Restructure per review: state what the system promises before how the
code delivers it. The thin product-decision table becomes a full §1
behavioural spec written in zero implementation vocabulary -- user
operations, scheduling semantics, the skip-not-queue overlap decision,
the busy-wait guarantees (delayed, never lost; ordered by due time; no
catch-up of missed cron periods), the failure/recovery table, and an
explicit non-goals list (no queue, no punctuality guarantee, no task
credentials, single scheduler instance) -- each promise cross-referenced
to the section whose mechanism delivers it.
The mechanism chapters absorb what the spec now promises: §6.2 explains
where waiting goes (the table as an implicit priority queue via the
claim query's ordering), §6.3 and a new pitfall entry name the
budget-leak boundary when a completion callback is lost, §8's defence
table gains the race-window column and a per-layer error-translation
table as the journey's unhappy half, and the HTTP endpoint block moves
beside the commands it carries.
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