Add destination takeover config policy

internal/config/validate_test.go

@@ -142,6 +142,64 @@ func TestValidateReconciliationPolicy(t *testing.T) {
 	}
 }
 
+func TestValidateTakeoverPolicy(t *testing.T) {
+	tests := []struct {
+		name    string
+		mode    string
+		wantErr bool
+	}{
+		{name: "same pipeline", mode: TakeoverModeSamePipeline},
+		{name: "same source", mode: TakeoverModeSameSource},
+		{name: "any managed", mode: TakeoverModeAnyManaged},
+		{name: "never", mode: TakeoverModeNever},
+		{name: "invalid", mode: "unmanaged", wantErr: true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := Config{Pipelines: []Pipeline{{
+				ID:     "reports",
+				Source: Backend{Backend: BackendLocal, Path: "/source"},
+				Destinations: []Destination{{
+					ID:       "archive",
+					Backend:  BackendLocal,
+					Path:     "/destination",
+					Takeover: TakeoverPolicy{Mode: tt.mode},
+				}},
+			}}}
+			ApplyDefaults(&cfg)
+			err := Validate(cfg)
+			if tt.wantErr && err == nil {
+				t.Fatal("Validate() error = nil, want error")
+			}
+			if !tt.wantErr && err != nil {
+				t.Fatalf("Validate() error = %v", err)
+			}
+		})
+	}
+}
+
+func TestValidateTakeoverPolicyReportsFieldContext(t *testing.T) {
+	cfg := Config{Pipelines: []Pipeline{{
+		ID:     "reports",
+		Source: Backend{Backend: BackendLocal, Path: "/source"},
+		Destinations: []Destination{{
+			ID:       "archive",
+			Backend:  BackendLocal,
+			Path:     "/destination",
+			Takeover: TakeoverPolicy{Mode: "unmanaged"},
+		}},
+	}}}
+	ApplyDefaults(&cfg)
+	err := Validate(cfg)
+	if err == nil {
+		t.Fatal("Validate() error = nil, want error")
+	}
+	want := "pipelines[0].destinations[0].takeover.mode must be same_pipeline, same_source, any_managed, or never"
+	if !strings.Contains(err.Error(), want) {
+		t.Fatalf("Validate() error = %q, want %q", err, want)
+	}
+}
+
 func TestValidateStatePolicy(t *testing.T) {
 	tests := []struct {
 		name    string