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 d-o-hub/github-template-ai-agents --skill nested-build-isolationgit clone --depth 1 https://github.com/d-o-hub/github-template-ai-agentsWrote 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/d-o-hub/github-template-ai-agents/nested-build-isolation)<a href="https://agentmods.dev/skills/d-o-hub/github-template-ai-agents/nested-build-isolation"><img src="https://agentmods.dev/badge/skills/d-o-hub/github-template-ai-agents/nested-build-isolation/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/d-o-hub/github-template-ai-agents/nested-build-isolation"><img src="https://agentmods.dev/badge/skills/d-o-hub/github-template-ai-agents/nested-build-isolation.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 | $0.00110 | $0.00947 |
| Opus 5.5 | $0.00044 | $0.00379 |
| Sonnet 5.5 | $0.00022 | $0.00189 |
| Haiku 4.5 | $0.00011 | $0.00095 |
Grade A, and why
nested-build-isolation 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 2d 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 — 89 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Nested Build Isolation
Isolate nested build, test, and coverage subprocesses when invoked inside an outer build, coverage runner, or instrumentation session.
Source Attribution: Adapted from the
do-harnessnested-build-isolation skill for portable use across software repositories.
Quick Start Checklist
- Identify the outer runner (
cargo test,cargo llvm-cov,cargo nextest). - Inspect env vars passed to child processes (
CARGO_TARGET_DIR,RUSTFLAGS). - Centralize child process environment sanitization in a dedicated helper.
- Direct child process target and output files to isolated temporary dirs.
- Parse coverage metrics from structured reports (e.g. JSON report output).
- Verify tests pass both standalone and under outer instrumentation.
Core Principles
1. Identify Outer Environment Before Patching Tests
When a test spawning a subprocess fails, determine if it fails only under an
outer instrumentation or test runner session (such as cargo llvm-cov or
cargo nextest). Subprocesses inherit outer environment variables, compiler
flags, and target paths that cause unexpected build failures or collisions.
2. Centralize Child Process Environment Sanitization
Do not scatter ad hoc environment unsets (env::remove_var or command
env_remove) across individual tests. Create a centralized helper function to
sanitize child process environments consistently.
Key variables to strip or isolate for nested Rust/Cargo invocations:
CARGO_TARGET_DIR— Prevent target directory lock contention.RUSTFLAGS/CARGO_ENCODED_RUSTFLAGS— Strip outer instrumentation flags.LLVM_PROFILE_FILE— Avoid filename collisions in nested binaries.CARGO_MAKEFLAGS/CARGO_FLAGS— Avoid outer jobserver inheritance.
3. Stable Report Parsing Over Unstructured Stdout
Tool stdout summary text (e.g., human-readable progress tables) is subject to
formatting changes across tool versions and environment settings. Prefer
generating and parsing machine-readable coverage reports (such as cargo llvm-cov --json or LCOV reports) to obtain deterministic measurements.
What ships with it
2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 2d ago First seen · 89 lines · 110 tokens per session scan A 8476f9c9e14e
nested-build-isolation is a skill published in the GitHub repository d-o-hub/github-template-ai-agents (2 stars, last pushed yesterday), licensed MIT. It adds 110 tokens to every session and 947 once invoked, about $0.0004 per session on Opus 5.5. 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 2026-10-21.
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