feat: batches with dry run, undo, and CSV import and export

- POST /_seo/api/v1/batch runs changes in one transaction: dry_run
  answers the diff and the conflicts (loops, chains, noindex on a
  published record, canonicals to redirected or noindex addresses) and
  rolls back; a refused change refuses the batch (D-12)
- undo of a change or a whole batch from History and through MCP, with
  the undo_stale, undo_loop and undo_gone refusals (D-13)
- CSV export and import of redirects, rules and records by URL: BOM,
  comma or semicolon, formula cells escaped, a dry-run preview, all or
  nothing with via import; the screen's apply token is HMAC-SHA256 over
  the file and a fingerprint of the data (transfer.stale)
- Import and export singleton with the seo_transfer widget action,
  History record actions undo and undo_batch, navigation entry
- MCP tools undo_change, undo_batch, apply_batch, export_csv, import_csv
- TestBatch, TestUndo, TestCSVTransfer, TestLoopRefused mcp and import

controllers/api/batch.go

@@ -0,0 +1,61 @@
+package api
+
+import (
+	"context"
+	"errors"
+	"net/http"
+
+	"git.golem15.com/golem15/sm-seo-plugin/classes"
+)
+
+// ApplyBatchInput is the body of POST /_seo/api/v1/batch.
+type ApplyBatchInput struct {
+	DryRun  bool                  `json:"dry_run,omitempty" jsonschema:"answer the diff and the conflicts without writing anything"`
+	Changes []classes.BatchChange `json:"changes" jsonschema:"the changes, applied in order: op set_seo (url, locale, values, force_rule), create_redirect and update_redirect (id, redirect), delete_redirect (id), create_rule and update_rule (id, rule), delete_rule (id)"`
+}
+
+// ApplyBatch serves POST /_seo/api/v1/batch (D-12, P-26): the changes run
+// in one transaction. With dry_run the answer is every change's diff and
+// the conflicts (redirect loops and chains, noindex on a published
+// record's address, a canonical pointing to a redirected or noindex
+// address) and nothing is written. Without it the batch is applied as a
+// whole under one batch id, which history and undo_batch use. A refused
+// change refuses the whole batch with 422: redirect_loop with the change
+// and the loop's path, or batch_refused with the change's errors.
+func ApplyBatch(service func() *classes.Service) http.HandlerFunc {
+	return manage(service, func(ctx context.Context, svc *classes.Service, r *http.Request) (int, any, error) {
+		var in ApplyBatchInput
+		if err := decode(r, 4*maxBody, &in); err != nil {
+			return 0, nil, err
+		}
+		res, err := svc.RunBatch(ctx, in.Changes, classes.BatchOptions{DryRun: in.DryRun})
+		var refused *classes.BatchRefusedError
+		if errors.As(err, &refused) {
+			return 0, nil, &apiError{Status: http.StatusUnprocessableEntity, Body: BatchRefusal(refused.Result)}
+		}
+		if err != nil {
+			return 0, nil, err
+		}
+		return http.StatusOK, res, nil
+	})
+}
+
+// BatchRefusal is the 422 answer of a refused batch: the first refused
+// change, its error, path or field errors, and every change's outcome.
+func BatchRefusal(res classes.BatchResult) map[string]any {
+	item := res.Refused()
+	out := map[string]any{"error": "batch_refused", "changes": res.Changes}
+	if item == nil {
+		return out
+	}
+	out["change"] = item.Index
+	out["message"] = item.Message
+	if item.Error == classes.ConflictLoop {
+		out["error"] = "redirect_loop"
+		out["path"] = item.Path
+	}
+	if len(item.Errors) > 0 {
+		out["errors"] = item.Errors
+	}
+	return out
+}