fix(codegen-native): elide class-assignment AddRef when RHS owns +1

A function or method returning a class leaves its Result at refcount +1: the
callee's `Result := x` AddRef'd and the epilogue did not release Result. The
caller's assignment therefore consumes that transferred reference and must NOT
AddRef again. The native backend's plain class-variable assignment emitted
_ClassAddRef unconditionally, so `C := MakeIt()` (any object-returning call)
leaked exactly one reference per call.

Guard the AddRef with NativeExprOwnsRef, mirroring the tyString/tyDynArray
branches directly above it and the QBE backend's ExprOwnsRef elision (the QBE
path has always been leak-free here). Eliding is safe even for a borrowed return
(`Result := G`): the callee's Result assignment still AddRef'd, so the
transient genuinely owns +1 — verified no use-after-free when the source object
outlives the assignment.

Found via a TList<TCreature> + `L[I].HitPoints := ...` program reporting leaks
under --debug; reduced to a non-generic `C := MakeIt(); C := nil` minimal case.

NOTE: this fixes the assignment-site half. Object-returning call results used as
a field/method *receiver* or as a subscript getter result (e.g. L[I].Field) are
a separate, deeper gap — the native backend lacks the QBE backend's
statement-level deferred-release (PendingRelease/Flush) — addressed next.

cp.test.e2e.leakcheck.TestDebug_FuncReturnAssign_NoLeak pins both backends.
Full suite 3850 green; native fixpoint reproduces (and shrank the compiler's own
emitted asm by ~1400 lines of redundant retains).

compiler/src/main/pascal/blaise.codegen.native.x86_64.pas

@@ -11283,8 +11283,17 @@ begin
     begin
       Self.EmitExprToEax(Asgn.Expr);
       Self.Emit(#9'pushq %rax');
-      Self.Emit(#9'movq %rax, %rdi');
-      Self.Emit(#9'callq _ClassAddRef');
+      { Elide the retain when the RHS already owns +1 (a call result): a
+        function/method returning a class leaves Result at +1 (the callee's
+        `Result := x` AddRef'd and the epilogue did not release it), so the
+        assignment consumes that transferred reference.  AddRef'ing again leaks
+        one ref per call.  This matches the tyString/tyDynArray branches above
+        and the QBE backend's ExprOwnsRef elision. }
+      if not NativeExprOwnsRef(Asgn.Expr) then
+      begin
+        Self.Emit(#9'movq %rax, %rdi');
+        Self.Emit(#9'callq _ClassAddRef');
+      end;
       if Asgn.IsVarParam then
       begin
         Self.Emit(Format(#9'movq %s, %%rcx', [Self.VarOperand(Asgn.Name)]));

compiler/src/test/pascal/cp.test.e2e.leakcheck.pas

@@ -38,6 +38,10 @@ type
 
     { obj.Field := MakeClass() consumes the call's +1 — no leak per store. }
     procedure TestDebug_ClassFieldFromCall_NoLeak;
+
+    { local := MakeClass() consumes the call's +1 — no leak per assignment.
+      Pins the native class-assignment AddRef elision against the QBE backend. }
+    procedure TestDebug_FuncReturnAssign_NoLeak;
     { Multiple same-named typed handlers share one slot — no over-release. }
     procedure TestDebug_MultiHandlerVar_NoOverRelease;
     { for-in over a TList: GetEnumerator's +1 result must be transferred
@@ -512,6 +516,35 @@ const
     end.
     ''';
 
+  { A function returning a class leaves Result at +1 (the callee's `Result := x`
+    AddRef'd and the epilogue did not release it).  Assigning that call result to
+    a local consumes the transferred reference — the assignment site must NOT
+    AddRef again, or one object leaks per call.  The native backend used to
+    AddRef class assignments unconditionally; this pins the elision. }
+  SrcFuncReturnAssign = '''
+    program P;
+    type
+      TThing = class N: Integer; end;
+    function MakeThing(): TThing;
+    begin
+      Result := TThing.Create();
+      Result.N := 9;
+    end;
+    var
+      T: TThing;
+      I, Sum: Integer;
+    begin
+      Sum := 0;
+      for I := 1 to 100 do
+      begin
+        T := MakeThing();
+        Sum := Sum + T.N;
+        T := nil;
+      end;
+      WriteLn(Sum);
+    end.
+    ''';
+
   SrcMultiHandlerVar = '''
     program P;
     type
@@ -550,6 +583,24 @@ begin
   AssertTrue('no leak report (native)', Pos('leak', Output) < 0);
 end;
 
+procedure TE2ELeakCheckTests.TestDebug_FuncReturnAssign_NoLeak;
+var
+  Output: string;
+  ExitCode: Integer;
+begin
+  if not ToolchainAvailable() then begin Ignore('toolchain unavailable'); Exit end;
+  AssertTrue('compile+run (qbe)',
+    CompileAndRunWithRTLDebugOn(beQBE, SrcFuncReturnAssign, Output, ExitCode, True));
+  AssertEquals('exit 0 (qbe)', 0, ExitCode);
+  AssertEquals('stdout (qbe)', '900' + LE, Output);
+  AssertTrue('no leak report (qbe)', Pos('leak', Output) < 0);
+  AssertTrue('compile+run (native)',
+    CompileAndRunWithRTLDebugOn(beNative, SrcFuncReturnAssign, Output, ExitCode, True));
+  AssertEquals('exit 0 (native)', 0, ExitCode);
+  AssertEquals('stdout (native)', '900' + LE, Output);
+  AssertTrue('no leak report (native)', Pos('leak', Output) < 0);
+end;
+
 procedure TE2ELeakCheckTests.TestDebug_MultiHandlerVar_NoOverRelease;
 var
   Output: string;