unknown_cross_ref_provider

Cross-ref :provider names an extractor no loaded plugin declares.

A (cross-ref :provider p …) draws its member set from a (cross-ref-provider :name p …) declared by some plugin. This fires when no loaded plugin declares p.

Usual causes: the plugin that declares the provider is missing from :plugins, or the name is misspelled. Providers live in their own catalog, so an expression function or form of the same name does not satisfy the reference.

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Run sjon explain unknown_cross_ref_provider to read this at a terminal, browse every code, or work through diagnostics-driven repair if you want the habit rather than the answer.