[Epic 3] create-python-app-core — scaffolding engine

[ulises-jeremias]

Summary

Port @create-node-app/core capabilities: paths, git cache, loaders, cpa.config.json, installer (uv), errors, env/version helpers.

CNA mapping

packages/create-node-app-core/*.ts (~2.5k LOC).

Why

CLI is a thin UI over the engine; engine is the product kernel.

Sub-issues

• Core public API + package metadata (hatchling/src layout) #23 Core public API + package metadata (hatchling/src layout)
• Errors and abort semantics (CPA_* codes) #24 Errors and abort semantics (CPA_* codes)
• Paths resolution (GitHub URL, file://, slugs, ?ref=) #25 Paths resolution (GitHub URL, file://, slugs, ?ref=)
• Git download + disk cache (~/.cache/cpa) + refresh modes #26 Git download + disk cache (~/.cache/cpa) + refresh modes
• Template/extension loaders + merge model #27 Template/extension loaders + merge model
• cpa.config.json schema + custom options #28 cpa.config.json schema + custom options
• Installer: scaffold → uv sync → git init #29 Installer: scaffold → uv sync → git init
• Env info helper (--info equivalent) #30 Env info helper (--info equivalent)
• PyPI latest-version check #31 PyPI latest-version check
• Unit tests for each core module #32 Unit tests for each core module

Blocks / dependencies

Blocks #5 (CLI).

Blocked by: #2 (package stubs)

Reference

Parity matrix (workspace): knowledge/create-python-app-parity-matrix.md
Reference repo: https://github.com/Create-Node-App/create-node-app