fix(auctions): prevent time drift + consistent now

- Clamp end_time on updates to prevent drift from rounded time-left sources (e.g. Sav)
- Use a single request 'now' for time_remaining formatting across endpoints
- Avoid 'Ended' flicker caused by processing delays

backend/app/api/auctions.py

@@ -161,11 +161,14 @@ class MarketFeedResponse(BaseModel):
 
 # ============== Helper Functions ==============
 
-def _format_time_remaining(end_time: datetime) -> str:
+def _format_time_remaining(end_time: datetime, now: Optional[datetime] = None) -> str:
     """Format time remaining in human-readable format."""
-    delta = end_time - datetime.utcnow()
+    ref = now or datetime.utcnow()
+    delta = end_time - ref
     
-    if delta.total_seconds() <= 0:
+    # Small grace window to avoid displaying "Ended" due to request processing time.
+    # If an auction ends within the next ~2 seconds, we show "0m".
+    if delta.total_seconds() <= -2:
         return "Ended"
     
     hours = int(delta.total_seconds() // 3600)
@@ -177,7 +180,7 @@ def _format_time_remaining(end_time: datetime) -> str:
     elif hours > 0:
         return f"{hours}h {minutes}m"
     else:
-        return f"{minutes}m"
+        return f"{max(minutes, 0)}m"
 
 
 def _get_affiliate_url(platform: str, domain: str, auction_url: str) -> str:
@@ -203,7 +206,8 @@ def _get_affiliate_url(platform: str, domain: str, auction_url: str) -> str:
 async def _convert_to_listing(
     auction: DomainAuction, 
     db: AsyncSession, 
-    include_valuation: bool = True
+    include_valuation: bool = True,
+    now: Optional[datetime] = None,
 ) -> AuctionListing:
     """Convert database auction to API response."""
     valuation_data = None
@@ -234,7 +238,7 @@ async def _convert_to_listing(
         currency=auction.currency,
         num_bids=auction.num_bids,
         end_time=auction.end_time,
-        time_remaining=_format_time_remaining(auction.end_time),
+        time_remaining=_format_time_remaining(auction.end_time, now=now),
         buy_now_price=auction.buy_now_price,
         reserve_met=auction.reserve_met,
         traffic=auction.traffic,
@@ -383,7 +387,7 @@ async def search_auctions(
     # Convert to response with valuations
     listings = []
     for auction in auctions:
-        listing = await _convert_to_listing(auction, db, include_valuation=True)
+        listing = await _convert_to_listing(auction, db, include_valuation=True, now=now)
         listings.append(listing)
     
     # Sort by value_ratio if requested (after valuation)
@@ -426,7 +430,8 @@ async def get_ending_soon(
     
     Data is scraped from public auction sites - no mock data.
     """
-    cutoff = datetime.utcnow() + timedelta(hours=hours)
+    now = datetime.utcnow()
+    cutoff = now + timedelta(hours=hours)
     
     query = (
         select(DomainAuction)
@@ -434,7 +439,7 @@ async def get_ending_soon(
             and_(
                 DomainAuction.is_active == True,
                 DomainAuction.end_time <= cutoff,
-                DomainAuction.end_time > datetime.utcnow(),
+                DomainAuction.end_time > now,
             )
         )
         .order_by(DomainAuction.end_time.asc())
@@ -446,7 +451,7 @@ async def get_ending_soon(
     
     listings = []
     for auction in auctions:
-        listing = await _convert_to_listing(auction, db, include_valuation=True)
+        listing = await _convert_to_listing(auction, db, include_valuation=True, now=now)
         listings.append(listing)
     
     return listings
@@ -481,7 +486,7 @@ async def get_hot_auctions(
     
     listings = []
     for auction in auctions:
-        listing = await _convert_to_listing(auction, db, include_valuation=True)
+        listing = await _convert_to_listing(auction, db, include_valuation=True, now=now)
         listings.append(listing)
     
     return listings
@@ -716,7 +721,7 @@ async def get_smart_opportunities(
         if opportunity_score < 3:
             continue
         
-        listing = await _convert_to_listing(auction, db, include_valuation=False)
+        listing = await _convert_to_listing(auction, db, include_valuation=False, now=now)
         
         recommendation = (
             "🔥 Hot" if opportunity_score >= 10 else
@@ -1064,7 +1069,7 @@ async def get_market_feed(
                 source=auction.platform,
                 is_pounce=False,
                 verified=False,
-                time_remaining=_format_time_remaining(auction.end_time),
+                time_remaining=_format_time_remaining(auction.end_time, now=now),
                 end_time=auction.end_time,
                 num_bids=auction.num_bids,
                 url=_get_affiliate_url(auction.platform, auction.domain, auction.auction_url),

backend/app/services/auction_scraper.py

@@ -312,6 +312,18 @@ class AuctionScraperService:
         existing = existing.scalar_one_or_none()
 
         if existing:
+            # Prevent "end_time drift" on sources that only provide rounded time-left.
+            # `end_time` must be monotonically decreasing (or stable) across scrapes.
+            try:
+                incoming_end = cleaned.get("end_time")
+                if isinstance(incoming_end, datetime) and existing.end_time:
+                    # Allow tiny increases due to rounding/clock skew, but never extend materially.
+                    tolerance = timedelta(minutes=2)
+                    if incoming_end > existing.end_time + tolerance:
+                        cleaned["end_time"] = existing.end_time
+            except Exception:
+                pass
+
             for key, value in cleaned.items():
                 setattr(existing, key, value)
             existing.updated_at = datetime.utcnow()