[codex] Harden DiffScope review operations #409

Job	Run time
cargo-deny (advisories + licenses)	24s
Coverage (llvm-cov)	1m 27s
test (ubuntu-latest)	1m 24s
test (windows-latest)	3m 19s
security	23s
lint	1m 17s
mutation	15m 17s
version	3s
test (macos-latest)	1m 42s
	25m 16s

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