFile, src/shared/EngineCreate.cpp:345)

prompt: /fix-crashes

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: kjk

src/Tabs.cpp

@@ -199,6 +199,12 @@ static void MaybeMigrateTab(WindowTab* tab, MainWindow* newWin, Point releasePt)
     }
     if (nDocTabs == 1 && !newWin) return;
 
+    // migration reloads by path; a document opened from memory (an embedded
+    // attachment) has none
+    if (len(tab->filePath) == 0) {
+        return;
+    }
+
     auto* engine = tab->GetEngine();
     if (EngineHasUnsavedAnnotations(engine)) {
         return;

tests/drag-out-attachment-tab.ts

@@ -0,0 +1,127 @@
+// Dragging a tab out of its window reloads the document by path in the new
+// window. A tab opened from an embedded attachment has no path: the drag closed
+// it and fired the empty-path debug report in CreateEngineFromFile()
+// (crash 2026-10-13-12-51-c0c4). Such a tab now stays where it is.
+
+import { mkdirSync, rmSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { ControlCommand } from "./control.ts";
+import { assemblePdf, pollUntil, runStandalone, SLOW_BUILD_FACTOR, tmpPath } from "./util.ts";
+import {
+  clientToScreen,
+  getClientRect,
+  getWindowText,
+  MK_LBUTTON,
+  packCoords,
+  postMessage,
+  setCursorPos,
+  sleep,
+  WM_LBUTTONDOWN,
+  WM_LBUTTONUP,
+  WM_MOUSEMOVE,
+} from "./winapi.ts";
+import { clickAt, findChildByClass, killAndWait, launchControlled } from "./win-automation.ts";
+
+const TABS_CLASS = "SumatraTabsCtrlClass";
+const ATTACHMENT = "image002.png";
+
+// 1x1 red PNG
+const PNG_BASE64 = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8DwHwAFBQIAX8jx0gAAAABJRU5ErkJggg==";
+
+function makePdfWithImageAttachment(): string {
+  const png = Buffer.from(PNG_BASE64, "base64").toString("latin1");
+  return assemblePdf([
+    "<< /Type /Catalog /Pages 2 0 R >>",
+    "<< /Type /Pages /Count 1 /Kids [3 0 R] >>",
+    "<< /Type /Page /Parent 2 0 R /MediaBox [0 0 612 792] /Annots [4 0 R] >>",
+    "<< /Type /Annot /Subtype /FileAttachment /P 3 0 R /Rect [200 400 400 600] /FS 5 0 R /Name /PushPin >>",
+    `<< /Type /Filespec /F (${ATTACHMENT}) /UF (${ATTACHMENT}) /EF << /F 6 0 R >> >>`,
+    `<< /Type /EmbeddedFile /Length ${png.length} /Params << /Size ${png.length} >> >>\nstream\n${png}\nendstream`,
+  ]);
+}
+
+// x of a point on the attachment's tab: the tab a click there selects.
+// Scans from the left so the first hit is far from the tab's close button.
+async function findAttachmentTabX(frame: number, tabs: number, y: number): Promise<number> {
+  const width = getClientRect(tabs).right;
+  const step = 30;
+  // start on the first tab (Home)
+  await clickAt(tabs, step, y, 50);
+  for (let x = 2 * step; x < width; x += step) {
+    await clickAt(tabs, x, y, 50);
+    if (getWindowText(frame).includes(ATTACHMENT)) {
+      return x;
+    }
+  }
+  throw new Error("drag-out-attachment-tab: could not find the attachment's tab");
+}
+
+export async function testit(): Promise<void> {
+  const dir = tmpPath("drag-out-attachment-tab");
+  rmSync(dir, { recursive: true, force: true });
+  mkdirSync(dir, { recursive: true });
+  const pdf = join(dir, "outer.pdf");
+  writeFileSync(pdf, makePdfWithImageAttachment(), "latin1");
+
+  const { proc, client, frame } = await launchControlled(["-view", "single page", "-zoom", "fit page", pdf]);
+  try {
+    await client.waitForRenderIdle();
+    await client.setNotificationsEnabled(false);
+
+    await pollUntil(
+      async () => {
+        const res = await client.request(ControlCommand.TestMarkupAnnots, ["open-embedded", 0, 0]);
+        return { code: res[0], text: String(res[1] ?? "") };
+      },
+      (r) => r.code === 0 && /OK/.test(r.text),
+      {
+        timeoutMs: 8000 * SLOW_BUILD_FACTOR,
+        error: (r) => `drag-out-attachment-tab: open-embedded failed: code=${r.code} ${r.text}`,
+      },
+    );
+    await pollUntil(
+      () => getWindowText(frame),
+      (t) => t.includes(ATTACHMENT),
+      {
+        timeoutMs: 8000 * SLOW_BUILD_FACTOR,
+        error: (t) => `drag-out-attachment-tab: expected tab ${ATTACHMENT}, title='${t}'`,
+      },
+    );
+    await client.waitForRenderIdle();
+
+    const tabs = findChildByClass(frame, TABS_CLASS);
+    if (!tabs) {
+      throw new Error("drag-out-attachment-tab: no tab bar");
+    }
+    const y = Math.floor(getClientRect(tabs).bottom / 2);
+    const x = await findAttachmentTabX(frame, tabs, y);
+
+    // press on the tab, pull it down past the drag threshold, drop below the bar
+    const dropY = y + 300;
+    const at = clientToScreen(tabs, x, y);
+    setCursorPos(at.x, at.y);
+    postMessage(tabs, WM_LBUTTONDOWN, MK_LBUTTON, packCoords(x, y));
+    postMessage(tabs, WM_MOUSEMOVE, MK_LBUTTON, packCoords(x, y + 40));
+    postMessage(tabs, WM_MOUSEMOVE, MK_LBUTTON, packCoords(x, dropY));
+    postMessage(tabs, WM_LBUTTONUP, 0, packCoords(x, dropY));
+    await sleep(300 * SLOW_BUILD_FACTOR);
+
+    // a debug report under -for-testing ends the process
+    if (proc.exitCode !== null) {
+      throw new Error(`drag-out-attachment-tab: the app exited with ${proc.exitCode} after the drag`);
+    }
+    await client.waitForRenderIdle();
+    const title = getWindowText(frame);
+    if (!title.includes(ATTACHMENT)) {
+      throw new Error(`drag-out-attachment-tab: the attachment tab is gone, title='${title}'`);
+    }
+  } finally {
+    client.close();
+    await killAndWait(proc);
+  }
+  console.log("drag-out-attachment-tab: OK");
+}
+
+if (import.meta.main) {
+  await runStandalone(testit);
+}

tests/run-almost-all.ts

@@ -180,6 +180,7 @@ import { testit as issue6305 } from "./issue-6305.ts";
 import { testit as epubThemeRestyle } from "./epub-theme-restyle.ts";
 import { testit as showChaptersInEbooks } from "./show-chapters-in-ebooks.ts";
 import { testit as embeddedImageAttachment } from "./embedded-image-attachment.ts";
+import { testit as dragOutAttachmentTab } from "./drag-out-attachment-tab.ts";
 import { testit as ttsEngineCrashRecovery } from "./tts-engine-crash-recovery.ts";
 import { testit as readAloudCloseDuringSpeak } from "./read-aloud-close-during-speak.ts";
 import { testit as readAloudRestyleStalePage } from "./read-aloud-restyle-stale-page.ts";
@@ -504,6 +505,7 @@ export const tests: NamedTest[] = [
   ["issue-6135", issue6135],
   ["issue-4276", issue4276],
   ["embedded-image-attachment", embeddedImageAttachment],
+  ["drag-out-attachment-tab", dragOutAttachmentTab],
   ["tts-engine-crash-recovery", ttsEngineCrashRecovery],
   ["read-aloud-close-during-speak", readAloudCloseDuringSpeak],
   ["read-aloud-restyle-stale-page", readAloudRestyleStalePage],