feat: Enable SSE transport for mcp service and update test fixtures

Changes:
- Remove streamable-http transport override from mcp service in docker-compose.yml
- Service now uses CLI default SSE transport on /sse endpoint
- Add create_mcp_client_session_sse() helper for SSE connections
- Update nc_mcp_client fixture to use SSE transport
- Fix unpacking for SSE client (yields 2 values vs 3 for streamable-http)

Testing:
- All 4 smoke tests pass with SSE transport
- 32/34 affected tests pass (2 skipped for vector sync)
- OAuth services remain on streamable-http (unchanged)

Note: SSE transport is being deprecated in favor of streamable-http.
This enables minimal validation testing before deprecation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docker-compose.yml

@@ -69,7 +69,6 @@ services:
 
   mcp:
     build: .
-    command: ["--transport", "streamable-http"]
     restart: always
     depends_on:
       app:

tests/conftest.py

@@ -9,6 +9,7 @@ import pytest
 from httpx import HTTPStatusError
 from mcp import ClientSession
 from mcp.client.session import RequestContext
+from mcp.client.sse import sse_client
 from mcp.client.streamable_http import streamablehttp_client
 from mcp.types import ElicitRequestParams, ElicitResult, ErrorData
 
@@ -165,6 +166,51 @@ async def create_mcp_client_session(
     logger.debug(f"{client_name} client session cleaned up successfully")
 
 
+async def create_mcp_client_session_sse(
+    url: str,
+    token: str | None = None,
+    client_name: str = "MCP",
+    elicitation_callback: Any = None,
+) -> AsyncGenerator[ClientSession, Any]:
+    """
+    Factory function to create an MCP client session using SSE transport.
+
+    Similar to create_mcp_client_session but uses SSE transport instead of streamable-http.
+    Uses native async context managers to ensure correct LIFO cleanup order.
+
+    Args:
+        url: MCP server URL (e.g., "http://localhost:8000/sse")
+        token: Optional OAuth access token for Bearer authentication
+        client_name: Client name for logging (e.g., "Basic MCP (SSE)")
+        elicitation_callback: Optional callback for handling elicitation requests
+
+    Yields:
+        Initialized MCP ClientSession
+
+    Note:
+        SSE transport is being deprecated in favor of streamable-http.
+        This function exists for compatibility testing only.
+    """
+    logger.info(f"Creating SSE client for {client_name}")
+
+    # Prepare headers with OAuth token if provided
+    headers = {"Authorization": f"Bearer {token}"} if token else None
+
+    # Use native async with - Python ensures LIFO cleanup
+    # Cleanup order will be: ClientSession.__aexit__ -> sse_client.__aexit__
+    # Note: sse_client yields only (read_stream, write_stream), not 3 values like streamablehttp_client
+    async with sse_client(url, headers=headers) as (read_stream, write_stream):
+        async with ClientSession(
+            read_stream, write_stream, elicitation_callback=elicitation_callback
+        ) as session:
+            await session.initialize()
+            logger.info(f"{client_name} client session initialized successfully")
+            yield session
+
+    # Cleanup happens automatically in LIFO order - no exception suppression needed
+    logger.debug(f"{client_name} client session cleaned up successfully")
+
+
 @pytest.fixture(scope="session")
 async def nc_client(anyio_backend) -> AsyncGenerator[NextcloudClient, Any]:
     """
@@ -203,12 +249,14 @@ async def nc_client(anyio_backend) -> AsyncGenerator[NextcloudClient, Any]:
 @pytest.fixture(scope="session")
 async def nc_mcp_client(anyio_backend) -> AsyncGenerator[ClientSession, Any]:
     """
-    Fixture to create an MCP client session for integration tests using streamable-http.
+    Fixture to create an MCP client session for integration tests using SSE transport.
 
     Uses anyio pytest plugin for proper async fixture handling.
+
+    Note: SSE transport is being deprecated. This fixture uses SSE for compatibility testing.
     """
-    async for session in create_mcp_client_session(
-        url="http://localhost:8000/mcp", client_name="Basic MCP"
+    async for session in create_mcp_client_session_sse(
+        url="http://localhost:8000/sse", client_name="Basic MCP (SSE)"
     ):
         yield session