uniqueness only on nondeleted data4 import metadata

common/proto/table_structure.proto

@@ -23,6 +23,12 @@ service TableStructureService {
   // - Returns an error if any validated table has no visible columns in
   //   information_schema (e.g., physical table missing)
   rpc GetTableStructure(GetTableStructureRequest) returns (GetTableStructureResponse);
+
+  // Describes the public values accepted by staged table-data import. Unlike
+  // GetTableStructure, this is an input contract: it includes logical types,
+  // omission/null behavior, stable identities and link targets.
+  rpc GetTableImportDescriptor(GetTableImportDescriptorRequest)
+      returns (GetTableImportDescriptorResponse);
 }
 
 // Request identifying the profile (schema) and tables to inspect.
@@ -91,3 +97,52 @@ message TableColumn {
   // Stable public identity of a managed user column. Zero for system columns.
   int64 column_id = 10;
 }
+
+message GetTableImportDescriptorRequest {
+  string profile_name = 1;
+  string table_name = 2;
+}
+
+enum ImportValueKind {
+  IMPORT_VALUE_KIND_UNSPECIFIED = 0;
+  IMPORT_VALUE_KIND_NULL = 1;
+  IMPORT_VALUE_KIND_STRING = 2;
+  IMPORT_VALUE_KIND_BOOLEAN = 3;
+  IMPORT_VALUE_KIND_NUMBER = 4;
+  IMPORT_VALUE_KIND_INTEGER_STRING = 5;
+  IMPORT_VALUE_KIND_LINK_DISPLAY = 6;
+}
+
+message ImportLinkDescriptor {
+  int64 target_table_id = 1;
+  string target_profile_name = 2;
+  string target_table_name = 3;
+  repeated string target_row_display_columns = 4;
+}
+
+message ImportFieldDescriptor {
+  // Stable identity of a managed user column. System columns have zero here
+  // and are identified by their server-owned name.
+  int64 column_id = 1;
+  string name = 2;
+  string logical_type = 3;
+  string storage_type = 4;
+  bool writable = 5;
+  bool required = 6;
+  bool may_omit = 7;
+  bool accepts_null = 8;
+  bool system = 9;
+  bool generated = 10;
+  string generated_from = 11;
+  optional ImportLinkDescriptor link = 12;
+  repeated ImportValueKind accepted_value_kinds = 13;
+}
+
+message GetTableImportDescriptorResponse {
+  string requested_profile_name = 1;
+  string storage_profile_name = 2;
+  string table_name = 3;
+  int64 table_id = 4;
+  int64 table_revision = 5;
+  repeated ImportFieldDescriptor fields = 6;
+}