sync --once times out silently on large groups, no progress indication

[kfastov]

Problem

Running sync --once on a large group exits with code 124 (timeout) without any output or progress indication. It's unclear whether it's making progress, stuck on connection, or hitting rate limits.

Repro

# Add backfill job for a large forum group (~430k messages)
tgcli sync jobs add --chat <large-group-id> --depth 5000

# Run sync — hangs with no output, eventually times out
timeout 90 tgcli sync --once
# → exit code 124, no stdout/stderr

Expected

• Progress output: Backfilling <group>: 150/5000 messages...
• Graceful handling of partial progress (resume on next run)
• If rate-limited, show a message instead of hanging silently