Merge upstream9d1067fc, preserving both progress-document histories.
Copy the session highlighter choice into command previews, and verify that the
preview toggles the chosen colour without changing the document or undo history.
Document the shared-registry constructor as well as the public constructor.
Validation: complete integrated cargo xtask ci passed all8 gates, including all4
highlight regressions; RUST_TEST_THREADS=1. Local named-function doc audit16/16.
Native Word comparison pending. No new interface strings in this fix.