fix(vinpin): warm Fiat window-fault falls back to cold (not throw→null)

The last gap: when ensureWarmWindow('fiat') can't bring the Fiat ePER to its VIN
panel (partial Rpartstore-down session leaves it off-panel + re-nav can't recover),
warmDecode threw SessionDropped → re-warm → null, turning a DECODABLE Fiat VIN into
a not_found. Fall back to the proven cold Fiat path instead, so a warm-window fault
never loses a real decode. Completes the FIX2 cold-fallback (previously only the
unusable-parse branch had it; now the can't-reach-panel branch does too).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/api/src/integrations/vinpin/vinpin-driver.service.ts

@@ -638,7 +638,17 @@ export class VinpinDriverService implements OnModuleDestroy {
       }
       if (win === "fiat") {
         if (!(await this.ensureWarmWindow(page, "fiat", cfg))) {
-          throw new VinpinSessionDroppedError("could not focus the Fiat ePER window");
+          // The warm Fiat window can't be brought to its VIN panel (e.g. a partial
+          // Rpartstore-down session left it off-panel and the re-nav couldn't recover
+          // it). Don't throw → re-warm → null (which loses a DECODABLE VIN). Fall back
+          // to the proven cold Fiat path (fresh establish + its own retries), so a
+          // warm-window fault never turns a real decode into a not_found.
+          this.logger.warn(
+            `warm ${vin}: could not reach the Fiat ePER VIN panel — cold Fiat fallback`,
+          );
+          this.warm = false;
+          await this.close();
+          return this.decodeFiatLocked(vin, cfg, deadline);
         }
         const text = await this.runVinFlow(page, vin);
         // Dismiss the modal so the field is ready for the NEXT VIN in this session.