Verify the Step D baseline still launches after the environment mutations
we may have caused during the E bisection (docker image rebuild, tauri-cli
version drift, etc). Build.rs is now byte-identical to commit a852cad
(Step D) except for the git hash capture block that already existed at
that point.
If this launches cleanly → the cpp_smoke addition genuinely breaks
something, bisection continues.
If this crashes → the environment regressed between Step D and now,
and we need to rebuild the docker image to an earlier snapshot.
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