fix: legacy offer countdown + add countdown to cart page

Two coupled fixes the live shop.unturf.com data exposed:

1. Legacy accepted offers (those flipped to ACCEPTED before the
   accepted_timestamp column existed) have NULL there, so
   acceptance_pay_deadline_ms returned None and the countdown never
   rendered. Fall back to last_action_timestamp — for an
   untouched-since-acceptance offer that IS the moment of acceptance
   (the accept event was the last action recorded). Also guard the
   property to only return a deadline when state == ACCEPTED, so
   PAID / EXPIRED / WITHDRAWN offers don't accidentally surface
   stale deadlines.

2. Cart page (/cart/{id}) had no countdown — the buyer landed in
   the cart from the offer accept email, saw the agreed price, but
   no live indicator of when this deal expires. Cart.negotiation_pay_
   deadline_ms exposes the linked offer or auction's deadline;
   cart.negotiation_pay_deadline_human renders ago.human() for the
   no-JS fallback. cart.j2 adds a "Pay <strong>in 23 hours, 14
   minutes</strong>, or this offer expires." line inside the green
   negotiation card.

Pulled the countdown tick out of offer.js into a shared
static/js/pay-countdown.js so cart.j2 can include just the ticker
without pulling the offer-detail form wiring it doesn't need.
Other pages still load their own JS — offer.js and auction.js keep
their own implementations for now; this is the cart-page addition.

make_post_sell/models/cart.py

@@ -426,6 +426,37 @@ class Cart(RBase, Base):
     def savings(self):
         return cents_to_dollars(self.savings_in_cents)
 
+    @property
+    def negotiation_pay_deadline_ms(self):
+        """When this negotiated cart must be paid by, in absolute ms.
+        Returns None if the cart isn't negotiated or no deadline is set
+        on the linked offer / auction.
+
+        - cart_offers → offer.acceptance_pay_deadline_ms
+        - cart_auctions → auction.payment_deadline_timestamp
+        """
+        if self.cart_offers:
+            return self.cart_offers[0].offer.acceptance_pay_deadline_ms
+        if self.cart_auctions:
+            return self.cart_auctions[0].auction.payment_deadline_timestamp
+        return None
+
+    @property
+    def negotiation_pay_deadline_human(self):
+        """Human-readable delta of the pay-by deadline ("in 23 hours,
+        14 minutes"), via ago.human. None when no deadline applies."""
+        ms = self.negotiation_pay_deadline_ms
+        if ms is None:
+            return None
+        import ago
+        from datetime import datetime, timezone
+        dt = datetime.fromtimestamp(ms / 1000, tz=timezone.utc)
+        return ago.human(
+            dt, precision=2,
+            past_tense="expired {} ago",
+            future_tense="in {}",
+        )
+
     @property
     def total_price_in_cents(self):
         """

make_post_sell/models/offer.py

@@ -218,17 +218,26 @@ class MpsOffer(RBase, Base):
     @property
     def acceptance_pay_deadline_ms(self):
         """ACCEPTED offers must be paid before this absolute timestamp,
-        else they auto-expire. Returns None for offers that never reached
-        acceptance.
+        else they auto-expire. Returns None for offers that never
+        reached acceptance.
+
+        accepted_timestamp was added in migration 632878c8f243; offers
+        already in ACCEPTED state at deploy time have NULL there. For
+        those legacy rows we fall back to last_action_timestamp, which
+        for an untouched-since-acceptance offer was the moment of
+        acceptance (the accept event was the last action).
         """
-        if self.accepted_timestamp is None:
+        if self.state != OFFER_STATE_ACCEPTED:
+            return None
+        base = self.accepted_timestamp or self.last_action_timestamp
+        if base is None:
             return None
         hours = (
             self.shop.offer_acceptance_payment_hours
             if self.shop is not None
             else DEFAULT_OFFER_ACCEPTANCE_PAYMENT_HOURS
         )
-        return self.accepted_timestamp + (hours * 3600 * 1000)
+        return base + (hours * 3600 * 1000)
 
     @property
     def pay_time_remaining_ms(self):

make_post_sell/static/css/common.css

@@ -3189,6 +3189,20 @@ img.crypto-button-icon {
     font-weight: var(--weight-bold, 700);
 }
 
+.cart-negotiation-deadline {
+    grid-column: 1 / -1;
+    margin: var(--space-3, 12px) 0 0 0;
+    padding-top: var(--space-3, 12px);
+    border-top: 1px dashed var(--alert-success-border, #c3e6cb);
+    font-size: var(--text-sm, 0.875rem);
+    color: var(--text-body, #515151);
+}
+
+.cart-negotiation-deadline strong {
+    color: var(--color-green-dark, #8ab34e);
+    font-variant-numeric: tabular-nums;
+}
+
 .cart-negotiation-footer {
     text-align: right;
 }

make_post_sell/static/js/pay-countdown.js

@@ -0,0 +1,58 @@
+/* Shared pay-by countdown — rewrites every [data-pay-deadline] element
+ * on the page once per second with a prose human delta matching the
+ * server-rendered ago.human() output:
+ *
+ *   "in 23 hours, 14 minutes"  →  "in 23 hours, 14 minutes, 8 seconds"
+ *
+ * Same shape used on /o/{id} (offer detail), /a/{id} (auction detail),
+ * and /cart/{id} (negotiation card). Each page sets:
+ *
+ *   <strong data-pay-deadline="<absolute ms>">in 23 hours, 14 minutes</strong>
+ *
+ * The script-only version refines the precision; the server-rendered
+ * version is the no-JS fallback.
+ */
+(function () {
+  "use strict";
+
+  function fmtRemaining(ms) {
+    if (ms <= 0) return "expired";
+    var totalSeconds = Math.floor(ms / 1000);
+    var units = [
+      { name: "day", value: Math.floor(totalSeconds / 86400) },
+      { name: "hour", value: Math.floor((totalSeconds % 86400) / 3600) },
+      { name: "minute", value: Math.floor((totalSeconds % 3600) / 60) },
+      { name: "second", value: totalSeconds % 60 },
+    ];
+    var parts = [];
+    for (var i = 0; i < units.length && parts.length < 2; i++) {
+      var u = units[i];
+      if (u.value === 0 && parts.length === 0 && i < units.length - 1) continue;
+      parts.push(u.value + " " + u.name + (u.value === 1 ? "" : "s"));
+    }
+    return "in " + parts.join(", ");
+  }
+
+  function tick() {
+    var nodes = document.querySelectorAll("[data-pay-deadline]");
+    if (!nodes.length) return;
+    var now = Date.now();
+    Array.prototype.forEach.call(nodes, function (node) {
+      var raw = node.getAttribute("data-pay-deadline");
+      var deadline = parseInt(raw, 10);
+      if (isNaN(deadline)) return;
+      node.textContent = fmtRemaining(deadline - now);
+    });
+  }
+
+  function start() {
+    tick();
+    setInterval(tick, 1000);
+  }
+
+  if (document.readyState === "loading") {
+    document.addEventListener("DOMContentLoaded", start);
+  } else {
+    start();
+  }
+})();

make_post_sell/templates/cart.j2

@@ -50,6 +50,12 @@
         {% endif %}
       </dl>
 
+      {% if cart.negotiation_pay_deadline_ms %}
+      <p class="cart-negotiation-deadline">
+        Pay <strong data-pay-deadline="{{ cart.negotiation_pay_deadline_ms }}">{{ cart.negotiation_pay_deadline_human }}</strong>, or this {{ cart.negotiation_kind }} expires.
+      </p>
+      {% endif %}
+
       <div class="cart-negotiation-footer">
         <a href="{{ cart.negotiation_path }}" class="cart-negotiation-link shop-theme-link-color">
           {% if cart.negotiation_kind == "auction" %}View auction details &rarr;{% else %}View offer details &rarr;{% endif %}
@@ -58,6 +64,7 @@
     </div>
   </section>
   <br/>
+  <script src="/static/js/pay-countdown.js?v={{ request.git_hash }}"></script>
   {% endif %}
 
   {% for coupon in cart.coupons %}