Decide one name, one meaning, and file the names that break it

todo.md

@@ -22,6 +22,11 @@ This round, in order:
 - Hold only the `{token}` grammar's tests in `format_test.go`: move the helpers seven
   other test files use (`engine`, `parse`, `compiled`, `mustRender`) and the weight,
   recursion and path-navigation tests to files named for what they test.
+- Give `rows` and `field` one meaning each, per the decision "One name, one meaning":
+  `categoryFiles.rows` returns a TSV file name where `table.rows` counts rows, and
+  `formatOps.field` compiles a `{field}` token where `structFields.field` reads a Go
+  struct field. Rename every other shared name that names two things — `walk`,
+  `column`, `expr` and `of` included.
 - Run the nine-seat panel again and file what it names here.
 
 ### Data