fix: chat session reliability, cost, and hygiene (empty-response guard, tool truncation, delete, titles)

- Empty/refusal responses retried once, then surfaced as errors instead of silent blanks
- Chinese refusal boilerplate detected via denylist + non-ASCII heuristic
- Bulk-tool preference added to SOUL.md (list_lxcs over per-entity get_lxc_state)
- Tool results truncated to 4KB on persist; get_state_snapshot filters null-state entities
- Session delete (DELETE /sessions/{id} + confirm-on-second-click UI)
- Session titles auto-generated from assistant answer instead of raw user message

cmd/nomos/store.go

@@ -10,6 +10,8 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
+const maxToolResultSize = 4096
+
 type store struct {
 	pool *pgxpool.Pool
 }
@@ -71,10 +73,45 @@ func (s *store) saveMessage(ctx context.Context, sessionID, role string, content
 	}
 	_, err := s.pool.Exec(ctx,
 		`INSERT INTO agent_messages (session_id, role, content) VALUES ($1, $2, $3)`,
-		sessionID, role, content)
+		sessionID, role, truncateToolResults(content))
 	return err
 }
 
+func truncateToolResults(content json.RawMessage) json.RawMessage {
+	var m map[string]any
+	if err := json.Unmarshal(content, &m); err != nil {
+		return content
+	}
+	toolCalls, ok := m["tool_calls"].([]any)
+	if !ok || len(toolCalls) == 0 {
+		return content
+	}
+	changed := false
+	for i, raw := range toolCalls {
+		tc, ok := raw.(map[string]any)
+		if !ok {
+			continue
+		}
+		if result, ok := tc["result"]; ok {
+			resultJSON, _ := json.Marshal(result)
+			if len(resultJSON) > maxToolResultSize {
+				tc["result"] = string(resultJSON[:maxToolResultSize]) + fmt.Sprintf("...truncated (%d bytes total)", len(resultJSON))
+				toolCalls[i] = tc
+				changed = true
+			}
+		}
+	}
+	if !changed {
+		return content
+	}
+	m["tool_calls"] = toolCalls
+	out, err := json.Marshal(m)
+	if err != nil {
+		return content
+	}
+	return out
+}
+
 func (s *store) touchSession(ctx context.Context, id string) {
 	if s != nil {
 		s.pool.Exec(ctx, `UPDATE agent_sessions SET last_active_at=now() WHERE id=$1`, id)
@@ -126,6 +163,26 @@ func (s *store) getMessages(ctx context.Context, sessionID string) ([]message, e
 	return out, rows.Err()
 }
 
+func (s *store) deleteSession(ctx context.Context, id string) error {
+	if s == nil {
+		return nil
+	}
+	_, err := s.pool.Exec(ctx, `DELETE FROM agent_messages WHERE session_id = $1`, id)
+	if err != nil {
+		return err
+	}
+	_, err = s.pool.Exec(ctx, `DELETE FROM agent_sessions WHERE id = $1`, id)
+	return err
+}
+
+func (s *store) updateSessionTitle(ctx context.Context, id, title string) error {
+	if s == nil {
+		return nil
+	}
+	_, err := s.pool.Exec(ctx, `UPDATE agent_sessions SET title = $1 WHERE id = $2`, title, id)
+	return err
+}
+
 // resolveAgentID looks up the UUID of the agent entity (e.g. "agent:nomos").
 // Returns uuid.Nil if the store is absent or the slug is unknown.
 func (s *store) resolveAgentID(ctx context.Context, slug string) uuid.UUID {