Decides whether a behavior-changing fix needs an in-app notice, then builds one that reaches only the affected users and can be removed later. Use when a change alters what an existing user sees without them doing anything — a metric moves, a chart shifts, a count drops, a date range resolves differently, a matcher matches differently — and when adding, reviewing, or removing such a notice. Trigger terms: behavior change, breaking change, semantics change, "results may differ", change notice, deprecation banner, migration banner. Carries the gate (narrow to the affected users with a tested predicate, or do not ship a notice at all), the pattern from `SqlInsightDateFilterNotice`, where to anchor the notice, and the flag-based removal path. Not for new features (use the changelog), not for permanent per-object warnings computed by the backend, and not for the wording itself (see `/writing-user-facing-copy`).