I build checks that can fail, and I try to keep what I claim under what I can show.

Receipts first — the externally-checkable parts, and their status:

• mutmut#546 · merged — a branch nothing in that mutation tester mutated; the fix was accepted upstream.
• nox#1153 · merged — an environment-dependent test failure; the fix was accepted upstream.
• StringZilla#328 · wrapt#347 · fixed upstream — two reproduced free-threading crashes their maintainers fixed (1831ccb; 2.4.0.dev3, which I re-measured at the maintainer's request: 10/10 SIGSEGV → 0/10). Neither fix is mine.
• Pillow#9854 · python-rapidjson#235 · open, unreviewed — my own fixes for two of the others; the rapidjson one after its maintainer asked for help.
• tree#143 · confluent-kafka-python#2319 · open, no response — reproduced free-threading use-after-frees, untouched.
• private work · not publicly claimable — judge me on the lines above, not on what I say is behind the wall.

The rest of this page is the longer version of those lines.

That sounds like a slogan, so here is what it costs. The robot below won its contest and I published the source unmodified, with the bug still in it and a note on why it stays. The audit pipeline in my own public repo turned out to emit hardcoded scores — composite: 8.2, recommendation: ACCEPT, computed from nothing — so I deleted it instead of repairing it, because repairing it would have turned a red X into a green badge certifying invented numbers.

firing-checks · Small checks that prove they can fail.

A guardrail nobody has seen fire is theater. The usual failure isn't a missing test — it's a check that reports clean because it silently couldn't run: a parser that returned an empty list, a subprocess whose exit code got dropped, a predicate never reached. Each tool ships negative controls that construct the violation and assert rejection; --selftest runs them. Three tools, and the third enforces that contract over the other two — and over itself, registered in its own registry with no exemption for the enforcer. It counts the control lines a run printed rather than trusting the summary a script writes about itself. No dependencies, Python 3.10+, each file standalone.

free-threading-memory-safety · Six reproduced crashes in free-threaded CPython C extensions, and the denominator.

Every finding is a minimal reproducer plus three controls — no mutator, a decoy object, and the same test with the GIL on — so what is shown is a free-threading fault rather than a generic race. Before each disclosure I checked the target's whole issue and PR tracker, the diffs of anything open near the code, and the current source, because a finding that already exists is noise. Two are fixed upstream, two have my fix PRs open, two have had no reply, and the page says so in those words. It also carries the bounded claim I drew about where these crashes concentrate — and the later pre-registered work that falsified it, along with the four detection axes that found nothing.

scanner-false-negatives · A pre-registered study that refuted its own hypothesis, twice.

I built a scanner, hypothesized where its false negatives cluster, and designed the test so it could kill the claim rather than confirm it. It did — the naive version on Bandit, and the successor on semgrep, using a discipline rating of each layer sealed before any defect was classified, so the concordance could not be circular. All 61 labels are published so a stranger can re-grade them. Exploratory: one grader, no inter-rater agreement yet, and the topic is not new — the limits and prior art are on the page.

WarmLogic-OSS · Evidence-centric governance tooling — public subset.

An evaluation harness where a run produces a manifest, a decision log, and a verify report, and verification refuses a run whose stored verdict its own event log does not support. Toy workloads; the refusal is real and one shipped run triggers it.

xinrui-robot-2023 · 1st place, 7th Xinrui Innovation Robotics Contest — HIT, May 2023.

Team 21, out of 20 teams and ~90 participants. Freshman year, four of us from four countries. Two Arduino boards split by concern, joined over serial. The source is published exactly as it ran, including a bug, with the reasoning for leaving it there. Match report (university, third-party record).

Elsewhere. Three patches to projects I do not own: two merged, one closed — and the closed one's maintainer had a better reason than my patch.

mutmut#546 — merged. A ternary is a branch nothing in that mutation tester mutated, and branch coverage cannot see an uncovered arm either, so an untested arm read as a pass twice over. Two mutants per ternary now force it down each side. The review on an earlier attempt had asked to drop the precedence wrapping; that is right for or True and wrong for and False, because and binds tighter than a top-level or — over all 16 assignments of a if b or c else d, the unwrapped form differs from the original on 2 of 16 rather than 6, and only when b is falsy, i.e. a mutant tests mostly cannot kill. I brought the table rather than the opinion. Closes their #196.

nox#1153 — merged. Their uv download tests failed on a machine without uv installed. +15/-0.

PyO3#5774 — closed, and rightly. A Vec<u8> fast path for u8-compatible buffer exporters. The maintainer's reason was better than my patch: there is no guarantee the exporting buffer is properly synchronized, so that choice belongs to user code rather than to the extraction impl. CodSpeed also measured an 11.6% regression. Worth the round trip, and it stays on this list — a record that only shows the accepted ones is not a record.

Free-threading (no-GIL) memory safety. Two use-after-free reports in C extensions, each with a minimal reproducer and three controls — no-mutator, decoy, and GIL-on — so the crash is shown to be a free-threading fault, not a generic race.

google-deepmind/tree#143 — a borrowed dict key from PyDict_Next is dereferenced across __hash__/__eq__ in assert_same_structure; 10/10 SIGSEGV, and live by default because pybind11 declares the module no-GIL-safe when it is not.

confluentinc/confluent-kafka-python#2319 — a borrowed NewTopic list item is cast to a C struct and its fields read against a stale count; 10/10 SIGSEGV with the GIL forced off, and latent until the module opts into free-threading — the GIL-on control stays clean, and the report leads with that rather than overstating. The scanner that surfaced these is a static tool I wrote; a general release is deliberately withheld.

Most of my work is in private repositories, and it stays private — so I will not dress it up as an accomplishment here. A claim you cannot check is exactly the thing this profile is about not making. Judge me on the public evidence: the reproducers, the negative controls, and the labels published for re-grading.

Reach me at espressolee1@gmail.com. It is in the sidebar too, but GitHub shows a profile email only to signed-in visitors, so it is repeated here where everyone can read it.