fix: cheapest/how-much answers use Buy button only, not full price grid

.agent/PRICE_INTELLIGENCE_RULES.md

@@ -46,7 +46,8 @@ No new endpoints.
 
 ## 5. UI
 
-- **Widget:** 3-column grid Platform | Price | Buy under bot bubble
+- **Widget:** 3-column grid Platform | Price | Buy under bot bubble — **only** for list-all / compare turns
+- **Single-winner turns** (cheapest, most expensive, how much, buy link for X): text + one Buy button; no grid
 - **Empty price:** display `See site`; Buy uses that platform's `listing_url`
 - **Telegram:** stacked URL buttons (`Platform — $x.xx`), max 4
 

app/services/price_catalog_service.py

@@ -306,13 +306,11 @@ class PriceCatalogService:
                 "platform_offers": [offer_to_platform_item(o) for o in offers],
             }
         best = min(priced, key=lambda o: o.price_cents or 10**9)
-        others = [o for o in offers if o.platform_id != best.platform_id]
         text = (
             f"The lowest listed price for {book_title} is {best.price_display} "
             f"on {best.platform}."
         )
-        platform_offers = [offer_to_platform_item(best, is_best=True)]
-        platform_offers.extend(offer_to_platform_item(o) for o in others[:5])
+        # Single winner + Buy button only — no full Platform/Price/Buy grid.
         return {
             "text": text,
             "links": [{
@@ -322,7 +320,7 @@ class PriceCatalogService:
                 "icon": "🛒",
             }],
             "has_links": True,
-            "platform_offers": platform_offers,
+            "platform_offers": None,
         }
 
     def _build_expensive_answer(self, offers: list[Offer], book_title: str) -> dict[str, Any]:
@@ -343,10 +341,7 @@ class PriceCatalogService:
                 "icon": "🛒",
             }],
             "has_links": True,
-            "platform_offers": [
-                offer_to_platform_item(top, is_best=True),
-                *[offer_to_platform_item(o) for o in offers if o.platform_id != top.platform_id][:5],
-            ],
+            "platform_offers": None,
         }
 
     def _build_compare_answer(
@@ -405,7 +400,7 @@ class PriceCatalogService:
                     "icon": "🛒",
                 }],
                 "has_links": True,
-                "platform_offers": [offer_to_platform_item(target, is_best=True)],
+                "platform_offers": None,
             }
         if target is None:
             target = next((o for o in offers if o.is_source), offers[0])
@@ -427,7 +422,7 @@ class PriceCatalogService:
                 "icon": "🛒",
             }],
             "has_links": True,
-            "platform_offers": [offer_to_platform_item(target, is_best=True)],
+            "platform_offers": None,
         }
 
     def _build_how_much_answer(
@@ -462,5 +457,5 @@ class PriceCatalogService:
                 "icon": "🛒",
             }],
             "has_links": True,
-            "platform_offers": [offer_to_platform_item(target, is_best=True)],
+            "platform_offers": None,
         }

tests/unit/test_price_catalog_service.py

@@ -93,8 +93,22 @@ async def test_build_cheapest_marks_is_best():
     result = svc._build_cheapest_answer(offers, "Lethal Lines")
     assert "Kobo" in result["text"]
     assert "$9.99" in result["text"]
-    assert result["platform_offers"][0]["is_best"] is True
-    assert result["platform_offers"][0]["platform"] == "Kobo"
+    assert result["platform_offers"] is None
+    assert result["links"][0]["url"] == "https://k.com"
+    assert "Buy on Kobo" in result["links"][0]["label"]
+
+
+@pytest.mark.asyncio
+async def test_google_books_link_ask_redirects_to_retail():
+    svc = PriceCatalogService.__new__(PriceCatalogService)
+    offers = [
+        Offer("amazon", "Amazon", "$14.99", 1499, "https://a.com", True),
+    ]
+    result = svc._build_platform_link_answer(offers, "Lethal Lines", ("google_books",))
+    assert "Google Books" in result["text"]
+    assert "Amazon" in result["text"]
+    assert result["links"][0]["url"] == "https://a.com"
+    assert result["platform_offers"] is None
 
 
 @pytest.mark.asyncio
@@ -177,19 +191,6 @@ async def test_catalog_for_book_excludes_google_books():
     assert [o.platform_id for o in offers] == ["amazon"]
 
 
-@pytest.mark.asyncio
-async def test_google_books_link_ask_redirects_to_retail():
-    svc = PriceCatalogService.__new__(PriceCatalogService)
-    offers = [
-        Offer("amazon", "Amazon", "$14.99", 1499, "https://a.com", True),
-    ]
-    result = svc._build_platform_link_answer(offers, "Lethal Lines", ("google_books",))
-    assert "Google Books" in result["text"]
-    assert "Amazon" in result["text"]
-    assert result["links"][0]["url"] == "https://a.com"
-    assert result["platform_offers"][0]["platform_id"] == "amazon"
-
-
 @pytest.mark.asyncio
 async def test_handle_how_much_uses_source():
     svc = PriceCatalogService(MagicMock())
@@ -201,3 +202,4 @@ async def test_handle_how_much_uses_source():
     assert "$14.99" in result["text"]
     assert "Amazon" in result["text"]
     assert result["links"][0]["url"] == "https://a.com"
+    assert result.get("platform_offers") is None