bug: rtk proxy does not stream long-running command output progressively

[pavelbe]

Summary

rtk proxy does not stream stdout/stderr progressively for long-running commands.
In TTY usage, output is often delivered in one block only after command completion ("silent hang" UX).

Environment

• rtk: 0.22.0
• OS: Linux (WSL2 Ubuntu)
• checked on: 19 February 2026

Reproduction

/home/pavelbe/bin/rtk proxy bash -lc 'for i in 1 2 3; do date +%s; echo probe-$i; sleep 3; done; date +%s; echo done'

Observed in TTY polling:

• command runs ~9 seconds,
• no intermediate output during execution,
• then full output appears at once at the end.

Example output block received only after completion:

1771540196
probe-1
1771540199
probe-2
1771540202
probe-3
1771540205
done

Expected

• progressive output streaming (first lines visible quickly),
• no long silent period for long-running proxy commands.

Actual

• delayed/block output delivery until process end (or near end).

Impact

• hard to distinguish "still running" vs "stuck",
• poor UX for deploy/test/log-tail workflows,
• causes extra retries/splits for chained operational commands.

Notes

No duplicate open/closed issue was found with queries:

• rtk proxy long running output
• rtk proxy no output until command finishes
• streaming stdout proxy

[pavelbe]

Update (19 February 2026): reproduced on rtk 0.22.1 as well. Same command still shows long silent period and flushes output in one block near completion.