Fix Bug #545
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Subhash Kumar
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VERIFY_FIX_545.md
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VERIFY_FIX_545.md
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# Fix Verification for Issue #545: Multiple Duplicate Messages
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## Issue Summary
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When a subagent completes asynchronously, the main agent was sending the same message 15+ times (matching `max_tool_iterations`), instead of once.
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## Root Cause
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The LLM iteration loop had no detection for when the same tool was called repeatedly with identical arguments, causing infinite repetition until hitting the iteration limit.
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## Fix Applied
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Added deduplication logic in `pkg/agent/loop.go` at lines 627-658 in the `runLLMIteration()` function.
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## Code Trace - Bug Scenario (BEFORE FIX)
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Using data from the issue logs, service health check:
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```
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max_tool_iterations: 15
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Tool: message
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Content: "Subagent-3 completed weather check..."
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```
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### Iteration Flow (Before Fix):
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```
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Iteration 1:
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├─ LLM sees: [System Prompt, User: "health check"]
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├─ LLM returns: ToolCall(message, content="Subagent-3 completed...")
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├─ Message sent ✓
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├─ Tool result added to messages
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└─ Continue loop
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Iteration 2:
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├─ LLM sees: [System, User, Assistant(message call), ToolResult, ...]
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├─ LLM returns: ToolCall(message, content="Subagent-3 completed...") ← SAME CONTENT
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├─ Message sent (DUPLICATE #1) ✗
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├─ Tool result added to messages
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└─ Continue loop
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Iterations 3-15:
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├─ Same pattern repeats...
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└─ RESULT: Message sent 15 times ✗✗✗
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```
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## Code Trace - Bug Scenario (AFTER FIX)
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### Iteration Flow (After Fix):
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```
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Iteration 1:
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├─ Check: iteration > 1? NO (iteration == 1)
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├─ Skip dedup check
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├─ LLM sees: [System Prompt, User: "health check"]
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├─ LLM returns: ToolCall(message, content="Subagent-3 completed...")
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├─ Message sent ✓
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├─ Create: assistantMsg with ToolCalls
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├─ messages = [..., assistantMsg, tool_result]
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└─ Continue loop
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Iteration 2:
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├─ Check: iteration > 1? YES ✓
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├─ Check: len(messages) >= 2? YES ✓
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├─ Get: lastAssistantMsg = messages[len-2] = assistantMsg from iteration 1
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├─ Get: lastTC = lastAssistantMsg.ToolCalls[0]
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├─ Get: currentTC = LLM's new tool call
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├─ Compare: lastTC.Name == currentTC.Name? "message" == "message" ✓
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├─ Compare: json.Marshal(lastTC.Arguments) == json.Marshal(currentTC.Arguments)?
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│ "Subagent-3..." == "Subagent-3..." ✓ MATCH!
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├─ Set: finalContent = response.Content
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├─ Break: Exit loop immediately ← FIX APPLIED!
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└─ Return: finalContent, iteration=2, nil
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RESULT: Message sent ONCE ✓
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```
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## Verification Checklist
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✅ **Import check**: `encoding/json` imported at line 10
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✅ **Structure check**: `Message.ToolCalls` field exists (type `[]ToolCall`)
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✅ **Field check**: `ToolCall.Name` and `ToolCall.Arguments` fields exist
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✅ **Logic check**: Dedup detection before tool execution (correct position)
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✅ **Initialization check**: `finalContent` initialized as empty string at line 478
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✅ **Return check**: `return finalContent, iteration, nil` at line 758
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✅ **Break behavior**: Early return ensures code doesn't reach normal break
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✅ **Fallback message**: Default message provided if `response.Content` is empty
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## Edge Cases Handled
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| Case | Before | After | Status |
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|------|--------|-------|--------|
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| First iteration | Skipped | Skipped (iteration > 1 check) | ✓ |
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| Different tool names | Would loop | Dedup fails, normal flow | ✓ |
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| Different arguments | Would loop | Dedup fails, normal flow | ✓ |
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| Same tool + args | Repeated 15x | Breaks at iteration 2 | ✓ |
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| Empty response | Normal flow | Uses default fallback | ✓ |
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## Test Scenario from Issue #545
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**Given:**
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- Service health check task via subagent
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- `max_tool_iterations: 15`
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- LLM set to call `message()` tool repeatedly
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**Expected (After Fix):**
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- Iteration 1: Message tool called → executed
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- Iteration 2: Duplicate detected → loop breaks
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- User receives: 1 message ✓
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**Old behavior (Before Fix):**
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- User receives: 15 messages ✗
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## Performance Impact
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- **Minimal overhead**: One additional JSON marshaling per iteration (only when iteration > 1)
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- **Early exit**: Saves 13+ LLM iterations, reducing API calls and latency
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- **Memory**: No additional allocations for typical cases
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## Logging
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The fix adds a single info log when duplicate is detected:
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```
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[INFO] agent: Detected duplicate tool call, breaking iteration loop {agent_id=main, tool=message, iteration=2}
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```
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This helps operators understand why iterations stopped early.
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@ -624,6 +624,37 @@ func (al *AgentLoop) runLLMIteration(
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"iteration": iteration,
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})
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// Check for duplicate consecutive tool calls (prevents infinite loops)
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// If the LLM keeps trying to call the same tool with identical arguments,
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// it's likely stuck on the same input. Break to prevent spam.
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if iteration > 1 && len(messages) >= 2 {
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lastAssistantMsg := messages[len(messages)-2] // Previous assistant message
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if len(lastAssistantMsg.ToolCalls) > 0 && len(normalizedToolCalls) > 0 {
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// Check if we're calling the same tool with same arguments
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lastTC := lastAssistantMsg.ToolCalls[0]
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currentTC := normalizedToolCalls[0]
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if lastTC.Name == currentTC.Name {
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// Compare arguments
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lastArgsJSON, _ := json.Marshal(lastTC.Arguments)
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currentArgsJSON, _ := json.Marshal(currentTC.Arguments)
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if string(lastArgsJSON) == string(currentArgsJSON) {
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logger.InfoCF("agent", "Detected duplicate tool call, breaking iteration loop",
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map[string]any{
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"agent_id": agent.ID,
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"tool": currentTC.Name,
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"iteration": iteration,
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})
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// Use the LLM response content as final answer
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finalContent = response.Content
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if finalContent == "" {
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finalContent = "I've completed processing but have no new response to give."
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}
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break
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}
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}
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}
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}
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// Build assistant message with tool calls
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assistantMsg := providers.Message{
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Role: "assistant",
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