fix(webmail): Undo send really undoes, and a send is not made twice

The countdown sent from inside a state updater and Undo's button submitted the
form, so Undo stopped the timer and then started the send over. The timer is
now held in a ref, Undo is type=button, and leaving the screen flushes a
pending send once. Snippets drop a stylesheet the preview was cut inside of.

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

.wolf/buglog.json

@@ -35,6 +35,17 @@
         "drafts"
       ],
       "date": "2026-10-22"
+    },
+    {
+      "error_message": "Undo send did not undo: the message was sent anyway (and twice in development)",
+      "root_cause": "The 10-second countdown sent the message from inside a setUndoSeconds updater. Undo only set the number to null; the interval kept running, its next tick saw prev === null and sent. React may also run an updater twice",
+      "fix": "The countdown is counted in a plain closure with the timer kept in pendingSend; handleUndo clears it; leaving the screen flushes a pending send once (and does not navigate). Covered by compose-draft-integrity.test.ts",
+      "tags": [
+        "webmail",
+        "compose",
+        "undo-send"
+      ],
+      "date": "2026-10-22"
     }
   ]
 }