GET /api/agents/{name}/subagents reads each subagent's newest row with
get_last_raw_message_by_subject, which publishes
$JS.API.STREAM.MSG.GET.term-sub-<agent>. The controller's NATS grant had
no STREAM.MSG.GET, so every lookup was refused and waited the 10s request
timeout, one subagent after another; six subagents passed nginx's 60s.
Grant `$JS.API.STREAM.MSG.GET.*`. A wildcard matches a whole subject
token only, so a `term-sub-*` spelling would name one stream literally;
`*` is the narrowest grant that covers the per-agent streams, the same
width as the controller's STREAM.INFO.* grant.
The lookups now run concurrently (16 at a time) with a 2s timeout each.
A lookup that fails or times out lists its subagent with a null
last_row_unix, and one warn per request names how many failed and the
first error.
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