feat: add slog structured logging

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/service/process_service.go

@@ -1,6 +1,8 @@
 package service
 
 import (
+	"log/slog"
+
 	"codespace/internal/process"
 	"codespace/internal/workspace"
 )
@@ -9,11 +11,16 @@ import (
 type ProcessService struct {
 	workspaces workspace.Manager
 	processes  process.Manager
+	logger     *slog.Logger
 }
 
 // NewProcessService creates a ProcessService.
-func NewProcessService(workspaces workspace.Manager, processes process.Manager) *ProcessService {
-	return &ProcessService{workspaces: workspaces, processes: processes}
+// If lg is nil, slog.Default() is used.
+func NewProcessService(workspaces workspace.Manager, processes process.Manager, lg *slog.Logger) *ProcessService {
+	if lg == nil {
+		lg = slog.Default()
+	}
+	return &ProcessService{workspaces: workspaces, processes: processes, logger: lg}
 }
 
 // Start starts an OpenCode process for the given workspace.
@@ -22,12 +29,23 @@ func (s *ProcessService) Start(workspaceID string) error {
 	if err != nil {
 		return err
 	}
-	return s.processes.Start(workspaceID, ws.Root)
+	if err := s.processes.Start(workspaceID, ws.Root); err != nil {
+		s.logger.Error("process start failed", "workspace_id", workspaceID, "error", err)
+		return err
+	}
+	status := s.processes.Status(workspaceID)
+	s.logger.Info("process started", "workspace_id", workspaceID, "pid", status.PID)
+	return nil
 }
 
 // Stop stops the OpenCode process for the given workspace.
 func (s *ProcessService) Stop(workspaceID string) error {
-	return s.processes.Stop(workspaceID)
+	if err := s.processes.Stop(workspaceID); err != nil {
+		s.logger.Error("process stop failed", "workspace_id", workspaceID, "error", err)
+		return err
+	}
+	s.logger.Info("process stopped", "workspace_id", workspaceID)
+	return nil
 }
 
 // Restart restarts the OpenCode process for the given workspace.
@@ -36,7 +54,13 @@ func (s *ProcessService) Restart(workspaceID string) error {
 	if err != nil {
 		return err
 	}
-	return s.processes.Restart(workspaceID, ws.Root)
+	if err := s.processes.Restart(workspaceID, ws.Root); err != nil {
+		s.logger.Error("process restart failed", "workspace_id", workspaceID, "error", err)
+		return err
+	}
+	status := s.processes.Status(workspaceID)
+	s.logger.Info("process restarted", "workspace_id", workspaceID, "pid", status.PID)
+	return nil
 }
 
 // Status returns the process status for the given workspace.