Building a 1,056-Test Rust CLI Without Writing Rust — Claude Code Did It

I don't write Rust. I can read it well enough to catch obvious bugs, but I've never typed impl or fn main() from scratch. Yet I shipped a 40-module Rust CLI with 1,056 tests in 3 weeks. Claude Code wrote every line of Rust. I wrote prompts, reviewed diffs, and made architecture decisions. The tool — ContextZip — compresses Claude Code's own context window. So the AI built a tool to make itself work better. That irony wasn't lost on me. Here's exactly how the process worked, including the parts that went wrong. The Subagent Pattern I never gave Claude Code a vague instruction like "build a context compressor." Every task was a subagent dispatch — a scoped prompt with clear inputs, expected outputs, and test requirements. A typical dispatch: "Implement an error stacktrace filter for Node.js. Input: raw stderr with Express middleware frames. Output: error message + user code frames only. Write 20+ test cases covering nested errors, empty traces, and mixed stdout/stderr. Put the filter in