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/agent/state_test.go

@@ -0,0 +1,189 @@
+package agent
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestStateConstants(t *testing.T) {
+	tests := []struct {
+		name  string
+		state State
+		value string
+	}{
+		{"StateStopped", StateStopped, "stopped"},
+		{"StateRunning", StateRunning, "running"},
+		{"StatePaused", StatePaused, "paused"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if string(tt.state) != tt.value {
+				t.Errorf("State constant = %q, want %q", tt.state, tt.value)
+			}
+		})
+	}
+}
+
+func TestStateManager_StateFile(t *testing.T) {
+	tmpDir := t.TempDir()
+	manager := NewStateManager[TestState](tmpDir, "test-state.json", func() *TestState {
+		return &TestState{Value: "default"}
+	})
+
+	expectedPath := filepath.Join(tmpDir, ".runtime", "test-state.json")
+	if manager.StateFile() != expectedPath {
+		t.Errorf("StateFile() = %q, want %q", manager.StateFile(), expectedPath)
+	}
+}
+
+func TestStateManager_Load_NoFile(t *testing.T) {
+	tmpDir := t.TempDir()
+	manager := NewStateManager[TestState](tmpDir, "nonexistent.json", func() *TestState {
+		return &TestState{Value: "default"}
+	})
+
+	state, err := manager.Load()
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+	if state.Value != "default" {
+		t.Errorf("Load() value = %q, want %q", state.Value, "default")
+	}
+}
+
+func TestStateManager_Load_Save_Load(t *testing.T) {
+	tmpDir := t.TempDir()
+	manager := NewStateManager[TestState](tmpDir, "test-state.json", func() *TestState {
+		return &TestState{Value: "default"}
+	})
+
+	// Save initial state
+	state := &TestState{Value: "test-value", Count: 42}
+	if err := manager.Save(state); err != nil {
+		t.Fatalf("Save() error = %v", err)
+	}
+
+	// Load it back
+	loaded, err := manager.Load()
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+	if loaded.Value != state.Value {
+		t.Errorf("Load() value = %q, want %q", loaded.Value, state.Value)
+	}
+	if loaded.Count != state.Count {
+		t.Errorf("Load() count = %d, want %d", loaded.Count, state.Count)
+	}
+}
+
+func TestStateManager_Load_CreatesDirectory(t *testing.T) {
+	tmpDir := t.TempDir()
+	manager := NewStateManager[TestState](tmpDir, "test-state.json", func() *TestState {
+		return &TestState{Value: "default"}
+	})
+
+	// Save should create .runtime directory
+	state := &TestState{Value: "test"}
+	if err := manager.Save(state); err != nil {
+		t.Fatalf("Save() error = %v", err)
+	}
+
+	// Verify directory was created
+	runtimeDir := filepath.Join(tmpDir, ".runtime")
+	if _, err := os.Stat(runtimeDir); err != nil {
+		t.Errorf("Save() should create .runtime directory: %v", err)
+	}
+}
+
+func TestStateManager_Load_InvalidJSON(t *testing.T) {
+	tmpDir := t.TempDir()
+	manager := NewStateManager[TestState](tmpDir, "test-state.json", func() *TestState {
+		return &TestState{Value: "default"}
+	})
+
+	// Write invalid JSON
+	statePath := manager.StateFile()
+	if err := os.MkdirAll(filepath.Dir(statePath), 0755); err != nil {
+		t.Fatalf("Failed to create directory: %v", err)
+	}
+	if err := os.WriteFile(statePath, []byte("invalid json"), 0644); err != nil {
+		t.Fatalf("Failed to write file: %v", err)
+	}
+
+	_, err := manager.Load()
+	if err == nil {
+		t.Error("Load() with invalid JSON should return error")
+	}
+}
+
+func TestState_String(t *testing.T) {
+	tests := []struct {
+		state State
+		want  string
+	}{
+		{StateStopped, "stopped"},
+		{StateRunning, "running"},
+		{StatePaused, "paused"},
+	}
+
+	for _, tt := range tests {
+		if string(tt.state) != tt.want {
+			t.Errorf("State(%q) = %q, want %q", tt.state, string(tt.state), tt.want)
+		}
+	}
+}
+
+func TestStateManager_GenericType(t *testing.T) {
+	// Test that StateManager works with different types
+
+	type ComplexState struct {
+		Name      string   `json:"name"`
+		Values    []int    `json:"values"`
+		Enabled   bool     `json:"enabled"`
+		Nested    struct {
+			X int `json:"x"`
+		} `json:"nested"`
+	}
+
+	tmpDir := t.TempDir()
+	manager := NewStateManager[ComplexState](tmpDir, "complex.json", func() *ComplexState {
+		return &ComplexState{Name: "default", Values: []int{}}
+	})
+
+	original := &ComplexState{
+		Name:    "test",
+		Values:  []int{1, 2, 3},
+		Enabled: true,
+	}
+	original.Nested.X = 42
+
+	if err := manager.Save(original); err != nil {
+		t.Fatalf("Save() error = %v", err)
+	}
+
+	loaded, err := manager.Load()
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+
+	if loaded.Name != original.Name {
+		t.Errorf("Name = %q, want %q", loaded.Name, original.Name)
+	}
+	if len(loaded.Values) != len(original.Values) {
+		t.Errorf("Values length = %d, want %d", len(loaded.Values), len(original.Values))
+	}
+	if loaded.Enabled != original.Enabled {
+		t.Errorf("Enabled = %v, want %v", loaded.Enabled, original.Enabled)
+	}
+	if loaded.Nested.X != original.Nested.X {
+		t.Errorf("Nested.X = %d, want %d", loaded.Nested.X, original.Nested.X)
+	}
+}
+
+// TestState is a simple type for testing
+type TestState struct {
+	Value string `json:"value"`
+	Count int    `json:"count"`
+}