How to configure Claude Code (and Cursor) so it stops ignoring your conventions

Most developers install Claude Code or Cursor, try a few prompts, and walk away unimpressed. The agent edits the wrong files, ignores their conventions, and confidently invents a project structure that doesn't exist. The tools aren't the problem. The missing config is. An AI coding agent is like a brilliant contractor who's never seen your codebase. Drop them in with no brief and they'll guess. Give them a one-page brief — your stack, your rules, your commands, what not to touch — and they beh...