Feature request: let MDL position microflow/nanoflow parameters (`MicroflowParameter` has coordinates, but no annotation reaches it)

[TDSC0706]

Use case

We lint the canvas of every microflow and nanoflow we generate, and one of our house rules
is where the parameters sit: above the start event, in a two-column grid filled row by
row from the bottom up, in parameter order.

        p4   p3        row 2        col0.cx = start.cx
        p2   p1        row 1        col1.cx = start.cx − 100
             o         start        row k.cy = start.cy − (100 + (k−1)·100)

Parameters are stored nodes with real geometry — every MicroflowParameter in our project
is 30×30 with its own RelativeMiddlePoint (263 of 263 measured) — and Studio Pro lets
you drag them. But no MDL annotation reaches them, so a generated flow's parameter block
lands wherever the writer puts it and stays there.

The rest of the canvas is already scriptable: @position on statements, @anchor and
@curve on edges, @start on the start event (new in 0.20.0), @merge on an end-if.
Parameters are the one remaining node family with coordinates and no way to set them —
which means a flow that is otherwise byte-identical to a hand-aligned reference still
needs a manual pass for the parameter block alone.

This is the same argument as @start: the start event also had coordinates and no
annotation, and #951 closed that gap. Parameters are the sibling case.

Proposed syntax or behavior

The annotation form the grammar already uses, applied to a parameter declaration:

CREATE NANOFLOW MyFirstModule.NF_ParamPos (
  @position(300, 100)
  $A: Integer
)
RETURNS Integer AS $R
BEGIN
  @position(300, 200)
  DECLARE $R Integer = $A + 1;
  @position(500, 200)
  RETURN $R;
END;
/

Today this is a parse error — verified on a blank project
(mx create-project --app-name ReproApp, Mendix 11.12.1), identical on v0.19.0 and v0.20.0:

line 2:2  extraneous input '@' expecting the start of a statement (create, alter, drop, show, describe, …)
line 2:11 mismatched input '(' expecting ':'
line 2:17 mismatched input '100' expecting the start of a statement (…)

For reference, the same blank project shows the node does carry geometry: writing the
nanoflow without the annotation stores its MicroflowParameter at RelativeMiddlePoint 200;53, Size 30;30 — a real position, just not one a script can choose.

Failing loudly is the right behaviour for something unsupported — no complaint there; this
is a request for the capability, not a bug report about the error.

An alternative that avoids touching the parameter list grammar would be a single
block-level annotation before BEGIN, e.g.:

@parameters((300, 100), (200, 100))
BEGIN

but the per-parameter form reads better and matches how @position already attaches to
the thing it positions.

describe should emit it too. Today describe microflow / describe nanoflow emit no
parameter geometry at all, so even a hand-aligned flow round-trips with its parameter block
reset — the same silent-loss shape as the mapping round-trips closed in 0.20.0.

Mendix version relevance

Not version-specific as far as we can tell. Measured on Mendix 11.12.1 (MPR v2);
MicroflowParameter carries RelativeMiddlePoint + Size the same way an activity does.

Why it matters more for nanoflows

Studio Pro's PED API (ped_update_document) can patch a microflow's node coordinates,
so for microflows this is a convenience. It does not write nanoflows — so for a
nanoflow, MDL is the only writer, and parameter placement is simply out of reach from any
script.

Environment

mxcli version v0.19.0 (2026-08-21T13:13:26Z)   -- PATH binary
mxcli version v0.20.0 (2026-08-28T13:22:53Z)   -- current release, same result
Mendix Studio Pro 11.12.1, MPR v2, 1971 units