feat: recall an already-registered address without REGISTER

web/index.html

@@ -94,7 +94,7 @@
   <section>
     <h3><span id="step-server" class="step" data-n="1">1</span> your server</h3>
     <p class="hint">Pin the key of the server that will hold your mail. Get it from its operator over a
-      channel you already trust — registering and fetching both refuse an unpinned server (SPEC.md §4).</p>
+      channel you already trust — registering, recalling and fetching all refuse an unpinned server (SPEC.md §4).</p>
     <form id="pin-form">
       <label>host<input name="host" placeholder="example.org" spellcheck="false" required></label>
       <label>public key<input name="key" placeholder="base32" spellcheck="false" required></label>
@@ -111,6 +111,16 @@
       <label>invite token<input name="token" placeholder="if required"></label>
       <button class="filled">register</button>
     </form>
+    <details>
+      <summary>already registered elsewhere?</summary>
+      <p class="hint">Restoring a seed brings back the identity, not the memory of what address it was
+        registered under in a different browser — the server was never asked. Recall it here: this
+        looks the address up and checks it resolves to this identity's key, without registering anything.</p>
+      <form id="recall-form">
+        <label>address<input name="address" placeholder="alice@example.org" spellcheck="false" required></label>
+        <button>recall</button>
+      </form>
+    </details>
   </section>
 
   <section>

web/js/app.js

@@ -883,6 +883,37 @@ $("register-form").onsubmit = async (event) => {
   }
 };
 
+// Restoring a seed brings back the identity, not the memory of what address a
+// *different* browser registered it under — "account" is local-only state,
+// never asked of the server. This binds it without REGISTER: RESOLVE the
+// address and require it name this exact key, so a typo or someone else's
+// address can't silently misfile outgoing Reply-To / fetch under it.
+$("recall-form").onsubmit = async (event) => {
+  event.preventDefault();
+  const form = event.target;
+  try {
+    const me = store.identity();
+    if (!me) throw new SmolError("no identity yet");
+    const addr = parseAddress(form.address.value.trim());
+    const opened = await connect(addr, { requirePin: true });
+    let current;
+    try {
+      ({ identity: current } = await resolveOp(opened.session, addr.user));
+    } finally {
+      opened.session.stream.close();
+    }
+    if (!timingSafeEqual(current, me.publicKey))
+      throw new SmolError(`${addr.short} resolves to a different key — not this identity`);
+    store.setAccount(addr);
+    status(`recalled ${addr.short}\nshare: ${addr.uri(me.publicKey)}`);
+    renderAccount();
+    renderSettings();
+    form.reset();
+  } catch (err) {
+    status(err.message, true);
+  }
+};
+
 async function rotateIdentity() {
   const me = store.identity();
   const addr = accountAddress();