fix: keep text typed under the signature when the signature is swapped or removed

components/email/__tests__/compose-format.test.ts

@@ -117,6 +117,17 @@ describe('switching identity swaps the signature', () => {
         .toBe(dom(`<p>Hi</p>${embed(other)}<blockquote>original</blockquote>`));
     });
 
+    it('keeps text typed on the line under the signature', () => {
+      const typedBelow = embed(identity).replace(
+        `<p ${SIGNATURE_RANGE_MARKER}="end"></p>`,
+        `<p ${SIGNATURE_RANGE_MARKER}="end">P.S. see you</p>`,
+      );
+      expect(replaceEmbeddedSignature(`<p>Hi</p>${typedBelow}`, embed(none)))
+        .toBe('<p>Hi</p><p>P.S. see you</p>');
+      expect(replaceEmbeddedSignature(`<p>Hi</p>${typedBelow}`, embed(other)))
+        .toBe(dom(`<p>Hi</p>${embed(other)}<p>P.S. see you</p>`));
+    });
+
     it('adds a signature at the end when there is no quote', () => {
       expect(replaceEmbeddedSignature('<p>Hi</p>', embed(other))).toBe(dom(`<p>Hi</p>${embed(other)}`));
     });

components/email/compose-format.ts

@@ -89,8 +89,17 @@ export function removeSignatureRange(
     if (!removeUntil && isQuoteBoundary(next)) break;
     cursor = next;
   }
-  const insertBefore = toRemove[toRemove.length - 1]?.nextSibling ?? null;
+  let insertBefore = toRemove[toRemove.length - 1]?.nextSibling ?? null;
   toRemove.forEach((node) => parent.removeChild(node));
+  // The end marker is the empty line under the signature, so a click below
+  // the signature puts the caret there. Text typed into it is the user's,
+  // not part of the signature: keep it as an ordinary paragraph after it.
+  if (removeUntil && removeUntil.textContent?.trim()) {
+    const kept = removeUntil.cloneNode(true) as Element;
+    kept.removeAttribute(SIGNATURE_RANGE_MARKER);
+    parent.insertBefore(kept, insertBefore);
+    insertBefore = kept;
+  }
   return { parent, insertBefore };
 }