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PowerShell 5.1 `Out-File -Encoding utf8` prepends a UTF-8 BOM. The act_runner GITHUB_OUTPUT parser then read the key as "artifact-path", so steps.invoke-ci.outputs.artifact-path resolved empty. Combined with the trailing backslash, the upload path became "\" -> the F: drive root, causing upload-artifact to ingest the entire drive (hundreds of GB of unrelated files). - Append outputs with UTF8Encoding($false) (no BOM). - Throw if artifactPath is empty instead of emitting nothing. - Drop the trailing backslash; use /*.log for the diagnostic glob. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>