Add resolver dependency injection for MCPServer tools (#2969)

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

docs_src/elicitation/tutorial004.py

@@ -0,0 +1,47 @@
+from typing import Annotated
+
+from pydantic import BaseModel
+
+from mcp.server import MCPServer
+from mcp.server.mcpserver import (
+    AcceptedElicitation,
+    CancelledElicitation,
+    DeclinedElicitation,
+    Elicit,
+    ElicitationResult,
+    Resolve,
+)
+
+mcp = MCPServer("Files")
+
+_FOLDERS: dict[str, list[str]] = {"/tmp/empty": [], "/tmp/project": ["main.py", "README.md"]}
+
+
+class Confirm(BaseModel):
+    ok: bool
+
+
+async def confirm_delete(path: str) -> Confirm | Elicit[Confirm]:
+    """Resolver: ask for confirmation only when the folder is not empty."""
+    file_count = len(_FOLDERS.get(path, []))
+    if file_count == 0:
+        return Confirm(ok=True)  # nothing to confirm, no round-trip to the client
+    return Elicit(f"{path} has {file_count} file(s). Delete anyway?", Confirm)
+
+
+@mcp.tool()
+async def delete_folder(
+    path: str,
+    confirm: Annotated[ElicitationResult[Confirm], Resolve(confirm_delete)],
+) -> str:
+    """Delete a folder, asking for confirmation when it is not empty."""
+    match confirm:
+        case AcceptedElicitation(data=Confirm(ok=True)):
+            _FOLDERS.pop(path, None)
+            return f"deleted {path}"
+        case AcceptedElicitation():
+            return "kept the folder"
+        case DeclinedElicitation():
+            return "declined: folder not deleted"
+        case CancelledElicitation():
+            return "cancelled: folder not deleted"