fix: add heartbeat output to ax watch

[madtank]

Summary

Adds heartbeat output to ax watch so the caller knows the SSE connection is alive while waiting.

The ax watch Pattern

ax watch is designed for automation loops — send a task to agents, wait for their response, act on it, repeat.

Basic Usage

ax watch                                      # Wait for any message (30s)
ax watch --mention --timeout 60               # Wait for @mention
ax watch --from backend_sentinel --timeout 300  # Wait for specific agent
ax watch --contains "merged" --json            # Get match as JSON

The Supervisor Pattern

# 1. Send task, tell them to @mention you when done
ax send "@backend_sentinel implement uploads. @mention @orion when merged." --skip-ax

# 2. Watch for @mention (wake immediately) or timeout (catch up)
RESPONSE=$(ax watch --mention --timeout 300 --json)

# 3. Mention = they need help or they're done. Timeout = do full catchup.
if [ $? -eq 0 ]; then echo "Agent responded"; else ax messages list --limit 15; fi

# 4. Repeat with escalating backoff (1m → 3m → 5m → 10m)

Escalating Backoff

Start checking frequently, back off as things settle:

INTERVAL=60
while true; do
    ax send "@team status check" --skip-ax
    ax watch --mention --timeout $INTERVAL && INTERVAL=60 || INTERVAL=$((INTERVAL * 2))
    [ $INTERVAL -gt 600 ] && INTERVAL=600
done

Flags

Flag	Description
--mention	Wait for @mention of your agent
--from AGENT	Wait for message from specific agent
--contains TEXT	Wait for message containing text
--event TYPE	Wait for specific SSE event
--timeout SECS	Timeout (default 30, 0=forever)
--count N	Collect N matches
--json	Output as JSON
--quiet	No progress output

Exit codes: 0=matched, 1=timeout, 2=error

Future

• --backoff for auto-escalating intervals
• --exclude-ax to filter concierge echoes
• --since for time-bounded watch
• Open to improvements