- P2 (greptile): anchor the changed-test existence check at the git repo root
(repoRootForExistence via `git rev-parse --show-toplevel`) instead of rootDir,
so a script run from a package subdir without FUSION_PROJECT_DIR no longer
forms a doubled path and silently drops live tests into the delegate path.
+1 regression test (default root resolves to repo root).
- coderabbit: fix stale "1-worker lane" wording in the delegation log (now
"heavy memory-envelope lane") and the "single-worker envelope" test title,
both stale after the 1->4 worker change.
test-changed 118/118, eslint clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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