Base fix in the User config and Setup #223

Parent

#221

What to build

Base fixes can be turned on per machine. The User config gets base.fix (true or false, default false), validated like merge.always. With it true, every Run may start a Base fix with no flag. no-base-fix (or --no-base-fix) forbids it for one Run. Giving base-fix and no-base-fix together is rejected as contradictory, like merge and no-merge. Setup asks whether to allow Base fixes only when merging is on. Otherwise it writes base.fix out at its default, so the file still shows the setting.

Acceptance criteria

• base.fix = true in the User config lets a Run start a Base fix without the flag.
• no-base-fix overrides it for one Run; base-fix with no-base-fix is an error before any work.
• A non-boolean base.fix is rejected with a message naming the file, like merge.always.
• Setup asks about Base fixes when merging is on, skips the question otherwise, and always writes the setting.
• Tested through the binary, following the User config, Setup and command surface tests.

Blocked by

• A Base fix, when the base-fix flag is given #222