Detect drift in the Claude system prompt that agent-container sends to Anthropic. Captures two axes — the bare `claude_code` preset (Anthropic baseline) and agent-container's fully custom wire request — at the SDK version pinned in `agent-container/package-lock.json`, then stores versioned snapshots in `<skill>/snapshots/` (gitignored). Because SuperAgent REPLACES the preset with its own system prompt, preset drift never reaches our sessions automatically — every pure-claude change must be triaged for porting into system-prompt.md. Use when bumping `@anthropic-ai/claude-agent-sdk`, debugging unexpected model behavior after an SDK upgrade, previewing what a PR changes in the on-wire prompt, or auditing what Anthropic silently changed in the Claude Code preset.