What one edit to one task would move, before it is made

Read-only. Makes the edit on a copy of the project the way a task update writes it, then runs the same schedule calculation and reflow the update would start, and returns every task whose dates would change, the project finish before and after, and who would become overallocated. Writes nothing. apply is the one row to write to make exactly this change (the edited task's dates and constraint, through PUT /tasks/{id} or POST /tasks/bulk-update); null when the edit changes nothing. A typed start becomes Start No Earlier Than and a typed finish Finish No Earlier Than; a Must Start On or Must Finish On keeps its type and moves. Refusals: summaryDates (a summary task), finishBeforeStart, undated (a slip on a task with no dates). Needs read access to the project. Only while the server switch gantt_what_if_enabled is on; off, it answers 404.