StreamingBenchmark: testMemoryUsageWith2MBChunk peaks ~213MB vs 70MB assertion (flaky in test job)

[arkavo-com]

Summary

StreamingBenchmarkTests.testMemoryUsageWith2MBChunk asserts peak memory < 70 MB when streaming-encrypting a 50 MB file in 2 MB chunks, but actual peak is ~213 MB — over 3× the threshold. The test fails deterministically locally and is environment-flaky in CI's test job.

Evidence

OpenTDFKitTests/StreamingBenchmarkTests.swift:156

XCTAssertLessThan(peakMemory, Int64(70 * 1024 * 1024), "Peak memory should be less than 70MB for 50MB file")
// XCTAssertLessThan failed: ("213483520") is not less than ("73400320")

• Fails in both debug and release (swift test and swift test -c release) → not a debug-only artifact.
• Pre-existing: reproduces identically on 77920b3 (predates the ConnectRPC work in feat(kas)!: ConnectRPC transport + well-known discovery (CWT) #39).
• Flaky in CI: the test job runs all tests in debug, including this benchmark; it has passed some CI runs and failed others depending on memory-measurement timing.

Why it matters

1. A perpetually-/intermittently-red test job hides real regressions. This (together with a now-fixed stale unwrap test) kept the test check red on main from 2026-03-20, which masked other failures.
2. It may indicate a real memory inefficiency — a streaming encryptor processing 2 MB chunks of a 50 MB file should not need to hold ~213 MB resident. Worth confirming whether TDFEncryptor.encryptFile is buffering more than it should (e.g. holding the whole input/output in memory) rather than truly streaming.

Proposed remediation (pick per investigation)

• Investigate TDFEncryptor.encryptFile peak memory for chunked input. If it's genuinely buffering the whole file, fix the streaming path (the real win). If ~213 MB is expected/acceptable, recalibrate the assertion to a realistic, stable bound.
• Move the benchmark suites (*BenchmarkTests) out of the default test job so test is deterministic — they already have a dedicated benchmark job (release). Memory/timing assertions don't belong in the correctness gate.

Repro

swift test --filter "StreamingBenchmarkTests/testMemoryUsageWith2MBChunk"
swift test -c release --filter "StreamingBenchmarkTests/testMemoryUsageWith2MBChunk"

Surfaced while getting CI green for #39.