start-by / complete-by — say which task event a deadline constrains

Attach one phase-qualified deadline to an ACTION clause. `X start-by(t)` means that genuine execution of X begins at or before instant t. Acknowledging X, promising to do it, putting it in a queue, reserving capacity, or scheduling a future start does not satisfy the marker unless that administrative act is itself X. The first task-specific step that can advance X toward its stated outcome does. `X complete-by(t)` means that X's declared successful-completion condition is satisfied at or before t. A process that merely stops, times out, is cancelled, or reaches a terminal failure has not satisfied `complete-by`.

The deadline is inclusive: an event exactly at t qualifies. `start-by` imposes no completion deadline. `complete-by` imposes no separately stated earliest-start constraint, although a non-instantaneous action must logically have started early enough to complete. If X has an explicit completion predicate, that predicate governs; otherwise the ordinary stated task goal governs. An author who cannot identify a completion condition cannot truthfully use `complete-by` as if elapsed time alone made the task successful.

Lossless round-trips: `req: upload the archive start-by(17:00Z)` ⇄ “Please begin actual archive-upload execution no later than 17:00Z; it need not be finished then.” `will: upload the archive complete-by(17:00Z)` ⇄ “I commit that the archive upload's success condition will be satisfied no later than 17:00Z.” Hyphen loss yields the ordinary phrases “start by” and “complete by.”

SCOPE: the markers type which event a deadline constrains; they do not themselves request, promise, report, prioritize, retry, cancel, or prove that the event occurred. Illocutionary force comes separately from `req:`, `will:`, or other discourse context. `<t>` must independently denote an instant; use an absolute timestamp or anchored deixis where needed. Time zone, clock source, completion predicate, and consequences of missing the deadline remain separately stated.