createTabGroupAnnouncements

Description#

Pure factory bundling the <cngx-tab-group> AT-announcement + descriptor surfaces. Owns one internal linkedSignal (prior-active-index, drives the success-arm direction prefix) — lazy by linkedSignal semantics, so the organism reads liveAnnouncement once at construction to seed it.

UX / a11y

• The live region is declarative, never imperative: liveAnnouncement is a signal the polite region renders, empty between transitions so AT stays silent on no-op ticks.
• Direction is spoken on every change: a move carries a previous/next prefix plus the landing tab; a rollback announces the safe-harbour tab or a retry, so the outcome is never silent.
• Accessible names carry position ("Tab 2 of 5: Settings") so AT does not infer it from tablist enumeration.
• Role descriptions stay distinct from the label: the tablist aria-roledescription is separate from the region aria-label, so AT never reads the same word twice.
• aria-label and aria-labelledby stay mutually exclusive (resolvedAriaLabel returns null when labelledby is bound).
• The per-tab descriptor is ARIA-by-value: the cngx-sr-only span is always in the DOM; statusPhrase only fills its content, keeping the aria-describedby reference stable.