diff --git a/supervisor/supervisor-poll.sh b/supervisor/supervisor-poll.sh
index 34894c3..7d57233 100755
--- a/supervisor/supervisor-poll.sh
+++ b/supervisor/supervisor-poll.sh
@@ -680,6 +680,114 @@ Instructions:
     fi
   done
 
+  # ===========================================================================
+  # P4-PROJECT: Orphaned tmux sessions — PR/issue closed externally
+  # ===========================================================================
+  status "P4: ${proj_name}: sweeping orphaned dev sessions"
+
+  while IFS= read -r _sess; do
+    [ -z "$_sess" ] && continue
+
+    # Extract issue number from dev-{project}-{issue}
+    _sess_issue="${_sess#dev-"${proj_name}"-}"
+    [[ "$_sess_issue" =~ ^[0-9]+$ ]] || continue
+
+    # Check Codeberg: is the issue still open?
+    _issue_state=$(codeberg_api GET "/issues/${_sess_issue}" 2>/dev/null \
+      | jq -r '.state // "open"' 2>/dev/null || echo "open")
+
+    _should_cleanup=false
+    _cleanup_reason=""
+
+    if [ "$_issue_state" = "closed" ]; then
+      _should_cleanup=true
+      _cleanup_reason="issue #${_sess_issue} closed externally"
+    else
+      # Issue still open — skip cleanup during active-wait phases (no PR yet is normal)
+      _phase_file="/tmp/dev-session-${proj_name}-${_sess_issue}.phase"
+      _curr_phase=$(head -1 "$_phase_file" 2>/dev/null | tr -d '[:space:]' || true)
+      case "${_curr_phase:-}" in
+        PHASE:needs_human|PHASE:awaiting_ci|PHASE:awaiting_review)
+          continue  # session has legitimate pending work
+          ;;
+      esac
+
+      # Check if associated PR is open (paginated)
+      _pr_branch="fix/issue-${_sess_issue}"
+      _has_open_pr=0
+      _pr_page=1
+      while true; do
+        _pr_page_json=$(codeberg_api GET "/pulls?state=open&limit=50&page=${_pr_page}" \
+          2>/dev/null || echo "[]")
+        _pr_page_len=$(printf '%s' "$_pr_page_json" | jq 'length' 2>/dev/null || echo 0)
+        _pr_match=$(printf '%s' "$_pr_page_json" | \
+          jq --arg b "$_pr_branch" '[.[] | select(.head.ref == $b)] | length' \
+          2>/dev/null || echo 0)
+        _has_open_pr=$(( _has_open_pr + ${_pr_match:-0} ))
+        [ "${_has_open_pr:-0}" -gt 0 ] && break
+        [ "${_pr_page_len:-0}" -lt 50 ] && break
+        _pr_page=$(( _pr_page + 1 ))
+        [ "$_pr_page" -gt 20 ] && break
+      done
+
+      if [ "$_has_open_pr" -eq 0 ]; then
+        # No open PR — check for a closed/merged PR with this branch (paginated)
+        _has_closed_pr=0
+        _pr_page=1
+        while true; do
+          _pr_page_json=$(codeberg_api GET "/pulls?state=closed&limit=50&page=${_pr_page}" \
+            2>/dev/null || echo "[]")
+          _pr_page_len=$(printf '%s' "$_pr_page_json" | jq 'length' 2>/dev/null || echo 0)
+          _pr_match=$(printf '%s' "$_pr_page_json" | \
+            jq --arg b "$_pr_branch" '[.[] | select(.head.ref == $b)] | length' \
+            2>/dev/null || echo 0)
+          _has_closed_pr=$(( _has_closed_pr + ${_pr_match:-0} ))
+          [ "${_has_closed_pr:-0}" -gt 0 ] && break
+          [ "${_pr_page_len:-0}" -lt 50 ] && break
+          _pr_page=$(( _pr_page + 1 ))
+          [ "$_pr_page" -gt 20 ] && break
+        done
+
+        if [ "$_has_closed_pr" -gt 0 ]; then
+          _should_cleanup=true
+          _cleanup_reason="PR for issue #${_sess_issue} is closed/merged"
+        else
+          # No PR at all — clean up if session idle >30min
+          # On query failure, skip rather than defaulting to epoch 0
+          if ! _sess_activity=$(tmux display-message -t "$_sess" \
+              -p '#{session_activity}' 2>/dev/null); then
+            flog "${proj_name}: Could not query activity for session ${_sess}, skipping"
+            continue
+          fi
+          _now_ts=$(date +%s)
+          _idle_min=$(( (_now_ts - _sess_activity) / 60 ))
+          if [ "$_idle_min" -gt 30 ]; then
+            _should_cleanup=true
+            _cleanup_reason="no PR found, session idle ${_idle_min}min"
+          fi
+        fi
+      fi
+    fi
+
+    if [ "$_should_cleanup" = true ]; then
+      tmux kill-session -t "$_sess" 2>/dev/null || true
+      _wt="/tmp/${proj_name}-worktree-${_sess_issue}"
+      if [ -d "$_wt" ]; then
+        git -C "$PROJECT_REPO_ROOT" worktree remove --force "$_wt" 2>/dev/null || true
+      fi
+      # Remove lock only if its recorded PID is no longer alive
+      _lock="/tmp/dev-agent-${proj_name}.lock"
+      if [ -f "$_lock" ]; then
+        _lock_pid=$(cat "$_lock" 2>/dev/null || true)
+        if [ -n "${_lock_pid:-}" ] && ! kill -0 "$_lock_pid" 2>/dev/null; then
+          rm -f "$_lock"
+        fi
+      fi
+      rm -f "/tmp/dev-session-${proj_name}-${_sess_issue}.phase"
+      fixed "${proj_name}: Cleaned orphaned session ${_sess} (${_cleanup_reason})"
+    fi
+  done < <(tmux list-sessions -F '#{session_name}' 2>/dev/null | grep "^dev-${proj_name}-" || true)
+
   # ===========================================================================
   # P4-PROJECT: Clean stale worktrees for this project
   # ===========================================================================