test: cover compatibility method addition diagnostics

docs/ROADMAP.md

@@ -37,7 +37,7 @@ See `CURRENT_STATUS.md` for the detailed feature matrix.
 4. Add small examples for each foundation feature before adding bigger syntax. The object-field foundation now includes positive and negative validation for field expressions such as `SET player.score player.name`, `SET player.score player.score + 1`, `SET player.name player.score + 1`, explicitly typed field assignments, explicit typed assignments to undeclared fields, simple and chained aliases such as `SET alias player`, `SET backup alias`, followed by `SET backup.score ...` or `CHECK TYPE backup.score IS ...`, chained aliases in object-method calls through both modern `DO` and compatibility `CALL ... WITH` forms (including a dedicated positive modern `DO` fixture), and arithmetic/text expression mismatches; typed containers also accept a map with nested type metadata when it is added to a `LIST OF MAP`; broader alias/control-flow checking remains planned.
 5. Keep the focused typecheck validator complete: every `typecheck_*.claro` fixture, including positive fixtures, is now exercised by both the standalone diagnostic validator and `claro validate`.
 6. Continue narrowing expression diagnostics: known TEXT operands now remain visible through arithmetic, with focused numeric-subtraction, numeric-division, and numeric-multiplication positives plus text-operand addition, subtraction, multiplication, and division coverage. Typed function returns now include positive subtraction and division examples alongside multiplication. Text concatenation into TEXT fields is covered in both operand orders, including field-to-field concatenation. Each numeric operator names the text operand and explains that it needs NUMBER values. `CHECK TYPE` also rejects misspelled expected type names.
-- Keep typed method return examples balanced: numeric addition, subtraction, division, and multiplication now have dedicated positive compatibility `TAKES` / `LEARNED` method fixtures in the focused validator, alongside the existing method return mismatch diagnostics.
+- Keep typed method return examples balanced: numeric addition, subtraction, division, and multiplication now have dedicated positive compatibility `TAKES` / `LEARNED` method fixtures in the focused validator, alongside compatibility addition mismatch coverage and the existing method return mismatch diagnostics.
 - Keep IDE metadata aligned with the current beginner syntax: typed-language keywords such as `RETURNS`, `CHECK`, and `TYPE` are now included in the metadata used by editor helpers.
 - Keep compatibility-call coverage aligned with modern calls: empty `CALL object.method WITH` forms now have a focused missing-argument diagnostic fixture alongside the modern `DO object.method` case.
 Keep declared return types honest: `claro typecheck` now reports friendly diagnostics for unknown declared return types, mismatched, not-yet-inferable, and empty return expressions, declarations with no `RETURN`, and incomplete conditional branches, when a simple function or object method declares `RETURNS TYPE`; the declaration keyword is case-insensitive like other Claro keywords, with positive coverage in modern and compatibility function forms, including lowercase compatibility declarations and lowercase compatibility method declarations, plus a lowercase compatibility-method mismatch fixture. Complete `IF`/`ELSE` return branches, including nested complete conditionals in functions and methods, are accepted, and modern and compatibility function syntax plus compatibility method syntax are covered by focused fixtures. `CHECK TYPE` parameter metadata also informs arithmetic return-expression checking, including object methods; positive numeric multiplication return coverage now sits beside the mismatch fixtures, including a dedicated compatibility-method multiplication success fixture; typed methods can also return class-declared fields by simple name, with positive and mismatch fixtures, and unknown method return expressions now have dedicated modern and compatibility diagnostic fixtures, and NUMBER return expressions with known TEXT arithmetic operands identify the operation and offending operand, including focused addition, subtraction, multiplication, and division coverage for functions and methods. Full path-sensitive analysis across nested conditionals and loops remains planned.