## Summary
The PUT handler at `/realtime/v1/streams/:runId/:target/:streamId` ran
`taskRun.update({ realtimeStreams: { push: streamId } })` on every call,
even when the `streamId` was already present. SDK call patterns that
re-initialize the same stream key on every chunk produce a per-write row
UPDATE, duplicate entries pile up in the array, and the row-lock + TOAST
rewrite cost grows unbounded on long-running stream sessions.
## Fix
Mirror the sibling append handler: read the array first and only push
when the `streamId` isn't already present. Identical behavior for
first-time stream creation; repeat creates short-circuit to a single
indexed read. The dashboard's per-run stream listing keeps working
because the first create still records the entry.
## Test plan
- [ ] A fresh PUT for a new `(run, streamId)` adds the entry to the
array
- [ ] A repeat PUT for the same pair leaves the array unchanged
- [ ] 404 is returned when the run doesn't exist; 400 when the run is
completed
Eric Allam
f88d4018cc