From 4dca460b3aa3b47a00e13ea94ae337fb9f3d0844 Mon Sep 17 00:00:00 2001
From: "microsoft-agent-framework-for-go[bot]"
 <324824725+microsoft-agent-framework-for-go[bot]@users.noreply.github.com>
Date: Tue, 3 Nov 2026 02:31:37 +0000
Subject: [PATCH] Fall back when a restored agent mode is no longer configured

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 agent/harness/agentmode/agentmode.go      | 15 ++++++++++
 agent/harness/agentmode/agentmode_test.go | 35 +++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/agent/harness/agentmode/agentmode.go b/agent/harness/agentmode/agentmode.go
index 17bbc641..651aabb4 100644
--- a/agent/harness/agentmode/agentmode.go
+++ b/agent/harness/agentmode/agentmode.go
@@ -238,11 +238,26 @@ func (p *Provider) loadSessionState(session *agent.Session) *state {
 	}
 	var s state
 	if found, _ := session.Get(stateKey, &s); found {
+		p.ensureConfiguredMode(session, &s)
 		return &s
 	}
 	return &state{CurrentMode: p.defaultMode}
 }
 
+// ensureConfiguredMode resets a restored mode that is no longer configured to
+// the default mode and persists the correction.
+func (p *Provider) ensureConfiguredMode(session *agent.Session, s *state) {
+	if _, ok := p.validModes[s.CurrentMode]; ok {
+		return
+	}
+	s.CurrentMode = p.defaultMode
+	// A pending notification must not announce a default-to-default change.
+	if s.PreviousMode == p.defaultMode {
+		s.PreviousMode = ""
+	}
+	p.saveSessionState(session, s)
+}
+
 func (p *Provider) saveSessionState(session *agent.Session, s *state) {
 	if session == nil || s == nil {
 		return
diff --git a/agent/harness/agentmode/agentmode_test.go b/agent/harness/agentmode/agentmode_test.go
index 75274a86..13a8d364 100644
--- a/agent/harness/agentmode/agentmode_test.go
+++ b/agent/harness/agentmode/agentmode_test.go
@@ -197,6 +197,41 @@ func TestCustomModes_SetModeValidatesAgainstList(t *testing.T) {
 	}
 }
 
+func TestRestoredUnconfiguredModeFallsBackToDefault(t *testing.T) {
+	v1 := agentmode.New(agentmode.Config{
+		Modes: []agentmode.Mode{
+			{Name: "draft", Instructions: "Draft instructions."},
+			{Name: "review", Instructions: "Review instructions."},
+		},
+	})
+	opts := sessionOpts()
+	session := mustSession(t, opts)
+	if err := v1.SetMode(session, "review", false); err != nil {
+		t.Fatal(err)
+	}
+
+	v2 := agentmode.New(agentmode.Config{
+		Modes: []agentmode.Mode{
+			{Name: "draft", Instructions: "Draft instructions."},
+			{Name: "publish", Instructions: "Publish instructions."},
+		},
+	})
+	if mode := v2.Mode(session); mode != "draft" {
+		t.Fatalf("expected fallback to 'draft', got %q", mode)
+	}
+
+	ctx := context.Background()
+	msgs, _, err := invokeProvider(v2, ctx, newMessages("hi"), opts...)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, m := range msgs {
+		if strings.Contains(m.Contents.Text(), "Mode changed") {
+			t.Errorf("unexpected mode change notification: %q", m.Contents.Text())
+		}
+	}
+}
+
 // 5. Options_CustomDefaultMode_IsUsed
 func TestCustomDefaultMode_IsUsed(t *testing.T) {
 	p := agentmode.New(agentmode.Config{