Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add PostHog/posthog-foss --skill extending-personhog-test-harnessgit clone --depth 1 https://github.com/PostHog/posthog-fossWrote 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/skills/posthog/posthog-foss/extending-personhog-test-harness)<a href="https://agentmods.dev/skills/posthog/posthog-foss/extending-personhog-test-harness"><img src="https://agentmods.dev/badge/skills/posthog/posthog-foss/extending-personhog-test-harness/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/skills/posthog/posthog-foss/extending-personhog-test-harness"><img src="https://agentmods.dev/badge/skills/posthog/posthog-foss/extending-personhog-test-harness.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00134 | $0.01174 |
| Opus 5 | $0.00067 | $0.00587 |
| Sonnet 5 | $0.00027 | $0.00235 |
| Haiku 4.5 | $0.00013 | $0.00117 |
Grade A, and why
extending-personhog-test-harness 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 7d 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.
How it starts
The opening of the file, as written. The whole thing — 92 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Extending the personhog test harness
The harness (rust/personhog-test-harness/, see its README for usage) spawns a
real personhog stack and asserts one invariant three ways: every acked write
is visible afterwards — live via read-your-write probers, at end-of-run via
strong reads, and durably via Postgres at the acked version. It has caught real
bugs (eviction data loss, unordered lifecycle shutdown, coordinator failover
stalls) precisely because chaos scenarios run against those assertions.
When to add a scenario
Add one whenever you fix a personhog bug whose trigger the harness can reproduce — a crash, drain, restart, lag, election, or eviction condition. The fix's PR should show the scenario red before the fix and green after; that run becomes the permanent regression test. Also add one when introducing a new failure mode (a new process to disrupt, a new timing window) or a new correctness property (a new journal check).
Don't add scenarios for behavior already covered by an existing flag combination — compose existing flags instead — and don't add unit-testable logic here: the harness is for whole-stack behavior only.
Where things live
src/cli.rs— every scenario is driven byGateArgsflags.src/scenarios/gate.rs—ChaosEventenum,chaos_timeline()(offset-sorted events, paired stop/resume events), the dispatch loop, and verification ordering (probers → regressions → strong reads → Postgres quiesce).src/stack/mod.rs— stack primitives: spawn/kill/restart leaders (SIGKILL, SIGTERM drain, SIGSTOP/SIGCONT zombie), writer crash/pause, coordinator kill, etcd lease revocation, per-service env. New disruptions are new methods here.src/scenarios/merge.rs— the merge lane (--merge-concurrency): MergePersons calls with one or more sources (--merge-sources) against live persons while the other lanes write to them. Merged sources hang off the survivor in the journal tree and are retired from the sharedsrc/pool.rstarget pool.src/state.rs— the acked-write journal and its verifiers. New invariants go here, and their decision tables get unit tests: a false-negative verifier looks identical to a healthy stack, so e2e runs cannot reveal it.README.md— every scenario gets a runnable example; scenarios that stay red because of a known unfixed defect go in the "Known defects" section with their observable signature and fix direction.
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.
- 7d ago Changed · +4 lines 341675b0f304
- 11d ago First seen · 88 lines · 134 tokens per session scan A bc7c6ee1ded1
extending-personhog-test-harness is a skill published in the GitHub repository PostHog/posthog-foss (715 stars, last pushed yesterday), licensed MIT. It adds 134 tokens to every session and 1,174 once invoked, about $0.0007 per session on Opus 5. 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 2026-08-30.
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