fix: support slug and where[] query params in custom posts route

The custom /api/posts route intercepted all post queries but only
supported listing parameters (category, type, page). Frontend detail
pages sending where[slug][equals]=X got all posts back, always
showing the latest post regardless of which article was clicked.

Now parses slug from both ?slug=X and ?where[slug][equals]=X format.
Replaced getPostsByCategory with direct payload.find using properly
typed Where conditions. Detail queries (with slug) include content
and readingTime in the response.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/(frontend)/api/posts/route.ts

@@ -3,8 +3,8 @@
 
 import { NextRequest, NextResponse } from 'next/server'
 import { getPayload } from 'payload'
+import type { Where } from 'payload'
 import config from '@payload-config'
-import { getPostsByCategory } from '@/lib/search'
 import type { Category } from '@/payload-types'
 import {
   searchLimiter,
@@ -42,11 +42,12 @@ export async function GET(request: NextRequest) {
       )
     }
 
-    // Parse query parameters
+    // Parse query parameters (supports both ?key=val and ?where[key][equals]=val formats)
     const { searchParams } = new URL(request.url)
     const category = searchParams.get('category')?.trim()
     const type = searchParams.get('type')?.trim() as 'blog' | 'news' | 'press' | 'announcement' | undefined
     const tenantParam = searchParams.get('tenant') || searchParams.get('where[tenant][equals]')
+    const slugParam = searchParams.get('slug')?.trim() || searchParams.get('where[slug][equals]')?.trim()
     const pageParam = searchParams.get('page')
     const limitParam = searchParams.get('limit')
     const localeParam = searchParams.get('locale')?.trim()
@@ -90,47 +91,82 @@ export async function GET(request: NextRequest) {
     // Get payload instance
     const payload = await getPayload({ config })
 
-    // Get posts
-    const result = await getPostsByCategory(payload, {
-      tenantId,
-      categorySlug: category,
-      type,
-      locale,
+    // Build query: slug lookup uses direct payload.find for full where support
+    const whereConditions: Where[] = [
+      { tenant: { equals: tenantId } },
+      { status: { equals: 'published' } },
+    ]
+    if (slugParam) {
+      whereConditions.push({ slug: { equals: slugParam } })
+    }
+    if (type) {
+      whereConditions.push({ type: { equals: type } })
+    }
+    if (category) {
+      // Category filter by slug: look up category first
+      const catResult = await payload.find({
+        collection: 'categories',
+        where: {
+          slug: { equals: category },
+          ...(tenantId ? { tenant: { equals: tenantId } } : {}),
+        },
+        locale: locale as 'de' | 'en',
+        limit: 1,
+      })
+      if (catResult.docs.length > 0) {
+        whereConditions.push({ categories: { contains: catResult.docs[0].id } })
+      }
+    }
+
+    const result = await payload.find({
+      collection: 'posts',
+      where: { and: whereConditions },
+      locale: locale as 'de' | 'en',
+      fallbackLocale: 'de',
       page,
       limit,
+      sort: '-publishedAt',
+      depth: slugParam ? 2 : 1,
     })
 
-    // Transform response
+    // Transform response — slug lookup returns full post, listing returns summary
     const response = {
-      docs: result.docs.map((post) => ({
-        id: post.id,
-        title: post.title,
-        slug: post.slug,
-        excerpt: post.excerpt || null,
-        publishedAt: post.publishedAt || null,
-        type: (post as typeof post & { type?: string }).type || 'blog',
-        featuredImage: post.featuredImage && typeof post.featuredImage === 'object'
-          ? {
-              url: post.featuredImage.url,
-              alt: post.featuredImage.alt,
-              width: post.featuredImage.width,
-              height: post.featuredImage.height,
-            }
-          : null,
-        category: Array.isArray(post.categories) && post.categories.length > 0
-          ? (() => {
-              const firstCat = post.categories.find(
-                (cat): cat is Category => cat !== null && typeof cat === 'object' && 'name' in cat
-              )
-              return firstCat ? { name: firstCat.name, slug: firstCat.slug } : null
-            })()
-          : null,
-        categories: Array.isArray(post.categories)
-          ? post.categories
-              .filter((cat): cat is Category => cat !== null && typeof cat === 'object' && 'name' in cat)
-              .map((cat) => ({ name: cat.name, slug: cat.slug }))
-          : [],
-      })),
+      docs: result.docs.map((post) => {
+        const base = {
+          id: post.id,
+          title: post.title,
+          slug: post.slug,
+          excerpt: post.excerpt || null,
+          publishedAt: post.publishedAt || null,
+          type: (post as typeof post & { type?: string }).type || 'blog',
+          featuredImage: post.featuredImage && typeof post.featuredImage === 'object'
+            ? {
+                url: post.featuredImage.url,
+                alt: post.featuredImage.alt,
+                width: post.featuredImage.width,
+                height: post.featuredImage.height,
+              }
+            : null,
+          category: Array.isArray(post.categories) && post.categories.length > 0
+            ? (() => {
+                const firstCat = post.categories.find(
+                  (cat): cat is Category => cat !== null && typeof cat === 'object' && 'name' in cat
+                )
+                return firstCat ? { name: firstCat.name, slug: firstCat.slug } : null
+              })()
+            : null,
+          categories: Array.isArray(post.categories)
+            ? post.categories
+                .filter((cat): cat is Category => cat !== null && typeof cat === 'object' && 'name' in cat)
+                .map((cat) => ({ name: cat.name, slug: cat.slug }))
+            : [],
+        }
+        // Include content and extra fields for detail queries (slug lookup)
+        if (slugParam) {
+          return { ...base, content: post.content, readingTime: (post as typeof post & { readingTime?: number }).readingTime }
+        }
+        return base
+      }),
       pagination: {
         page: result.page,
         limit,
@@ -140,8 +176,8 @@ export async function GET(request: NextRequest) {
         hasPrevPage: result.hasPrevPage,
       },
       filters: {
-        category,
-        type,
+        ...(category ? { category } : {}),
+        ...(type ? { type } : {}),
         locale,
         tenant: tenantId,
       },