fix: use sha256 descriptor digest and keep operator errors fully sanitized

backend/src/workspaces/preprocessing-service.ts

@@ -129,8 +129,7 @@ export class WorkspacePreprocessingService {
           { kind: "runtime_config", digest: runtime.configLease.configDigest },
         ],
       });
-    } catch (error) {
-      const detail = error instanceof Error ? error.message : String(error);
+    } catch {
       return {
         schemaVersion: 1,
         status: "failed",
@@ -140,7 +139,6 @@ export class WorkspacePreprocessingService {
         descriptorBlob: "",
         operation: "inspect",
         completedStages: [],
-        warnings: detail.length > 0 ? [detail.slice(0, 512)] : undefined,
       };
     }
   }