makeDetailFetcher's read switched to a plain fetch in a82e6a1, leaving a
lone void-statement as the ctx parameter's only use — yet ctx kept being
threaded through detailStoreOf, useTimelineSource, and makeAgentHeads.
All four drop the parameter; the spec's ctxWithCall factory (which only
ever stubbed global fetch and returned a ctx nobody read) collapses to
a plain stubDetailFetch.