build: app pins for MCP (#1845)

Author: anakin87

.github/workflows/mcp.yml

@@ -74,9 +74,16 @@ jobs:
       - name: Run tests
         run: hatch run cov-retry
 
+      - name: Run unit tests with lowest direct dependencies
+        run: |
+          hatch run uv pip compile pyproject.toml --resolution lowest-direct --output-file requirements_lowest_direct.txt
+          hatch run uv pip install -r requirements_lowest_direct.txt
+          hatch run test -m "not integration"        
+
       - name: Nightly - run unit tests with Haystack main branch
         if: github.event_name == 'schedule'
         run: |
+          hatch env prune
           hatch run uv pip install git+https://github.com/deepset-ai/haystack.git@main
           hatch run cov-retry -m "not integration"
 

integrations/mcp/pyproject.toml

@@ -28,7 +28,7 @@ classifiers = [
     "Programming Language :: Python :: Implementation :: CPython",
 ]
 dependencies = [
-    "mcp",
+    "mcp>=1.8.0",
     "haystack-ai>=2.13.0",
     "exceptiongroup",  # Backport of ExceptionGroup for Python < 3.11
     "httpx"  # HTTP client library used for SSE connections