diff --git a/Project.toml b/Project.toml
index 5d1d1e9..fa28a2b 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "YiemAgent"
 uuid = "e012c34b-7f78-48e0-971c-7abb83b6f0a2"
-version = "0.9.0"
+version = "0.9.1"
 authors = ["narawat lamaiin <narawat@outlook.com>"]
 
 [deps]
diff --git a/src/agentCore.jl b/src/agentCore.jl
index 5c2cc74..acc80b2 100644
--- a/src/agentCore.jl
+++ b/src/agentCore.jl
@@ -170,7 +170,7 @@ function yiemAgent(
 
   tools = OrderedDict{String, agentTool}()
   registerAllTools(tools, mcpServer; eventSink=eventSink, sessionId=sessionId)
-
+  eventSink("instantiate an agent")
   # Create struct with a placeholder task, then spawn and replace it
   agent = yiemAgent(
     agentState(systemPrompt, model, tools, messages),
@@ -194,7 +194,7 @@ function yiemAgent(
 
   # Spawn the background loop and attach it
   agent._agentLoop = @spawn _agentLoop(agent)
-
+  eventSink("agent instantiated")
   return agent
 end
 
@@ -260,31 +260,36 @@ function _agentLoop(agent::yiemAgent)
       agent.inputChannel -> nothing
       agent.followUpChannel -> nothing
     """
-
+    agent.eventSink("_agentLoop starting")
     while true
       while newUserMsg === nothing 
         if isready(agent.inputChannel)
           # agent process new user msg immediately after the current tool call finished.
           newUserMsg = take!(agent.inputChannel)   
+          agent.eventSink("take new user message")
         else
           # check followUp message after _processMessage() is done
           if typeof(processingTask) == Task && istaskdone(processingTask) == true
+            agent.eventSink("_processMessage() done")
             # if agent runs is done but followUpChannel has messages,
             # put new message in inputChannel instead
             if isready(agent.followUpChannel)
               while isready(agent.followUpChannel)
+                agent.eventSink("put followUp message to input channel")
                 followUpMsg = take!(agent.followUpChannel)
                 put!(agent.inputChannel, followUpMsg)
               end
               processingTask = nothing        # reset
               result = nothing                # reset
             else  # _processMessage() done and no followUp message.
+              agent.eventSink("no followUp message")
               result = deepcopy(agent._state.messages[end])
               # filter out reasoningContent in-place
               filter!(c -> !(c isa reasoningContent), result.content)
               # format output
               respondToUI = _assistantMessageToOpenAI(result)
               put!(agent.outputChannel, respondToUI)
+              agent.eventSink("put result to output channel")
               processingTask = nothing        # reset
               result = nothing                # reset
             end
@@ -314,6 +319,7 @@ function _agentLoop(agent::yiemAgent)
       else
         # spawn new _processMessage() if it is not already running.
         if processingTask === nothing
+          agent.eventSink("spawn new _processMessage()")
           # discard all messages in followUpChannel
           while isready(agent.followUpChannel)
             _ = take!(agent.followUpChannel)
@@ -335,8 +341,10 @@ function _agentLoop(agent::yiemAgent)
           ) 
         end
         put!(processMessageInputCh, newUserMsg)
+        agent.eventSink("put new user msg to processMessageInputCh")
         newUserMsg = nothing # reset
       end
+
     end
   catch e
     bt = catch_backtrace()
@@ -344,7 +352,7 @@ function _agentLoop(agent::yiemAgent)
         showerror(io, e, bt)
         println(io)
     end
-    eventSink(errMsg; publish=true)
+    agent.eventSink(errMsg; publish=true)
 
     # On any error, send error response and exit the loop
     @error "Agent loop failed" error=e
@@ -395,6 +403,8 @@ function _processMessage(
   # loop until llmCall() response didn't use tool calls
   final_response = nothing
 
+  eventSink("▶ _processMessage: entered")
+
   """ example message in inputChannel
   Dict(
       "role" => "user",
@@ -420,6 +430,7 @@ function _processMessage(
         end
         newUserMsg = OpenAiToUserMessage(newUserMsg_openai)
         push!(agentMsgHistory, newUserMsg)
+        eventSink("▶ _processMessage: user msg pushed")
       end
       # call prepareContext()
       state = agentState(systemPrompt, nothing, tools, agentMsgHistory)
@@ -427,6 +438,7 @@ function _processMessage(
       # Call formatMessagesForLLM() to format for LLM
       formattedMessages = formatMessagesForLLM(preparedContext, eventSink)
 
+      eventSink("▶ _processMessage: context")
       eventSink("Thinking...")
       """ response example
       response = JSON.Object{String, Any}("finish_reason" => "tool_calls", "index" => 0, "message" => JSON.Object{String, Any}("role" => "assistant", "content" => "", "reasoning_content" => "Here's a thinking process:\n\n1.  **Identify User Request**: The user is asking for the weather in Bangkok.\n2.  **Locate Relevant Tool**: I have a `getWeather` function available.\n3.  **Check Function Parameters**:\n   - `city` (required): City and country, e.g., 'San Francisco, CA' or 'Tokyo, Japan'\n   - `units` (optional, default \"celsius\"): Temperature scale (\"celsius\" or \"fahrenheit\")\n4.  **Prepare Parameters**:\n   - `city`: \"Bangkok, Thailand\" (adding country for clarity, though just \"Bangkok\" might work, following the example format is safer)\n   - `units`: Not specified, so I'll use the default (\"celsius\")\n5.  **Execute Tool Call**: Call `getWeather` with `city: \"Bangkok, Thailand\"`\n6.  **Anticipate Response**: The function will return current weather and forecast data for Bangkok. I'll then format it nicely for the user.\n   - *Self-Correction/Verification during thought*: The prompt says \"city: City and country, e.g., 'San Francisco, CA' or 'Tokyo, Japan'\". I'll use \"Bangkok, Thailand\". The `units` parameter is optional, so I'll omit it to use the default.\n   - Proceed with tool call.✅\n", "tool_calls" => Any[JSON.Object{String, Any}("type" => "function", "function" => JSON.Object{String, Any}("name" => "getWeather", "arguments" => "{\"city\":\"Bangkok, Thailand\"}"), "id" => "6fOilR5QPcdppbAAHluhkRyUDu3oWMAL")]))
@@ -434,12 +446,15 @@ function _processMessage(
       response = llmCall(formattedMessages, eventSink=eventSink)
 
       # Extract tool calls from LLM response content blocks
-      hasToolCalls, toolCallList, assistant_msg = _extractToolCalls(response)
+      hasToolCalls, toolCallList, assistant_msg = _extractToolCalls(response, eventSink)
 
       # Add assistant message (tool calls or text) to history for next LLM turn
       push!(agentMsgHistory, assistant_msg)
+      eventSink("▶ _processMessage: LLM response")
 
       if hasToolCalls && length(toolCallList) > 0
+        eventSink("▶ _processMessage: tool calls")
+
         # Build context and config for executeToolCalls
 
         config = agentLoopConfig(
@@ -452,11 +467,13 @@ function _processMessage(
         # call executeToolCalls()
         toolResultBatch = executeToolCalls(preparedContext, assistant_msg, toolCallList, config, 
                                           signal, eventSink)      
+        eventSink("▶ _processMessage: tool batch")
         # save toolResults to messages
         for toolResult in toolResultBatch.messages
           push!(agentMsgHistory, toolResult)
         end
         if toolResultBatch.terminate
+          eventSink("▶ _processMessage: TERMINATE branch")
           # If toolResultBatch requested termination, build a final response
           final_content = [textContent("Tool execution completed.")]
           for toolResult in toolResultBatch.messages
@@ -488,6 +505,7 @@ function _processMessage(
           break
         end
       else
+        eventSink("▶ _processMessage: FINAL response")
         # LLM did not use tool calls — 
         break
       end
@@ -499,9 +517,11 @@ function _processMessage(
         end
 
         eventSink(err_msg; publish=true)
+        eventSink("▶ _processMessage: CAUGHT ERROR")
     end
   end
 
+  eventSink("▶ _processMessage: exited")
   return nothing
 end
 
@@ -611,9 +631,12 @@ The message is constructed from:
   1)  llm_useTool = JSON.Object{String, Any}("finish_reason" => "tool_calls", "index" => 0, "message" => JSON.Object{String, Any}("role" => "assistant", "content" => "", "reasoning_content" => "Here's a thinking process:\n\n1.  **Identify User Request**: The user is asking for the weather in Bangkok.\n2.  **Locate Relevant Tool**: I have a `getWeather` function available.\n3.  **Check Function Parameters**:\n   - `city` (required): City and country, e.g., 'San Francisco, CA' or 'Tokyo, Japan'\n   - `units` (optional, default \"celsius\"): Temperature scale (\"celsius\" or \"fahrenheit\")\n4.  **Prepare Parameters**:\n   - `city`: \"Bangkok, Thailand\" (adding country for clarity, though just \"Bangkok\" might work, following the example format is safer)\n   - `units`: Not specified, so I'll use the default (\"celsius\")\n5.  **Execute Tool Call**: Call `getWeather` with `city: \"Bangkok, Thailand\"`\n6.  **Anticipate Response**: The function will return current weather and forecast data for Bangkok. I'll then format it nicely for the user.\n   - *Self-Correction/Verification during thought*: The prompt says \"city: City and country, e.g., 'San Francisco, CA' or 'Tokyo, Japan'\". I'll use \"Bangkok, Thailand\". The `units` parameter is optional, so I'll omit it to use the default.\n   - Proceed with tool call.✅\n", "tool_calls" => Any[JSON.Object{String, Any}("type" => "function", "function" => JSON.Object{String, Any}("name" => "getWeather", "arguments" => "{\"city\":\"Bangkok, Thailand\"}"), "id" => "6fOilR5QPcdppbAAHluhkRyUDu3oWMAL")]))
   2)  llm_notUseTool = JSON.Object{String, Any}("finish_reason" => "stop", "index" => 0, "message" => JSON.Object{String, Any}("role" => "assistant", "content" => "The weather in London, UK is currently Sunny with a temperature of 22°C.", "reasoning_content" => "The user asked for the weather in London.\nI called the `getWeather` tool for London, UK.\nThe response indicates it's Sunny and 22°C.\nI will convey this information to the user.\n"))
 """
-function _extractToolCalls(response)
+function _extractToolCalls(response, eventSink=nothing)
     hasToolCalls = false
     toolCallList = agentToolCall[]
+    if eventSink !== nothing
+        eventSink("▶ _extractToolCalls: parsing response")
+    end
 
     # Helper: parse args (JSON string -> Dict, or pass through)
     parse_args(raw) = raw isa AbstractDict && !(raw isa Dict{String,Any}) ? 
@@ -943,9 +966,11 @@ function prepareToolCall(
 )::Union{preparedToolCall,immediateOutcome}
 
   # pick a called tool from tool store
+  eventSink("▶ prepareToolCall: resolving")
   tool = get(context.tools, toolCall.name, nothing) 
   
   if tool === nothing
+    eventSink("▶ prepareToolCall: NOT FOUND")
     return immediateOutcome(createErrorToolResult("Tool $toolCall.name not found"), true)
   end
 
@@ -953,6 +978,7 @@ function prepareToolCall(
     # 1. prepare arguments (tool-specific transform)
     prepared = prepareToolCallArguments(tool, toolCall)
     validatedArgs = validateToolArguments(tool, prepared)
+    eventSink("▶ prepareToolCall: validated")
     # 2. beforeToolCall hook — can block
     if config.beforeToolCall !== nothing
 
@@ -1032,8 +1058,10 @@ function executePreparedToolCall(
     eventSink,
   )::executedOutcome
 
+  eventSink("▶ execute: START")
   try
     result = prep.tool.execute(prep.toolCall.id, prep.args, signal, eventSink)
+    eventSink("▶ execute: END")
     return executedOutcome(result, false)
   catch e
     bt = catch_backtrace()
@@ -1042,6 +1070,7 @@ function executePreparedToolCall(
         println(io)
     end
     eventSink(errMsg; publish=true)
+    eventSink("▶ execute: ERROR")
 
     return executedOutcome(createErrorToolResult(sprint(showerror, e)), true)
   end
@@ -1115,6 +1144,7 @@ function finalizeExecutedToolCall(
     eventSink
 )::finalizedOutcome
 
+  eventSink("▶ finalize: START")
   result = executed.result
   isError = executed.isError
   if config.afterToolCall !== nothing
@@ -1140,6 +1170,7 @@ function finalizeExecutedToolCall(
       isError = true
     end
   end
+  eventSink("▶ finalize: END")
   return finalizedOutcome(prep.toolCall, result, isError)
 end
 
@@ -1207,6 +1238,7 @@ function executeToolCallsSequential(
 )::agentToolCallBatch
   finalizedCalls = finalizedOutcome[]
   messages = toolResultMessage[]
+  eventSink("▶ executeToolCallsSequential: batch start")
 
   for tc in toolCalls
     prep = prepareToolCall(context, assistantMsg, tc, config, signal, eventSink)
@@ -1224,6 +1256,7 @@ function executeToolCallsSequential(
         break
     end
   end
+  eventSink("▶ executeToolCallsSequential: batch end")
   return agentToolCallBatch(messages, shouldTerminate(finalizedCalls))
 end
 
@@ -1294,6 +1327,7 @@ function executeToolCallsParallel(
 )::agentToolCallBatch
 
   entries = Union{finalizedOutcome,Task}[]
+  eventSink("▶ executeToolCallsParallel: batch start")
 
   for tc in toolCalls
     toolExecStartEvent(tc.id, tc.name, tc.arguments)
@@ -1333,6 +1367,7 @@ function executeToolCallsParallel(
       push!(messages, createToolResultMessage(f))
   end
 
+  eventSink("▶ executeToolCallsParallel: batch end")
   return agentToolCallBatch(messages, shouldTerminate(finalizedCalls))
 end
 
@@ -1403,6 +1438,7 @@ function executeToolCalls(
           break
       end
   end
+  eventSink("▶ executeToolCalls: dispatch")
   if config.toolExecution == "sequential" || hasSequential
     return executeToolCallsSequential(context, assistantMsg, toolCalls, config, signal,
                                       eventSink)
@@ -1447,8 +1483,11 @@ OpenAiToUserMessage(msg)
 # => userMessage("user", [textContent("Hello")], DateTime(...))
 ```
 """
-function OpenAiToUserMessage(msg::AbstractDict)::userMessage
+function OpenAiToUserMessage(msg::AbstractDict, eventSink=nothing)::userMessage
     content_blocks = Vector{messageContent}()
+    if eventSink !== nothing
+        eventSink("▶ OpenAiToUserMessage: parsing")
+    end
 
     raw_content = get(msg, "content", Any[])
     if raw_content isa Vector
@@ -1472,6 +1511,9 @@ function OpenAiToUserMessage(msg::AbstractDict)::userMessage
         end
     end
 
+    if eventSink !== nothing
+        eventSink("▶ OpenAiToUserMessage: done")
+    end
     return userMessage(content=content_blocks)
 end
 
diff --git a/src/toolRegistry.jl b/src/toolRegistry.jl
index 49e5ad8..95c4784 100644
--- a/src/toolRegistry.jl
+++ b/src/toolRegistry.jl
@@ -198,7 +198,7 @@ Add `tool` to `tools`, overwriting any existing tool with the same name.
 function registerTool(tools::OrderedDict{String, agentTool}, tool::agentTool; eventSink=nothing
   )::OrderedDict{String, agentTool}
     tools[tool.name] = tool
-    println("[toolRegistry] Registered tool: $(tool.name)")
+    eventSink("[toolRegistry] Registered tool: $(tool.name)")
     return tools
 end
 
@@ -282,7 +282,9 @@ Register all tools for an agent:
 """
 function registerAllTools(tools::OrderedDict{String, agentTool}, mcpserver=nothing; eventSink=nothing, sessionId=nothing)
     list_t = listTool(tools, mcpserver; eventSink=eventSink, sessionId=sessionId)
+    eventSink("registering tools")
     registerTool(tools, list_t; eventSink=eventSink)
+    eventSink("registering tools done")
 end
 
 end # module