Premium unlock: refresh preview pane in place with a reveal flash

Previously, after clicking Unlock from the preview pane, the pane
kept showing the watermarked locked version until the user closed
and re-opened it. That made the "I just bought this" moment feel
inert, and could read as "did the payment work?" friction.

Now, on a successful unlock from openUnlockConfirm:
  - Check if #nostrPreviewPanel is currently showing the row we
    just unlocked (it stashes the row reference on the panel).
  - If so, rebuild the row from _feedCache.events so it reflects
    the freshly-decrypted payload (passes skipVersionFilter so the
    cache stays fresh even for legacy version fields), and call
    openDesignPreview(freshRow). The pane re-paints: the action
    rail's "⚡ Unlock for N sats" swaps to "Use/Fork", the
    watermarked JPEG body swaps to the real renderTemplate /
    renderCustomArt etc. preview DOM, and Save JSON re-enables.
  - Apply a new .premiumRevealFlash class to the panel right
    after the swap. Defined as a 0.55 s premiumRevealFade
    keyframe that fades from opacity 0 + 0.985 scale + slight
    brightness boost to fully visible — reads as "the content
    just appeared" without being garish.

Failure cases stay non-blocking: a try/catch around the preview
refresh logs to console without affecting the rest of the unlock
toast or the feed rerender.

Tested via CDP: synthetic premium event in the cache, open
preview pane (locked: watermarked image + Unlock CTA),
stub payZapSplit + upsertPurchaseVaultItem + native confirm so
openUnlockConfirm runs through. After the call returns the
preview pane has Use/Fork button, no JPEG image in the body, and
the premiumRevealFlash class set.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/index.html

@@ -2113,6 +2113,15 @@
       background-image:linear-gradient(var(--panel),var(--panel)),linear-gradient(135deg,#ffd166 0%,#ef476f 50%,#06d6a0 100%);
     }
     .feedCard.feedCardPremium:hover{box-shadow:0 0 0 1px rgba(239,71,111,.20), 0 6px 22px rgba(239,71,111,.18)}
+    /* Reveal animation when a premium design switches from locked to
+       unlocked inside the preview pane — fades the new content in over the
+       watermark with a subtle scale. */
+    @keyframes premiumRevealFade {
+      0%   { opacity: 0; transform: scale(.985); filter: brightness(1.04); }
+      60%  { opacity: 1; transform: none;        filter: brightness(1.04); }
+      100% { opacity: 1; transform: none;        filter: none; }
+    }
+    .premiumRevealFlash { animation: premiumRevealFade .55s ease-out; }
     .feedCardPremiumRibbon{
       position:absolute;top:6px;left:6px;z-index:7;
       font-size:.62rem;font-weight:800;letter-spacing:.04em;
@@ -5709,6 +5718,30 @@
         if (typeof _currentFeedRerender === 'function') {
           try { _currentFeedRerender(); } catch {}
         }
+        // If the user opened the preview pane for THIS design before clicking
+        // unlock, refresh the pane to show the decrypted preview (instead of
+        // the watermarked locked version) and flash the reveal animation.
+        try {
+          const previewedRow = $('nostrPreviewPanel')?._row;
+          if (previewedRow?.e?.id === eventId) {
+            const freshEvent = (_feedCache.events || []).find((ev) => ev.id === eventId) || row.e;
+            const freshRows = buildRowsFromEvents([freshEvent], 'any', '', true);
+            const freshRow = freshRows[0] || row;
+            // openDesignPreview wipes #nostrPreviewPanel; refresh from the
+            // updated cache state.
+            openDesignPreview(freshRow);
+            const panel = $('nostrPreviewPanel');
+            if (panel) {
+              panel.classList.remove('premiumRevealFlash');
+              // Force reflow so the animation re-triggers if it had been
+              // applied previously.
+              void panel.offsetWidth;
+              panel.classList.add('premiumRevealFlash');
+            }
+          }
+        } catch (refreshErr) {
+          console.warn('[unlock] preview refresh failed', refreshErr);
+        }
       } catch (err) {
         if (statusToast?.dismiss) statusToast.dismiss();
         const msg = err?.message || 'Unlock failed.';