`IndexStatusChanged` was pushed on a 3 s ticker for the life of the
process, byte-identical once the index was ready, and `config-page`
assigns it to a @state field — so a user who had once opened Settings
paid a full re-render of a 2 000-line template every 3 s, forever, for
no news. Measured sitting on Settings: 5 events and 5 re-renders per
15 s, against 0 and 0.
`emitStatus` drops a status equal to the last one it sent, which is
the rule stated once instead of at twenty call sites. The corollary is
load-bearing: every mutation of something the status derives must now
call `emitStatus` itself. Two were relying on the ticker — `si.ready`
when an existing index is adopted, and `si.cancel` when a build ends —
and without them the header badge said "Building search index" over an
index the settings page called ready. A polling loop is a hidden
dependency for every state transition that forgot to announce itself.
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