refactor: use baudbot- prefix for scalable tmux cleanup

Replace per-session cleanup with prefix-based pattern. Now adding new
tmux sessions requires zero cleanup code.

## Changes

1. Rename session: slack-bridge → baudbot-slack-bridge
2. Kill all 'baudbot-*' sessions instead of individual session names

## Scalability

Before (not scalable):
  • Add new tmux session → add new kill-session command
  • O(n) cleanup code per session

After (scalable):
  • Add new tmux session with baudbot- prefix
  • Zero additional cleanup code needed
  • O(1) regardless of number of sessions

## Pattern

All agent tmux sessions use 'baudbot-' prefix:
  - baudbot-slack-bridge (Slack integration)
  - baudbot-metrics (future: metrics collection)
  - baudbot-health-monitor (future: health checks)
  - etc.

One command kills them all:
  tmux list-sessions -F '#{session_name}' | grep '^baudbot-' | xargs tmux kill-session -t

## Hybrid Approach

- Most services: killed via PGID (automatic, zero code)
- Tmux sessions: killed via prefix pattern (scalable, minimal code)

This combines the best of both: automatic cleanup for regular processes,
convention-based cleanup for tmux (which escapes PGID due to setsid).

Author: Baudbot

pi/skills/control-agent/startup-pi.sh

@@ -86,11 +86,10 @@ fi
 BRIDGE_LOG_DIR="$HOME/.pi/agent/logs"
 BRIDGE_LOG_FILE="$BRIDGE_LOG_DIR/slack-bridge.log"
 BRIDGE_DIR="/opt/baudbot/current/slack-bridge"
-BRIDGE_TMUX_SESSION="slack-bridge"
+BRIDGE_TMUX_SESSION="baudbot-slack-bridge"
 
 mkdir -p "$BRIDGE_LOG_DIR"
 
-
 # --- Detect bridge mode ---
 BRIDGE_SCRIPT=""
 if [ -f "$BRIDGE_DIR/broker-bridge.mjs" ] && varlock run --path "$HOME/.config/" -- sh -c '
@@ -127,10 +126,14 @@ fi
 # termination. We need to explicitly kill old sessions before creating new ones.
 MAX_CONSECUTIVE_FAILURES=10
 
-# Kill old tmux session if it exists (tmux sessions have their own PGID)
-if tmux has-session -t "$BRIDGE_TMUX_SESSION" 2>/dev/null; then
-  echo "Killing old tmux session: $BRIDGE_TMUX_SESSION"
-  tmux kill-session -t "$BRIDGE_TMUX_SESSION" 2>/dev/null || true
+# Kill all agent tmux sessions (prefix: baudbot-*)
+# Tmux sessions create their own PGID, so they survive process group cleanup.
+# Using a naming convention allows us to kill all agent sessions without
+# tracking individual session names.
+AGENT_SESSIONS=$(tmux list-sessions -F '#{session_name}' 2>/dev/null | grep '^baudbot-' || true)
+if [ -n "$AGENT_SESSIONS" ]; then
+  echo "Killing agent tmux sessions: $AGENT_SESSIONS"
+  echo "$AGENT_SESSIONS" | xargs -r -I{} tmux kill-session -t {} 2>/dev/null || true
   sleep 1
 fi