[rafikk]

Bazel adds every declared output directory (tree artifact) to the input root as an empty directory (bazelbuild/bazel#15366, MerkleTreeComputer). In actiondfs_strict mode outputs are collected from the stage only, so an output directory the action never writes into is silently skipped and Bazel fails with mandatory output <path> was not created.

This breaks rules_go's nogo on every package: RunNogo declares a <pkg>_nogo directory that it only writes into when an analyzer suggests fixes.

Per the REAPI spec, ActionResult.output_directories must contain an entry for each requested output directory that "existed after the action completed", so the empty directory should be returned. BuildBuddy and Buildbarn both do this because they collect outputs from the merged input/output tree.

Change

• OutputParentValidator.validate now walks the full output path and reports whether the path itself is a directory in the input root. Parent conflict checks (input file/symlink as an output parent) are unchanged.
• In strict mode, validateOutputParentsAgainstInputsWithCancellation collects those paths during the existing validation pass, and they are created in the stage before execution. actiondfs already merges staged and input directories, so the action's view is unchanged, and the directory is now collected like any other staged output.
• Output directories that are not in the input root are still not created, so this keeps the spec's "parents only" rule and the existing prepareOutputParents test.
• Overlay mode (mutates_inputs) is unaffected; its collection path already sees input directories.