A pull_request run of free-tests.yml reuses a green push or dispatch run on main, or a dispatch run on its own branch, at the merge commit's exact tree, only when the merge commit leaves the workflow, scripts/ci-tree-reuse.ts and lib/run-evidence.ts byte-identical to main. A pull_request run is never a source. Opt-in per workflow with find --pull-request; windows-free-tests.yml is unchanged.
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