What is arbor CLAUDE.md?

A project instruction file for the penso/arbor repository. It records priorities, required tools and commands, and rules for commits and pushes.

Use it to guide repository work with the pinned Rust toolchain, run the required checks through `just`, follow commit naming rules, and update the README when adding features.

It gives coding agents a shared reference for how to format, lint, test, run, and commit changes in that repository.

arbor CLAUDE.md — Instructions file by penso

Install

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.

agentmods

npx agentmods add instructions/penso/arbor/claude-md

Clone the repo

git clone --depth 1 https://github.com/penso/arbor

Per session 1,620 This file is loaded in full into every session.

When invoked 1,620 The same file — it is already loaded in full.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

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	$0.01620	$0.01620
Opus 5	$0.00810	$0.00810
Sonnet 5	$0.00324	$0.00324
Haiku 4.5	$0.00162	$0.00162

Measured 2d ago against content hash 6506a2dbb052, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

arbor CLAUDE.md 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.

CLAUDE.md · 133 lines

How it starts

The opening of the file, as written. The whole thing — 133 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLAUDE.md

This file provides instructions for Claude Code when working in this repository.

Priorities

Keep code simple, explicit, and maintainable.
Fix root causes, avoid temporary band-aids.
Preserve user changes, never revert unrelated edits.

Toolchain

This project uses a pinned Rust nightly toolchain: nightly-2025-11-30. All commands go through just recipes which apply the correct toolchain automatically.

Commands

Format: just format
Format check: just format-check
Lint (clippy): just lint
Test: just test
Full CI suite: just ci
Run app: just run
Run HTTP daemon: just run-httpd

Before Committing / Pushing

Always run these checks before committing and fix any issues:

just format — auto-fix formatting
just lint — must pass with zero warnings (-D warnings)
just test — all tests must pass

If any check fails, fix the issue, then commit the fix. Never skip just format or just lint before a commit, even for small changes.

Git Workflow

Rust Rules

Do not use unwrap() or expect() in non-test code. In test modules, use #[allow(clippy::unwrap_used, clippy::expect_used)] on the module.
Use clear error handling with typed errors (thiserror/anyhow where appropriate).
Use arbor_core::ResultExt and arbor_core::OptionExt for .context() on Result<T, E> and Option<T> — prefer these over ad-hoc .map_err() with format strings.
Use SessionId and WorkspaceId newtypes from arbor_core::id instead of raw String for session/workspace identifiers. These are #[serde(transparent)] for wire compatibility.
Keep modules focused and delete dead code instead of leaving it around.
Collapse nested if / if let statements when possible (clippy collapsible_if).
Never shell out to external CLIs (gh, git via Command::new, etc.) for GitHub API calls or operations that can be done with Rust crates. Use octocrab, reqwest, or other Rust HTTP/API crates instead. The only acceptable use of std::process::Command is where no Rust crate equivalent exists.

Read the full file on GitHub · 133 lines

Changes

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 · 133 lines · 1,620 tokens per session scan A 6506a2dbb052

Subscribe to this mod's changes

arbor CLAUDE.md is an instructions file published in the GitHub repository penso/arbor (809 stars, last pushed 2mo ago), licensed MIT. It adds 1,620 tokens to every session, about $0.0081 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.

Git and workflow Languages Writing and docs

spec-kit AGENTS.md

AGENTS.md instructions for github/spec-kit, covering agents.md, about spec kit and specify, quickstart — add a new integration in 5 steps, integration architecture and integrationmanifest — file tracking.

github/spec-kit · 7,104 tokens

vscode buildNext.instructions.md

Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).

microsoft/vscode · 6,785 tokens

arbor CLAUDE.md