diff --git a/pkg/routing/route.go b/pkg/routing/route.go
index 9eb060c53..f57edec08 100644
--- a/pkg/routing/route.go
+++ b/pkg/routing/route.go
@@ -44,8 +44,8 @@ func (r *RouteResolver) ResolveRoute(input RouteInput) ResolvedRoute {
 	accountID := NormalizeAccountID(input.AccountID)
 	peer := input.Peer
 
-	dmScope := DMScope(r.cfg.Session.DMScope)
-	if dmScope == "" {
+	dmScope, ok := NormalizeDMScope(r.cfg.Session.DMScope)
+	if !ok {
 		dmScope = DMScopeMain
 	}
 	identityLinks := r.cfg.Session.IdentityLinks
diff --git a/pkg/routing/session_key.go b/pkg/routing/session_key.go
index eab592bec..cd96129fa 100644
--- a/pkg/routing/session_key.go
+++ b/pkg/routing/session_key.go
@@ -15,6 +15,22 @@ const (
 	DMScopePerAccountChannelPeer DMScope = "per-account-channel-peer"
 )
 
+// NormalizeDMScope converts known legacy aliases to their canonical backend values.
+func NormalizeDMScope(scope string) (DMScope, bool) {
+	switch strings.ToLower(strings.TrimSpace(scope)) {
+	case string(DMScopeMain), "global":
+		return DMScopeMain, true
+	case string(DMScopePerPeer):
+		return DMScopePerPeer, true
+	case string(DMScopePerChannelPeer), "per-channel":
+		return DMScopePerChannelPeer, true
+	case string(DMScopePerAccountChannelPeer):
+		return DMScopePerAccountChannelPeer, true
+	default:
+		return "", false
+	}
+}
+
 // RoutePeer represents a chat peer with kind and ID.
 type RoutePeer struct {
 	Kind string // "direct", "group", "channel"
@@ -56,8 +72,8 @@ func BuildAgentPeerSessionKey(params SessionKeyParams) string {
 	}
 
 	if peerKind == "direct" {
-		dmScope := params.DMScope
-		if dmScope == "" {
+		dmScope, ok := NormalizeDMScope(string(params.DMScope))
+		if !ok {
 			dmScope = DMScopeMain
 		}
 		peerID := strings.TrimSpace(peer.ID)
diff --git a/pkg/routing/session_key_test.go b/pkg/routing/session_key_test.go
index ad7a1ca02..892dd6d67 100644
--- a/pkg/routing/session_key_test.go
+++ b/pkg/routing/session_key_test.go
@@ -18,6 +18,32 @@ func TestBuildAgentMainSessionKey_Normalizes(t *testing.T) {
 	}
 }
 
+func TestNormalizeDMScope(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  DMScope
+		ok    bool
+	}{
+		{name: "main", input: "main", want: DMScopeMain, ok: true},
+		{name: "global alias", input: "global", want: DMScopeMain, ok: true},
+		{name: "per peer", input: "per-peer", want: DMScopePerPeer, ok: true},
+		{name: "per channel peer", input: "per-channel-peer", want: DMScopePerChannelPeer, ok: true},
+		{name: "per channel alias", input: "per-channel", want: DMScopePerChannelPeer, ok: true},
+		{name: "per account channel peer", input: "per-account-channel-peer", want: DMScopePerAccountChannelPeer, ok: true},
+		{name: "unknown", input: "shared", want: "", ok: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, ok := NormalizeDMScope(tt.input)
+			if got != tt.want || ok != tt.ok {
+				t.Fatalf("NormalizeDMScope(%q) = (%q, %v), want (%q, %v)", tt.input, got, ok, tt.want, tt.ok)
+			}
+		})
+	}
+}
+
 func TestBuildAgentPeerSessionKey_DMScopeMain(t *testing.T) {
 	got := BuildAgentPeerSessionKey(SessionKeyParams{
 		AgentID: "main",
@@ -31,6 +57,19 @@ func TestBuildAgentPeerSessionKey_DMScopeMain(t *testing.T) {
 	}
 }
 
+func TestBuildAgentPeerSessionKey_DMScopeGlobalAlias(t *testing.T) {
+	got := BuildAgentPeerSessionKey(SessionKeyParams{
+		AgentID: "main",
+		Channel: "telegram",
+		Peer:    &RoutePeer{Kind: "direct", ID: "user123"},
+		DMScope: DMScope("global"),
+	})
+	want := "agent:main:main"
+	if got != want {
+		t.Errorf("DMScope(global) = %q, want %q", got, want)
+	}
+}
+
 func TestBuildAgentPeerSessionKey_DMScopePerPeer(t *testing.T) {
 	got := BuildAgentPeerSessionKey(SessionKeyParams{
 		AgentID: "main",
@@ -57,6 +96,19 @@ func TestBuildAgentPeerSessionKey_DMScopePerChannelPeer(t *testing.T) {
 	}
 }
 
+func TestBuildAgentPeerSessionKey_DMScopePerChannelAlias(t *testing.T) {
+	got := BuildAgentPeerSessionKey(SessionKeyParams{
+		AgentID: "main",
+		Channel: "telegram",
+		Peer:    &RoutePeer{Kind: "direct", ID: "user123"},
+		DMScope: DMScope("per-channel"),
+	})
+	want := "agent:main:telegram:direct:user123"
+	if got != want {
+		t.Errorf("DMScope(per-channel) = %q, want %q", got, want)
+	}
+}
+
 func TestBuildAgentPeerSessionKey_DMScopePerAccountChannelPeer(t *testing.T) {
 	got := BuildAgentPeerSessionKey(SessionKeyParams{
 		AgentID:   "main",
diff --git a/web/backend/api/config.go b/web/backend/api/config.go
index 618b8438d..e8e3f6693 100644
--- a/web/backend/api/config.go
+++ b/web/backend/api/config.go
@@ -10,6 +10,7 @@ import (
 
 	"github.com/sipeed/picoclaw/pkg/config"
 	"github.com/sipeed/picoclaw/pkg/logger"
+	"github.com/sipeed/picoclaw/pkg/routing"
 )
 
 // registerConfigRoutes binds configuration management endpoints to the ServeMux.
@@ -250,6 +251,21 @@ func (h *Handler) handleTestCommandPatterns(w http.ResponseWriter, r *http.Reque
 func validateConfig(cfg *config.Config) []string {
 	var errs []string
 
+	if rawScope := strings.TrimSpace(cfg.Session.DMScope); rawScope != "" {
+		normalizedScope, ok := routing.NormalizeDMScope(rawScope)
+		if !ok {
+			errs = append(
+				errs,
+				fmt.Sprintf(
+					"session.dm_scope %q is invalid; supported values: main, per-peer, per-channel-peer, per-account-channel-peer",
+					cfg.Session.DMScope,
+				),
+			)
+		} else {
+			cfg.Session.DMScope = string(normalizedScope)
+		}
+	}
+
 	// Validate model_list entries
 	if err := cfg.ValidateModelList(); err != nil {
 		errs = append(errs, err.Error())
diff --git a/web/backend/api/config_test.go b/web/backend/api/config_test.go
index 36acd95b0..6f7dc0b63 100644
--- a/web/backend/api/config_test.go
+++ b/web/backend/api/config_test.go
@@ -143,6 +143,45 @@ func TestHandlePatchConfig_AllowsInvalidExecRegexPatternsWhenExecDisabled(t *tes
 	}
 }
 
+func TestValidateConfig_NormalizesLegacyDMScopeAliases(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{name: "global", input: "global", want: "main"},
+		{name: "per-channel", input: "per-channel", want: "per-channel-peer"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := config.DefaultConfig()
+			cfg.Session.DMScope = tt.input
+
+			errs := validateConfig(cfg)
+			if len(errs) != 0 {
+				t.Fatalf("validateConfig() errors = %v, want none", errs)
+			}
+			if cfg.Session.DMScope != tt.want {
+				t.Fatalf("Session.DMScope = %q, want %q", cfg.Session.DMScope, tt.want)
+			}
+		})
+	}
+}
+
+func TestValidateConfig_RejectsUnknownDMScope(t *testing.T) {
+	cfg := config.DefaultConfig()
+	cfg.Session.DMScope = "shared"
+
+	errs := validateConfig(cfg)
+	if len(errs) == 0 {
+		t.Fatal("validateConfig() errors = nil, want dm_scope validation error")
+	}
+	if !bytes.Contains([]byte(errs[0]), []byte("session.dm_scope")) {
+		t.Fatalf("validateConfig() first error = %q, want dm_scope validation", errs[0])
+	}
+}
+
 // setupPicoEnabledEnv creates a test environment with Pico channel enabled and
 // its token stored only in .security.yml (not in the JSON payload).
 func setupPicoEnabledEnv(t *testing.T) (string, func()) {
diff --git a/web/frontend/src/components/config/form-model.ts b/web/frontend/src/components/config/form-model.ts
index 10c5c71bb..94b6cfeef 100644
--- a/web/frontend/src/components/config/form-model.ts
+++ b/web/frontend/src/components/config/form-model.ts
@@ -40,11 +40,12 @@ export const DM_SCOPE_OPTIONS = [
     descDefault: "Separate context for each user in each channel.",
   },
   {
-    value: "per-channel",
-    labelKey: "pages.config.session_scope_per_channel",
-    labelDefault: "Per Channel",
-    descKey: "pages.config.session_scope_per_channel_desc",
-    descDefault: "One shared context per channel.",
+    value: "per-account-channel-peer",
+    labelKey: "pages.config.session_scope_per_account_channel_peer",
+    labelDefault: "Per Account + Channel + Peer",
+    descKey: "pages.config.session_scope_per_account_channel_peer_desc",
+    descDefault:
+      "Separate context for each user on each channel account instance.",
   },
   {
     value: "per-peer",
@@ -54,7 +55,7 @@ export const DM_SCOPE_OPTIONS = [
     descDefault: "One context per user across channels.",
   },
   {
-    value: "global",
+    value: "main",
     labelKey: "pages.config.session_scope_global",
     labelDefault: "Global",
     descKey: "pages.config.session_scope_global_desc",
@@ -62,6 +63,11 @@ export const DM_SCOPE_OPTIONS = [
   },
 ] as const
 
+const DM_SCOPE_ALIASES: Record<string, string> = {
+  global: "main",
+  "per-channel": "per-channel-peer",
+}
+
 export const EMPTY_FORM: CoreConfigForm = {
   workspace: "",
   restrictToWorkspace: true,
@@ -104,6 +110,19 @@ function asString(value: unknown): string {
   return typeof value === "string" ? value : ""
 }
 
+function normalizeDmScope(value: unknown): string {
+  const raw = asString(value).trim()
+  if (!raw) {
+    return EMPTY_FORM.dmScope
+  }
+
+  const normalized = DM_SCOPE_ALIASES[raw] ?? raw
+
+  return DM_SCOPE_OPTIONS.some((scope) => scope.value === normalized)
+    ? normalized
+    : raw
+}
+
 function asBool(value: unknown): boolean {
   return value === true
 }
@@ -195,7 +214,7 @@ export function buildFormFromConfig(config: unknown): CoreConfigForm {
       defaults.summarize_token_percent,
       EMPTY_FORM.summarizeTokenPercent,
     ),
-    dmScope: asString(session.dm_scope) || EMPTY_FORM.dmScope,
+    dmScope: normalizeDmScope(session.dm_scope),
     heartbeatEnabled:
       heartbeat.enabled === undefined
         ? EMPTY_FORM.heartbeatEnabled
diff --git a/web/frontend/src/i18n/locales/en.json b/web/frontend/src/i18n/locales/en.json
index d15cde693..28439cafb 100644
--- a/web/frontend/src/i18n/locales/en.json
+++ b/web/frontend/src/i18n/locales/en.json
@@ -460,6 +460,8 @@
       "session_scope_hint": "How chat context is isolated across peers/channels.",
       "session_scope_per_channel_peer": "Per Channel + Peer",
       "session_scope_per_channel_peer_desc": "Separate context for each user in each channel.",
+      "session_scope_per_account_channel_peer": "Per Account + Channel + Peer",
+      "session_scope_per_account_channel_peer_desc": "Separate context for each user on each channel account instance.",
       "session_scope_per_channel": "Per Channel",
       "session_scope_per_channel_desc": "One shared context per channel.",
       "session_scope_per_peer": "Per Peer",
diff --git a/web/frontend/src/i18n/locales/zh.json b/web/frontend/src/i18n/locales/zh.json
index 7eb14e983..c2f4d1679 100644
--- a/web/frontend/src/i18n/locales/zh.json
+++ b/web/frontend/src/i18n/locales/zh.json
@@ -460,6 +460,8 @@
       "session_scope_hint": "定义不同用户/频道之间如何隔离会话上下文。",
       "session_scope_per_channel_peer": "按频道+用户隔离",
       "session_scope_per_channel_peer_desc": "同一频道内不同用户使用独立上下文。",
+      "session_scope_per_account_channel_peer": "按账号+频道+用户隔离",
+      "session_scope_per_account_channel_peer_desc": "不同频道账号实例中的不同用户使用独立上下文。",
       "session_scope_per_channel": "按频道隔离",
       "session_scope_per_channel_desc": "同一频道内共享一个上下文。",
       "session_scope_per_peer": "按用户隔离",