Every extension gets a declarative extension-manifest.json (id, tier,
provides, dependencies). A persistent registry at ~/.gsd/extensions/registry.json
tracks enabled/disabled state. `gsd extensions` command family (list, enable,
disable, info) lets users manage extensions without touching source code.
Registry gate filters disabled extensions in loader.ts and resource-loader.ts
before paths reach loadExtensions(). Zero breakage: extensions without manifests
default to enabled, fresh installs have an empty registry.
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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