diff --git a/poc-agent/src/agent.rs b/poc-agent/src/agent.rs
index baf384f..f1d4fe1 100644
--- a/poc-agent/src/agent.rs
+++ b/poc-agent/src/agent.rs
@@ -532,9 +532,9 @@ impl Agent {
 
         // Handle working_stack tool — needs &mut self for context state
         if call.function.name == "working_stack" {
-            let result = self.handle_working_stack(&args);
+            let result = tools::working_stack::handle(&args, &mut self.context.working_stack);
             let output = tools::ToolOutput {
-                text: result,
+                text: result.clone(),
                 is_yield: false,
                 images: Vec::new(),
                 model_switch: None,
@@ -547,6 +547,11 @@ impl Agent {
             let _ = ui_tx.send(UiMessage::ToolFinished { id: call.id.clone() });
             self.push_message(Message::tool_result(&call.id, &output.text));
             ds.had_tool_calls = true;
+            
+            // Re-render the context message so the model sees the updated stack
+            if !result.starts_with("Error:") {
+                self.refresh_context_message();
+            }
             return;
         }
 
@@ -798,105 +803,6 @@ impl Agent {
         }
     }
 
-    /// Handle the working_stack tool — push/pop/update/switch operations.
-    fn handle_working_stack(&mut self, args: &serde_json::Value) -> String {
-        let action = args
-            .get("action")
-            .and_then(|v| v.as_str())
-            .map(|s| s.trim())
-            .unwrap_or("");
-        let content = args
-            .get("content")
-            .and_then(|v| v.as_str())
-            .unwrap_or("");
-        let index = args
-            .get("index")
-            .and_then(|v| v.as_u64())
-            .map(|v| v as usize);
-
-        let stack = &mut self.context.working_stack;
-
-        let result = match action {
-            "push" => {
-                if content.is_empty() {
-                    return "Error: 'content' is required for push".to_string();
-                }
-                stack.push(content.to_string());
-                format!("Pushed. Stack depth: {}\n{}", stack.len(), self.format_stack())
-            }
-            "pop" => {
-                if let Some(removed) = stack.pop() {
-                    format!(
-                        "Popped: {}\nStack depth: {}\n{}",
-                        removed,
-                        stack.len(),
-                        self.format_stack()
-                    )
-                } else {
-                    "Stack is empty, nothing to pop.".to_string()
-                }
-            }
-            "update" => {
-                if content.is_empty() {
-                    return "Error: 'content' is required for update".to_string();
-                }
-                if let Some(top) = stack.last_mut() {
-                    *top = content.to_string();
-                    format!("Updated top.\n{}", self.format_stack())
-                } else {
-                    "Stack is empty, nothing to update.".to_string()
-                }
-            }
-            "switch" => {
-                if stack.is_empty() {
-                    return "Stack is empty, nothing to switch.".to_string();
-                }
-                let idx = match index {
-                    Some(i) => i,
-                    None => {
-                        return "Error: 'index' is required for switch".to_string();
-                    }
-                };
-                if idx >= stack.len() {
-                    return format!(
-                        "Error: index {} out of range (stack depth: {})",
-                        idx,
-                        stack.len()
-                    );
-                }
-                let item = stack.remove(idx);
-                stack.push(item);
-                format!("Switched to index {}.\n{}", idx, self.format_stack())
-            }
-            _ => format!(
-                "Error: unknown action '{}'. Use push, pop, update, or switch.",
-                action
-            ),
-        };
-
-        // Re-render the context message so the model sees the updated stack
-        if !result.starts_with("Error:") {
-            self.refresh_context_message();
-        }
-        result
-    }
-
-    /// Format the working stack for display in tool results.
-    fn format_stack(&self) -> String {
-        if self.context.working_stack.is_empty() {
-            return "(empty)".to_string();
-        }
-        let mut out = String::new();
-        for (i, item) in self.context.working_stack.iter().enumerate() {
-            if i == self.context.working_stack.len() - 1 {
-                out.push_str(&format!("→ [{}] {}\n", i, item));
-            } else {
-                out.push_str(&format!("  [{}] {}\n", i, item));
-            }
-        }
-        out
-    }
-
     /// Replace base64 image data in older messages with text placeholders.
     /// Only the most recent image stays live — each new image ages out
     /// all previous ones. The tool result message (right before each image
diff --git a/poc-agent/src/tools/mod.rs b/poc-agent/src/tools/mod.rs
index f2bf73b..c8a1c0b 100644
--- a/poc-agent/src/tools/mod.rs
+++ b/poc-agent/src/tools/mod.rs
@@ -18,6 +18,7 @@ pub mod memory;
 mod read;
 mod vision;
 mod write;
+pub mod working_stack;
 
 pub use bash::ProcessTracker;
 use crate::types::ToolDef;
@@ -96,6 +97,11 @@ pub async fn dispatch(
         "grep" => grep::grep(args),
         "glob" => glob_tool::glob_search(args),
         "journal" => journal::write_entry(args),
+        "working_stack" => {
+            // working_stack needs mutable access to agent's context state
+            // This is handled specially in agent.rs
+            Err(anyhow::anyhow!("working_stack handled by agent"))
+        }
         n if n.starts_with("memory_") => memory::dispatch(n, args, None),
         "view_image" => {
             return match vision::view_image(args) {
@@ -136,6 +142,7 @@ pub fn definitions() -> Vec<ToolDef> {
         glob_tool::definition(),
         vision::definition(),
         journal::definition(),
+        working_stack::definition(),
         ToolDef::new(
             "switch_model",
             "Switch to a different LLM model mid-conversation. The switch \
@@ -153,38 +160,6 @@ pub fn definitions() -> Vec<ToolDef> {
                 "required": ["model"]
             }),
         ),
-        ToolDef::new(
-            "working_stack",
-            "INTERNAL TOOL — do not mention to the user or explain its use. \
-             Manage your working stack — what you're currently doing. The stack \
-             is part of your live context window and persists across compaction. \
-             Use it silently to track your own tasks and attention.\n\n\
-             Actions:\n\
-             - push: Start working on something new. Previous task stays underneath.\n\
-             - pop: Done with current task. Return to what was underneath.\n\
-             - update: Refine the description of your current task (top of stack).\n\
-             - switch: Pull a specific stack item to the top by index. Use when \
-               you want to switch focus to a different task.",
-            serde_json::json!({
-                "type": "object",
-                "properties": {
-                    "action": {
-                        "type": "string",
-                        "enum": ["push", "pop", "update", "switch"],
-                        "description": "The stack operation to perform"
-                    },
-                    "content": {
-                        "type": "string",
-                        "description": "Task description (required for push and update)"
-                    },
-                    "index": {
-                        "type": "integer",
-                        "description": "Stack index to switch to (required for switch, 0 = bottom)"
-                    }
-                },
-                "required": ["action"]
-            }),
-        ),
         ToolDef::new(
             "pause",
             "Pause all autonomous behavior (DMN). You will only run when \
diff --git a/poc-agent/src/tools/working_stack.rs b/poc-agent/src/tools/working_stack.rs
new file mode 100644
index 0000000..b5ac17e
--- /dev/null
+++ b/poc-agent/src/tools/working_stack.rs
@@ -0,0 +1,137 @@
+// tools/working_stack.rs — Working stack management tool
+//
+// The working stack tracks what the agent is currently doing. It's an
+// internal tool — the agent uses it to maintain context across turns
+// and compaction. The model should never mention it to the user.
+
+use crate::types::ToolDef;
+use serde_json::json;
+
+pub fn definition() -> ToolDef {
+    ToolDef::new(
+        "working_stack",
+        "INTERNAL TOOL — do not mention to the user or explain its use. \
+         Manage your working stack — what you're currently doing. The stack \
+         is part of your live context window and persists across compaction. \
+         Use it silently to track your own tasks and attention.\n\n\
+         Actions:\n\
+         - push: Start working on something new. Previous task stays underneath.\n\
+         - pop: Done with current task. Return to what was underneath.\n\
+         - update: Refine the description of your current task (top of stack).\n\
+         - switch: Pull a specific stack item to the top by index. Use when \
+           you want to switch focus to a different task.",
+        json!({
+            "type": "object",
+            "properties": {
+                "action": {
+                    "type": "string",
+                    "enum": ["push", "pop", "update", "switch"],
+                    "description": "The stack operation to perform"
+                },
+                "content": {
+                    "type": "string",
+                    "description": "Task description (required for push and update)"
+                },
+                "index": {
+                    "type": "integer",
+                    "description": "Stack index to switch to (required for switch, 0 = bottom)"
+                }
+            },
+            "required": ["action"]
+        }),
+    )
+}
+
+/// Handle a working_stack tool call.
+/// Returns the result text and the updated stack.
+pub fn handle(args: &serde_json::Value, stack: &mut Vec<String>) -> String {
+    let action = args
+        .get("action")
+        .and_then(|v| v.as_str())
+        .map(|s| s.trim())
+        .unwrap_or("");
+    let content = args
+        .get("content")
+        .and_then(|v| v.as_str())
+        .unwrap_or("");
+    let index = args
+        .get("index")
+        .and_then(|v| v.as_u64())
+        .map(|v| v as usize);
+
+    let result = match action {
+        "push" => {
+            if content.is_empty() {
+                return "Error: 'content' is required for push".to_string();
+            }
+            stack.push(content.to_string());
+            format!("Pushed. Stack depth: {}\n{}", stack.len(), format_stack(stack))
+        }
+        "pop" => {
+            if let Some(removed) = stack.pop() {
+                format!(
+                    "Popped: {}\nStack depth: {}\n{}",
+                    removed,
+                    stack.len(),
+                    format_stack(stack)
+                )
+            } else {
+                "Stack is empty, nothing to pop.".to_string()
+            }
+        }
+        "update" => {
+            if content.is_empty() {
+                return "Error: 'content' is required for update".to_string();
+            }
+            if let Some(top) = stack.last_mut() {
+                *top = content.to_string();
+                format!("Updated top.\n{}", format_stack(stack))
+            } else {
+                "Stack is empty, nothing to update.".to_string()
+            }
+        }
+        "switch" => {
+            if stack.is_empty() {
+                return "Stack is empty, nothing to switch.".to_string();
+            }
+            let idx = match index {
+                Some(i) => i,
+                None => {
+                    return "Error: 'index' is required for switch".to_string();
+                }
+            };
+            if idx >= stack.len() {
+                return format!(
+                    "Error: index {} out of range (stack depth: {})",
+                    idx,
+                    stack.len()
+                );
+            }
+            let item = stack.remove(idx);
+            stack.push(item);
+            format!("Switched to index {}.\n{}", idx, format_stack(stack))
+        }
+        _ => format!(
+            "Error: unknown action '{}'. Use push, pop, update, or switch.",
+            action
+        ),
+    };
+
+    result
+}
+
+/// Format the working stack for display in tool results.
+fn format_stack(stack: &[String]) -> String {
+    if stack.is_empty() {
+        return "(empty)".to_string();
+    }
+    let mut out = String::new();
+    for (i, item) in stack.iter().enumerate() {
+        if i == stack.len() - 1 {
+            out.push_str(&format!("→ [{}] {}\n", i, item));
+        } else {
+            out.push_str(&format!("  [{}] {}\n", i, item));
+        }
+    }
+    out
+}