test(brc105): fix ~1/256 flaky nonce-tamper test (red 3.12 shard)#2
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test_tampered_nonce_rejected built the tampered nonce as "ff" + nonce[2:], which is a no-op when the random first byte was already 0xff (~1/256), so the unmodified nonce verified and the test failed. This is what failed the 3.12 shard on master (135/136), not the brc105 lazy-import change. Flip the first byte via XOR 0xff so it always differs. Verified: old logic = 7 false-passes / 2560 runs; new logic = 0 / 600; full suite 136 passed. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
Makes
test_tampered_nonce_rejecteddeterministic. It built the tampered nonce as"ff" + nonce[2:], which is a no-op when the random first byte is already 0xff (~1/256). In that case the unmodified, still-valid nonce verifies and the test fails.Why this matters
This is the actual cause of the red 3.12 shard on master (135/136 passed, only
TestNonceManager::test_tampered_nonce_rejectedfailed) — not the brc105 lazy-import change in #1, whose middleware tests all pass. The HMAC verification innonce.pyis correct; only the test's tampering was non-deterministic.Fix
Flip the first byte with
^ 0xffso it always changes regardless of value.Verification
🤖 Generated with Claude Code