Sanitize upon saving

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/validator/validator_prosemirror.go

@@ -0,0 +1,40 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package validator
+
+import (
+	"strings"
+
+	"go.probo.inc/probo/pkg/prosemirror"
+)
+
+// ProseMirrorDocumentContent requires non-empty string values to be valid
+// ProseMirror/Tiptap JSON with root type "doc". Empty and whitespace-only
+// strings are allowed.
+func ProseMirrorDocumentContent() ValidatorFunc {
+	return func(value any) *ValidationError {
+		s, ok := value.(string)
+		if !ok {
+			return newValidationError(ErrorCodeInvalidFormat, "value must be a string")
+		}
+		if strings.TrimSpace(s) == "" {
+			return nil
+		}
+		if err := prosemirror.ValidateDocumentContentJSON(s); err != nil {
+			return newValidationError(ErrorCodeInvalidFormat, err.Error())
+		}
+		return nil
+	}
+}

pkg/validator/validator_prosemirror_test.go

@@ -0,0 +1,51 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package validator
+
+import "testing"
+
+func TestProseMirrorDocumentContent(t *testing.T) {
+	t.Parallel()
+
+	validDoc := `{"type":"doc","content":[{"type":"paragraph","content":[{"type":"text","text":"hi"}]}]}`
+
+	tests := []struct {
+		name      string
+		value     any
+		wantError bool
+	}{
+		{"empty string", "", false},
+		{"whitespace only", "   \n\t  ", false},
+		{"valid doc", validDoc, false},
+		{"plain text", "not json", true},
+		{"non-doc root", `{"type":"paragraph","content":[]}`, true},
+		{"non-string", 1, true},
+	}
+
+	fn := ProseMirrorDocumentContent()
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			err := fn(tt.value)
+			if (err != nil) != tt.wantError {
+				t.Errorf("ProseMirrorDocumentContent() error = %v, wantError %v", err, tt.wantError)
+			}
+			if err != nil && err.Code != ErrorCodeInvalidFormat {
+				t.Errorf("expected code %s, got %s", ErrorCodeInvalidFormat, err.Code)
+			}
+		})
+	}
+}