block anchor spelling normalizes to [[id]] over [#id] where the reader records the respelling as render-equal

Ruled by Dan (2026-09-06, on #217): not a preserved choice. Normalize only where the reader has recorded a fact that the respelling is render-equal; keep the author's spelling where no fact licenses the change. Before any code: this row's proof source, the generated whitespace battery (#239) run over the pair's domain through both programs, with the negative shapes pinned; the fact joins the block-level record the whitespace-fact change (#240) establishes; the printer never decides safety itself (no fact, no rewrite).

The pair

[[id]] over [#id] for a block anchor (the shorthand form is the target). Both spell the same anchor; the domain question is where [#id] carries more than an id (roles, options) and where the two forms sit in metadata runs the reader stacks differently.

Start with this row's proof source: the generated whitespace battery from #239, run over the pair's domain through both programs with the negative shapes pinned. Review how the whitespace-fact change in #240 establishes the block-level fact and ensure the printer relies on that fact; done means rewriting [[id]] over [#id] only when render-equality is recorded.