Table: merge_queue_landing_attempts

A pull request opened for an item that already landed. The item's merge_queue_* columns keep naming its current landing while the attempt is in flight; the landing observer moves them onto the attempt only when GitHub reports it merged. See Re-landing an item that already landed.

item_id INTEGER NOT NULL -- FK → items(id)
project_id INTEGER NOT NULL -- FK → projects(id)
pr_number TEXT NOT NULL -- the attempt's pull request
enqueued_at TIMESTAMPTZ -- the attempt's arming episode; NULL until armed
opened_at TIMESTAMPTZ NOT NULL -- when the merge boundary first recorded it
closed_at TIMESTAMPTZ -- NULL while the attempt is in flight
closed_reason TEXT NOT NULL DEFAULT '' -- merged, superseded, closed unmerged, or cleared at close-out
PRIMARY KEY (item_id, pr_number)

A partial unique index keeps at most one open attempt (closed_at IS NULL) per item. Rows are kept after closing so the reason stays readable through yoke items detail get under merge_queue.attempt.

The table is additive and converges on boot; it needs no governed migration.

An unarmed attempt retains the prior landed observation. Arming replaces that observation episode; a never-armed attempt closed unmerged leaves it intact.