doing the table definition columns in add_table

common/proto/table_definition.proto

@@ -362,18 +362,69 @@ message DeleteTableResponse {
   string message = 2;
 }
 
-// Response listing every column type a table may declare.
+// How a column type is spelled in ColumnDefinition.field_type.
+enum ColumnTypeSpelling {
+  // The name is the whole spelling: "text", "money", "gtin_13".
+  COLUMN_TYPE_SPELLING_BARE = 0;
+
+  // The name takes a precision and a scale: "decimal(12,3)". Precision must be
+  // at least 1 and scale no greater than precision; neither may carry a sign,
+  // a decimal point, or leading zeros.
+  COLUMN_TYPE_SPELLING_DECIMAL = 1;
+}
+
+// Response describing the whole column-type vocabulary.
+//
+// This is the authority a client builds its column-type picker from: every rule
+// a client would otherwise hardcode about what a type means is a field here. The
+// list covers types clients may NOT declare as well (see `declarable`), so that
+// the same call also explains the types GetProfileDetails reports back for
+// server-generated companion columns.
 message ListColumnTypesResponse {
-  // One declared column type and the SQL type it maps to.
+  // One column type and everything a client needs to know to offer it.
   message ColumnType {
     // Logical column type (e.g. "money", "instant"). Passed to the server as
-    // ColumnDefinition.field_type.
+    // ColumnDefinition.field_type — see `spelling`, which is what says whether
+    // this name is the whole spelling.
     string name = 1;
 
     // Underlying PostgreSQL type the logical type maps to (e.g. "NUMERIC").
+    // Empty when `compound` is true. For COLUMN_TYPE_SPELLING_DECIMAL this is
+    // the unparameterised type; the declared precision and scale are appended.
     string sql_type = 2;
+
+    // False for types the server generates on its own and rejects when a client
+    // declares them: the phone and IBAN companions, and the accounting-transfer
+    // connectors. A column-type picker must offer only declarable types.
+    bool declarable = 3;
+
+    // True when the type is a definition row rather than a column: it expands
+    // into several schema-managed companion columns and no column of this name
+    // survives. A compound type can therefore never be indexed, never be a row
+    // display column, and has no single sql_type of its own.
+    bool compound = 4;
+
+    // Whether `name` is the whole spelling or takes arguments.
+    ColumnTypeSpelling spelling = 5;
+
+    // Whether ColumnDefinition.currency is required. Currency is rejected on
+    // every type where this is false.
+    bool requires_currency = 6;
+
+    // True when the type may only be chosen while the table is being created.
+    // AddTableColumns rejects these, because they bring schema-managed columns
+    // that cannot be bolted onto a table that already exists.
+    bool creation_only = 7;
+
+    // Whether ColumnDefinition.quantity_ledger may be set on this type.
+    bool allows_quantity_ledger = 8;
+
+    // Optional name grouping several types a client offers behind one choice —
+    // "temporal" for the date and time types, "gtin" for the GTIN lengths.
+    // Empty when the type stands on its own.
+    string group = 9;
   }
 
-  // All declared column types.
+  // Every column type, declarable or not, ordered by name.
   repeated ColumnType column_types = 1;
 }