fix: buyer can withdraw offer while waiting on seller

The withdraw form on /o/<id> was nested inside the buyer's
`can_act` (your-turn) block, so a buyer who'd just opened an offer
or whose counter was awaiting the seller's response saw the
"Waiting on the other party" panel with no way to back out — they
either had to wait for auto-expiry or message the seller.

Add a symmetric withdraw form inside the `is_open` waiting block,
gated on actor_party == 0 (viewer is the buyer). The lib already
permits withdraw at any non-terminal pre-accept state
(lib/offer.py withdraw_offer); only the UI was the bottleneck.

Sellers don't get a symmetric "pull out" here — they decline
instead, which lives in their can_act block.

Regression test test_buyer_sees_withdraw_button_while_waiting_on_seller
asserts the form action and "Withdraw offer" copy render on a
PENDING offer from the buyer's view.

make_post_sell/templates/offer.j2

@@ -96,6 +96,16 @@
         They have <strong data-pay-deadline="{{ respond_deadline_timestamp_ms }}">{{ respond_deadline_human }}</strong> to respond, or this offer auto-expires.
         {% endif %}
       </p>
+      {# Buyer can withdraw their offer at any non-terminal pre-accept
+         state — including when it's the seller's turn. The seller has
+         no symmetric "pull out" action; they decline instead, which
+         lives in their can_act block above. #}
+      {% if actor_party == 0 %}
+        <form method="post" action="/o/{{ id }}/withdraw" class="offer-action-form" style="margin-top: var(--space-3);"
+              onsubmit="return confirm('Withdraw your offer? This ends the negotiation.');">
+          <input type="submit" class="mps-button" value="Withdraw offer" />
+        </form>
+      {% endif %}
     </section>
   {% endif %}
 

make_post_sell/tests/test_functional.py

@@ -6943,6 +6943,51 @@ class TestOfferCheckout(_AuthenticatedBase):
         # itself carries the message now.
         self.assertNotIn("offer-state-notice", body)
 
+    def test_buyer_sees_withdraw_button_while_waiting_on_seller(self):
+        """When the offer is PENDING (seller's turn to respond), the
+        buyer should still be able to withdraw — the previous template
+        only rendered the withdraw form inside the buyer's `can_act`
+        block, so a buyer waiting for the seller had no way out except
+        wait for auto-expiry.
+        """
+        from ..models.offer import (
+            MpsOffer, OFFER_STATE_PENDING, now_timestamp,
+        )
+        from ..models.product import Product
+        from ..models.user import get_or_create_user_by_email
+
+        shop = self._create_shop_helper(user_creds=self.user1_creds)
+        shop.offer_enabled = True
+        product = Product(title="Negotiable", description="...")
+        product.shop = shop
+        product.price_in_cents = 10000
+        product.is_physical = False
+        product.is_sellable = True
+        product.pricing_mode = 3
+        self.dbsession.add(product)
+        self.dbsession.flush()
+
+        buyer = get_or_create_user_by_email(self.dbsession, "test2@example.com")
+        offer = MpsOffer(
+            product=product, shop=shop, buyer=buyer,
+            amount_in_cents=5000,
+            expires_timestamp=now_timestamp() + 86_400_000,
+        )
+        offer.state = OFFER_STATE_PENDING  # seller's turn
+        self.dbsession.add(offer)
+        self.dbsession.flush()
+        offer_id = offer.uuid_str
+        transaction.commit()
+
+        # Log in as the buyer and visit the offer page.
+        self.testapp.get("/log-out")
+        self.log_in_user(self.user2_creds)
+        body = self.testapp.get(f"/o/{offer_id}", status=200).body.decode()
+        # The buyer sees the waiting block AND a withdraw form.
+        self.assertIn("Waiting on the other party", body)
+        self.assertIn(f"/o/{offer_id}/withdraw", body)
+        self.assertIn("Withdraw offer", body)
+
     def test_pending_offer_renders_respond_countdown(self):
         """A PENDING / COUNTERED offer carries a 'respond by' countdown
         (separate from the post-acceptance pay countdown). Both render