checkpointSettle's stopped-turn arm journals nothing #989

What goes wrong

checkpointSettle's stopped-turn arm (internal/session/checkpoint.go) journals no row: a mark drawing that lands after the turn has stopped leaves no record of what was drawn or that it was discarded. Since #962 (dev 3114937) that arm is more reachable, because a drawing now reliably reaches the boundary. This is a missing row rather than a wrong one, and giving it a word means widening checkpointDecisionAbandoned, which the bench reads.

Replication a stranger can run

internal/session/cutboundary_test.go's fixtures stage a drawing landing after the last step; assert the task journal carries a mark row for it. Today there is none.

Acceptance

• A drawing that lands on a stopped turn writes one journal row naming its decision and that the turn had stopped, in the same shape the other decisions use (late, split, continue, told).
• The bench's reader of checkpointDecisionAbandoned keeps working on the widened word (one source of truth for the decision vocabulary).

Reported by L13 (#962's report) and confirmed unfiled by the post-merge review (~/af-review-962.md). Related: #956.

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