feat: add sync checkpoint restore for last successful sync

Capture rolling online DB snapshots after push/drain/reconcile and expose SyncPage 数据恢复 plus checkpoint/restore APIs; mark Z12h and restore done in coop docs.

Co-authored-by: Cursor <cursoragent@cursor.com>

platform/internal/dbsync/checkpoint_test.go

@@ -0,0 +1,89 @@
+package dbsync
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestCheckpointSaveRestoreRoundTrip(t *testing.T) {
+	dir := t.TempDir()
+	store, err := NewFileStore(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	remoteDSN := "file:" + filepath.ToSlash(filepath.Join(dir, "online.db")) + "?_pragma=busy_timeout(5000)"
+	ch := &Channel{
+		ID:       "ch-cp-1",
+		TenantID: 1,
+		Name:     "test",
+		Remote: Endpoint{
+			Driver: DriverSQLite,
+			DSN:    remoteDSN,
+		},
+		PKColumns: map[string]string{"demo": "id"},
+	}
+	ctx := context.Background()
+	db, err := Open(DriverSQLite, remoteDSN)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		_ = db.Close()
+		InvalidateRemote(DriverSQLite, remoteDSN)
+	})
+	if _, err := db.ExecContext(ctx, `CREATE TABLE demo (id TEXT PRIMARY KEY, name TEXT)`); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := db.ExecContext(ctx, `INSERT INTO demo(id,name) VALUES('a','one'),('b','two')`); err != nil {
+		t.Fatal(err)
+	}
+	if err := EnsureMeta(ctx, db, DriverSQLite); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := SaveCheckpoint(ctx, store, ch, "test"); err != nil {
+		t.Fatal(err)
+	}
+	meta, err := LoadCheckpointMeta(store, ch.ID)
+	if err != nil || meta.Latest == nil || meta.Latest.RowCount != 2 {
+		t.Fatalf("meta=%+v err=%v", meta, err)
+	}
+
+	// mutate then restore
+	if _, err := db.ExecContext(ctx, `DELETE FROM demo WHERE id='a'`); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := db.ExecContext(ctx, `INSERT INTO demo(id,name) VALUES('c','three')`); err != nil {
+		t.Fatal(err)
+	}
+	res, err := RestoreCheckpoint(ctx, store, ch, "latest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !res.OK || res.Upserted < 2 {
+		t.Fatalf("restore=%+v", res)
+	}
+	var n int
+	if err := db.QueryRowContext(ctx, `SELECT COUNT(*) FROM demo`).Scan(&n); err != nil || n != 2 {
+		t.Fatalf("count=%d err=%v", n, err)
+	}
+	var name string
+	if err := db.QueryRowContext(ctx, `SELECT name FROM demo WHERE id='a'`).Scan(&name); err != nil || name != "one" {
+		t.Fatalf("row a name=%q err=%v", name, err)
+	}
+
+	// second save rotates
+	time.Sleep(10 * time.Millisecond)
+	if _, err := db.ExecContext(ctx, `UPDATE demo SET name='one2' WHERE id='a'`); err != nil {
+		t.Fatal(err)
+	}
+	if err := SaveCheckpoint(ctx, store, ch, "test2"); err != nil {
+		t.Fatal(err)
+	}
+	meta2, _ := LoadCheckpointMeta(store, ch.ID)
+	if meta2.Previous == nil || meta2.Previous.RowCount != 2 {
+		t.Fatalf("expected previous after rotate: %+v", meta2)
+	}
+}