Add resolver dependency injection for MCPServer tools (#2969)

Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com>

tests/server/mcpserver/test_server.py

@@ -1,5 +1,6 @@
 import base64
 from pathlib import Path
+from types import SimpleNamespace
 from typing import Any
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -1801,6 +1802,33 @@ async def test_report_progress_delegates_to_session_report_progress():
     mock_session.report_progress.assert_awaited_once_with(50, 100, "halfway")
 
 
+def _request_context(request: object | None) -> ServerRequestContext[None, object]:
+    return ServerRequestContext(
+        session=AsyncMock(),
+        method="tools/call",
+        lifespan_context=None,
+        protocol_version="2025-11-25",
+        request=request,
+    )
+
+
+def test_context_headers_returns_request_headers():
+    request = SimpleNamespace(headers={"x-github-user": "octocat"})
+    ctx = Context(request_context=_request_context(request), mcp_server=MagicMock())
+    assert ctx.headers == {"x-github-user": "octocat"}
+
+
+def test_context_headers_is_none_without_request():
+    ctx = Context(request_context=_request_context(None), mcp_server=MagicMock())
+    assert ctx.headers is None
+
+
+def test_context_headers_is_none_when_request_carries_no_headers():
+    """A transport may attach a custom request object that has no headers attribute."""
+    ctx = Context(request_context=_request_context(object()), mcp_server=MagicMock())
+    assert ctx.headers is None
+
+
 async def test_read_resource_template_error():
     """Template-creation failure must surface as INTERNAL_ERROR, not INVALID_PARAMS (not-found)."""
     mcp = MCPServer()