- writeCentralConfig now always strips core-module keys from every
[modules.<code>] bucket, even when the module's schema is not
available in src/ (external / marketplace modules like cis, bmb).
Core values belong in [core] only; workflows read them directly.
- When the module's own schema IS available (built-in modules),
also drop any key it does not declare as a prompt — same
spread-pollution filter as before, now layered on top.
- Section-aware headers on both _bmad/config.toml and
_bmad/config.user.toml: [core] / [modules.*] values are
editable (installer reads them as defaults on next install);
[agents.*] is regenerated from module.yaml and will be wiped —
overrides for agents go in _bmad/custom/config*.toml instead.
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