{"record":{"id":"b6905ba823b7103c","repo":"mvanhorn/last30days-skill","slug":"engine-write-sentinel-w","errorCode":null,"errorMessage":"engine: write sentinel: %w","messagePattern":"engine: write sentinel: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"mcp/internal/engine/extract.go","lineNumber":89,"sourceCode":"func ensureLocked(src fs.FS, cacheDir, version string) error {\n\tif sentinelMatches(cacheDir, version) {\n\t\treturn nil\n\t}\n\ttmpDir := cacheDir + \".tmp\"\n\tif err := os.RemoveAll(tmpDir); err != nil {\n\t\treturn fmt.Errorf(\"engine: clean tmp cache: %w\", err)\n\t}\n\tif err := os.MkdirAll(tmpDir, 0o755); err != nil {\n\t\treturn fmt.Errorf(\"engine: create tmp cache (%s, set %s to override): %w\", tmpDir, CacheEnvOverride, err)\n\t}\n\tif err := extractAll(src, tmpDir); err != nil {\n\t\t_ = os.RemoveAll(tmpDir)\n\t\treturn err\n\t}\n\tsentinel := filepath.Join(tmpDir, SentinelFilename)\n\tif err := os.WriteFile(sentinel, []byte(version), 0o644); err != nil {\n\t\t_ = os.RemoveAll(tmpDir)\n\t\treturn fmt.Errorf(\"engine: write sentinel: %w\", err)\n\t}\n\tif err := os.RemoveAll(cacheDir); err != nil {\n\t\t_ = os.RemoveAll(tmpDir)\n\t\treturn fmt.Errorf(\"engine: clean old cache: %w\", err)\n\t}\n\tif err := os.Rename(tmpDir, cacheDir); err != nil {\n\t\t_ = os.RemoveAll(tmpDir)\n\t\treturn fmt.Errorf(\"engine: promote tmp cache: %w\", err)\n\t}\n\treturn nil\n}\n\nfunc sentinelMatches(cacheDir, version string) bool {\n\tdata, err := os.ReadFile(filepath.Join(cacheDir, SentinelFilename))\n\tif err != nil {\n\t\treturn false\n\t}\n\treturn string(data) == version","sourceCodeStart":71,"sourceCodeEnd":107,"githubUrl":"https://github.com/mvanhorn/last30days-skill/blob/c7460f6114449ddfe6ea3fc2f23c3d910c0e740c/mcp/internal/engine/extract.go#L71-L107","documentation":"Error \"engine: write sentinel: %w\" thrown in mvanhorn/last30days-skill.","triggerScenarios":"Fires when the engine cannot write the sentinel marker file into the freshly extracted cache, usually a permissions or filesystem error in the cache directory.","commonSituations":"See trigger scenarios.","solutions":["Check write permissions on the temporary cache directory and retry.","Free disk space if the filesystem is full; the sentinel write is tiny, so failure usually means a full or read-only filesystem."],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"c7460f6114449ddfe6ea3fc2f23c3d910c0e740c","analyzedAt":"2026-08-15T03:34:49.540Z","schemaVersion":2},"datasetVersion":"2026-08-15T22:17:37.221Z"}