docs(repo): document setup and usage

CONTRIBUTING.md

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+# Contributing
+
+## Dependencies on core
+
+Core packages are not installed from a registry. `flake.nix` pins core at a full commit (input `core`) and
+`nix build .#sfs-deps` links the core tarballs this lockfile names. `pnpm-workspace.yaml` maps every core package
+(and its transitive core closure) to `file:.sfs-deps/<name>-<version>.tgz` through `overrides`; the moved manifests
+name ordinary semver ranges.
+
+To take newer core packages:
+
+1. Bump the `core` input.
+2. Update the override versions.
+3. Rebuild `.sfs-deps`.
+4. Run `pnpm install`.
+
+Other external dependencies use the configured npm registry (the default is the public npm registry), so registry access
+is needed when they are not cached. The verified `pnpm install` reused a warm store; it was not a cold or offline verification.
+
+## Local setup
+
+```bash
+mkdir -p .sfs-deps && cp -L --no-preserve=mode "$(nix build --no-link --print-out-paths .#sfs-deps)"/*.tgz .sfs-deps/
+pnpm install
+```

README.md

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+# effect-e2e
+
+Effect-native end-to-end testing: the effect-e2e core, its web engine, its CLI and the private engine conformance suite.
+
+## Packages
+
+- [`@systemfsoftware/effect-e2e`](packages/effect-e2e/README.md)
+- [`@systemfsoftware/effect-e2e-web`](packages/effect-e2e-web/README.md)
+- [`@systemfsoftware/effect-e2e-cli`](packages/effect-e2e-cli/README.md)
+- [`@systemfsoftware/effect-e2e-conformance`](packages/effect-e2e-conformance) (private)
+
+## Install
+
+The following installs locally built tarballs into a new consumer directory. Run it from a checkout of this repository with Nix, Node.js 24 or newer, npm, and registry access for the other dependencies.
+
+The npm registry returned 404 for the three effect-e2e packages when checked; this example does not install them from npm. The core dependency tarball version comes from the checkout's [workspace overrides](pnpm-workspace.yaml).
+
+```bash
+consumer="$(mktemp -d)"
+core="$(nix build --no-link --print-out-paths .#sfs-deps)"
+runtime="$(nix build --no-link --print-out-paths .#effect-e2e)"
+cli="$(nix build --no-link --print-out-paths .#effect-e2e-cli)"
+npm install --prefix "$consumer" --no-audit --no-fund "$core/effect-cell-types-12.0.2.tgz" effect@4.1.2
+npm install --prefix "$consumer" --no-audit --no-fund "$runtime"
+npm install --prefix "$consumer" --no-audit --no-fund "$cli"
+```
+
+## Usage
+
+Use the installed CLI to generate a suite without installing its dependencies:
+
+```bash
+"$consumer/node_modules/.bin/effect-e2e" init --dir "$consumer/demo" --engine web --gateway openrouter --no-install
+```
+
+```text
+effect-e2e init: scaffolding demo in <consumer-directory>/demo
+  wrote e2e.config.ts
+  wrote vitest.config.ts
+  wrote runner.ts
+  wrote global-setup.ts
+  wrote tests/example.e2e.ts
+  wrote tests/example-agent.e2e.ts
+  wrote package.json
+  wrote .gitignore
+Run the suite with its test:e2e script from <consumer-directory>/demo
+```
+
+The scaffold was generated without running a browser, a test suite, or a model. Its dependencies must be installed before running the suite.
+
+[`@systemfsoftware/effect-e2e` usage](packages/effect-e2e/README.md#usage) · [`@systemfsoftware/effect-e2e-cli` usage](packages/effect-e2e-cli/README.md#usage)
+
+## Contributing
+
+[CONTRIBUTING.md](CONTRIBUTING.md)
+
+## License
+
+[Apache-2.0](packages/effect-e2e/LICENSE)