fix(tui): provide fallback response when subagent produces no text output

cortex-tui/src/runner/event_loop.rs

@@ -844,6 +844,41 @@ impl EventLoop {
                 tool_calls_executed.join("\n")
             };
 
+            // CRITICAL: Handle case where LLM produced no text output
+            // This can happen when the LLM only makes tool calls without explanation
+            // In this case, provide a meaningful summary so the parent agent gets feedback
+            let effective_content = if final_content.trim().is_empty() {
+                if tool_calls_executed.is_empty() {
+                    // No tools and no content - something went wrong
+                    format!(
+                        "The {} subagent completed but produced no output or tool calls. \
+                         This may indicate an issue with the task or model response.",
+                        subagent_type
+                    )
+                } else {
+                    // Tools executed but no text explanation - provide summary
+                    let success_count = tool_calls_executed
+                        .iter()
+                        .filter(|s| s.contains("success"))
+                        .count();
+                    let error_count = tool_calls_executed
+                        .iter()
+                        .filter(|s| s.contains("error") || s.contains("failed"))
+                        .count();
+                    format!(
+                        "The {} subagent completed {} tool call(s) ({} successful, {} failed) \
+                         but did not provide a textual summary. Task: {}",
+                        subagent_type,
+                        tool_calls_executed.len(),
+                        success_count,
+                        error_count,
+                        description
+                    )
+                }
+            } else {
+                final_content
+            };
+
             let output = format!(
                 "{}\n\n\
                  Tools executed:\n{}\n\n\
@@ -852,7 +887,7 @@ impl EventLoop {
                  agent_type: {}\n\
                  description: {}\n\
                  </task_metadata>",
-                final_content, tools_summary, id, subagent_type, description
+                effective_content, tools_summary, id, subagent_type, description
             );
 
             let duration = started_at.elapsed();