Implement Phase 4: gRPC sync service

- Proto definitions (engpad.v1.EngPadSync) with 6 RPCs
- Generated Go gRPC code
- Auth interceptor: username/password from metadata
- SyncNotebook: upsert with full page/stroke replacement in a tx
- DeleteNotebook, ListNotebooks handlers
- Share link RPCs: CreateShareLink, RevokeShareLink, ListShareLinks
- Share link token management (32-byte random, optional expiry)
- gRPC server with TLS 1.3

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/grpcserver/sync.go

@@ -0,0 +1,142 @@
+package grpcserver
+
+import (
+	"context"
+	"database/sql"
+	"time"
+
+	pb "git.wntrmute.dev/kyle/eng-pad-server/gen/engpad/v1"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/types/known/timestamppb"
+)
+
+type SyncService struct {
+	pb.UnimplementedEngPadSyncServer
+	DB      *sql.DB
+	BaseURL string
+}
+
+func (s *SyncService) SyncNotebook(ctx context.Context, req *pb.SyncNotebookRequest) (*pb.SyncNotebookResponse, error) {
+	userID, ok := UserIDFromContext(ctx)
+	if !ok {
+		return nil, status.Error(codes.Internal, "missing user context")
+	}
+
+	tx, err := s.DB.BeginTx(ctx, nil)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "begin tx: %v", err)
+	}
+	defer func() { _ = tx.Rollback() }()
+
+	now := time.Now().UnixMilli()
+
+	// Upsert notebook
+	var notebookID int64
+	err = tx.QueryRowContext(ctx,
+		"SELECT id FROM notebooks WHERE user_id = ? AND remote_id = ?",
+		userID, req.NotebookId,
+	).Scan(&notebookID)
+
+	if err == sql.ErrNoRows {
+		res, err := tx.ExecContext(ctx,
+			"INSERT INTO notebooks (user_id, remote_id, title, page_size, synced_at) VALUES (?, ?, ?, ?, ?)",
+			userID, req.NotebookId, req.Title, req.PageSize, now,
+		)
+		if err != nil {
+			return nil, status.Errorf(codes.Internal, "insert notebook: %v", err)
+		}
+		notebookID, _ = res.LastInsertId()
+	} else if err != nil {
+		return nil, status.Errorf(codes.Internal, "query notebook: %v", err)
+	} else {
+		// Update existing — delete all pages (cascade deletes strokes)
+		if _, err := tx.ExecContext(ctx, "DELETE FROM pages WHERE notebook_id = ?", notebookID); err != nil {
+			return nil, status.Errorf(codes.Internal, "delete pages: %v", err)
+		}
+		if _, err := tx.ExecContext(ctx,
+			"UPDATE notebooks SET title = ?, page_size = ?, synced_at = ? WHERE id = ?",
+			req.Title, req.PageSize, now, notebookID,
+		); err != nil {
+			return nil, status.Errorf(codes.Internal, "update notebook: %v", err)
+		}
+	}
+
+	// Insert pages and strokes
+	for _, page := range req.Pages {
+		res, err := tx.ExecContext(ctx,
+			"INSERT INTO pages (notebook_id, remote_id, page_number) VALUES (?, ?, ?)",
+			notebookID, page.PageId, page.PageNumber,
+		)
+		if err != nil {
+			return nil, status.Errorf(codes.Internal, "insert page: %v", err)
+		}
+		pageID, _ := res.LastInsertId()
+
+		for _, stroke := range page.Strokes {
+			if _, err := tx.ExecContext(ctx,
+				"INSERT INTO strokes (page_id, pen_size, color, style, point_data, stroke_order) VALUES (?, ?, ?, ?, ?, ?)",
+				pageID, stroke.PenSize, stroke.Color, stroke.Style, stroke.PointData, stroke.StrokeOrder,
+			); err != nil {
+				return nil, status.Errorf(codes.Internal, "insert stroke: %v", err)
+			}
+		}
+	}
+
+	if err := tx.Commit(); err != nil {
+		return nil, status.Errorf(codes.Internal, "commit: %v", err)
+	}
+
+	return &pb.SyncNotebookResponse{
+		ServerNotebookId: notebookID,
+		SyncedAt:         timestamppb.Now(),
+	}, nil
+}
+
+func (s *SyncService) DeleteNotebook(ctx context.Context, req *pb.DeleteNotebookRequest) (*pb.DeleteNotebookResponse, error) {
+	userID, ok := UserIDFromContext(ctx)
+	if !ok {
+		return nil, status.Error(codes.Internal, "missing user context")
+	}
+
+	_, err := s.DB.ExecContext(ctx,
+		"DELETE FROM notebooks WHERE user_id = ? AND remote_id = ?",
+		userID, req.NotebookId,
+	)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "delete: %v", err)
+	}
+
+	return &pb.DeleteNotebookResponse{}, nil
+}
+
+func (s *SyncService) ListNotebooks(ctx context.Context, req *pb.ListNotebooksRequest) (*pb.ListNotebooksResponse, error) {
+	userID, ok := UserIDFromContext(ctx)
+	if !ok {
+		return nil, status.Error(codes.Internal, "missing user context")
+	}
+
+	rows, err := s.DB.QueryContext(ctx,
+		`SELECT n.id, n.remote_id, n.title, n.page_size, n.synced_at,
+		        (SELECT COUNT(*) FROM pages WHERE notebook_id = n.id) as page_count
+		 FROM notebooks n WHERE n.user_id = ? ORDER BY n.synced_at DESC`,
+		userID,
+	)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "query: %v", err)
+	}
+	defer func() { _ = rows.Close() }()
+
+	var notebooks []*pb.NotebookSummary
+	for rows.Next() {
+		var nb pb.NotebookSummary
+		var syncedAt int64
+		if err := rows.Scan(&nb.ServerId, &nb.RemoteId, &nb.Title, &nb.PageSize, &syncedAt, &nb.PageCount); err != nil {
+			return nil, status.Errorf(codes.Internal, "scan: %v", err)
+		}
+		nb.SyncedAt = timestamppb.New(time.UnixMilli(syncedAt))
+		notebooks = append(notebooks, &nb)
+	}
+
+	return &pb.ListNotebooksResponse{Notebooks: notebooks}, nil
+}