Nest disagreement's other-item switch in the fixed item's text arm

datatype.go

@@ -183,7 +183,7 @@ func disagreement(a *template, da DataType, b *template, db DataType) error {
 			return fmt.Errorf("%s, so %s", held, typedAs(fix, want))
 		}
 		return fmt.Errorf("%s, so to read %q as text, %s", held, fix.format, asText(fix))
-	}
+	case kindText:
 		switch kindOf(other) {
 		case kindText:
 			panic(internalError("two text items hold one datatype, so they never disagree"))
@@ -197,6 +197,8 @@ func disagreement(a *template, da DataType, b *template, db DataType) error {
 		}
 		return fmt.Errorf(`item %q declares no datatype beside one holding %s; a column holds one, so give it "datatype": %q`, fix.format, want, want)
 	}
+	panic(internalError("disagreement has no case for item kind %d", kindOf(fix)))
+}
 
 // typedAs names the spelling giving a column-read item datatype d, keeping the other keys an object
 // item carries.