Configuration file

~/.tg.json is a user-home state file. Theme Manager recovers from a missing or malformed file with defaults and preserves unknown keys when it writes known state.

Field	Default / shape	Owner
customThemes	string[]	Theme discovery during generation.
lastAppliedTheme	theme ID or null	Generation/apply flow state.
favoriteSeedColors	{ color, variant }[]	Favorites flow; legacy string favorites migrate on read.
lastUsedSeedColor	hex or null	Seed generation.
lastUsedVariant	variant or null	Seed generation.
lastUsedThemes	optional { dark?, light? }	Selection’s mode-specific state.

Writes use the shared same-directory temporary-file-plus-rename helper. This gives atomic replacement for the ordinary state-file path, but does not create backups or offer a global rollback.