AI coding tools let you define subagents: a name, a description of when to use it, a model and a prompt. Claude Code reads them from `.claude/agents`, OpenCode from `.opencode/agents`. The files are quick to write and quick to copy, and that is the problem. Each repository and each laptop ends up with its own version, and nobody can say which text ran last night.
A catalog moves the definitions to one place the whole team reads. Each change is saved as a new revision instead of overwriting the old one, so there is a history to compare and a known version to go back to. A run then names the agent it needs, and the catalog answers with the exact text.