ci: cache pnpm store instead of node_modules to avoid stale server state

Caching node_modules directly caused postinstall hooks (e.g. prisma
generate) to be skipped, leading to stale generated artifacts that
didn't match the current langfuse-server schema. Cache the pnpm store
instead so installs are still fast but hooks run properly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wochinge

.github/workflows/ci.yml

@@ -81,21 +81,26 @@ jobs:
           version: 10.33.0
 
       - name: Clone langfuse server
+        id: clone-server
         run: |
-          git clone https://github.com/langfuse/langfuse.git ./langfuse-server && echo $(cd ./langfuse-server && git rev-parse HEAD)
+          git clone https://github.com/langfuse/langfuse.git ./langfuse-server
+          echo "sha=$(cd ./langfuse-server && git rev-parse HEAD)" >> "$GITHUB_OUTPUT"
 
       - name: Setup node (for langfuse server)
         uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6.3.0
         with:
           node-version: 24
 
-      - name: Cache langfuse server dependencies
+      # Cache the pnpm store (download cache) instead of node_modules directly.
+      # Caching node_modules skips postinstall hooks (e.g. prisma generate),
+      # which leads to stale generated artifacts that don't match the current schema.
+      - name: Cache pnpm store
         uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5
         with:
-          path: ./langfuse-server/node_modules
-          key: |
-            langfuse-server-${{ hashFiles('./langfuse-server/package-lock.json') }}
-            langfuse-server-
+          path: ~/.local/share/pnpm/store/v3
+          key: pnpm-store-${{ steps.clone-server.outputs.sha }}
+          restore-keys: |
+            pnpm-store-
 
       - name: Run langfuse server
         run: |