chore(): Improve product list when there is a single sales channel (#14082)

FIXES https://github.com/medusajs/medusa/issues/13976

**What**
Before applying the sales channel link filter, check if there is a single sales channel or many, if will add a bit of overhead but marginal compare to the improvement for big catalog with single sales channel


---

> [!NOTE]
> Optimizes store products listing by conditionally skipping sales channel link filtering when the index can be used or only one sales channel exists.
> 
> - **Store API – `products`** (`packages/medusa/src/api/store/products/middlewares.ts`):
>   - Adds `applyMaybeLinkFilterIfNecessary` middleware:
>     - Skips link filtering when `IndexEngine` is enabled and no tag/category filters are present.
>     - Queries `sales_channels` count; if only one exists, removes `sales_channel_id` filter and proceeds.
>   - Integrates this middleware into `GET /store/products` before default filters; `GET /store/products/:id` remains unchanged with `maybeApplyLinkFilter`.
> - **Release**:
>   - Adds patch changeset for `@medusajs/medusa`.
> 
> <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 8a0b024ea1bc9696f350f34fa77df321e5ecf553. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>

.changeset/many-experts-provide.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/medusa": patch
+---
+
+chore(): Improve product list when there is a single sales channel

packages/medusa/src/api/store/products/middlewares.ts

@@ -5,9 +5,13 @@ import {
   authenticate,
   clearFiltersByKey,
   maybeApplyLinkFilter,
+  MedusaNextFunction,
+  MedusaRequest,
+  MedusaResponse,
   MiddlewareRoute,
 } from "@medusajs/framework/http"
 import {
+  ContainerRegistrationKeys,
   FeatureFlag,
   isPresent,
   ProductStatus,
@@ -22,6 +26,42 @@ import {
 import * as QueryConfig from "./query-config"
 import { StoreGetProductsParams } from "./validators"
 
+async function applyMaybeLinkFilterIfNecessary(
+  req: MedusaRequest,
+  res: MedusaResponse,
+  next: MedusaNextFunction
+) {
+  const canUseIndex = !(
+    isPresent(req.filterableFields.tags) ||
+    isPresent(req.filterableFields.categories)
+  )
+  if (FeatureFlag.isFeatureEnabled(IndexEngineFeatureFlag.key) && canUseIndex) {
+    return next()
+  }
+
+  const query = req.scope.resolve(ContainerRegistrationKeys.QUERY)
+  const salesChannelsQueryRes = await query.graph({
+    entity: "sales_channels",
+    fields: ["id"],
+    pagination: {
+      skip: 0,
+      take: 1,
+    },
+  })
+
+  const salesChannelCount = salesChannelsQueryRes.metadata?.count ?? 0
+  if (!(salesChannelCount > 1)) {
+    delete req.filterableFields.sales_channel_id
+    return next()
+  }
+
+  return maybeApplyLinkFilter({
+    entryPoint: "product_sales_channel",
+    resourceId: "product_id",
+    filterableField: "sales_channel_id",
+  })(req, res, next)
+}
+
 export const storeProductRoutesMiddlewares: MiddlewareRoute[] = [
   {
     method: ["GET"],
@@ -35,24 +75,7 @@ export const storeProductRoutesMiddlewares: MiddlewareRoute[] = [
         QueryConfig.listProductQueryConfig
       ),
       filterByValidSalesChannels(),
-      (req, res, next) => {
-        const canUseIndex = !(
-          isPresent(req.filterableFields.tags) ||
-          isPresent(req.filterableFields.categories)
-        )
-        if (
-          FeatureFlag.isFeatureEnabled(IndexEngineFeatureFlag.key) &&
-          canUseIndex
-        ) {
-          return next()
-        }
-
-        return maybeApplyLinkFilter({
-          entryPoint: "product_sales_channel",
-          resourceId: "product_id",
-          filterableField: "sales_channel_id",
-        })(req, res, next)
-      },
+      applyMaybeLinkFilterIfNecessary,
       applyDefaultFilters({
         status: ProductStatus.PUBLISHED,
         // TODO: the type here seems off and the implementation does not take into account $and and $or possible filters. Might be worth re working (original type used here was StoreGetProductsParamsType)