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Passing a captured dynamic array by var from a parallel-for body segfaults

Repro (compiles clean, segfaults)

program Cap3;
uses palparallel;
type TArr = array of Integer;
procedure Sink(i: Integer; var a: TArr);
begin a[i] := i; end;
procedure Run;
var i: Integer; la: TArr;
begin
  SetLength(la, 100);
  parallel for i := 0 to 99 do Sink(i, la);
  writeln(la[42]);
end;
begin Run; end.



$ pxx --threadsafe cap3.pas /tmp/cap3
ok: /tmp/cap3  [code=73339B  data=1576B  bss=9572B  procs=160]
$ /tmp/cap3
Segmentation fault (core dumped)

la is a LOCAL of a NAMED type, which is exactly the supported B-1 aggregate capture shape (cf. test/test_parallel_for_capture_aggr.pas). Capturing it and indexing it directly in the body is covered by that test and works; capturing it and passing it by var to a callee compiles and then crashes.

The likely shape: the capture frame holds the array by reference, and the callee's var parameter is handed the frame slot (a reference to the reference) rather than the array's own data pointer — one indirection too many. Worth checking whether a by-value (const / plain) aggregate parameter has the same problem.

Why it matters

It is silent: no diagnostic, a clean ok: line, and the crash lands at runtime in whatever the worker touches first. Splitting a parallel loop body into a helper procedure is the recommended pattern (the helper's scratch is private per worker) — so this bites exactly the code shape the docs steer people toward.

Acceptance

[[bug-parallel-for-captured-boolean-loses-type]] (found in the same session, same capture path) · [[feature-demo-mandelbrot-asm-autozoom]] (the consumer; it works around this by putting the framebuffer in a global, which workers reach directly) · test/test_parallel_for_capture_aggr.pas.

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