api-ground

name	api-ground
description	Ground the agent in a library's real API before writing code against it — generate a version-pinned reference from the installed package, not from training data. Use before adopting a library, after a major upgrade, or when generated code keeps calling methods that do not exist.

API Ground

Models write library code from training data. Training data describes whatever version was current when the tutorials were written. When a library reorganizes between majors, the generated code is confidently wrong — and a green typecheck does not always catch it.

This skill produces a version-pinned reference read off node_modules, so the agent has the API that is installed rather than the one that was popular.

Use it when: adopting a library, after a major-version bump, or when generated code repeatedly calls methods that do not exist.

Do NOT build a RAG index over library source for this. The question is "does this method exist in the installed version" — an exact lookup, answered by type definitions and grep. Similarity search returns approximately right, which is the failure being eliminated.

The two failure shapes

1. Package reorganization. A major version folds satellite packages into the core module, or splits them out. The old names still resolve on npm, tutorials still reference them, and the packages may still install — as stubs shipping no JavaScript. Anything written from recall imports a package that resolves to nothing.

2. Interface merging without registration. declare module / declare global merges members onto types the package does not own. TypeScript applies those merges globally. If the augmentation ships inside a package that gets imported anyway, the merged members type-resolve unconditionally — but only work after a separate runtime step (graph.use(new Plugin()), a setup file, a middleware wrapper). TypeScript cannot see that step. This shape compiles clean and throws TypeError at runtime, and it is the one that reaches production.

Shape 2 is the reason a passing build is not evidence of correctness here.

Locating the script

A global install puts it beside the other expert scripts; a project-mode install puts them under .opencode/scripts/ (install.sh copies scripts/ in BOTH modes — skipping it in project mode was a bug, because every script-backed skill names a path under the install dir). Resolve it once, then use $EXPERTS below:

for d in ~/.config/opencode/scripts ~/.claude/scripts ./.opencode/scripts ./scripts ./frontend/scripts; do
  [ -f "$d/api-surface.mjs" ] && EXPERTS="$d" && break
done
[ -n "$EXPERTS" ] && echo "using $EXPERTS/api-surface.mjs" || echo "NOT INSTALLED — vendor it (below)"

If that prints NOT INSTALLED, the expert scripts are not reachable from here. Copy api-surface.mjs from the expert-system repo into the target project (scripts/ or frontend/scripts/), commit it, and set EXPERTS to that directory.

Vendoring is the intended fallback, not a workaround: the script imports nothing beyond node:fs and node:path, and a copy living in the repo is what lets CI run the gate without the expert system installed. Do not proceed with an empty $EXPERTS — every command below would silently target /api-surface.mjs.

Resolving "what is the current API?" — in this order

Each rung answers a different question. Stop at the first that answers yours; fall to the next when it cannot.

1. The installed tree — --package=. Ground truth for this project. Nothing else can tell you what your code is actually compiled against. Always wins a disagreement.

2. Context7 MCP (resolve-library-id → get-library-docs). Current published docs and worked examples — the fastest path to usage patterns and the right first stop before writing new code. It is frequently more current than the top web result; measured against AntV X6 on 2026-07-27 its corpus was cleanly v3, with zero references to the superseded plugin packages.

Its limit is not accuracy, it is scope: Context7 answers "how do I call this", never "which version is this" or "what will npm install give me". The same X6 corpus — 116 KB — contained no version string at all. An agent can follow Context7 perfectly, write correct calls, and still install a package family that mixes majors. Rungs 1 and 3 are what cover that; they do not replace Context7, they answer questions it does not take.

3. The registry — --family=<pkg>. The rung below Context7, and the one that catches what docs cannot: latest is published per package, but compatibility is per family. A library split across a scope can ship a new major on its core while satellite packages keep latest pointing at the old one. Installing "the latest" of each then silently mixes majors — no import error, no type error.

node "$EXPERTS/api-surface.mjs" --family=@antv/x6

Enumerates the family from the registry (not just package.json, so it works before anything is installed), and flags every member whose latest is a different major than the anchor. Exits non-zero when any exist.

4. The package's own types. If a package is not in Context7 and its docs are thin, npm pack <name>@<version> and read the .d.ts — the type definitions ship with the package and cannot disagree with it. This is what --package= automates once installed.

5. Upstream source / release notes, via the project's web-retrieval tooling, for why something changed when the above tell you that it changed.

Never substitute recall for any of these, and never let a green typecheck stand in for rung 1 — see the registration trap below.

Workflow

0. Before adopting a library — check the family

node "$EXPERTS/api-surface.mjs" --family=<package>

Do this at adoption time and at every major upgrade, not just when something breaks. It is the cheapest of these steps and the only one that catches a bad install line before the code is written against it.

1. Rank the project's dependencies by risk

node "$EXPERTS/api-surface.mjs" --scan

Ranks every dependency by structural risk: interface merges, packages shipping no JavaScript, and whether merged members are already being called. Run from the directory holding package.json, or pass --root=<dir> --src=<dir>.

Read the output, don't just take the top row. High augs with low calls is latent exposure; NO — LIVE BUG in the registered column is an active defect.

Frameworks rank on structure alone — Next.js merges a dozen members onto Window and HTMLAttributes with no registration step behind any of them. That is not actionable. The rows worth acting on are feature libraries whose merged members the project actually calls.

2. Generate a reference for the libraries that matter

node "$EXPERTS/api-surface.mjs" --package=@antv/x6

Writes docs/development/<PKG>_API.md: installed version, exported classes with inherited members resolved, every interface merge with the feature that must be registered, and which merged members this codebase actually calls.

Generate for libraries the project builds on, not every flagged dependency. A framework the whole app already imports correctly is lower value than the one feature library nobody understands.

3. Add what the generator cannot know

The generated file is mechanical and must stay that way — never hand-edit it. Put judgment in a sibling doc or a CLAUDE.md / AGENTS.md rule:

• Which in-repo file is the canonical example to copy from.
• Directories that look canonical but are not (spikes, labs, legacy).
• Version-specific traps confirmed by reading the installed types.

Derive every trap from the installed package. If you cannot show the grep or the type definition that proves it, do not write it down — a confabulated trap list is worse than none.

4. Gate it

node "$EXPERTS/api-surface.mjs" --check

Exits non-zero on: a declared dependency shipping no JavaScript that nothing references, and augmented members called with no import of the package declaring them. Wire into the project's CI standards script and expose as an npm script.

Guard the CI invocation on the whole source tree, not one feature directory — a new module elsewhere is exactly the case that regresses.

5. Point the agent at it

One line in CLAUDE.md / AGENTS.md. A reference nothing links to is dead weight — the pointer is what gets loaded every session.

Rules

• Regenerate after every upgrade. A stale reference is worse than none — it reads as authoritative. The header records the version it was generated from.
• Never hand-edit generated output. Fix the generator instead.
• Usage-driven beats surface-driven. A library with 800 exported symbols and 30 in use needs the 30 listed, with the rest reachable. Dumping the surface recreates the noise problem.
• Don't claim a method is missing without checking inheritance. Base-class and merged members are real API; the generator resolves both.
• Report counts honestly. Call counts are textual matches and over-count common names. Rank with them; do not present them as a census.

Related

• references/library-adoption-protocol.md — the four questions, which source is authoritative for each, and the X6 walkthrough showing that answering only the first ships broken code with every instruction satisfied.
• references/antv-x6-v3.md — a worked, portable instance: AntV X6 v3, where npm's own latest tags point at v2 for 10 of 12 satellite packages. Read it if the project uses X6; read it as an example of what a hand-written companion to the generated doc contains.
• references/library-api-grounding.md — the trap taxonomy and detection method.
• references/context7-mcp.md — live upstream docs. Complementary: Context7 gives current published docs, this gives the installed truth. When they disagree, the installed package wins.