refactor: extract shared flattenArtifactTree helper to remove duplicate flatten logic

[Copilot]

Three functions in pkg/cli/logs_download.go (flattenUnifiedArtifact, flattenActivationArtifact, flattenAgentOutputsArtifact) contained ~150 lines of near-identical walk → move → cleanup code, making any behavioral fix a triple-apply problem.

Changes

• New helper flattenArtifactTree(sourceDir, artifactDir, outputDir, label string, verbose bool) error — encapsulates the filepath.Walk traversal, os.MkdirAll/os.Rename per entry, and warn-only os.RemoveAll cleanup; label drives all log and user-facing messages
• flattenUnifiedArtifact — retains old/new structure detection (tmp/gh-aw prefix check), then delegates with sourceDir != artifactDir when the old layout is present
• flattenActivationArtifact / flattenAgentOutputsArtifact — reduced to path resolution + single delegate call
• New tests for flattenArtifactTree in logs_flatten_test.go covering: basic move, nested dirs, detached sourceDir/artifactDir (old-structure case), empty source, multiple files, verbose mode

// Before: ~50 lines each, copy-pasted 3×
func flattenActivationArtifact(outputDir string, verbose bool) error {
    activationDir := findArtifactDir(outputDir, "activation", "")
    // ... 45 lines of walk/move/cleanup ...
}

// After: meaningful logic only
func flattenActivationArtifact(outputDir string, verbose bool) error {
    activationDir := findArtifactDir(outputDir, "activation", "")
    if activationDir == "" {
        return nil
    }
    logsDownloadLog.Printf("Flattening activation artifact directory: %s", activationDir)
    return flattenArtifactTree(activationDir, activationDir, outputDir, "activation artifact", verbose)
}

[Copilot]

Pull request overview

This PR refactors artifact-flattening in the logs download flow by extracting the shared walk/move/cleanup logic into a single helper, reducing duplication and adding direct unit tests for the helper.

Changes:

• Added flattenArtifactTree(...) helper to centralize traversal, file moves, and cleanup for artifact directories.
• Updated unified/activation/agent_outputs flatteners to delegate to the shared helper (while preserving unified old/new structure detection).
• Added focused unit tests for flattenArtifactTree covering common flatten scenarios.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pkg/cli/logs_download.go	Extracts shared flatten logic into flattenArtifactTree and updates callers to use it.
pkg/cli/logs_flatten_test.go	Adds direct unit tests for flattenArtifactTree and introduces testify assertions for the new cases.

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