{"record":{"id":"640a4ac88182efb2","repo":"dagger/dagger","slug":"load-dth-value-from-t-reconstruct-result-w","errorCode":null,"errorMessage":"load %dth value from %T: reconstruct result: %w","messagePattern":"load (.+?)th value from %T: reconstruct result: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"dagql/cache.go","lineNumber":2945,"sourceCode":"\t\tsrv := CurrentDagqlServer(ctx)\n\t\tif srv == nil {\n\t\t\treturn nil, fmt.Errorf(\"load %dth value from %T: missing dagql server in context\", nth, self)\n\t\t}\n\t\tclientMetadata, err := engine.ClientMetadataFromContext(ctx)\n\t\tif err != nil {\n\t\t\treturn nil, fmt.Errorf(\"load %dth value from %T: current client metadata: %w\", nth, self, err)\n\t\t}\n\t\tif clientMetadata.SessionID == \"\" {\n\t\t\treturn nil, fmt.Errorf(\"load %dth value from %T: empty session ID\", nth, self)\n\t\t}\n\t\tcache, err := EngineCache(ctx)\n\t\tif err != nil {\n\t\t\treturn nil, fmt.Errorf(\"load %dth value from %T: current dagql cache: %w\", nth, self, err)\n\t\t}\n\t\ttouchSharedResultLastUsed(childShared, time.Now().UnixNano())\n\t\tretResAny, err := wrapSharedResultWithResolver(ctx, childShared, true, srv)\n\t\tif err != nil {\n\t\t\treturn nil, fmt.Errorf(\"load %dth value from %T: reconstruct result: %w\", nth, self, err)\n\t\t}\n\t\tif err := cache.trackSessionResult(ctx, clientMetadata.SessionID, retResAny, true); err != nil {\n\t\t\treturn nil, fmt.Errorf(\"load %dth value from %T: claim cache-backed result: %w\", nth, self, err)\n\t\t}\n\t\treturn retResAny, nil\n\t}\n\n\tsrv := CurrentDagqlServer(ctx)\n\tif srv == nil {\n\t\treturn nil, fmt.Errorf(\"load %dth value from %T: missing dagql server in context\", nth, self)\n\t}\n\tif parentCall.Type == nil || parentCall.Type.Elem == nil {\n\t\treturn nil, fmt.Errorf(\"cannot get %dth value from %T without element type\", nth, self)\n\t}\n\treq := &CallRequest{\n\t\tResultCall: parentCall.fork(),\n\t}\n\treq.Type = req.Type.Elem.clone()","sourceCodeStart":2927,"sourceCodeEnd":2963,"githubUrl":"https://github.com/dagger/dagger/blob/82ba2681dbe30d3547a1dc50ea495900ab5b6047/dagql/cache.go#L2927-L2963","documentation":"Result[T].NthValue (dagql/cache.go:2945) fails at the last rehydration step: wrapSharedResultWithResolver is called to rebuild a live result (rebinding the resolver) from the stored shared result. Any failure inside that reconstruction — decoding the stored result, missing type/resolver registration, or an internal dagql error — is surfaced wrapped as 'reconstruct result'.","triggerScenarios":"wrapSharedResultWithResolver errors while re-wrapping a cache-backed shared result during NthValue: corrupt/evicted cache entry read mid-decode, result type whose resolver registration is missing on this build, or an internal error in the server's wrap path.","commonSituations":"Cache entries touched concurrently with GC/reaping (session released mid-load); engine binary mix where old cached entries reference types not registered after an upgrade/downgrade; genuinely corrupt engine cache state on disk.","solutions":["Retry the operation with a fresh session — if the entry was reaped mid-load, the new call recreates the result normally.","Restart/clear the engine cache if entries are persistently corrupt (delete the engine cache data directory), then rerun.","Ensure all DAG types/resolvers are registered on the server before any results can be reconstructed (complete object registration at server setup).","Align engine versions between components so cached entries match the current schema/type registrations; check dagql server setup for missing Register calls."],"exampleFix":"// before\n// types registered lazily/late; cached results may resolve before Register happens\nserver := dagql.New(ctx, dagql.CacheConfig{})\n\n// after\nserver := dagql.New(ctx, dagql.CacheConfig{})\ncore.RegisterTypes(ctx, server) // register everything up-front","handlingStrategy":"retry","validationCode":"// ensure types are registered before resolving cached results\nfunc serverReady(ctx context.Context, srv *dagql.Server) error {\n\t// registration happens at startup; here just verify ctx inputs\n\tif _, err := engine.ClientMetadataFromContext(ctx); err != nil {\n\t\treturn err\n\t}\n\tif _, err := EngineCache(ctx); err != nil {\n\t\treturn err\n\t}\n\treturn nil\n}","typeGuard":"func isReconstructionError(err error) bool {\n\treturn err != nil && strings.Contains(err.Error(), \"reconstruct result\")\n}","tryCatchPattern":"val, err := listResult.NthValue(ctx, nth)\nif err != nil {\n\tif isReconstructionError(err) {\n\t\t// likely a reaped/racing entry: retry with a fresh call/session\n\t\treturn retryNthValueWithFreshSession(ctx, listResult, nth)\n\t}\n\treturn nil, err\n}","preventionTips":["Retry once with a fresh session on reconstruction errors — transient reaping races self-heal.","Register all DAG types/resolvers at server startup, never lazily after results exist.","Keep engine versions consistent across components so cached entries match current schemas.","If errors persist, clear the engine cache data directory to purge corrupt entries."],"tags":["dagql","cache","result-reconstruction","serialization"],"backgroundTag":"cache-result-reconstruction-failed","analyzedSha":"82ba2681dbe30d3547a1dc50ea495900ab5b6047","analyzedAt":"2026-09-05T07:21:37.930Z","contentChangedAt":"2026-09-05T07:21:37.930Z","schemaVersion":2},"datasetVersion":"2026-09-12T12:17:11.808Z"}