Setup Codebase Harness skill

Set up the codebase harness

Harness engineering: the model is fixed — what you engineer is the scaffolding around it (the environment, the docs, the feedback loops) so an agent can build and verify software with minimal human attention. Humans steer; agents execute. Your job is to make the repo legible, executable, and verifiable.

Work incrementally and depth-first: assess what exists, build the one missing capability, use it to unlock the next. Don't boil the ocean — set up what the repo actually needs. When the agent struggles, the fix is almost never "try harder" — ask "what capability is missing, and how do I make it legible and enforceable?" and add it.

This skill orchestrates the focused sub-skills: dev-local-setup, e2e-setup, crabbox-setup (cloud/parallel), and verifier-setup (scaffolds a repo-specific /verify loop; supersedes the older pr skill).

0. Assess

Survey the repo: stack, package manager, services/ports, infra deps, existing docs/tests/CI, and the implicit rules (buried in READMEs, PR comments, people's heads). Note what's missing per pillar below.

1. Legible — the agent can reason about the repo

What the agent can't see doesn't exist. Knowledge in chat threads / heads is invisible — push it into versioned, repo-local artifacts.

• a) Map, not manual. Shrink the root agent doc (AGENTS.md / CLAUDE.md) to a ~100-line table of contents: one-line overview, project tree, golden rules (the hard invariants), and a "where to look" table. Move the depth into a structured docs/ system-of-record (architecture, frontend, testing, domain topics) with a docs/index.md. A monolithic instruction file rots and crowds out the task — keep the map small and stable, disclose detail progressively.
• b) Custom lints with remediation. Promote the prose golden rules into mechanical checks — human taste captured once, enforced everywhere, every run. One lint per invariant (layering / dependency direction, naming, no-any, forbidden imports, file-size, structured logging). Write the error message to inject the fix ("X isn't allowed here — do Y") so the remediation lands in agent context. Wire them into the repo's linter + CI.
• c) Queryable code graph. Index the repo with codebase-memory-mcp so the agent traces callers, data flow, and architecture from a knowledge graph instead of blind grepping — faster, more precise navigation on large codebases.
• d) (later) Keep docs honest. A freshness / doc-gardening pass that flags docs that no longer match the code and opens fix-up PRs.

2. Executable — the agent can run & drive the app

• dev-local-setup → a one-command, reproducible local stack (scripts/dev-local.sh up) running every service + infra.
• Make the app drivable: browser via the playwright-cli skill (installed by verifier-setup); logs reachable.
• crabbox-setup → an isolated cloud box per agent — the parallel-safe counterpart to dev-local. Reach for it when loops run concurrently: one laptop can't host N full stacks (fixed ports, one Docker daemon, one DB), and per-worktree local doesn't fix it — the worktrees still share the host. crabbox gives each agent its own stack + an in-box browser, so parallel verification never collides.
• Advanced: a local, ephemeral observability stack (queryable logs/metrics) for perf/reliability prompts.

3. Verifiable — the agent can prove it works

• e2e-setup → a trustworthy e2e gate: real flows (not bypass), a reusable auth/session helper, layered client → server → product assertions, video/trace evidence, sandbox-only external services.
• verifier-setup → scaffolds a repo-specific /verify skill (the verify-before-ship loop): a fresh verifier sub-agent drives the real app to confirm the just-built feature works; the main agent fixes until green, runs the codified regression sweep, and opens a PR with a reviewable proof link. Add the session helper so the verifier can reach login-gated features.

4. Others — keep it coherent over time

• Commit hygiene: conventional commits + format/lint on commit (e.g. husky lint-staged + commitlint). Keep merge gates light — at high agent throughput, corrections are cheap and waiting is expensive.
• Garbage collection: encode "golden principles", then run periodic cleanup passes that open small refactor PRs — pay tech debt down continuously, not in painful bursts. Human taste captured once, enforced on every line.
• Agent-to-agent review for correctness-critical changes (independent reviewers, not self-review).

Order & what you leave behind

1a (map) → 2 (dev-local) → 3 (e2e + verifier-setup), then 1b (lints) and 4 as the repo matures. The artifacts — slim map + docs/, scripts/dev-local.sh, an e2e/ suite, the generated /verify skill, and custom lints — are each a reusable, legible capability that compounds. Prefer "boring", composable, stable tech the agent can fully model.