Try to guide AI more so it writes better tests

Author: Byron

.github/copilot-instructions.md

@@ -347,3 +347,4 @@ corepack prepare pnpm@10.17.0 --activate
 8. **Test on target platform** if making platform-specific changes
 9. **Security**: Check dependencies for vulnerabilities before adding them
 10. **Code marked for refactoring**: Be extra careful with crates in the "Code Hitlist" section
+11. **but CLI happy path testing only**: CLI tests are expensive and should be limited to what really matters.

crates/but/tests/but/command/mod.rs

@@ -1,5 +1,6 @@
 //! Put command-specific tests here. They should be focused on what's important for each command.
 //! Ideally they *show* the initial state, and the *post* state, to validate the commands actually do what they claim.
+//! **Only** test the *happy path* of a typical user journey, while keeping details in unit tests with private module access.
 mod branch;
 #[cfg(feature = "legacy")]
 mod commit;