fix: detect typing inside the QuotedHtml shadow island via composedPath #654

lib/keyboard.ts

@@ -0,0 +1,26 @@
+// Shared helper for global key listeners to decide whether a keyboard event
+// originated from a typing context (input, textarea, select, contentEditable).
+//
+// Checking `document.activeElement` / `event.target` is NOT enough: inside a
+// shadow root both are retargeted to the host element, so the QuotedHtml
+// island's inner contentEditable (components/email/quoted-html.ts) looks like
+// a plain <div> from outside. Single-key mailbox shortcuts then fire while the
+// user is editing quoted text — up to and including deleting the open email on
+// Backspace (#654). `composedPath()` sees through the shadow boundary and
+// starts at the real inner target, so it is the reliable signal.
+export function isEditableEventTarget(event: Event): boolean {
+  const path =
+    typeof event.composedPath === "function"
+      ? event.composedPath()
+      : [event.target];
+  return path.some((node) => {
+    if (!(node instanceof HTMLElement)) return false;
+    const tag = node.tagName.toLowerCase();
+    if (tag === "input" || tag === "textarea" || tag === "select") return true;
+    if (node.isContentEditable) return true;
+    // jsdom (tests) doesn't implement isContentEditable; browsers reflect the
+    // property into the attribute, so this also covers "plaintext-only".
+    const attr = node.getAttribute("contenteditable");
+    return attr === "" || attr === "true" || attr === "plaintext-only";
+  });
+}