diff --git a/internal/ui/model_test.go b/internal/ui/model_test.go
new file mode 100644
index 00000000..6ccfde0c
--- /dev/null
+++ b/internal/ui/model_test.go
@@ -0,0 +1,553 @@
+package ui
+
+import (
+	"errors"
+	"testing"
+
+	tea "charm.land/bubbletea/v2"
+	"charm.land/fantasy"
+	"github.com/mark3labs/mcphost/internal/app"
+)
+
+// --------------------------------------------------------------------------
+// Stub AppController
+// --------------------------------------------------------------------------
+
+// stubAppController is a minimal implementation of AppController for tests.
+// It records which methods were called and allows the test to inspect the results.
+type stubAppController struct {
+	runCalls         []string
+	cancelCalled     int
+	clearQueueCalled int
+	clearMsgCalled   int
+	queueLen         int
+}
+
+func (s *stubAppController) Run(prompt string) {
+	s.runCalls = append(s.runCalls, prompt)
+}
+
+func (s *stubAppController) CancelCurrentStep() {
+	s.cancelCalled++
+}
+
+func (s *stubAppController) QueueLength() int {
+	return s.queueLen
+}
+
+func (s *stubAppController) ClearQueue() {
+	s.clearQueueCalled++
+	s.queueLen = 0
+}
+
+func (s *stubAppController) ClearMessages() {
+	s.clearMsgCalled++
+}
+
+// --------------------------------------------------------------------------
+// Stub child components
+// --------------------------------------------------------------------------
+
+// stubStreamComponent satisfies streamComponentIface without rendering anything.
+type stubStreamComponent struct {
+	resetCalled int
+	height      int
+	lastMsg     tea.Msg
+}
+
+func (s *stubStreamComponent) Init() tea.Cmd { return nil }
+func (s *stubStreamComponent) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	s.lastMsg = msg
+	return s, nil
+}
+func (s *stubStreamComponent) View() tea.View  { return tea.NewView("") }
+func (s *stubStreamComponent) Reset()          { s.resetCalled++ }
+func (s *stubStreamComponent) SetHeight(h int) { s.height = h }
+
+// stubInputComponent satisfies inputComponentIface without rendering anything.
+type stubInputComponent struct {
+	lastMsg tea.Msg
+}
+
+func (s *stubInputComponent) Init() tea.Cmd { return nil }
+func (s *stubInputComponent) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	s.lastMsg = msg
+	return s, nil
+}
+func (s *stubInputComponent) View() tea.View { return tea.NewView("") }
+
+// --------------------------------------------------------------------------
+// newTestAppModel creates an AppModel with stub children for unit tests.
+// --------------------------------------------------------------------------
+
+func newTestAppModel(ctrl AppController) (*AppModel, *stubStreamComponent, *stubInputComponent) {
+	stream := &stubStreamComponent{}
+	input := &stubInputComponent{}
+	m := &AppModel{
+		state:       stateInput,
+		appCtrl:     ctrl,
+		stream:      stream,
+		input:       input,
+		renderer:    NewMessageRenderer(80, false),
+		compactRdr:  NewCompactRenderer(80, false),
+		compactMode: false,
+		modelName:   "test-model",
+		width:       80,
+		height:      24,
+	}
+	return m, stream, input
+}
+
+// --------------------------------------------------------------------------
+// Helpers
+// --------------------------------------------------------------------------
+
+// sendMsg calls m.Update once with the given message and returns the updated model.
+func sendMsg(m *AppModel, msg tea.Msg) *AppModel {
+	updated, _ := m.Update(msg)
+	return updated.(*AppModel)
+}
+
+// makeTestResponse constructs a fantasy.Response with the given text content.
+// Uses fantasy.TextContent (the type that ResponseContent.Text() recognises) rather
+// than TextPart (which is a request-side type).
+func makeTestResponse(text string) *fantasy.Response {
+	return &fantasy.Response{
+		Content: fantasy.ResponseContent{fantasy.TextContent{Text: text}},
+	}
+}
+
+// --------------------------------------------------------------------------
+// State transitions
+// --------------------------------------------------------------------------
+
+// TestStateTransition_InputToWorking verifies that a submitMsg while in
+// stateInput transitions the model to stateWorking.
+func TestStateTransition_InputToWorking(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+
+	if m.state != stateInput {
+		t.Fatalf("expected stateInput, got %v", m.state)
+	}
+
+	m = sendMsg(m, submitMsg{Text: "hello"})
+
+	if m.state != stateWorking {
+		t.Fatalf("expected stateWorking after submitMsg, got %v", m.state)
+	}
+	if len(ctrl.runCalls) != 1 || ctrl.runCalls[0] != "hello" {
+		t.Fatalf("expected Run called with 'hello', got %v", ctrl.runCalls)
+	}
+}
+
+// TestStateTransition_WorkingToApproval verifies that a ToolApprovalNeededEvent
+// while in stateWorking transitions the model to stateApproval and creates the
+// ApprovalComponent.
+func TestStateTransition_WorkingToApproval(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	responseChan := make(chan bool, 1)
+	m = sendMsg(m, app.ToolApprovalNeededEvent{
+		ToolName:     "test_tool",
+		ToolArgs:     `{"arg":"val"}`,
+		ResponseChan: responseChan,
+	})
+
+	if m.state != stateApproval {
+		t.Fatalf("expected stateApproval after ToolApprovalNeededEvent, got %v", m.state)
+	}
+	if m.approval == nil {
+		t.Fatal("expected approval component to be set")
+	}
+	if m.approvalChan == nil {
+		t.Fatal("expected approvalChan to be set")
+	}
+}
+
+// TestStateTransition_ApprovalToWorking verifies that an approvalResultMsg
+// while in stateApproval sends the result on approvalChan and transitions back
+// to stateWorking.
+func TestStateTransition_ApprovalToWorking(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateApproval
+
+	responseChan := make(chan bool, 1)
+	m.approvalChan = responseChan
+
+	m = sendMsg(m, approvalResultMsg{Approved: true})
+
+	if m.state != stateWorking {
+		t.Fatalf("expected stateWorking after approvalResultMsg, got %v", m.state)
+	}
+	if m.approvalChan != nil {
+		t.Fatal("expected approvalChan to be cleared")
+	}
+
+	// Verify the approval result was sent on the channel.
+	select {
+	case approved := <-responseChan:
+		if !approved {
+			t.Fatal("expected approved=true to be sent on responseChan")
+		}
+	default:
+		t.Fatal("expected a value on responseChan")
+	}
+}
+
+// TestStateTransition_WorkingToInput_StepComplete verifies that StepCompleteEvent
+// transitions from stateWorking back to stateInput and resets the stream component.
+func TestStateTransition_WorkingToInput_StepComplete(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, stream, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	m = sendMsg(m, app.StepCompleteEvent{
+		Response: makeTestResponse("all done"),
+		Usage:    fantasy.Usage{},
+	})
+
+	if m.state != stateInput {
+		t.Fatalf("expected stateInput after StepCompleteEvent, got %v", m.state)
+	}
+	if stream.resetCalled != 1 {
+		t.Fatalf("expected stream.Reset() called once, got %d", stream.resetCalled)
+	}
+}
+
+// TestStateTransition_WorkingToInput_StepError verifies that StepErrorEvent
+// transitions from stateWorking back to stateInput and resets the stream component.
+func TestStateTransition_WorkingToInput_StepError(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, stream, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	m = sendMsg(m, app.StepErrorEvent{Err: errors.New("something broke")})
+
+	if m.state != stateInput {
+		t.Fatalf("expected stateInput after StepErrorEvent, got %v", m.state)
+	}
+	if stream.resetCalled != 1 {
+		t.Fatalf("expected stream.Reset() called once, got %d", stream.resetCalled)
+	}
+}
+
+// TestStepError_nilErr verifies that a StepErrorEvent with a nil error does not
+// panic and still transitions to stateInput.
+func TestStepError_nilErr(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	m = sendMsg(m, app.StepErrorEvent{Err: nil})
+
+	if m.state != stateInput {
+		t.Fatalf("expected stateInput for nil-error StepErrorEvent, got %v", m.state)
+	}
+}
+
+// --------------------------------------------------------------------------
+// ESC cancel flow
+// --------------------------------------------------------------------------
+
+// TestESCCancel_singleTap verifies that the first ESC press during stateWorking
+// sets canceling=true (and does not call CancelCurrentStep).
+func TestESCCancel_singleTap(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	m = sendMsg(m, tea.KeyPressMsg{Code: tea.KeyEscape})
+
+	if !m.canceling {
+		t.Fatal("expected canceling=true after first ESC in stateWorking")
+	}
+	if ctrl.cancelCalled != 0 {
+		t.Fatalf("expected no CancelCurrentStep call after first ESC, got %d", ctrl.cancelCalled)
+	}
+}
+
+// TestESCCancel_doubleTap verifies that a second ESC press while canceling=true
+// calls CancelCurrentStep() and resets canceling.
+func TestESCCancel_doubleTap(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+	m.canceling = true // simulate first ESC already pressed
+
+	m = sendMsg(m, tea.KeyPressMsg{Code: tea.KeyEscape})
+
+	if m.canceling {
+		t.Fatal("expected canceling=false after second ESC")
+	}
+	if ctrl.cancelCalled != 1 {
+		t.Fatalf("expected CancelCurrentStep called once after double ESC, got %d", ctrl.cancelCalled)
+	}
+}
+
+// TestESCCancel_timerExpiry verifies that cancelTimerExpiredMsg resets canceling
+// to false (timer fires before second ESC).
+func TestESCCancel_timerExpiry(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+	m.canceling = true
+
+	m = sendMsg(m, cancelTimerExpiredMsg{})
+
+	if m.canceling {
+		t.Fatal("expected canceling=false after timer expiry")
+	}
+	if ctrl.cancelCalled != 0 {
+		t.Fatalf("expected no CancelCurrentStep after timer expiry, got %d", ctrl.cancelCalled)
+	}
+}
+
+// TestESCCancel_noEffectInStateInput verifies that ESC in stateInput does not set
+// canceling (it's passed to child components instead).
+func TestESCCancel_noEffectInStateInput(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	// state is stateInput by default
+
+	m = sendMsg(m, tea.KeyPressMsg{Code: tea.KeyEscape})
+
+	if m.canceling {
+		t.Fatal("expected canceling=false when ESC pressed in stateInput")
+	}
+	if ctrl.cancelCalled != 0 {
+		t.Fatalf("expected no CancelCurrentStep in stateInput, got %d", ctrl.cancelCalled)
+	}
+}
+
+// TestESCCancel_clearedOnStepComplete verifies that completing a step clears
+// any pending canceling state.
+func TestESCCancel_clearedOnStepComplete(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+	m.canceling = true
+
+	m = sendMsg(m, app.StepCompleteEvent{
+		Response: makeTestResponse("done"),
+	})
+
+	if m.canceling {
+		t.Fatal("expected canceling=false after StepCompleteEvent")
+	}
+}
+
+// --------------------------------------------------------------------------
+// Queue badge update
+// --------------------------------------------------------------------------
+
+// TestQueueBadge_updatesOnEvent verifies that QueueUpdatedEvent sets queueCount.
+func TestQueueBadge_updatesOnEvent(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+
+	if m.queueCount != 0 {
+		t.Fatalf("expected queueCount=0 initially, got %d", m.queueCount)
+	}
+
+	m = sendMsg(m, app.QueueUpdatedEvent{Length: 3})
+
+	if m.queueCount != 3 {
+		t.Fatalf("expected queueCount=3 after QueueUpdatedEvent, got %d", m.queueCount)
+	}
+}
+
+// TestQueueBadge_resetsToZero verifies that a QueueUpdatedEvent with Length=0
+// resets the badge count.
+func TestQueueBadge_resetsToZero(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.queueCount = 5
+
+	m = sendMsg(m, app.QueueUpdatedEvent{Length: 0})
+
+	if m.queueCount != 0 {
+		t.Fatalf("expected queueCount=0 after QueueUpdatedEvent{Length:0}, got %d", m.queueCount)
+	}
+}
+
+// --------------------------------------------------------------------------
+// Window resize
+// --------------------------------------------------------------------------
+
+// TestWindowResize_updatesWidthHeight verifies that tea.WindowSizeMsg updates
+// m.width and m.height.
+func TestWindowResize_updatesWidthHeight(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+
+	m = sendMsg(m, tea.WindowSizeMsg{Width: 120, Height: 40})
+
+	if m.width != 120 {
+		t.Fatalf("expected width=120, got %d", m.width)
+	}
+	if m.height != 40 {
+		t.Fatalf("expected height=40, got %d", m.height)
+	}
+}
+
+// TestWindowResize_propagatesToStream verifies that tea.WindowSizeMsg is forwarded
+// to the stream component.
+func TestWindowResize_propagatesToStream(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, stream, _ := newTestAppModel(ctrl)
+
+	m = sendMsg(m, tea.WindowSizeMsg{Width: 100, Height: 30})
+
+	if stream.lastMsg == nil {
+		t.Fatal("expected stream component to receive WindowSizeMsg")
+	}
+	if _, ok := stream.lastMsg.(tea.WindowSizeMsg); !ok {
+		t.Fatalf("expected stream.lastMsg to be WindowSizeMsg, got %T", stream.lastMsg)
+	}
+}
+
+// TestWindowResize_distributeHeight verifies that distributeHeight correctly
+// sets the stream height after a resize.
+func TestWindowResize_distributeHeight(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, stream, _ := newTestAppModel(ctrl)
+
+	// With height=30, stream height = 30 - 1 (separator) - 5 (input) = 24
+	m = sendMsg(m, tea.WindowSizeMsg{Width: 80, Height: 30})
+	_ = m
+
+	if stream.height != 24 {
+		t.Fatalf("expected stream height=24, got %d", stream.height)
+	}
+}
+
+// --------------------------------------------------------------------------
+// tea.Println on step complete
+// --------------------------------------------------------------------------
+
+// TestStepComplete_printCmd verifies that StepCompleteEvent produces a non-nil
+// tea.Cmd (the tea.Println call). We verify the Cmd is non-nil rather than
+// executing it, since tea.Println is a runtime command.
+func TestStepComplete_printCmd(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	_, cmd := m.Update(app.StepCompleteEvent{
+		Response: makeTestResponse("final answer"),
+		Usage:    fantasy.Usage{},
+	})
+
+	// A non-nil cmd means printCompletedResponse returned tea.Println(...)
+	if cmd == nil {
+		t.Fatal("expected non-nil cmd (tea.Println) on StepCompleteEvent with response")
+	}
+}
+
+// TestStepComplete_nilResponse_noCmd verifies that StepCompleteEvent with a nil
+// response produces a nil cmd (nothing to print).
+func TestStepComplete_nilResponse_noCmd(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	_, cmd := m.Update(app.StepCompleteEvent{Response: nil})
+
+	if cmd != nil {
+		t.Fatal("expected nil cmd on StepCompleteEvent with nil response")
+	}
+}
+
+// TestStepError_printCmd verifies that StepErrorEvent with a non-nil error
+// produces a non-nil cmd (the tea.Println call for the error message).
+func TestStepError_printCmd(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	_, cmd := m.Update(app.StepErrorEvent{Err: errors.New("agent failed")})
+
+	if cmd == nil {
+		t.Fatal("expected non-nil cmd (tea.Println) on StepErrorEvent with error")
+	}
+}
+
+// --------------------------------------------------------------------------
+// SpinnerEvent: stateWorking on Show=true
+// --------------------------------------------------------------------------
+
+// TestSpinnerEvent_showTransitionsToWorking verifies that SpinnerEvent{Show:true}
+// transitions the model to stateWorking (important for queued step drain path).
+func TestSpinnerEvent_showTransitionsToWorking(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	// After a step completes, model is back in stateInput. The next queued step
+	// starts and fires SpinnerEvent{Show: true}.
+	m.state = stateInput
+
+	m = sendMsg(m, app.SpinnerEvent{Show: true})
+
+	if m.state != stateWorking {
+		t.Fatalf("expected stateWorking after SpinnerEvent{Show:true} in stateInput, got %v", m.state)
+	}
+}
+
+// TestSpinnerEvent_hidDoesNotTransitionState verifies that SpinnerEvent{Show:false}
+// does not change the state.
+func TestSpinnerEvent_hideDoesNotTransitionState(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	m = sendMsg(m, app.SpinnerEvent{Show: false})
+
+	if m.state != stateWorking {
+		t.Fatalf("expected state to remain stateWorking, got %v", m.state)
+	}
+}
+
+// --------------------------------------------------------------------------
+// ctrl+c produces tea.Quit
+// --------------------------------------------------------------------------
+
+// TestCtrlC_producesQuit verifies that ctrl+c always returns a tea.Quit cmd.
+func TestCtrlC_producesQuit(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+
+	_, cmd := m.Update(tea.KeyPressMsg{Code: 'c', Mod: tea.ModCtrl})
+
+	if cmd == nil {
+		t.Fatal("expected tea.Quit cmd on ctrl+c, got nil")
+	}
+	// We verify it's a quit command by running it and checking the message type.
+	msg := cmd()
+	if _, ok := msg.(tea.QuitMsg); !ok {
+		t.Fatalf("expected QuitMsg from ctrl+c cmd, got %T", msg)
+	}
+}
+
+// --------------------------------------------------------------------------
+// submitMsg during stateWorking (queue path)
+// --------------------------------------------------------------------------
+
+// TestSubmit_duringWorking_stays verifies that submitting a new prompt while in
+// stateWorking keeps the model in stateWorking (queued via app.Run).
+func TestSubmit_duringWorking_stays(t *testing.T) {
+	ctrl := &stubAppController{}
+	m, _, _ := newTestAppModel(ctrl)
+	m.state = stateWorking
+
+	m = sendMsg(m, submitMsg{Text: "queued prompt"})
+
+	if m.state != stateWorking {
+		t.Fatalf("expected stateWorking to persist after submitMsg during working, got %v", m.state)
+	}
+	if len(ctrl.runCalls) != 1 || ctrl.runCalls[0] != "queued prompt" {
+		t.Fatalf("expected Run('queued prompt') called, got %v", ctrl.runCalls)
+	}
+}