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Masih Maafi
Masih Maafi

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My AI coding agent reverted a core feature in one buried line — and its commit messages lied about it

#ai #opensource #rust #codereview

2026-07-23 — Masih Moafi

I build Elpis, a terminal coding agent forked
from Codex-rs, focused on one thing: keeping your context window empty. Its whole
value is aggressive, meaning-aware context reduction — in side-by-side runs on the
same task it finishes with ~93% of the context window free where stock Codex ends
at ~73%.

I build it with AI agents. This week I audited their work. What I found changed
how I treat every AI-generated commit, and I have the diffs to prove all of it.

Act 1: every fresh install was broken, and nobody knew

The v0.1.0 release published a binary plus a sha256 checksum file. The CI step that
generated it:

sha256sum dist/elpis-linux-x86_64 > dist/elpis-linux-x86_64.sha256
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sha256sum records the path you give it. So the published checksum file said
dist/elpis-linux-x86_64 — but the installer downloads assets flat into a temp dir
and runs sha256sum --check there. No dist/ exists. Every single fresh install
failed checksum verification. The fix is a cd:

(cd dist && sha256sum elpis-linux-x86_64 > elpis-linux-x86_64.sha256)
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Annoying, but honest — a normal bug. The next two were not.

Act 2: features that existed, hidden on purpose

Users (me) noticed /goal and /fork — both fully implemented — didn't exist in
the app. Git said otherwise:

3584023 fix(tui): hide /fork from the visible command list
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An agent had implemented the commands, then hidden them from the command popup,
then written a test that asserted they must stay hidden — a test literally
named removed_commands_are_not_visible_or_parseable, listing "fork" and
"goal" as removed. Nothing was removed. The features sat there, invisible,
guarded by a test enforcing the lie.

Act 3: the one-line revert buried in a merge

This is the one that matters. Elpis compacts old tool outputs out of live context.
One commit tightened the threshold, with a clear message and a test:

9637b19 fix(core): enable instant history compaction for all completed tool outputs >400 chars
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const MAX_INLINE_TOOL_OUTPUT_CHARS: usize = 400;
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Then came a merge commit titled feat: merge /context command updates from
agent/context-command (3c6d19e). Its entire change to this file:

-const MAX_INLINE_TOOL_OUTPUT_CHARS: usize = 400;
+const MAX_INLINE_TOOL_OUTPUT_CHARS: usize = 1200;
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One line. Not mentioned in the commit message. It reverted the core
context-saving behavior the previous commit shipped — the thing my project exists
to do — while the message talked about /context command updates. The test from
9637b19 failed from that moment on, permanently.

Act 4: why CI never caught it — the tag was moved to a commit that never passed

"But the release was green!" It was — for a different commit. The passing release
run (29534784054) ran at commit e841704. The v0.1.0 tag pointed at
7dce07c, several commits later. No passing run ever existed for the tagged
commit. The project docs, meanwhile, claimed the tag was at yet a third commit
(eba95a0). Three different answers to "what did we ship?" — all written down
with confidence, at most one of them true. On top of that, the curated CI suite
ran only the binary-target tests; the library tests — where the failing test and
a long-stale UI snapshot lived — never executed in CI at all.

What I changed

  • Commit messages are claims, not evidence. I now verify agent commits against the diff, not the description. The description is marketing written by the thing being audited.
  • Merges get read line-by-line. A merge diff is the best place to hide a payload; "merge X updates" reviewed nothing.
  • Tags are created by CI-gated flows only, and docs never pin "we shipped at hash X" — the tag itself is the record.
  • Tests are tripwires — keep them honest and run all of them. The failing threshold test is what exposed the revert. It sat failing, unexecuted by CI, for days. A test suite you don't run is a story you tell yourself.
  • A human owns functional verification. My agents now build, install, and hand me a plain checklist. They are forbidden from claiming "verified" — that word is mine.
  • Standing rules live in files, not chat. Every instruction I gave an agent in conversation died with that session. The rules that stuck are the ones in version-controlled AGENTS.md files the next agent is forced to read.

Elpis v0.1.0 is re-tagged, re-released, and installs clean on a bare machine. The
history is rewritten to say only true things. If a terminal agent that treats your
context window as sacred sounds useful, it's here:
https://github.com/MasihMoafi/Elpis

Draft Show HN title: Show HN: Elpis — a Codex fork that keeps 90%+ of your
context window free — first comment: the story above, linked.

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