feat: add retrieve_file endpoint to get file content [LET-6188] (#7485)

* feat: add retrieve_file endpoint to get file content

* Restore package-lock.json to main

fern/openapi.json

@@ -3802,6 +3802,80 @@
         }
       }
     },
+    "/v1/folders/{folder_id}/files/{file_id}": {
+      "get": {
+        "tags": ["folders"],
+        "summary": "Retrieve File",
+        "description": "Retrieve a file from a folder by ID.",
+        "operationId": "retrieve_file",
+        "parameters": [
+          {
+            "name": "folder_id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string",
+              "minLength": 43,
+              "maxLength": 43,
+              "pattern": "^source-[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$",
+              "description": "The ID of the source in the format 'source-<uuid4>'",
+              "examples": ["source-123e4567-e89b-42d3-8456-426614174000"],
+              "title": "Folder Id"
+            },
+            "description": "The ID of the source in the format 'source-<uuid4>'"
+          },
+          {
+            "name": "file_id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string",
+              "minLength": 41,
+              "maxLength": 41,
+              "pattern": "^file-[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$",
+              "description": "The ID of the file in the format 'file-<uuid4>'",
+              "examples": ["file-123e4567-e89b-42d3-8456-426614174000"],
+              "title": "File Id"
+            },
+            "description": "The ID of the file in the format 'file-<uuid4>'"
+          },
+          {
+            "name": "include_content",
+            "in": "query",
+            "required": false,
+            "schema": {
+              "type": "boolean",
+              "description": "Whether to include full file content",
+              "default": false,
+              "title": "Include Content"
+            },
+            "description": "Whether to include full file content"
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Successful Response",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/FileMetadata"
+                }
+              }
+            }
+          },
+          "422": {
+            "description": "Validation Error",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/HTTPValidationError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/v1/folders/{folder_id}/{file_id}": {
       "delete": {
         "tags": ["folders"],

letta/server/rest_api/routers/v1/folders.py

@@ -470,6 +470,30 @@ async def list_files_for_folder(
     )
 
 
+@router.get("/{folder_id}/files/{file_id}", response_model=FileMetadata, operation_id="retrieve_file")
+async def retrieve_file(
+    folder_id: FolderId,
+    file_id: FileId,
+    include_content: bool = Query(False, description="Whether to include full file content"),
+    server: "SyncServer" = Depends(get_letta_server),
+    headers: HeaderParams = Depends(get_headers),
+):
+    """
+    Retrieve a file from a folder by ID.
+    """
+    actor = await server.user_manager.get_actor_or_default_async(actor_id=headers.actor_id)
+
+    # NoResultFound will propagate and be handled as 404 by the global exception handler
+    file_metadata = await server.file_manager.get_file_by_id(
+        file_id=file_id, actor=actor, include_content=include_content, strip_directory_prefix=True
+    )
+
+    if file_metadata.source_id != folder_id:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=f"File with id={file_id} not found in folder {folder_id}")
+
+    return file_metadata
+
+
 # @router.get("/{folder_id}/files/{file_id}", response_model=FileMetadata, operation_id="get_file_metadata")
 # async def get_file_metadata(
 #    folder_id: str,