You could already say “never on Sundays” — a weekday, every Sunday. What was missing was the single date: “on 14 November I'm away”. You removed the session from your plan and it came back on the next regeneration, because the plan is rebuilt from your settings and that absence was recorded nowhere.
The gesture
On the Plan tab, switch to edit mode. The seven-day strip becomes clickable: one click closes a day, a second click reopens it. A closed day is told apart from a rest day by a dashed outline and a cross — not by colour alone.
A line appears under the strip: “You closed this day: the plan will schedule no session on it”, followed by the “Regenerate the plan” link. Regeneration is what redistributes the mileage across the remaining days so your objective still holds. The plan never regenerates on its own: you decide when.
You can also close a rest day. That may sound pointless — there is nothing to remove — but it is the opposite: on regeneration, the engine will know it cannot move a session onto that day.
What it does not do
Reopening a day puts no session back. The plan stays yours: if you want a session to return, regeneration will place it where it makes sense.
Closing a date never moves a race or a milestone. An event falls on its date whatever happens — a race does not shift because you closed the day. Same rule as for closed weekdays.
And closing a day does not yet offer you a realigned plan by itself: for now you press Regenerate. The automatic proposal is coming.
If the gesture is refused
If your kennel access has become read-only, closing is refused and the screen says so — rather than showing a closed day that was recorded nowhere.