diff --git a/CLAUDE.md b/CLAUDE.md
index 594d4c0..402eb18 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -38,38 +38,43 @@ The display `Service` registers with `forge.lthn.ai/core/go`'s service container
 
 All Wails application APIs are abstracted behind interfaces in `interfaces.go` (`App`, `WindowManager`, `MenuManager`, `DialogManager`, etc.). The `wailsApp` adapter wraps the real Wails app. Tests inject a `mockApp` instead — see `mocks_test.go` and the `newServiceWithMockApp(t)` helper.
 
-### Key files in pkg/display/
+### Package structure (pkg/)
 
-| File | Responsibility |
-|------|---------------|
-| `display.go` | Service struct, lifecycle (`Startup`), window CRUD, screen queries, tiling/snapping/layout, workflow presets |
-| `window.go` | `WindowOption` functional options pattern, `Window` type alias for `application.WebviewWindowOptions` |
-| `window_state.go` | `WindowStateManager` — persists window position/size across restarts |
-| `layout.go` | `LayoutManager` — save/restore named window arrangements |
-| `events.go` | `WSEventManager` — WebSocket pub/sub for window/theme/screen events |
-| `interfaces.go` | Abstract interfaces + Wails adapter implementations |
-| `actions.go` | `ActionOpenWindow` IPC message type |
-| `menu.go` | Application menu construction |
-| `tray.go` | System tray setup |
-| `dialog.go` | File/directory dialogs |
-| `clipboard.go` | Clipboard read/write |
-| `notification.go` | System notifications |
-| `theme.go` | Dark/light mode detection |
-| `mocks_test.go` | Mock implementations of all interfaces for testing |
+| Package | Responsibility |
+|---------|---------------|
+| `display` | Orchestrator service — bridges sub-service IPC to WebSocket events, menu/tray setup, config persistence |
+| `window` | Window lifecycle, `Manager`, `StateManager` (position persistence), `LayoutManager` (named arrangements), tiling/snapping |
+| `menu` | Application menu construction via platform abstraction |
+| `systray` | System tray icon, tooltip, menu via platform abstraction |
+| `dialog` | File open/save, message, confirm, and prompt dialogs |
+| `clipboard` | Clipboard read/write/clear |
+| `notification` | System notifications with permission management |
+| `screen` | Screen/monitor queries (list, primary, at-point, work areas) |
+| `environment` | Theme detection (dark/light) and OS environment info |
+| `keybinding` | Global keyboard shortcut registration |
+| `contextmenu` | Named context menu registration and lifecycle |
+| `browser` | Open URLs and files in the default browser |
+| `dock` | macOS dock icon visibility and badge |
+| `lifecycle` | Application lifecycle events (start, terminate, suspend, resume) |
+| `webview` | Webview automation (eval, click, type, screenshot, DOM queries) |
+| `mcp` | MCP tool subsystem — exposes all services as Model Context Protocol tools |
 
 ### Patterns used throughout
 
-- **Functional options**: `WindowOption` functions (`WindowName()`, `WindowTitle()`, `WindowWidth()`, etc.) configure `application.WebviewWindowOptions`
-- **Type alias**: `Window = application.WebviewWindowOptions` — direct alias, not a wrapper
+- **Platform abstraction**: Each sub-service defines a `Platform` interface and `PlatformWindow`/`PlatformTray`/etc. types; tests inject mocks
+- **Functional options**: `WindowOption` functions (`WithName()`, `WithTitle()`, `WithSize()`, etc.) configure `window.Window` descriptors
+- **IPC message bus**: Sub-services communicate via `core.QUERY`, `core.PERFORM`, and `core.ACTION` — display orchestrates and bridges to WebSocket events
 - **Event broadcasting**: `WSEventManager` uses gorilla/websocket with a buffered channel (`eventBuffer`) and per-client subscription filtering (supports `"*"` wildcard)
-- **Window lookup by name**: Most Service methods iterate `s.app.Window().GetAll()` and type-assert to `*application.WebviewWindow`, then match by `Name()`
+- **Error handling**: All errors use `coreerr.E(op, msg, err)` from `forge.lthn.ai/core/go-log` (aliased as `coreerr`), never `fmt.Errorf`
+- **File I/O**: Use `forge.lthn.ai/core/go-io` (`coreio.Local`) for filesystem operations, never `os.ReadFile`/`os.WriteFile`
 
 ## Testing
 
 - Framework: `testify` (assert + require)
-- Pattern: `newServiceWithMockApp(t)` creates a `Service` with mock Wails app — no real window system needed
-- `newTestCore(t)` creates a real `core.Core` instance for integration-style tests
-- Some tests use `defer func() { recover() }()` to handle nil panics from mock methods that return nil pointers (e.g., `Dialog().Info()`)
+- Each sub-package has its own `*_test.go` with mock platform implementations
+- `pkg/window`: `NewManagerWithDir` / `NewStateManagerWithDir` / `NewLayoutManagerWithDir` accept custom config dirs for isolated tests
+- `pkg/display`: `newTestCore(t)` creates a real `core.Core` instance for integration-style tests
+- Sub-services use `mock_platform.go` or `mock_test.go` for platform mocks
 
 ## CI/CD
 
@@ -82,9 +87,13 @@ Both use reusable workflows from `core/go-devops`.
 ## Dependencies
 
 - `forge.lthn.ai/core/go` — Core framework with service container and DI
+- `forge.lthn.ai/core/go-log` — Structured errors (`coreerr.E()`)
+- `forge.lthn.ai/core/go-io` — Filesystem abstraction (`coreio.Local`)
+- `forge.lthn.ai/core/config` — Configuration file management
 - `github.com/wailsapp/wails/v3` — Desktop app framework (alpha.74)
 - `github.com/gorilla/websocket` — WebSocket for real-time events
 - `github.com/stretchr/testify` — Test assertions
+- `github.com/modelcontextprotocol/go-sdk` — MCP tool registration
 
 ## Repository migration note
 
diff --git a/go.mod b/go.mod
index 653c918..227fed1 100644
--- a/go.mod
+++ b/go.mod
@@ -5,6 +5,8 @@ go 1.26.0
 require (
 	forge.lthn.ai/core/config v0.1.6
 	forge.lthn.ai/core/go v0.3.1
+	forge.lthn.ai/core/go-io v0.1.5
+	forge.lthn.ai/core/go-log v0.0.4
 	forge.lthn.ai/core/go-webview v0.1.5
 	github.com/gorilla/websocket v1.5.3
 	github.com/leaanthony/u v1.1.1
@@ -16,8 +18,6 @@ require (
 
 require (
 	dario.cat/mergo v1.0.2 // indirect
-	forge.lthn.ai/core/go-io v0.1.5 // indirect
-	forge.lthn.ai/core/go-log v0.0.4 // indirect
 	github.com/Microsoft/go-winio v0.6.2 // indirect
 	github.com/ProtonMail/go-crypto v1.4.0 // indirect
 	github.com/adrg/xdg v0.5.3 // indirect
diff --git a/pkg/contextmenu/service.go b/pkg/contextmenu/service.go
index 973346d..44ef16b 100644
--- a/pkg/contextmenu/service.go
+++ b/pkg/contextmenu/service.go
@@ -3,8 +3,8 @@ package contextmenu
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/go/pkg/core"
 )
 
@@ -92,7 +92,7 @@ func (s *Service) taskAdd(t TaskAdd) error {
 		})
 	})
 	if err != nil {
-		return fmt.Errorf("contextmenu: platform add failed: %w", err)
+		return coreerr.E("contextmenu.taskAdd", "platform add failed", err)
 	}
 
 	s.menus[t.Name] = t.Menu
@@ -106,7 +106,7 @@ func (s *Service) taskRemove(t TaskRemove) error {
 
 	err := s.platform.Remove(t.Name)
 	if err != nil {
-		return fmt.Errorf("contextmenu: platform remove failed: %w", err)
+		return coreerr.E("contextmenu.taskRemove", "platform remove failed", err)
 	}
 
 	delete(s.menus, t.Name)
diff --git a/pkg/display/display.go b/pkg/display/display.go
index 9b6b77a..96e031d 100644
--- a/pkg/display/display.go
+++ b/pkg/display/display.go
@@ -9,6 +9,7 @@ import (
 
 	"forge.lthn.ai/core/config"
 	"forge.lthn.ai/core/go/pkg/core"
+	coreerr "forge.lthn.ai/core/go-log"
 	"encoding/json"
 
 	"forge.lthn.ai/core/gui/pkg/browser"
@@ -241,7 +242,7 @@ type WSMessage struct {
 func wsRequire(data map[string]any, key string) (string, error) {
 	v, _ := data[key].(string)
 	if v == "" {
-		return "", fmt.Errorf("ws: missing required field %q", key)
+		return "", coreerr.E("display.wsRequire", fmt.Sprintf("missing required field %q", key), nil)
 	}
 	return v, nil
 }
@@ -600,7 +601,7 @@ func (s *Service) GetWindowInfo(name string) (*window.WindowInfo, error) {
 		return nil, err
 	}
 	if !handled {
-		return nil, fmt.Errorf("window service not available")
+		return nil, coreerr.E("display.GetWindowInfo", "window service not available", nil)
 	}
 	info, _ := result.(*window.WindowInfo)
 	return info, nil
@@ -666,11 +667,11 @@ func (s *Service) CloseWindow(name string) error {
 func (s *Service) RestoreWindow(name string) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.RestoreWindow", "window service not available", nil)
 	}
 	pw, ok := ws.Manager().Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("display.RestoreWindow", "window not found: "+name, nil)
 	}
 	pw.Restore()
 	return nil
@@ -681,11 +682,11 @@ func (s *Service) RestoreWindow(name string) error {
 func (s *Service) SetWindowVisibility(name string, visible bool) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.SetWindowVisibility", "window service not available", nil)
 	}
 	pw, ok := ws.Manager().Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("display.SetWindowVisibility", "window not found: "+name, nil)
 	}
 	pw.SetVisibility(visible)
 	return nil
@@ -696,11 +697,11 @@ func (s *Service) SetWindowVisibility(name string, visible bool) error {
 func (s *Service) SetWindowAlwaysOnTop(name string, alwaysOnTop bool) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.SetWindowAlwaysOnTop", "window service not available", nil)
 	}
 	pw, ok := ws.Manager().Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("display.SetWindowAlwaysOnTop", "window not found: "+name, nil)
 	}
 	pw.SetAlwaysOnTop(alwaysOnTop)
 	return nil
@@ -711,11 +712,11 @@ func (s *Service) SetWindowAlwaysOnTop(name string, alwaysOnTop bool) error {
 func (s *Service) SetWindowTitle(name string, title string) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.SetWindowTitle", "window service not available", nil)
 	}
 	pw, ok := ws.Manager().Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("display.SetWindowTitle", "window not found: "+name, nil)
 	}
 	pw.SetTitle(title)
 	return nil
@@ -726,11 +727,11 @@ func (s *Service) SetWindowTitle(name string, title string) error {
 func (s *Service) SetWindowFullscreen(name string, fullscreen bool) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.SetWindowFullscreen", "window service not available", nil)
 	}
 	pw, ok := ws.Manager().Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("display.SetWindowFullscreen", "window not found: "+name, nil)
 	}
 	if fullscreen {
 		pw.Fullscreen()
@@ -745,11 +746,11 @@ func (s *Service) SetWindowFullscreen(name string, fullscreen bool) error {
 func (s *Service) SetWindowBackgroundColour(name string, r, g, b, a uint8) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.SetWindowBackgroundColour", "window service not available", nil)
 	}
 	pw, ok := ws.Manager().Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("display.SetWindowBackgroundColour", "window not found: "+name, nil)
 	}
 	pw.SetBackgroundColour(r, g, b, a)
 	return nil
@@ -773,7 +774,7 @@ func (s *Service) GetWindowTitle(name string) (string, error) {
 		return "", err
 	}
 	if info == nil {
-		return "", fmt.Errorf("window not found: %s", name)
+		return "", coreerr.E("display.GetWindowTitle", "window not found: "+name, nil)
 	}
 	return info.Title, nil
 }
@@ -816,7 +817,7 @@ type CreateWindowOptions struct {
 // CreateWindow creates a new window with the specified options.
 func (s *Service) CreateWindow(opts CreateWindowOptions) (*window.WindowInfo, error) {
 	if opts.Name == "" {
-		return nil, fmt.Errorf("window name is required")
+		return nil, coreerr.E("display.CreateWindow", "window name is required", nil)
 	}
 	result, _, err := s.Core().PERFORM(window.TaskOpenWindow{
 		Opts: []window.WindowOption{
@@ -840,7 +841,7 @@ func (s *Service) CreateWindow(opts CreateWindowOptions) (*window.WindowInfo, er
 func (s *Service) SaveLayout(name string) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.SaveLayout", "window service not available", nil)
 	}
 	states := make(map[string]window.WindowState)
 	for _, n := range ws.Manager().List() {
@@ -857,11 +858,11 @@ func (s *Service) SaveLayout(name string) error {
 func (s *Service) RestoreLayout(name string) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.RestoreLayout", "window service not available", nil)
 	}
 	layout, ok := ws.Manager().Layout().GetLayout(name)
 	if !ok {
-		return fmt.Errorf("layout not found: %s", name)
+		return coreerr.E("display.RestoreLayout", "layout not found: "+name, nil)
 	}
 	for wName, state := range layout.Windows {
 		if pw, ok := ws.Manager().Get(wName); ok {
@@ -890,7 +891,7 @@ func (s *Service) ListLayouts() []window.LayoutInfo {
 func (s *Service) DeleteLayout(name string) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.DeleteLayout", "window service not available", nil)
 	}
 	ws.Manager().Layout().DeleteLayout(name)
 	return nil
@@ -915,7 +916,7 @@ func (s *Service) GetLayout(name string) *window.Layout {
 func (s *Service) TileWindows(mode window.TileMode, windowNames []string) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.TileWindows", "window service not available", nil)
 	}
 	return ws.Manager().TileWindows(mode, windowNames, 1920, 1080) // TODO: use actual screen size
 }
@@ -924,7 +925,7 @@ func (s *Service) TileWindows(mode window.TileMode, windowNames []string) error
 func (s *Service) SnapWindow(name string, position window.SnapPosition) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.SnapWindow", "window service not available", nil)
 	}
 	return ws.Manager().SnapWindow(name, position, 1920, 1080) // TODO: use actual screen size
 }
@@ -933,7 +934,7 @@ func (s *Service) SnapWindow(name string, position window.SnapPosition) error {
 func (s *Service) StackWindows(windowNames []string, offsetX, offsetY int) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.StackWindows", "window service not available", nil)
 	}
 	return ws.Manager().StackWindows(windowNames, offsetX, offsetY)
 }
@@ -942,7 +943,7 @@ func (s *Service) StackWindows(windowNames []string, offsetX, offsetY int) error
 func (s *Service) ApplyWorkflowLayout(workflow window.WorkflowLayout) error {
 	ws := s.windowService()
 	if ws == nil {
-		return fmt.Errorf("window service not available")
+		return coreerr.E("display.ApplyWorkflowLayout", "window service not available", nil)
 	}
 	return ws.Manager().ApplyWorkflow(workflow, ws.Manager().List(), 1920, 1080)
 }
diff --git a/pkg/keybinding/service.go b/pkg/keybinding/service.go
index 048c259..8461292 100644
--- a/pkg/keybinding/service.go
+++ b/pkg/keybinding/service.go
@@ -3,8 +3,8 @@ package keybinding
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/go/pkg/core"
 )
 
@@ -75,7 +75,7 @@ func (s *Service) taskAdd(t TaskAdd) error {
 		_ = s.Core().ACTION(ActionTriggered{Accelerator: t.Accelerator})
 	})
 	if err != nil {
-		return fmt.Errorf("keybinding: platform add failed: %w", err)
+		return coreerr.E("keybinding.taskAdd", "platform add failed", err)
 	}
 
 	s.bindings[t.Accelerator] = BindingInfo{
@@ -87,12 +87,12 @@ func (s *Service) taskAdd(t TaskAdd) error {
 
 func (s *Service) taskRemove(t TaskRemove) error {
 	if _, exists := s.bindings[t.Accelerator]; !exists {
-		return fmt.Errorf("keybinding: not registered: %s", t.Accelerator)
+		return coreerr.E("keybinding.taskRemove", "not registered: "+t.Accelerator, nil)
 	}
 
 	err := s.platform.Remove(t.Accelerator)
 	if err != nil {
-		return fmt.Errorf("keybinding: platform remove failed: %w", err)
+		return coreerr.E("keybinding.taskRemove", "platform remove failed", err)
 	}
 
 	delete(s.bindings, t.Accelerator)
diff --git a/pkg/mcp/tools_clipboard.go b/pkg/mcp/tools_clipboard.go
index 827586a..629d46a 100644
--- a/pkg/mcp/tools_clipboard.go
+++ b/pkg/mcp/tools_clipboard.go
@@ -3,9 +3,9 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
 	"forge.lthn.ai/core/gui/pkg/clipboard"
+	coreerr "forge.lthn.ai/core/go-log"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
 
@@ -23,7 +23,7 @@ func (s *Subsystem) clipboardRead(_ context.Context, _ *mcp.CallToolRequest, _ C
 	}
 	content, ok := result.(clipboard.ClipboardContent)
 	if !ok {
-		return nil, ClipboardReadOutput{}, fmt.Errorf("unexpected result type from clipboard read query")
+		return nil, ClipboardReadOutput{}, coreerr.E("mcp.clipboardRead", "unexpected result type", nil)
 	}
 	return nil, ClipboardReadOutput{Content: content.Text}, nil
 }
@@ -44,7 +44,7 @@ func (s *Subsystem) clipboardWrite(_ context.Context, _ *mcp.CallToolRequest, in
 	}
 	success, ok := result.(bool)
 	if !ok {
-		return nil, ClipboardWriteOutput{}, fmt.Errorf("unexpected result type from clipboard write task")
+		return nil, ClipboardWriteOutput{}, coreerr.E("mcp.clipboardWrite", "unexpected result type", nil)
 	}
 	return nil, ClipboardWriteOutput{Success: success}, nil
 }
@@ -63,7 +63,7 @@ func (s *Subsystem) clipboardHas(_ context.Context, _ *mcp.CallToolRequest, _ Cl
 	}
 	content, ok := result.(clipboard.ClipboardContent)
 	if !ok {
-		return nil, ClipboardHasOutput{}, fmt.Errorf("unexpected result type from clipboard has query")
+		return nil, ClipboardHasOutput{}, coreerr.E("mcp.clipboardHas", "unexpected result type", nil)
 	}
 	return nil, ClipboardHasOutput{HasContent: content.HasContent}, nil
 }
@@ -82,7 +82,7 @@ func (s *Subsystem) clipboardClear(_ context.Context, _ *mcp.CallToolRequest, _
 	}
 	success, ok := result.(bool)
 	if !ok {
-		return nil, ClipboardClearOutput{}, fmt.Errorf("unexpected result type from clipboard clear task")
+		return nil, ClipboardClearOutput{}, coreerr.E("mcp.clipboardClear", "unexpected result type", nil)
 	}
 	return nil, ClipboardClearOutput{Success: success}, nil
 }
diff --git a/pkg/mcp/tools_contextmenu.go b/pkg/mcp/tools_contextmenu.go
index 74e9f8b..12eed8f 100644
--- a/pkg/mcp/tools_contextmenu.go
+++ b/pkg/mcp/tools_contextmenu.go
@@ -4,9 +4,9 @@ package mcp
 import (
 	"context"
 	"encoding/json"
-	"fmt"
 
 	"forge.lthn.ai/core/gui/pkg/contextmenu"
+	coreerr "forge.lthn.ai/core/go-log"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
 
@@ -27,11 +27,11 @@ func (s *Subsystem) contextMenuAdd(_ context.Context, _ *mcp.CallToolRequest, in
 	// Convert map[string]any to ContextMenuDef via JSON round-trip
 	menuJSON, err := json.Marshal(input.Menu)
 	if err != nil {
-		return nil, ContextMenuAddOutput{}, fmt.Errorf("failed to marshal menu definition: %w", err)
+		return nil, ContextMenuAddOutput{}, coreerr.E("mcp.contextMenuAdd", "failed to marshal menu definition", err)
 	}
 	var menuDef contextmenu.ContextMenuDef
 	if err := json.Unmarshal(menuJSON, &menuDef); err != nil {
-		return nil, ContextMenuAddOutput{}, fmt.Errorf("failed to unmarshal menu definition: %w", err)
+		return nil, ContextMenuAddOutput{}, coreerr.E("mcp.contextMenuAdd", "failed to unmarshal menu definition", err)
 	}
 	_, _, err = s.core.PERFORM(contextmenu.TaskAdd{Name: input.Name, Menu: menuDef})
 	if err != nil {
@@ -73,7 +73,7 @@ func (s *Subsystem) contextMenuGet(_ context.Context, _ *mcp.CallToolRequest, in
 	}
 	menu, ok := result.(*contextmenu.ContextMenuDef)
 	if !ok {
-		return nil, ContextMenuGetOutput{}, fmt.Errorf("unexpected result type from context menu get query")
+		return nil, ContextMenuGetOutput{}, coreerr.E("mcp.contextMenuGet", "unexpected result type", nil)
 	}
 	if menu == nil {
 		return nil, ContextMenuGetOutput{}, nil
@@ -81,11 +81,11 @@ func (s *Subsystem) contextMenuGet(_ context.Context, _ *mcp.CallToolRequest, in
 	// Convert to map[string]any via JSON round-trip to avoid cyclic type in schema
 	menuJSON, err := json.Marshal(menu)
 	if err != nil {
-		return nil, ContextMenuGetOutput{}, fmt.Errorf("failed to marshal context menu: %w", err)
+		return nil, ContextMenuGetOutput{}, coreerr.E("mcp.contextMenuGet", "failed to marshal context menu", err)
 	}
 	var menuMap map[string]any
 	if err := json.Unmarshal(menuJSON, &menuMap); err != nil {
-		return nil, ContextMenuGetOutput{}, fmt.Errorf("failed to unmarshal context menu: %w", err)
+		return nil, ContextMenuGetOutput{}, coreerr.E("mcp.contextMenuGet", "failed to unmarshal context menu", err)
 	}
 	return nil, ContextMenuGetOutput{Menu: menuMap}, nil
 }
@@ -104,16 +104,16 @@ func (s *Subsystem) contextMenuList(_ context.Context, _ *mcp.CallToolRequest, _
 	}
 	menus, ok := result.(map[string]contextmenu.ContextMenuDef)
 	if !ok {
-		return nil, ContextMenuListOutput{}, fmt.Errorf("unexpected result type from context menu list query")
+		return nil, ContextMenuListOutput{}, coreerr.E("mcp.contextMenuList", "unexpected result type", nil)
 	}
 	// Convert to map[string]any via JSON round-trip to avoid cyclic type in schema
 	menusJSON, err := json.Marshal(menus)
 	if err != nil {
-		return nil, ContextMenuListOutput{}, fmt.Errorf("failed to marshal context menus: %w", err)
+		return nil, ContextMenuListOutput{}, coreerr.E("mcp.contextMenuList", "failed to marshal context menus", err)
 	}
 	var menusMap map[string]any
 	if err := json.Unmarshal(menusJSON, &menusMap); err != nil {
-		return nil, ContextMenuListOutput{}, fmt.Errorf("failed to unmarshal context menus: %w", err)
+		return nil, ContextMenuListOutput{}, coreerr.E("mcp.contextMenuList", "failed to unmarshal context menus", err)
 	}
 	return nil, ContextMenuListOutput{Menus: menusMap}, nil
 }
diff --git a/pkg/mcp/tools_dialog.go b/pkg/mcp/tools_dialog.go
index 06bdf66..bfc6015 100644
--- a/pkg/mcp/tools_dialog.go
+++ b/pkg/mcp/tools_dialog.go
@@ -3,9 +3,9 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
 	"forge.lthn.ai/core/gui/pkg/dialog"
+	coreerr "forge.lthn.ai/core/go-log"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
 
@@ -33,7 +33,7 @@ func (s *Subsystem) dialogOpenFile(_ context.Context, _ *mcp.CallToolRequest, in
 	}
 	paths, ok := result.([]string)
 	if !ok {
-		return nil, DialogOpenFileOutput{}, fmt.Errorf("unexpected result type from open file dialog")
+		return nil, DialogOpenFileOutput{}, coreerr.E("mcp.dialogOpenFile", "unexpected result type", nil)
 	}
 	return nil, DialogOpenFileOutput{Paths: paths}, nil
 }
@@ -62,7 +62,7 @@ func (s *Subsystem) dialogSaveFile(_ context.Context, _ *mcp.CallToolRequest, in
 	}
 	path, ok := result.(string)
 	if !ok {
-		return nil, DialogSaveFileOutput{}, fmt.Errorf("unexpected result type from save file dialog")
+		return nil, DialogSaveFileOutput{}, coreerr.E("mcp.dialogSaveFile", "unexpected result type", nil)
 	}
 	return nil, DialogSaveFileOutput{Path: path}, nil
 }
@@ -87,7 +87,7 @@ func (s *Subsystem) dialogOpenDirectory(_ context.Context, _ *mcp.CallToolReques
 	}
 	path, ok := result.(string)
 	if !ok {
-		return nil, DialogOpenDirectoryOutput{}, fmt.Errorf("unexpected result type from open directory dialog")
+		return nil, DialogOpenDirectoryOutput{}, coreerr.E("mcp.dialogOpenDirectory", "unexpected result type", nil)
 	}
 	return nil, DialogOpenDirectoryOutput{Path: path}, nil
 }
@@ -115,7 +115,7 @@ func (s *Subsystem) dialogConfirm(_ context.Context, _ *mcp.CallToolRequest, inp
 	}
 	button, ok := result.(string)
 	if !ok {
-		return nil, DialogConfirmOutput{}, fmt.Errorf("unexpected result type from confirm dialog")
+		return nil, DialogConfirmOutput{}, coreerr.E("mcp.dialogConfirm", "unexpected result type", nil)
 	}
 	return nil, DialogConfirmOutput{Button: button}, nil
 }
@@ -142,7 +142,7 @@ func (s *Subsystem) dialogPrompt(_ context.Context, _ *mcp.CallToolRequest, inpu
 	}
 	button, ok := result.(string)
 	if !ok {
-		return nil, DialogPromptOutput{}, fmt.Errorf("unexpected result type from prompt dialog")
+		return nil, DialogPromptOutput{}, coreerr.E("mcp.dialogPrompt", "unexpected result type", nil)
 	}
 	return nil, DialogPromptOutput{Button: button}, nil
 }
diff --git a/pkg/mcp/tools_environment.go b/pkg/mcp/tools_environment.go
index 87eb0df..8d8ad49 100644
--- a/pkg/mcp/tools_environment.go
+++ b/pkg/mcp/tools_environment.go
@@ -3,9 +3,9 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
 	"forge.lthn.ai/core/gui/pkg/environment"
+	coreerr "forge.lthn.ai/core/go-log"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
 
@@ -23,7 +23,7 @@ func (s *Subsystem) themeGet(_ context.Context, _ *mcp.CallToolRequest, _ ThemeG
 	}
 	theme, ok := result.(environment.ThemeInfo)
 	if !ok {
-		return nil, ThemeGetOutput{}, fmt.Errorf("unexpected result type from theme query")
+		return nil, ThemeGetOutput{}, coreerr.E("mcp.themeGet", "unexpected result type", nil)
 	}
 	return nil, ThemeGetOutput{Theme: theme}, nil
 }
@@ -42,7 +42,7 @@ func (s *Subsystem) themeSystem(_ context.Context, _ *mcp.CallToolRequest, _ The
 	}
 	info, ok := result.(environment.EnvironmentInfo)
 	if !ok {
-		return nil, ThemeSystemOutput{}, fmt.Errorf("unexpected result type from environment info query")
+		return nil, ThemeSystemOutput{}, coreerr.E("mcp.themeSystem", "unexpected result type", nil)
 	}
 	return nil, ThemeSystemOutput{Info: info}, nil
 }
diff --git a/pkg/mcp/tools_layout.go b/pkg/mcp/tools_layout.go
index 24ec8fa..18066d3 100644
--- a/pkg/mcp/tools_layout.go
+++ b/pkg/mcp/tools_layout.go
@@ -3,8 +3,8 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/gui/pkg/window"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
@@ -57,7 +57,7 @@ func (s *Subsystem) layoutList(_ context.Context, _ *mcp.CallToolRequest, _ Layo
 	}
 	layouts, ok := result.([]window.LayoutInfo)
 	if !ok {
-		return nil, LayoutListOutput{}, fmt.Errorf("unexpected result type from layout list query")
+		return nil, LayoutListOutput{}, coreerr.E("mcp.layoutList", "unexpected result type", nil)
 	}
 	return nil, LayoutListOutput{Layouts: layouts}, nil
 }
@@ -95,7 +95,7 @@ func (s *Subsystem) layoutGet(_ context.Context, _ *mcp.CallToolRequest, input L
 	}
 	layout, ok := result.(*window.Layout)
 	if !ok {
-		return nil, LayoutGetOutput{}, fmt.Errorf("unexpected result type from layout get query")
+		return nil, LayoutGetOutput{}, coreerr.E("mcp.layoutGet", "unexpected result type", nil)
 	}
 	return nil, LayoutGetOutput{Layout: layout}, nil
 }
diff --git a/pkg/mcp/tools_notification.go b/pkg/mcp/tools_notification.go
index 259e59f..0629054 100644
--- a/pkg/mcp/tools_notification.go
+++ b/pkg/mcp/tools_notification.go
@@ -3,8 +3,8 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/gui/pkg/notification"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
@@ -46,7 +46,7 @@ func (s *Subsystem) notificationPermissionRequest(_ context.Context, _ *mcp.Call
 	}
 	granted, ok := result.(bool)
 	if !ok {
-		return nil, NotificationPermissionRequestOutput{}, fmt.Errorf("unexpected result type from notification permission request")
+		return nil, NotificationPermissionRequestOutput{}, coreerr.E("mcp.notificationPermissionRequest", "unexpected result type", nil)
 	}
 	return nil, NotificationPermissionRequestOutput{Granted: granted}, nil
 }
@@ -65,7 +65,7 @@ func (s *Subsystem) notificationPermissionCheck(_ context.Context, _ *mcp.CallTo
 	}
 	status, ok := result.(notification.PermissionStatus)
 	if !ok {
-		return nil, NotificationPermissionCheckOutput{}, fmt.Errorf("unexpected result type from notification permission check")
+		return nil, NotificationPermissionCheckOutput{}, coreerr.E("mcp.notificationPermissionCheck", "unexpected result type", nil)
 	}
 	return nil, NotificationPermissionCheckOutput{Granted: status.Granted}, nil
 }
diff --git a/pkg/mcp/tools_screen.go b/pkg/mcp/tools_screen.go
index 8a276b9..a89e879 100644
--- a/pkg/mcp/tools_screen.go
+++ b/pkg/mcp/tools_screen.go
@@ -3,8 +3,8 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/gui/pkg/screen"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
@@ -23,7 +23,7 @@ func (s *Subsystem) screenList(_ context.Context, _ *mcp.CallToolRequest, _ Scre
 	}
 	screens, ok := result.([]screen.Screen)
 	if !ok {
-		return nil, ScreenListOutput{}, fmt.Errorf("unexpected result type from screen list query")
+		return nil, ScreenListOutput{}, coreerr.E("mcp.screenList", "unexpected result type", nil)
 	}
 	return nil, ScreenListOutput{Screens: screens}, nil
 }
@@ -44,7 +44,7 @@ func (s *Subsystem) screenGet(_ context.Context, _ *mcp.CallToolRequest, input S
 	}
 	scr, ok := result.(*screen.Screen)
 	if !ok {
-		return nil, ScreenGetOutput{}, fmt.Errorf("unexpected result type from screen get query")
+		return nil, ScreenGetOutput{}, coreerr.E("mcp.screenGet", "unexpected result type", nil)
 	}
 	return nil, ScreenGetOutput{Screen: scr}, nil
 }
@@ -63,7 +63,7 @@ func (s *Subsystem) screenPrimary(_ context.Context, _ *mcp.CallToolRequest, _ S
 	}
 	scr, ok := result.(*screen.Screen)
 	if !ok {
-		return nil, ScreenPrimaryOutput{}, fmt.Errorf("unexpected result type from screen primary query")
+		return nil, ScreenPrimaryOutput{}, coreerr.E("mcp.screenPrimary", "unexpected result type", nil)
 	}
 	return nil, ScreenPrimaryOutput{Screen: scr}, nil
 }
@@ -85,7 +85,7 @@ func (s *Subsystem) screenAtPoint(_ context.Context, _ *mcp.CallToolRequest, inp
 	}
 	scr, ok := result.(*screen.Screen)
 	if !ok {
-		return nil, ScreenAtPointOutput{}, fmt.Errorf("unexpected result type from screen at point query")
+		return nil, ScreenAtPointOutput{}, coreerr.E("mcp.screenAtPoint", "unexpected result type", nil)
 	}
 	return nil, ScreenAtPointOutput{Screen: scr}, nil
 }
@@ -104,7 +104,7 @@ func (s *Subsystem) screenWorkAreas(_ context.Context, _ *mcp.CallToolRequest, _
 	}
 	areas, ok := result.([]screen.Rect)
 	if !ok {
-		return nil, ScreenWorkAreasOutput{}, fmt.Errorf("unexpected result type from screen work areas query")
+		return nil, ScreenWorkAreasOutput{}, coreerr.E("mcp.screenWorkAreas", "unexpected result type", nil)
 	}
 	return nil, ScreenWorkAreasOutput{WorkAreas: areas}, nil
 }
diff --git a/pkg/mcp/tools_tray.go b/pkg/mcp/tools_tray.go
index 0cbad22..d5efb45 100644
--- a/pkg/mcp/tools_tray.go
+++ b/pkg/mcp/tools_tray.go
@@ -3,8 +3,8 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/gui/pkg/systray"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
@@ -70,7 +70,7 @@ func (s *Subsystem) trayInfo(_ context.Context, _ *mcp.CallToolRequest, _ TrayIn
 	}
 	config, ok := result.(map[string]any)
 	if !ok {
-		return nil, TrayInfoOutput{}, fmt.Errorf("unexpected result type from tray config query")
+		return nil, TrayInfoOutput{}, coreerr.E("mcp.trayInfo", "unexpected result type", nil)
 	}
 	return nil, TrayInfoOutput{Config: config}, nil
 }
diff --git a/pkg/mcp/tools_webview.go b/pkg/mcp/tools_webview.go
index b598a4b..923fe36 100644
--- a/pkg/mcp/tools_webview.go
+++ b/pkg/mcp/tools_webview.go
@@ -3,8 +3,8 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/gui/pkg/webview"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
@@ -105,7 +105,7 @@ func (s *Subsystem) webviewScreenshot(_ context.Context, _ *mcp.CallToolRequest,
 	}
 	sr, ok := result.(webview.ScreenshotResult)
 	if !ok {
-		return nil, WebviewScreenshotOutput{}, fmt.Errorf("unexpected result type from webview screenshot")
+		return nil, WebviewScreenshotOutput{}, coreerr.E("mcp.webviewScreenshot", "unexpected result type", nil)
 	}
 	return nil, WebviewScreenshotOutput{Base64: sr.Base64, MimeType: sr.MimeType}, nil
 }
@@ -248,7 +248,7 @@ func (s *Subsystem) webviewConsole(_ context.Context, _ *mcp.CallToolRequest, in
 	}
 	msgs, ok := result.([]webview.ConsoleMessage)
 	if !ok {
-		return nil, WebviewConsoleOutput{}, fmt.Errorf("unexpected result type from webview console query")
+		return nil, WebviewConsoleOutput{}, coreerr.E("mcp.webviewConsole", "unexpected result type", nil)
 	}
 	return nil, WebviewConsoleOutput{Messages: msgs}, nil
 }
@@ -289,7 +289,7 @@ func (s *Subsystem) webviewQuery(_ context.Context, _ *mcp.CallToolRequest, inpu
 	}
 	el, ok := result.(*webview.ElementInfo)
 	if !ok {
-		return nil, WebviewQueryOutput{}, fmt.Errorf("unexpected result type from webview query")
+		return nil, WebviewQueryOutput{}, coreerr.E("mcp.webviewQuery", "unexpected result type", nil)
 	}
 	return nil, WebviewQueryOutput{Element: el}, nil
 }
@@ -312,7 +312,7 @@ func (s *Subsystem) webviewQueryAll(_ context.Context, _ *mcp.CallToolRequest, i
 	}
 	els, ok := result.([]*webview.ElementInfo)
 	if !ok {
-		return nil, WebviewQueryAllOutput{}, fmt.Errorf("unexpected result type from webview query all")
+		return nil, WebviewQueryAllOutput{}, coreerr.E("mcp.webviewQueryAll", "unexpected result type", nil)
 	}
 	return nil, WebviewQueryAllOutput{Elements: els}, nil
 }
@@ -335,7 +335,7 @@ func (s *Subsystem) webviewDOMTree(_ context.Context, _ *mcp.CallToolRequest, in
 	}
 	html, ok := result.(string)
 	if !ok {
-		return nil, WebviewDOMTreeOutput{}, fmt.Errorf("unexpected result type from webview DOM tree query")
+		return nil, WebviewDOMTreeOutput{}, coreerr.E("mcp.webviewDOMTree", "unexpected result type", nil)
 	}
 	return nil, WebviewDOMTreeOutput{HTML: html}, nil
 }
@@ -357,7 +357,7 @@ func (s *Subsystem) webviewURL(_ context.Context, _ *mcp.CallToolRequest, input
 	}
 	url, ok := result.(string)
 	if !ok {
-		return nil, WebviewURLOutput{}, fmt.Errorf("unexpected result type from webview URL query")
+		return nil, WebviewURLOutput{}, coreerr.E("mcp.webviewURL", "unexpected result type", nil)
 	}
 	return nil, WebviewURLOutput{URL: url}, nil
 }
@@ -379,7 +379,7 @@ func (s *Subsystem) webviewTitle(_ context.Context, _ *mcp.CallToolRequest, inpu
 	}
 	title, ok := result.(string)
 	if !ok {
-		return nil, WebviewTitleOutput{}, fmt.Errorf("unexpected result type from webview title query")
+		return nil, WebviewTitleOutput{}, coreerr.E("mcp.webviewTitle", "unexpected result type", nil)
 	}
 	return nil, WebviewTitleOutput{Title: title}, nil
 }
diff --git a/pkg/mcp/tools_window.go b/pkg/mcp/tools_window.go
index e5ac73f..16484d9 100644
--- a/pkg/mcp/tools_window.go
+++ b/pkg/mcp/tools_window.go
@@ -3,8 +3,8 @@ package mcp
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/gui/pkg/window"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
@@ -23,7 +23,7 @@ func (s *Subsystem) windowList(_ context.Context, _ *mcp.CallToolRequest, _ Wind
 	}
 	windows, ok := result.([]window.WindowInfo)
 	if !ok {
-		return nil, WindowListOutput{}, fmt.Errorf("unexpected result type from window list query")
+		return nil, WindowListOutput{}, coreerr.E("mcp.windowList", "unexpected result type", nil)
 	}
 	return nil, WindowListOutput{Windows: windows}, nil
 }
@@ -44,7 +44,7 @@ func (s *Subsystem) windowGet(_ context.Context, _ *mcp.CallToolRequest, input W
 	}
 	info, ok := result.(*window.WindowInfo)
 	if !ok {
-		return nil, WindowGetOutput{}, fmt.Errorf("unexpected result type from window get query")
+		return nil, WindowGetOutput{}, coreerr.E("mcp.windowGet", "unexpected result type", nil)
 	}
 	return nil, WindowGetOutput{Window: info}, nil
 }
@@ -63,7 +63,7 @@ func (s *Subsystem) windowFocused(_ context.Context, _ *mcp.CallToolRequest, _ W
 	}
 	windows, ok := result.([]window.WindowInfo)
 	if !ok {
-		return nil, WindowFocusedOutput{}, fmt.Errorf("unexpected result type from window list query")
+		return nil, WindowFocusedOutput{}, coreerr.E("mcp.windowFocused", "unexpected result type", nil)
 	}
 	for _, w := range windows {
 		if w.Focused {
@@ -110,7 +110,7 @@ func (s *Subsystem) windowCreate(_ context.Context, _ *mcp.CallToolRequest, inpu
 	}
 	info, ok := result.(window.WindowInfo)
 	if !ok {
-		return nil, WindowCreateOutput{}, fmt.Errorf("unexpected result type from window create task")
+		return nil, WindowCreateOutput{}, coreerr.E("mcp.windowCreate", "unexpected result type", nil)
 	}
 	return nil, WindowCreateOutput{Window: info}, nil
 }
diff --git a/pkg/systray/menu.go b/pkg/systray/menu.go
index 3032a6d..8594f33 100644
--- a/pkg/systray/menu.go
+++ b/pkg/systray/menu.go
@@ -1,12 +1,12 @@
 // pkg/systray/menu.go
 package systray
 
-import "fmt"
+import coreerr "forge.lthn.ai/core/go-log"
 
 // SetMenu sets a dynamic menu on the tray from TrayMenuItem descriptors.
 func (m *Manager) SetMenu(items []TrayMenuItem) error {
 	if m.tray == nil {
-		return fmt.Errorf("tray not initialised")
+		return coreerr.E("systray.SetMenu", "tray not initialised", nil)
 	}
 	menu := m.buildMenu(items)
 	m.tray.SetMenu(menu)
diff --git a/pkg/systray/tray.go b/pkg/systray/tray.go
index 05ffcdf..8d2e108 100644
--- a/pkg/systray/tray.go
+++ b/pkg/systray/tray.go
@@ -3,8 +3,9 @@ package systray
 
 import (
 	_ "embed"
-	"fmt"
 	"sync"
+
+	coreerr "forge.lthn.ai/core/go-log"
 )
 
 //go:embed assets/apptray.png
@@ -31,7 +32,7 @@ func NewManager(platform Platform) *Manager {
 func (m *Manager) Setup(tooltip, label string) error {
 	m.tray = m.platform.NewTray()
 	if m.tray == nil {
-		return fmt.Errorf("platform returned nil tray")
+		return coreerr.E("systray.Setup", "platform returned nil tray", nil)
 	}
 	m.tray.SetTemplateIcon(defaultIcon)
 	m.tray.SetTooltip(tooltip)
@@ -42,7 +43,7 @@ func (m *Manager) Setup(tooltip, label string) error {
 // SetIcon sets the tray icon.
 func (m *Manager) SetIcon(data []byte) error {
 	if m.tray == nil {
-		return fmt.Errorf("tray not initialised")
+		return coreerr.E("systray.SetIcon", "tray not initialised", nil)
 	}
 	m.tray.SetIcon(data)
 	return nil
@@ -51,7 +52,7 @@ func (m *Manager) SetIcon(data []byte) error {
 // SetTemplateIcon sets the template icon (macOS).
 func (m *Manager) SetTemplateIcon(data []byte) error {
 	if m.tray == nil {
-		return fmt.Errorf("tray not initialised")
+		return coreerr.E("systray.SetTemplateIcon", "tray not initialised", nil)
 	}
 	m.tray.SetTemplateIcon(data)
 	return nil
@@ -60,7 +61,7 @@ func (m *Manager) SetTemplateIcon(data []byte) error {
 // SetTooltip sets the tray tooltip.
 func (m *Manager) SetTooltip(text string) error {
 	if m.tray == nil {
-		return fmt.Errorf("tray not initialised")
+		return coreerr.E("systray.SetTooltip", "tray not initialised", nil)
 	}
 	m.tray.SetTooltip(text)
 	return nil
@@ -69,7 +70,7 @@ func (m *Manager) SetTooltip(text string) error {
 // SetLabel sets the tray label.
 func (m *Manager) SetLabel(text string) error {
 	if m.tray == nil {
-		return fmt.Errorf("tray not initialised")
+		return coreerr.E("systray.SetLabel", "tray not initialised", nil)
 	}
 	m.tray.SetLabel(text)
 	return nil
@@ -78,7 +79,7 @@ func (m *Manager) SetLabel(text string) error {
 // AttachWindow attaches a panel window to the tray.
 func (m *Manager) AttachWindow(w WindowHandle) error {
 	if m.tray == nil {
-		return fmt.Errorf("tray not initialised")
+		return coreerr.E("systray.AttachWindow", "tray not initialised", nil)
 	}
 	m.tray.AttachWindow(w)
 	return nil
diff --git a/pkg/window/layout.go b/pkg/window/layout.go
index 545a99f..7021a72 100644
--- a/pkg/window/layout.go
+++ b/pkg/window/layout.go
@@ -3,11 +3,13 @@ package window
 
 import (
 	"encoding/json"
-	"fmt"
 	"os"
 	"path/filepath"
 	"sync"
 	"time"
+
+	coreio "forge.lthn.ai/core/go-io"
+	coreerr "forge.lthn.ai/core/go-log"
 )
 
 // Layout is a named window arrangement.
@@ -65,13 +67,13 @@ func (lm *LayoutManager) load() {
 	if lm.configDir == "" {
 		return
 	}
-	data, err := os.ReadFile(lm.filePath())
+	content, err := coreio.Local.Read(lm.filePath())
 	if err != nil {
 		return
 	}
 	lm.mu.Lock()
 	defer lm.mu.Unlock()
-	_ = json.Unmarshal(data, &lm.layouts)
+	_ = json.Unmarshal([]byte(content), &lm.layouts)
 }
 
 func (lm *LayoutManager) save() {
@@ -84,14 +86,14 @@ func (lm *LayoutManager) save() {
 	if err != nil {
 		return
 	}
-	_ = os.MkdirAll(lm.configDir, 0o755)
-	_ = os.WriteFile(lm.filePath(), data, 0o644)
+	_ = coreio.Local.EnsureDir(lm.configDir)
+	_ = coreio.Local.Write(lm.filePath(), string(data))
 }
 
 // SaveLayout creates or updates a named layout.
 func (lm *LayoutManager) SaveLayout(name string, windowStates map[string]WindowState) error {
 	if name == "" {
-		return fmt.Errorf("layout name cannot be empty")
+		return coreerr.E("window.LayoutManager.SaveLayout", "layout name cannot be empty", nil)
 	}
 	now := time.Now().UnixMilli()
 	lm.mu.Lock()
diff --git a/pkg/window/mock_test.go b/pkg/window/mock_test.go
index 72d54ca..8bb08a9 100644
--- a/pkg/window/mock_test.go
+++ b/pkg/window/mock_test.go
@@ -33,6 +33,8 @@ type mockWindow struct {
 	maximised, focused   bool
 	visible, alwaysOnTop bool
 	closed               bool
+	minimised            bool
+	fullscreened         bool
 	eventHandlers        []func(WindowEvent)
 	fileDropHandlers     []func(paths []string, targetID string)
 }
@@ -51,13 +53,13 @@ func (w *mockWindow) SetVisibility(visible bool)              { w.visible = visi
 func (w *mockWindow) SetAlwaysOnTop(alwaysOnTop bool)         { w.alwaysOnTop = alwaysOnTop }
 func (w *mockWindow) Maximise()                               { w.maximised = true }
 func (w *mockWindow) Restore()                                { w.maximised = false }
-func (w *mockWindow) Minimise()                               {}
+func (w *mockWindow) Minimise()                               { w.minimised = true }
 func (w *mockWindow) Focus()                                  { w.focused = true }
 func (w *mockWindow) Close()                                  { w.closed = true }
 func (w *mockWindow) Show()                                   { w.visible = true }
 func (w *mockWindow) Hide()                                   { w.visible = false }
-func (w *mockWindow) Fullscreen()                             {}
-func (w *mockWindow) UnFullscreen()                           {}
+func (w *mockWindow) Fullscreen()                             { w.fullscreened = true }
+func (w *mockWindow) UnFullscreen()                           { w.fullscreened = false }
 func (w *mockWindow) OnWindowEvent(handler func(WindowEvent)) { w.eventHandlers = append(w.eventHandlers, handler) }
 func (w *mockWindow) OnFileDrop(handler func(paths []string, targetID string)) {
 	w.fileDropHandlers = append(w.fileDropHandlers, handler)
diff --git a/pkg/window/persistence_test.go b/pkg/window/persistence_test.go
new file mode 100644
index 0000000..6a4ee74
--- /dev/null
+++ b/pkg/window/persistence_test.go
@@ -0,0 +1,318 @@
+// pkg/window/persistence_test.go
+package window
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// --- StateManager Persistence Tests ---
+
+func TestStateManager_SetAndGet_Good(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+	state := WindowState{
+		X: 150, Y: 250, Width: 1024, Height: 768,
+		Maximized: true, Screen: "primary", URL: "/app",
+	}
+	sm.SetState("editor", state)
+
+	got, ok := sm.GetState("editor")
+	require.True(t, ok)
+	assert.Equal(t, 150, got.X)
+	assert.Equal(t, 250, got.Y)
+	assert.Equal(t, 1024, got.Width)
+	assert.Equal(t, 768, got.Height)
+	assert.True(t, got.Maximized)
+	assert.Equal(t, "primary", got.Screen)
+	assert.Equal(t, "/app", got.URL)
+	assert.NotZero(t, got.UpdatedAt, "UpdatedAt should be set by SetState")
+}
+
+func TestStateManager_UpdatePosition_Good(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+	sm.SetState("win", WindowState{X: 0, Y: 0, Width: 800, Height: 600})
+
+	sm.UpdatePosition("win", 300, 400)
+
+	got, ok := sm.GetState("win")
+	require.True(t, ok)
+	assert.Equal(t, 300, got.X)
+	assert.Equal(t, 400, got.Y)
+	// Width/Height should remain unchanged
+	assert.Equal(t, 800, got.Width)
+	assert.Equal(t, 600, got.Height)
+}
+
+func TestStateManager_UpdateSize_Good(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+	sm.SetState("win", WindowState{X: 100, Y: 200, Width: 800, Height: 600})
+
+	sm.UpdateSize("win", 1920, 1080)
+
+	got, ok := sm.GetState("win")
+	require.True(t, ok)
+	assert.Equal(t, 1920, got.Width)
+	assert.Equal(t, 1080, got.Height)
+	// Position should remain unchanged
+	assert.Equal(t, 100, got.X)
+	assert.Equal(t, 200, got.Y)
+}
+
+func TestStateManager_UpdateMaximized_Good(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+	sm.SetState("win", WindowState{Width: 800, Height: 600, Maximized: false})
+
+	sm.UpdateMaximized("win", true)
+
+	got, ok := sm.GetState("win")
+	require.True(t, ok)
+	assert.True(t, got.Maximized)
+
+	sm.UpdateMaximized("win", false)
+
+	got, ok = sm.GetState("win")
+	require.True(t, ok)
+	assert.False(t, got.Maximized)
+}
+
+func TestStateManager_CaptureState_Good(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+	pw := &mockWindow{
+		name: "captured", x: 75, y: 125,
+		width: 1440, height: 900, maximised: true,
+	}
+
+	sm.CaptureState(pw)
+
+	got, ok := sm.GetState("captured")
+	require.True(t, ok)
+	assert.Equal(t, 75, got.X)
+	assert.Equal(t, 125, got.Y)
+	assert.Equal(t, 1440, got.Width)
+	assert.Equal(t, 900, got.Height)
+	assert.True(t, got.Maximized)
+	assert.NotZero(t, got.UpdatedAt)
+}
+
+func TestStateManager_ApplyState_Good(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+	sm.SetState("target", WindowState{X: 55, Y: 65, Width: 700, Height: 500})
+
+	w := &Window{Name: "target", Width: 1280, Height: 800, X: 0, Y: 0}
+	sm.ApplyState(w)
+
+	assert.Equal(t, 55, w.X)
+	assert.Equal(t, 65, w.Y)
+	assert.Equal(t, 700, w.Width)
+	assert.Equal(t, 500, w.Height)
+}
+
+func TestStateManager_ApplyState_NoState(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+
+	w := &Window{Name: "untouched", Width: 1280, Height: 800, X: 10, Y: 20}
+	sm.ApplyState(w)
+
+	// Window should remain unchanged when no state is saved
+	assert.Equal(t, 10, w.X)
+	assert.Equal(t, 20, w.Y)
+	assert.Equal(t, 1280, w.Width)
+	assert.Equal(t, 800, w.Height)
+}
+
+func TestStateManager_ListStates_Good(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+	sm.SetState("alpha", WindowState{Width: 100})
+	sm.SetState("beta", WindowState{Width: 200})
+	sm.SetState("gamma", WindowState{Width: 300})
+
+	names := sm.ListStates()
+	assert.Len(t, names, 3)
+	assert.Contains(t, names, "alpha")
+	assert.Contains(t, names, "beta")
+	assert.Contains(t, names, "gamma")
+}
+
+func TestStateManager_Clear_Good(t *testing.T) {
+	sm := NewStateManagerWithDir(t.TempDir())
+	sm.SetState("a", WindowState{Width: 100})
+	sm.SetState("b", WindowState{Width: 200})
+	sm.SetState("c", WindowState{Width: 300})
+
+	sm.Clear()
+
+	names := sm.ListStates()
+	assert.Empty(t, names)
+
+	_, ok := sm.GetState("a")
+	assert.False(t, ok)
+}
+
+func TestStateManager_Persistence_Good(t *testing.T) {
+	dir := t.TempDir()
+
+	// First manager: write state and force sync to disk
+	sm1 := NewStateManagerWithDir(dir)
+	sm1.SetState("persist-win", WindowState{
+		X: 42, Y: 84, Width: 500, Height: 300,
+		Maximized: true, Screen: "secondary", URL: "/settings",
+	})
+	sm1.ForceSync()
+
+	// Second manager: load from the same directory
+	sm2 := NewStateManagerWithDir(dir)
+
+	got, ok := sm2.GetState("persist-win")
+	require.True(t, ok)
+	assert.Equal(t, 42, got.X)
+	assert.Equal(t, 84, got.Y)
+	assert.Equal(t, 500, got.Width)
+	assert.Equal(t, 300, got.Height)
+	assert.True(t, got.Maximized)
+	assert.Equal(t, "secondary", got.Screen)
+	assert.Equal(t, "/settings", got.URL)
+	assert.NotZero(t, got.UpdatedAt)
+}
+
+// --- LayoutManager Persistence Tests ---
+
+func TestLayoutManager_SaveAndGet_Good(t *testing.T) {
+	lm := NewLayoutManagerWithDir(t.TempDir())
+	windows := map[string]WindowState{
+		"editor":   {X: 0, Y: 0, Width: 960, Height: 1080},
+		"terminal": {X: 960, Y: 0, Width: 960, Height: 540},
+		"browser":  {X: 960, Y: 540, Width: 960, Height: 540},
+	}
+
+	err := lm.SaveLayout("coding", windows)
+	require.NoError(t, err)
+
+	layout, ok := lm.GetLayout("coding")
+	require.True(t, ok)
+	assert.Equal(t, "coding", layout.Name)
+	assert.Len(t, layout.Windows, 3)
+	assert.Equal(t, 960, layout.Windows["editor"].Width)
+	assert.Equal(t, 1080, layout.Windows["editor"].Height)
+	assert.Equal(t, 960, layout.Windows["terminal"].X)
+	assert.NotZero(t, layout.CreatedAt)
+	assert.NotZero(t, layout.UpdatedAt)
+	assert.Equal(t, layout.CreatedAt, layout.UpdatedAt, "CreatedAt and UpdatedAt should match on first save")
+}
+
+func TestLayoutManager_SaveLayout_EmptyName_Bad(t *testing.T) {
+	lm := NewLayoutManagerWithDir(t.TempDir())
+	err := lm.SaveLayout("", map[string]WindowState{
+		"win": {Width: 800},
+	})
+	assert.Error(t, err)
+}
+
+func TestLayoutManager_SaveLayout_Update_Good(t *testing.T) {
+	lm := NewLayoutManagerWithDir(t.TempDir())
+
+	// First save
+	err := lm.SaveLayout("evolving", map[string]WindowState{
+		"win1": {Width: 800, Height: 600},
+	})
+	require.NoError(t, err)
+
+	first, ok := lm.GetLayout("evolving")
+	require.True(t, ok)
+	originalCreatedAt := first.CreatedAt
+	originalUpdatedAt := first.UpdatedAt
+
+	// Small delay to ensure UpdatedAt differs
+	time.Sleep(2 * time.Millisecond)
+
+	// Second save with same name but different windows
+	err = lm.SaveLayout("evolving", map[string]WindowState{
+		"win1": {Width: 1024, Height: 768},
+		"win2": {Width: 640, Height: 480},
+	})
+	require.NoError(t, err)
+
+	updated, ok := lm.GetLayout("evolving")
+	require.True(t, ok)
+
+	// CreatedAt should be preserved from the original save
+	assert.Equal(t, originalCreatedAt, updated.CreatedAt, "CreatedAt should be preserved on update")
+	// UpdatedAt should be newer
+	assert.GreaterOrEqual(t, updated.UpdatedAt, originalUpdatedAt, "UpdatedAt should advance on update")
+	// Windows should reflect the second save
+	assert.Len(t, updated.Windows, 2)
+	assert.Equal(t, 1024, updated.Windows["win1"].Width)
+}
+
+func TestLayoutManager_ListLayouts_Good(t *testing.T) {
+	lm := NewLayoutManagerWithDir(t.TempDir())
+	require.NoError(t, lm.SaveLayout("coding", map[string]WindowState{
+		"editor": {Width: 960}, "terminal": {Width: 960},
+	}))
+	require.NoError(t, lm.SaveLayout("presenting", map[string]WindowState{
+		"slides": {Width: 1920},
+	}))
+	require.NoError(t, lm.SaveLayout("debugging", map[string]WindowState{
+		"code": {Width: 640}, "debugger": {Width: 640}, "console": {Width: 640},
+	}))
+
+	infos := lm.ListLayouts()
+	assert.Len(t, infos, 3)
+
+	// Build a lookup map for assertions regardless of order
+	byName := make(map[string]LayoutInfo)
+	for _, info := range infos {
+		byName[info.Name] = info
+	}
+
+	assert.Equal(t, 2, byName["coding"].WindowCount)
+	assert.Equal(t, 1, byName["presenting"].WindowCount)
+	assert.Equal(t, 3, byName["debugging"].WindowCount)
+}
+
+func TestLayoutManager_DeleteLayout_Good(t *testing.T) {
+	lm := NewLayoutManagerWithDir(t.TempDir())
+	require.NoError(t, lm.SaveLayout("temporary", map[string]WindowState{
+		"win": {Width: 800},
+	}))
+
+	// Verify it exists
+	_, ok := lm.GetLayout("temporary")
+	require.True(t, ok)
+
+	lm.DeleteLayout("temporary")
+
+	// Verify it is gone
+	_, ok = lm.GetLayout("temporary")
+	assert.False(t, ok)
+
+	// Verify list is empty
+	assert.Empty(t, lm.ListLayouts())
+}
+
+func TestLayoutManager_Persistence_Good(t *testing.T) {
+	dir := t.TempDir()
+
+	// First manager: save layout to disk
+	lm1 := NewLayoutManagerWithDir(dir)
+	err := lm1.SaveLayout("persisted", map[string]WindowState{
+		"main":    {X: 0, Y: 0, Width: 1280, Height: 800},
+		"sidebar": {X: 1280, Y: 0, Width: 640, Height: 800},
+	})
+	require.NoError(t, err)
+
+	// Second manager: load from the same directory
+	lm2 := NewLayoutManagerWithDir(dir)
+
+	layout, ok := lm2.GetLayout("persisted")
+	require.True(t, ok)
+	assert.Equal(t, "persisted", layout.Name)
+	assert.Len(t, layout.Windows, 2)
+	assert.Equal(t, 1280, layout.Windows["main"].Width)
+	assert.Equal(t, 800, layout.Windows["main"].Height)
+	assert.Equal(t, 640, layout.Windows["sidebar"].Width)
+	assert.NotZero(t, layout.CreatedAt)
+	assert.NotZero(t, layout.UpdatedAt)
+}
diff --git a/pkg/window/service.go b/pkg/window/service.go
index 040ab95..8260e45 100644
--- a/pkg/window/service.go
+++ b/pkg/window/service.go
@@ -2,8 +2,8 @@ package window
 
 import (
 	"context"
-	"fmt"
 
+	coreerr "forge.lthn.ai/core/go-log"
 	"forge.lthn.ai/core/go/pkg/core"
 )
 
@@ -207,7 +207,7 @@ func (s *Service) trackWindow(pw PlatformWindow) {
 func (s *Service) taskCloseWindow(name string) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskClose", "window not found: "+name, nil)
 	}
 	// Persist state BEFORE closing (spec requirement)
 	s.manager.State().CaptureState(pw)
@@ -220,7 +220,7 @@ func (s *Service) taskCloseWindow(name string) error {
 func (s *Service) taskSetPosition(name string, x, y int) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskSetPosition", "window not found: "+name, nil)
 	}
 	pw.SetPosition(x, y)
 	s.manager.State().UpdatePosition(name, x, y)
@@ -230,7 +230,7 @@ func (s *Service) taskSetPosition(name string, x, y int) error {
 func (s *Service) taskSetSize(name string, w, h int) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskSetSize", "window not found: "+name, nil)
 	}
 	pw.SetSize(w, h)
 	s.manager.State().UpdateSize(name, w, h)
@@ -240,7 +240,7 @@ func (s *Service) taskSetSize(name string, w, h int) error {
 func (s *Service) taskMaximise(name string) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskMaximise", "window not found: "+name, nil)
 	}
 	pw.Maximise()
 	s.manager.State().UpdateMaximized(name, true)
@@ -250,7 +250,7 @@ func (s *Service) taskMaximise(name string) error {
 func (s *Service) taskMinimise(name string) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskMinimise", "window not found: "+name, nil)
 	}
 	pw.Minimise()
 	return nil
@@ -259,7 +259,7 @@ func (s *Service) taskMinimise(name string) error {
 func (s *Service) taskFocus(name string) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskFocus", "window not found: "+name, nil)
 	}
 	pw.Focus()
 	return nil
@@ -268,7 +268,7 @@ func (s *Service) taskFocus(name string) error {
 func (s *Service) taskRestore(name string) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskRestore", "window not found: "+name, nil)
 	}
 	pw.Restore()
 	s.manager.State().UpdateMaximized(name, false)
@@ -278,7 +278,7 @@ func (s *Service) taskRestore(name string) error {
 func (s *Service) taskSetTitle(name, title string) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskSetTitle", "window not found: "+name, nil)
 	}
 	pw.SetTitle(title)
 	return nil
@@ -287,7 +287,7 @@ func (s *Service) taskSetTitle(name, title string) error {
 func (s *Service) taskSetVisibility(name string, visible bool) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskSetVisibility", "window not found: "+name, nil)
 	}
 	pw.SetVisibility(visible)
 	return nil
@@ -296,7 +296,7 @@ func (s *Service) taskSetVisibility(name string, visible bool) error {
 func (s *Service) taskFullscreen(name string, fullscreen bool) error {
 	pw, ok := s.manager.Get(name)
 	if !ok {
-		return fmt.Errorf("window not found: %s", name)
+		return coreerr.E("window.taskFullscreen", "window not found: "+name, nil)
 	}
 	if fullscreen {
 		pw.Fullscreen()
@@ -321,7 +321,7 @@ func (s *Service) taskSaveLayout(name string) error {
 func (s *Service) taskRestoreLayout(name string) error {
 	layout, ok := s.manager.Layout().GetLayout(name)
 	if !ok {
-		return fmt.Errorf("layout not found: %s", name)
+		return coreerr.E("window.taskRestoreLayout", "layout not found: "+name, nil)
 	}
 	for winName, state := range layout.Windows {
 		pw, found := s.manager.Get(winName)
@@ -348,7 +348,7 @@ var tileModeMap = map[string]TileMode{
 func (s *Service) taskTileWindows(mode string, names []string) error {
 	tm, ok := tileModeMap[mode]
 	if !ok {
-		return fmt.Errorf("unknown tile mode: %s", mode)
+		return coreerr.E("window.taskTileWindows", "unknown tile mode: "+mode, nil)
 	}
 	if len(names) == 0 {
 		names = s.manager.List()
@@ -368,7 +368,7 @@ var snapPosMap = map[string]SnapPosition{
 func (s *Service) taskSnapWindow(name, position string) error {
 	pos, ok := snapPosMap[position]
 	if !ok {
-		return fmt.Errorf("unknown snap position: %s", position)
+		return coreerr.E("window.taskSnapWindow", "unknown snap position: "+position, nil)
 	}
 	return s.manager.SnapWindow(name, pos, 1920, 1080)
 }
diff --git a/pkg/window/service_test.go b/pkg/window/service_test.go
index 1911044..4df1108 100644
--- a/pkg/window/service_test.go
+++ b/pkg/window/service_test.go
@@ -174,3 +174,238 @@ func TestFileDrop_Good(t *testing.T) {
 	assert.Equal(t, "upload-zone", dropped.TargetID)
 	mu.Unlock()
 }
+
+// --- TaskMinimise ---
+
+func TestTaskMinimise_Good(t *testing.T) {
+	svc, c := newTestWindowService(t)
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("test")}})
+
+	_, handled, err := c.PERFORM(TaskMinimise{Name: "test"})
+	require.NoError(t, err)
+	assert.True(t, handled)
+
+	pw, ok := svc.Manager().Get("test")
+	require.True(t, ok)
+	mw := pw.(*mockWindow)
+	assert.True(t, mw.minimised)
+}
+
+func TestTaskMinimise_Bad(t *testing.T) {
+	_, c := newTestWindowService(t)
+	_, handled, err := c.PERFORM(TaskMinimise{Name: "nonexistent"})
+	assert.True(t, handled)
+	assert.Error(t, err)
+}
+
+// --- TaskFocus ---
+
+func TestTaskFocus_Good(t *testing.T) {
+	svc, c := newTestWindowService(t)
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("test")}})
+
+	_, handled, err := c.PERFORM(TaskFocus{Name: "test"})
+	require.NoError(t, err)
+	assert.True(t, handled)
+
+	pw, ok := svc.Manager().Get("test")
+	require.True(t, ok)
+	mw := pw.(*mockWindow)
+	assert.True(t, mw.focused)
+}
+
+func TestTaskFocus_Bad(t *testing.T) {
+	_, c := newTestWindowService(t)
+	_, handled, err := c.PERFORM(TaskFocus{Name: "nonexistent"})
+	assert.True(t, handled)
+	assert.Error(t, err)
+}
+
+// --- TaskRestore ---
+
+func TestTaskRestore_Good(t *testing.T) {
+	svc, c := newTestWindowService(t)
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("test")}})
+
+	// First maximise, then restore
+	_, _, _ = c.PERFORM(TaskMaximise{Name: "test"})
+
+	_, handled, err := c.PERFORM(TaskRestore{Name: "test"})
+	require.NoError(t, err)
+	assert.True(t, handled)
+
+	pw, ok := svc.Manager().Get("test")
+	require.True(t, ok)
+	mw := pw.(*mockWindow)
+	assert.False(t, mw.maximised)
+
+	// Verify state was updated
+	state, ok := svc.Manager().State().GetState("test")
+	assert.True(t, ok)
+	assert.False(t, state.Maximized)
+}
+
+func TestTaskRestore_Bad(t *testing.T) {
+	_, c := newTestWindowService(t)
+	_, handled, err := c.PERFORM(TaskRestore{Name: "nonexistent"})
+	assert.True(t, handled)
+	assert.Error(t, err)
+}
+
+// --- TaskSetTitle ---
+
+func TestTaskSetTitle_Good(t *testing.T) {
+	svc, c := newTestWindowService(t)
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("test")}})
+
+	_, handled, err := c.PERFORM(TaskSetTitle{Name: "test", Title: "New Title"})
+	require.NoError(t, err)
+	assert.True(t, handled)
+
+	pw, ok := svc.Manager().Get("test")
+	require.True(t, ok)
+	assert.Equal(t, "New Title", pw.Title())
+}
+
+func TestTaskSetTitle_Bad(t *testing.T) {
+	_, c := newTestWindowService(t)
+	_, handled, err := c.PERFORM(TaskSetTitle{Name: "nonexistent", Title: "Nope"})
+	assert.True(t, handled)
+	assert.Error(t, err)
+}
+
+// --- TaskSetVisibility ---
+
+func TestTaskSetVisibility_Good(t *testing.T) {
+	svc, c := newTestWindowService(t)
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("test")}})
+
+	_, handled, err := c.PERFORM(TaskSetVisibility{Name: "test", Visible: true})
+	require.NoError(t, err)
+	assert.True(t, handled)
+
+	pw, ok := svc.Manager().Get("test")
+	require.True(t, ok)
+	mw := pw.(*mockWindow)
+	assert.True(t, mw.visible)
+
+	// Now hide it
+	_, handled, err = c.PERFORM(TaskSetVisibility{Name: "test", Visible: false})
+	require.NoError(t, err)
+	assert.True(t, handled)
+	assert.False(t, mw.visible)
+}
+
+func TestTaskSetVisibility_Bad(t *testing.T) {
+	_, c := newTestWindowService(t)
+	_, handled, err := c.PERFORM(TaskSetVisibility{Name: "nonexistent", Visible: true})
+	assert.True(t, handled)
+	assert.Error(t, err)
+}
+
+// --- TaskFullscreen ---
+
+func TestTaskFullscreen_Good(t *testing.T) {
+	svc, c := newTestWindowService(t)
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("test")}})
+
+	// Enter fullscreen
+	_, handled, err := c.PERFORM(TaskFullscreen{Name: "test", Fullscreen: true})
+	require.NoError(t, err)
+	assert.True(t, handled)
+
+	pw, ok := svc.Manager().Get("test")
+	require.True(t, ok)
+	mw := pw.(*mockWindow)
+	assert.True(t, mw.fullscreened)
+
+	// Exit fullscreen
+	_, handled, err = c.PERFORM(TaskFullscreen{Name: "test", Fullscreen: false})
+	require.NoError(t, err)
+	assert.True(t, handled)
+	assert.False(t, mw.fullscreened)
+}
+
+func TestTaskFullscreen_Bad(t *testing.T) {
+	_, c := newTestWindowService(t)
+	_, handled, err := c.PERFORM(TaskFullscreen{Name: "nonexistent", Fullscreen: true})
+	assert.True(t, handled)
+	assert.Error(t, err)
+}
+
+// --- TaskSaveLayout ---
+
+func TestTaskSaveLayout_Good(t *testing.T) {
+	svc, c := newTestWindowService(t)
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("editor"), WithSize(960, 1080), WithPosition(0, 0)}})
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("terminal"), WithSize(960, 1080), WithPosition(960, 0)}})
+
+	_, handled, err := c.PERFORM(TaskSaveLayout{Name: "coding"})
+	require.NoError(t, err)
+	assert.True(t, handled)
+
+	// Verify layout was saved with correct window states
+	layout, ok := svc.Manager().Layout().GetLayout("coding")
+	assert.True(t, ok)
+	assert.Equal(t, "coding", layout.Name)
+	assert.Len(t, layout.Windows, 2)
+
+	editorState, ok := layout.Windows["editor"]
+	assert.True(t, ok)
+	assert.Equal(t, 0, editorState.X)
+	assert.Equal(t, 960, editorState.Width)
+
+	termState, ok := layout.Windows["terminal"]
+	assert.True(t, ok)
+	assert.Equal(t, 960, termState.X)
+	assert.Equal(t, 960, termState.Width)
+}
+
+func TestTaskSaveLayout_Bad(t *testing.T) {
+	_, c := newTestWindowService(t)
+	// Saving an empty layout with empty name returns an error from LayoutManager
+	_, handled, err := c.PERFORM(TaskSaveLayout{Name: ""})
+	assert.True(t, handled)
+	assert.Error(t, err)
+}
+
+// --- TaskRestoreLayout ---
+
+func TestTaskRestoreLayout_Good(t *testing.T) {
+	svc, c := newTestWindowService(t)
+	// Open windows
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("editor"), WithSize(800, 600), WithPosition(0, 0)}})
+	_, _, _ = c.PERFORM(TaskOpenWindow{Opts: []WindowOption{WithName("terminal"), WithSize(800, 600), WithPosition(0, 0)}})
+
+	// Save a layout with specific positions
+	_, _, _ = c.PERFORM(TaskSaveLayout{Name: "coding"})
+
+	// Move the windows to different positions
+	_, _, _ = c.PERFORM(TaskSetPosition{Name: "editor", X: 500, Y: 500})
+	_, _, _ = c.PERFORM(TaskSetPosition{Name: "terminal", X: 600, Y: 600})
+
+	// Restore the layout
+	_, handled, err := c.PERFORM(TaskRestoreLayout{Name: "coding"})
+	require.NoError(t, err)
+	assert.True(t, handled)
+
+	// Verify windows were moved back to saved positions
+	pw, ok := svc.Manager().Get("editor")
+	require.True(t, ok)
+	x, y := pw.Position()
+	assert.Equal(t, 0, x)
+	assert.Equal(t, 0, y)
+
+	pw2, ok := svc.Manager().Get("terminal")
+	require.True(t, ok)
+	x2, y2 := pw2.Position()
+	assert.Equal(t, 0, x2)
+	assert.Equal(t, 0, y2)
+}
+
+func TestTaskRestoreLayout_Bad(t *testing.T) {
+	_, c := newTestWindowService(t)
+	_, handled, err := c.PERFORM(TaskRestoreLayout{Name: "nonexistent"})
+	assert.True(t, handled)
+	assert.Error(t, err)
+}
diff --git a/pkg/window/state.go b/pkg/window/state.go
index 3523cfe..2ff9d87 100644
--- a/pkg/window/state.go
+++ b/pkg/window/state.go
@@ -7,6 +7,8 @@ import (
 	"path/filepath"
 	"sync"
 	"time"
+
+	coreio "forge.lthn.ai/core/go-io"
 )
 
 // WindowState holds the persisted position/size of a window.
@@ -62,13 +64,13 @@ func (sm *StateManager) load() {
 	if sm.configDir == "" {
 		return
 	}
-	data, err := os.ReadFile(sm.filePath())
+	content, err := coreio.Local.Read(sm.filePath())
 	if err != nil {
 		return
 	}
 	sm.mu.Lock()
 	defer sm.mu.Unlock()
-	_ = json.Unmarshal(data, &sm.states)
+	_ = json.Unmarshal([]byte(content), &sm.states)
 }
 
 func (sm *StateManager) save() {
@@ -81,8 +83,8 @@ func (sm *StateManager) save() {
 	if err != nil {
 		return
 	}
-	_ = os.MkdirAll(sm.configDir, 0o755)
-	_ = os.WriteFile(sm.filePath(), data, 0o644)
+	_ = coreio.Local.EnsureDir(sm.configDir)
+	_ = coreio.Local.Write(sm.filePath(), string(data))
 }
 
 func (sm *StateManager) scheduleSave() {
diff --git a/pkg/window/tiling.go b/pkg/window/tiling.go
index 40669fe..e6ee430 100644
--- a/pkg/window/tiling.go
+++ b/pkg/window/tiling.go
@@ -1,7 +1,7 @@
 // pkg/window/tiling.go
 package window
 
-import "fmt"
+import coreerr "forge.lthn.ai/core/go-log"
 
 // TileMode defines how windows are arranged.
 type TileMode int
@@ -67,12 +67,12 @@ func (m *Manager) TileWindows(mode TileMode, names []string, screenW, screenH in
 	for _, name := range names {
 		pw, ok := m.Get(name)
 		if !ok {
-			return fmt.Errorf("window %q not found", name)
+			return coreerr.E("window.Manager.TileWindows", "window not found: "+name, nil)
 		}
 		windows = append(windows, pw)
 	}
 	if len(windows) == 0 {
-		return fmt.Errorf("no windows to tile")
+		return coreerr.E("window.Manager.TileWindows", "no windows to tile", nil)
 	}
 
 	halfW, halfH := screenW/2, screenH/2
@@ -146,7 +146,7 @@ func (m *Manager) TileWindows(mode TileMode, names []string, screenW, screenH in
 func (m *Manager) SnapWindow(name string, pos SnapPosition, screenW, screenH int) error {
 	pw, ok := m.Get(name)
 	if !ok {
-		return fmt.Errorf("window %q not found", name)
+		return coreerr.E("window.Manager.SnapWindow", "window not found: "+name, nil)
 	}
 
 	halfW, halfH := screenW/2, screenH/2
@@ -188,7 +188,7 @@ func (m *Manager) StackWindows(names []string, offsetX, offsetY int) error {
 	for i, name := range names {
 		pw, ok := m.Get(name)
 		if !ok {
-			return fmt.Errorf("window %q not found", name)
+			return coreerr.E("window.Manager.StackWindows", "window not found: "+name, nil)
 		}
 		pw.SetPosition(i*offsetX, i*offsetY)
 	}
@@ -198,7 +198,7 @@ func (m *Manager) StackWindows(names []string, offsetX, offsetY int) error {
 // ApplyWorkflow arranges windows in a predefined workflow layout.
 func (m *Manager) ApplyWorkflow(workflow WorkflowLayout, names []string, screenW, screenH int) error {
 	if len(names) == 0 {
-		return fmt.Errorf("no windows for workflow")
+		return coreerr.E("window.Manager.ApplyWorkflow", "no windows for workflow", nil)
 	}
 
 	switch workflow {
diff --git a/pkg/window/window.go b/pkg/window/window.go
index 3692fe8..937f1fd 100644
--- a/pkg/window/window.go
+++ b/pkg/window/window.go
@@ -2,8 +2,9 @@
 package window
 
 import (
-	"fmt"
 	"sync"
+
+	coreerr "forge.lthn.ai/core/go-log"
 )
 
 // Window is CoreGUI's own window descriptor — NOT a Wails type alias.
@@ -70,7 +71,7 @@ func NewManagerWithDir(platform Platform, configDir string) *Manager {
 func (m *Manager) Open(opts ...WindowOption) (PlatformWindow, error) {
 	w, err := ApplyOptions(opts...)
 	if err != nil {
-		return nil, fmt.Errorf("window.Manager.Open: %w", err)
+		return nil, coreerr.E("window.Manager.Open", "failed to apply options", err)
 	}
 	return m.Create(w)
 }
diff --git a/pkg/window/window_test.go b/pkg/window/window_test.go
index 44d1f09..4ed75e5 100644
--- a/pkg/window/window_test.go
+++ b/pkg/window/window_test.go
@@ -148,131 +148,6 @@ func TestManager_Remove_Good(t *testing.T) {
 	assert.False(t, ok)
 }
 
-// --- StateManager Tests ---
-
-// newTestStateManager creates a clean StateManager with a temp dir for testing.
-func newTestStateManager(t *testing.T) *StateManager {
-	return &StateManager{
-		configDir: t.TempDir(),
-		states:    make(map[string]WindowState),
-	}
-}
-
-func TestStateManager_SetGet_Good(t *testing.T) {
-	sm := newTestStateManager(t)
-	state := WindowState{X: 100, Y: 200, Width: 800, Height: 600, Maximized: false}
-	sm.SetState("main", state)
-	got, ok := sm.GetState("main")
-	assert.True(t, ok)
-	assert.Equal(t, 100, got.X)
-	assert.Equal(t, 800, got.Width)
-}
-
-func TestStateManager_SetGet_Bad(t *testing.T) {
-	sm := newTestStateManager(t)
-	_, ok := sm.GetState("nonexistent")
-	assert.False(t, ok)
-}
-
-func TestStateManager_CaptureState_Good(t *testing.T) {
-	sm := newTestStateManager(t)
-	w := &mockWindow{name: "cap", x: 50, y: 60, width: 1024, height: 768, maximised: true}
-	sm.CaptureState(w)
-	got, ok := sm.GetState("cap")
-	assert.True(t, ok)
-	assert.Equal(t, 50, got.X)
-	assert.Equal(t, 1024, got.Width)
-	assert.True(t, got.Maximized)
-}
-
-func TestStateManager_ApplyState_Good(t *testing.T) {
-	sm := newTestStateManager(t)
-	sm.SetState("win", WindowState{X: 10, Y: 20, Width: 640, Height: 480})
-	w := &Window{Name: "win", Width: 1280, Height: 800}
-	sm.ApplyState(w)
-	assert.Equal(t, 10, w.X)
-	assert.Equal(t, 20, w.Y)
-	assert.Equal(t, 640, w.Width)
-	assert.Equal(t, 480, w.Height)
-}
-
-func TestStateManager_ListStates_Good(t *testing.T) {
-	sm := newTestStateManager(t)
-	sm.SetState("a", WindowState{Width: 100})
-	sm.SetState("b", WindowState{Width: 200})
-	names := sm.ListStates()
-	assert.Len(t, names, 2)
-}
-
-func TestStateManager_Clear_Good(t *testing.T) {
-	sm := newTestStateManager(t)
-	sm.SetState("a", WindowState{Width: 100})
-	sm.Clear()
-	names := sm.ListStates()
-	assert.Empty(t, names)
-}
-
-func TestStateManager_Persistence_Good(t *testing.T) {
-	dir := t.TempDir()
-	sm1 := &StateManager{configDir: dir, states: make(map[string]WindowState)}
-	sm1.SetState("persist", WindowState{X: 42, Y: 84, Width: 500, Height: 300})
-	sm1.ForceSync()
-
-	sm2 := &StateManager{configDir: dir, states: make(map[string]WindowState)}
-	sm2.load()
-	got, ok := sm2.GetState("persist")
-	assert.True(t, ok)
-	assert.Equal(t, 42, got.X)
-	assert.Equal(t, 500, got.Width)
-}
-
-// --- LayoutManager Tests ---
-
-// newTestLayoutManager creates a clean LayoutManager with a temp dir for testing.
-func newTestLayoutManager(t *testing.T) *LayoutManager {
-	return &LayoutManager{
-		configDir: t.TempDir(),
-		layouts:   make(map[string]Layout),
-	}
-}
-
-func TestLayoutManager_SaveGet_Good(t *testing.T) {
-	lm := newTestLayoutManager(t)
-	states := map[string]WindowState{
-		"editor":   {X: 0, Y: 0, Width: 960, Height: 1080},
-		"terminal": {X: 960, Y: 0, Width: 960, Height: 1080},
-	}
-	err := lm.SaveLayout("coding", states)
-	require.NoError(t, err)
-
-	layout, ok := lm.GetLayout("coding")
-	assert.True(t, ok)
-	assert.Equal(t, "coding", layout.Name)
-	assert.Len(t, layout.Windows, 2)
-}
-
-func TestLayoutManager_GetLayout_Bad(t *testing.T) {
-	lm := newTestLayoutManager(t)
-	_, ok := lm.GetLayout("nonexistent")
-	assert.False(t, ok)
-}
-
-func TestLayoutManager_ListLayouts_Good(t *testing.T) {
-	lm := newTestLayoutManager(t)
-	_ = lm.SaveLayout("a", map[string]WindowState{})
-	_ = lm.SaveLayout("b", map[string]WindowState{})
-	layouts := lm.ListLayouts()
-	assert.Len(t, layouts, 2)
-}
-
-func TestLayoutManager_DeleteLayout_Good(t *testing.T) {
-	lm := newTestLayoutManager(t)
-	_ = lm.SaveLayout("temp", map[string]WindowState{})
-	lm.DeleteLayout("temp")
-	_, ok := lm.GetLayout("temp")
-	assert.False(t, ok)
-}
-
 // --- Tiling Tests ---
 
 func TestTileMode_String_Good(t *testing.T) {
@@ -328,3 +203,190 @@ func TestWorkflowLayout_Good(t *testing.T) {
 	assert.Equal(t, "coding", WorkflowCoding.String())
 	assert.Equal(t, "debugging", WorkflowDebugging.String())
 }
+
+// --- Comprehensive Tiling Tests ---
+
+func TestTileWindows_AllModes_Good(t *testing.T) {
+	const screenW, screenH = 1920, 1080
+	halfW, halfH := screenW/2, screenH/2
+
+	tests := []struct {
+		name       string
+		mode       TileMode
+		wantX      int
+		wantY      int
+		wantWidth  int
+		wantHeight int
+	}{
+		{"LeftHalf", TileModeLeftHalf, 0, 0, halfW, screenH},
+		{"RightHalf", TileModeRightHalf, halfW, 0, halfW, screenH},
+		{"TopHalf", TileModeTopHalf, 0, 0, screenW, halfH},
+		{"BottomHalf", TileModeBottomHalf, 0, halfH, screenW, halfH},
+		{"TopLeft", TileModeTopLeft, 0, 0, halfW, halfH},
+		{"TopRight", TileModeTopRight, halfW, 0, halfW, halfH},
+		{"BottomLeft", TileModeBottomLeft, 0, halfH, halfW, halfH},
+		{"BottomRight", TileModeBottomRight, halfW, halfH, halfW, halfH},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			m, _ := newTestManager()
+			_, err := m.Open(WithName("win"), WithSize(800, 600))
+			require.NoError(t, err)
+
+			err = m.TileWindows(tc.mode, []string{"win"}, screenW, screenH)
+			require.NoError(t, err)
+
+			pw, ok := m.Get("win")
+			require.True(t, ok)
+
+			x, y := pw.Position()
+			w, h := pw.Size()
+			assert.Equal(t, tc.wantX, x, "x position")
+			assert.Equal(t, tc.wantY, y, "y position")
+			assert.Equal(t, tc.wantWidth, w, "width")
+			assert.Equal(t, tc.wantHeight, h, "height")
+		})
+	}
+}
+
+func TestSnapWindow_AllPositions_Good(t *testing.T) {
+	const screenW, screenH = 1920, 1080
+	halfW, halfH := screenW/2, screenH/2
+
+	tests := []struct {
+		name       string
+		pos        SnapPosition
+		initW      int
+		initH      int
+		wantX      int
+		wantY      int
+		wantWidth  int
+		wantHeight int
+	}{
+		{"Right", SnapRight, 800, 600, halfW, 0, halfW, screenH},
+		{"Top", SnapTop, 800, 600, 0, 0, screenW, halfH},
+		{"Bottom", SnapBottom, 800, 600, 0, halfH, screenW, halfH},
+		{"TopLeft", SnapTopLeft, 800, 600, 0, 0, halfW, halfH},
+		{"TopRight", SnapTopRight, 800, 600, halfW, 0, halfW, halfH},
+		{"BottomLeft", SnapBottomLeft, 800, 600, 0, halfH, halfW, halfH},
+		{"BottomRight", SnapBottomRight, 800, 600, halfW, halfH, halfW, halfH},
+		{"Center", SnapCenter, 800, 600, (screenW - 800) / 2, (screenH - 600) / 2, 800, 600},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			m, _ := newTestManager()
+			_, err := m.Open(WithName("snap"), WithSize(tc.initW, tc.initH))
+			require.NoError(t, err)
+
+			err = m.SnapWindow("snap", tc.pos, screenW, screenH)
+			require.NoError(t, err)
+
+			pw, ok := m.Get("snap")
+			require.True(t, ok)
+
+			x, y := pw.Position()
+			w, h := pw.Size()
+			assert.Equal(t, tc.wantX, x, "x position")
+			assert.Equal(t, tc.wantY, y, "y position")
+			assert.Equal(t, tc.wantWidth, w, "width")
+			assert.Equal(t, tc.wantHeight, h, "height")
+		})
+	}
+}
+
+func TestStackWindows_ThreeWindows_Good(t *testing.T) {
+	m, _ := newTestManager()
+	names := []string{"s1", "s2", "s3"}
+	for _, name := range names {
+		_, err := m.Open(WithName(name), WithSize(800, 600))
+		require.NoError(t, err)
+	}
+
+	err := m.StackWindows(names, 30, 30)
+	require.NoError(t, err)
+
+	for i, name := range names {
+		pw, ok := m.Get(name)
+		require.True(t, ok, "window %s should exist", name)
+		x, y := pw.Position()
+		assert.Equal(t, i*30, x, "window %s x position", name)
+		assert.Equal(t, i*30, y, "window %s y position", name)
+	}
+}
+
+func TestApplyWorkflow_AllLayouts_Good(t *testing.T) {
+	const screenW, screenH = 1920, 1080
+
+	tests := []struct {
+		name     string
+		workflow WorkflowLayout
+		// Expected positions/sizes for the first two windows.
+		// For WorkflowSideBySide, TileWindows(LeftRight) divides equally.
+		win0X, win0Y, win0W, win0H int
+		win1X, win1Y, win1W, win1H int
+	}{
+		{
+			"Coding",
+			WorkflowCoding,
+			0, 0, 1344, screenH, // 70% of 1920 = 1344
+			1344, 0, screenW - 1344, screenH, // remaining 30%
+		},
+		{
+			"Debugging",
+			WorkflowDebugging,
+			0, 0, 1152, screenH, // 60% of 1920 = 1152
+			1152, 0, screenW - 1152, screenH, // remaining 40%
+		},
+		{
+			"Presenting",
+			WorkflowPresenting,
+			0, 0, screenW, screenH, // maximised
+			0, 0, 800, 600,        // second window untouched
+		},
+		{
+			"SideBySide",
+			WorkflowSideBySide,
+			0, 0, 960, screenH,   // left half (1920/2)
+			960, 0, 960, screenH, // right half
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			m, _ := newTestManager()
+			_, err := m.Open(WithName("editor"), WithSize(800, 600))
+			require.NoError(t, err)
+			_, err = m.Open(WithName("terminal"), WithSize(800, 600))
+			require.NoError(t, err)
+
+			err = m.ApplyWorkflow(tc.workflow, []string{"editor", "terminal"}, screenW, screenH)
+			require.NoError(t, err)
+
+			pw0, ok := m.Get("editor")
+			require.True(t, ok)
+			x0, y0 := pw0.Position()
+			w0, h0 := pw0.Size()
+			assert.Equal(t, tc.win0X, x0, "editor x")
+			assert.Equal(t, tc.win0Y, y0, "editor y")
+			assert.Equal(t, tc.win0W, w0, "editor width")
+			assert.Equal(t, tc.win0H, h0, "editor height")
+
+			pw1, ok := m.Get("terminal")
+			require.True(t, ok)
+			x1, y1 := pw1.Position()
+			w1, h1 := pw1.Size()
+			assert.Equal(t, tc.win1X, x1, "terminal x")
+			assert.Equal(t, tc.win1Y, y1, "terminal y")
+			assert.Equal(t, tc.win1W, w1, "terminal width")
+			assert.Equal(t, tc.win1H, h1, "terminal height")
+		})
+	}
+}
+
+func TestApplyWorkflow_Empty_Bad(t *testing.T) {
+	m, _ := newTestManager()
+	err := m.ApplyWorkflow(WorkflowCoding, []string{}, 1920, 1080)
+	assert.Error(t, err)
+}