TestSealOpenRoundtrip scanned the whole ~36-byte sealed frame for the
plaintext with bytes.Contains(sealed, pt). For the 1-byte case ("x"),
any of the ~29 random bytes (nonce+ciphertext+tag) equalling that byte
tripped the assertion, so it failed ~11% of runs (1-(255/256)^29).
Living on main, that spuriously failed ~11% of CI runs.
Replace the probabilistic per-byte scan with a deterministic check that
the sealed frame is never the bare plaintext (it always carries the
header+nonce+tag, so it differs in both length and content). The
round-trip Open(Seal(x)) == x assertion is unchanged. Verbatim-leak
coverage already lives deterministically in TestNoPlaintextLeak, which
uses a multi-byte marker where a chance match is negligible.
Test-only change; no production code touched.
Verified: go test ./internal/crypto/... -count=100 passes; the
previously-flaky test passes 500 consecutive runs; go vet ./... clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
JMR-devandClaude Opus 4.8