Read every board row's status in one query - #360
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The board asked the read side for each row's status on its own, so a page of N subjects ran N driving-run queries and each viewer's /stream repeated them every couple of seconds. Run.get_latest_for_subjects now returns the driving run of every subject on the page, with its agent calls, in one statement.
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Every app board asked the read side for one row's status at a time. A page of N subjects ran N driving-run queries, and each viewer's
/streamrepeated them every couple of seconds. The row cap an app writes intolist_summariesis the symptom.Run.get_latest_for_subjectsreturns the driving run of every subject on the page in one statement, with its agent calls.get_subject_statusescomposes those into the sameSubjectStatusvalues through the same_status, and the mounted board reads them once.The wire does not change, and no app changes: every board and every board stream gets this as it stands.
One cost moves the other way. The batch loads agent calls for the whole page, so a board of parked rows now runs one call query where it ran none. The test that pinned "a parked row loads no agent calls" is replaced by the invariant that matters for a board: the query count does not grow with the number of rows.
get_subject_statusand bothget_status()methods are untouched, and the batch takes noworkflownarrowing — a board never asks for one.