Five AI coding tools, five completely different ways to break

I've now routed five different AI coding tools through a proxy layer. Each one broke differently. None of them told me why. Writing this partly as a reference for myself, partly because the failure modes turn out to be genuinely interesting — they say a lot about how these tools are built. Claude Code: reads config once, then never again The simplest of the five. Config lives in ~/.claude/settings.json , two keys get modified: env.ANTHROPIC_BASE_URL env.ANTHROPIC_AUTH_TOKEN The failure mode: it reads that file exactly once, at startup. Change it while a session is running and nothing happens. No warning, no reload. This is the single most common "the switch is on but nothing works" report, across every tool. Close all windows, open a fresh one. One thing I appreciate: it only touches those two keys, backs up the original, and restores it exactly when you flip the switch off. Codex: doesn't read the model from your request This one is architecturally weird and cost me an hour. Every other tool specifies which model it wants in the request. Codex doesn't. It picks from its own internal model catalog. Consequence: if you don't explicitly select a model, it sits on a default internal GPT model that the market can't serve. And you don't get "please select a model" — you get a string of failures with no stated cause. The config it writes: ~/.codex/config.toml → model_provider, [model_providers.asale], model, model_catalog_json ~/.codex/auth.json → OPENAI_API_KEY Note model_catalog_json . That's the part that makes your selection show up in the app's model menu. And the desktop app reads that catalog at startup , so a model written while it's running won't appear until you restart. Two separate restart requirements stacked on each other. Credit where due: it preserves your existing comments and formatting in config.toml . Not every tool does. Gemini CLI: loses to your own shell config Config goes into ~/.gemini/.env . Two keys added, nothing else touched. The failure mode