One entry per agent, as SetupResult reports it.
The files to change.
Agents whose MCP server is added, by a command or a file.
Things to tell the user.
Commands that add an MCP server, for agents whose CLI adds them.
The agent.
Its arguments.
The program.
What was left out, and why.
The agent, or shell for the startup file.
Why.
What planSetup works out, for applySetup to write.