Vendor Codex and land Phase 1 Epiphany state slice

vendor/codex/codex-cli/scripts/README.md

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+# npm releases
+
+Use the staging helper in the repo root to generate npm tarballs for a release. For
+example, to stage the CLI, responses proxy, and SDK packages for version `0.6.0`:
+
+```bash
+./scripts/stage_npm_packages.py \
+  --release-version 0.6.0 \
+  --package codex \
+  --package codex-responses-api-proxy \
+  --package codex-sdk
+```
+
+This downloads the native artifacts once, hydrates `vendor/` for each package, and writes
+tarballs to `dist/npm/`.
+
+When `--package codex` is provided, the staging helper builds the lightweight
+`@openai/codex` meta package plus all platform-native `@openai/codex` variants
+that are later published under platform-specific dist-tags.
+
+If you need to invoke `build_npm_package.py` directly, run
+`codex-cli/scripts/install_native_deps.py` first and pass `--vendor-src` pointing to the
+directory that contains the populated `vendor/` tree.