Borrowing it
Nothing to install: this file belongs to frostyard/snosi. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/frostyard/snosi/main/.github/prompts/add-sysext.mdgit clone --depth 1 https://github.com/frostyard/snosiWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/commands/frostyard/snosi/add-sysext)<a href="https://agentmods.dev/commands/frostyard/snosi/add-sysext"><img src="https://agentmods.dev/badge/commands/frostyard/snosi/add-sysext/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/commands/frostyard/snosi/add-sysext"><img src="https://agentmods.dev/badge/commands/frostyard/snosi/add-sysext.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00000 | $0.00569 |
| Opus 5 | $0.00000 | $0.00284 |
| Sonnet 5 | $0.00000 | $0.00114 |
| Haiku 4.5 | $0.00000 | $0.00057 |
Grade A, and why
add-sysext scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
Prompt: add or change a sysext
Goal: <what the sysext must provide>
Read first: docs/design/sysexts.md, plus the "Sysext Constraints" section of
CLAUDE.md.
Work to do:
- Create or edit
mkosi.images/<name>/using an existing sysext as the template. SetKEYPACKAGE=in itsmkosi.conf; bumpSYSEXT_REVISION=when republishing a tree-only fix under an unchanged package version. - Ship matching
<name>.transferand<name>.featurefiles inmkosi.images/base/mkosi.extra/usr/lib/sysupdate.<name>.d/. Never add them to the sharedusr/lib/sysupdate.d/directory, which is reserved for the native A/B OS transfers. - List every path the sysext itself ships in
mkosi.images/<name>/required-paths.txt. ForOverlay=yesimages the finalize$BUILDROOTis the delta, so paths already present in the base image must not be listed. - Respect the immutable-filesystem rules:
/usronly. Relocate anything a package installs into/optto/usr/lib/<package>with symlinks in/usr/bin. Configs needed in/etcare captured into/usr/share/factory/etc(only the exact paths the tmpfiles rules reference) and injected via tmpfiles. - For services, ship a
usr/lib/systemd/system/multi-user.target.d/10-<name>.confdrop-in withUpholds=<name>.servicein addition to the preset — a plain.wantssymlink is dropped at boot because the sysext is not merged yet. - For desktop applications, include
shared/sysext/finalize/sysext-strip-icon-cache.shinFinalizeScripts=so no hicolor icon cache leaks into the delta. - Any direct download must go through
verified_download()with a pinned URL and an entry inshared/download/sysext-checksums.json, plus a check in.github/workflows/check-dependencies.yml(orcheck-packages.ymlfor APT sentinels).
Validate: just sysexts (or a targeted build of the one image), then the
relevant scripts under test/ and the checks in .github/workflows/validate.yml.
Finish by updating CLAUDE.md and docs/design/sysexts.md if any constraint or
contract changed.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 3d ago First seen · 41 lines · 0 tokens per session scan A 817be3a8b884
add-sysext is a command published in the GitHub repository frostyard/snosi (24 stars, last pushed yesterday), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 569 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-06.
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