test: Add test coverage for 16 files (40.3% → 45.5%) (#463)

* test: Add test coverage for 16 files (40.3% -> 45.5%)

Add comprehensive tests for previously untested packages:
- internal/agent/state_test.go
- internal/cmd/errors_test.go
- internal/crew/types_test.go
- internal/doctor/errors_test.go
- internal/dog/types_test.go
- internal/mail/bd_test.go
- internal/opencode/plugin_test.go
- internal/rig/overlay_test.go
- internal/runtime/runtime_test.go
- internal/session/town_test.go
- internal/style/style_test.go
- internal/ui/markdown_test.go
- internal/ui/terminal_test.go
- internal/wisp/io_test.go
- internal/wisp/types_test.go
- internal/witness/types_test.go

style_test.go uses func(...string) to match lipgloss variadic Render signature.

* fix(lint): remove unused error return from buildCVSummary

buildCVSummary always returned nil for its error value, causing
golangci-lint to fail with "result 1 (error) is always nil".

The function handles errors internally by returning partial data,
so the error return was misleading. Removed it and updated caller.

internal/cmd/errors_test.go

@@ -0,0 +1,93 @@
+package cmd
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestSilentExitError_Error(t *testing.T) {
+	tests := []struct {
+		name string
+		code int
+		want string
+	}{
+		{"zero code", 0, "exit 0"},
+		{"success code", 1, "exit 1"},
+		{"error code", 2, "exit 2"},
+		{"custom code", 42, "exit 42"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			e := &SilentExitError{Code: tt.code}
+			got := e.Error()
+			if got != tt.want {
+				t.Errorf("SilentExitError.Error() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestNewSilentExit(t *testing.T) {
+	tests := []struct {
+		code int
+	}{
+		{0},
+		{1},
+		{2},
+		{127},
+	}
+
+	for _, tt := range tests {
+		t.Run(fmt.Sprintf("code_%d", tt.code), func(t *testing.T) {
+			err := NewSilentExit(tt.code)
+			if err == nil {
+				t.Fatal("NewSilentExit should return non-nil")
+			}
+			if err.Code != tt.code {
+				t.Errorf("NewSilentExit(%d).Code = %d, want %d", tt.code, err.Code, tt.code)
+			}
+		})
+	}
+}
+
+func TestIsSilentExit(t *testing.T) {
+	tests := []struct {
+		name        string
+		err         error
+		wantCode    int
+		wantIsSilent bool
+	}{
+		{"nil error", nil, 0, false},
+		{"silent exit code 0", NewSilentExit(0), 0, true},
+		{"silent exit code 1", NewSilentExit(1), 1, true},
+		{"silent exit code 2", NewSilentExit(2), 2, true},
+		{"other error", errors.New("some error"), 0, false},
+		// Note: wrapped errors require errors.As fix - see PR #462
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			code, isSilent := IsSilentExit(tt.err)
+			if isSilent != tt.wantIsSilent {
+				t.Errorf("IsSilentExit(%v) isSilent = %v, want %v", tt.err, isSilent, tt.wantIsSilent)
+			}
+			if code != tt.wantCode {
+				t.Errorf("IsSilentExit(%v) code = %d, want %d", tt.err, code, tt.wantCode)
+			}
+		})
+	}
+}
+
+func TestSilentExitError_Is(t *testing.T) {
+	// Test that SilentExitError works with errors.Is
+	err := NewSilentExit(1)
+	var target *SilentExitError
+	if !errors.As(err, &target) {
+		t.Error("errors.As should find SilentExitError")
+	}
+	if target.Code != 1 {
+		t.Errorf("errors.As extracted code = %d, want 1", target.Code)
+	}
+}