principle-assert-invariants-not-last-bug SKILL.md skillA
principle-assert-invariants-not-last-bug from edbertchan/catstack is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add edbertchan/catstack/principle-assert-invariants-not-last-bug@git:20260915.8e3bf4ePins git:20260915.8e3bf4e in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- edbertchan/catstack
- Path
corpus/skills/principle-assert-invariants-not-last-bug/SKILL.md- Versions recorded
- 5
- Latest version
- git:20260915.8e3bf4e, committed Sep 15, 2026
- First version recorded
- Sep 7, 2026
- Size
- 5,569 bytes
- Repository stars
- 6
- License
- none declared
Apply after a bug ships past review or a passing grade/check: assert the general class of failure instead of patching only the specific instance that was caught. Use on /reflect, whenever a fix's own commit message reads like 'fix X for ticker/case Y', or whenever a fix makes a row disappear instead of shipping it with a status.
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# Assert invariants, not the last bug name After a bug ships past review or a passing check, encode the class of failure as an invariant, not a fix for the instance that was caught. Patching "the AUR case" does not stop a structurally identical bug from shipping as "the SERV case": the rule that would catch every instance is never written down or enforced, so review stays blind to every case except the one already fixed. Under its usual names — invariant, contract, property, regression test — this is standard practice (see Grounding). ## The method 1. **Name the invariant in one line**, as a predicate that holds in every state. Not "AUR shouldn't duplicate" — "every (period, entity) pair has exactly one row." 2. **Name its completeness twin in the next line.** Every "must not invent" (precision) rule gets a "must not be missing" (recall) rule; how a hard row ships is [[principle-explicit-errors]]. 3. **Encode both in code** — an assertion, a uniqueness or not-null expectation, a refuse-to-ship check, a record-count reconciliation — over every case of that shape, not the one that broke. A property-based test generates the cases you have not seen. …
Read the whole file at its exact version.
How to install
mdr add edbertchan/catstack/principle-assert-invariants-not-last-bug@sha256:f0d5a3478db39778The line at the top of this page pins the label git:20260915.8e3bf4e, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_uwhchonglad4ehel)
4 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 5 versions of this file, between Sep 7, 2026 and Sep 15, 2026, about one every 2 days.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| git:20260915.8e3bf4e latest | 2026-09-15 | 8e3bf4e | 5,569 B | A | view · diff |
| git:20260910.57b918f | 2026-09-10 | 57b918f | 5,563 B | A | view · diff |
| git:20260907.699d275 | 2026-09-07 | 699d275 | 5,268 B | A | view · diff |
| git:20260907.d724ee0 | 2026-09-07 | d724ee0 | 4,003 B | A | view · diff |
| git:20260907.14d3ce9 | 2026-09-07 | 14d3ce9 | 6,596 B | A | view |
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (5569 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
edbertchan/catstack · 6 stars · license none declared · pushed 2026-10-22 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_uwhchonglad4ehel GET https://markdownregistry.com/api/v1/resolve?ref=edbertchan/catstack/principle-assert-invariants-not-last-bug GET https://markdownregistry.com/api/v1/blob/f0d5a3478db3977894a624df54847835f18708c7cfcd4e8782403c44da6f4ad5
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.