TC.Foo implementation for a method the class never DECLARED compiles (FPC rejects)

• Track: P (Pascal frontend; shared parser — A's gate). compat tag.
• Found while fixing bug-pascal-undefined-field-on-empty-record-compiles (4d46a7ad); NOT silent-wrong-value — the registered method works and dispatches consistently, so this is a parity diagnostic, not a bug promo.

Repro

type
  TC0 = class
  end;
function TC0.Calc: longint;
begin
  Calc := 7;
end;

pxx: compiles, c.Calc returns 7. FPC: error (method not declared in class).

Where

parser.inc ~22522: the method-impl binder's not-found branch deliberately falls back to AddUMeth ("falling back to the name match for a not-yet-declared method"). Behind a strict flag per the strict-* policy (--strict-fpc umbrella), NOT default — the lax registration may be relied on. Related: bug-pascal-overload-impl-decl-signature-match.