Tidy Layout as signal flow; fixed-size wiresheet; signed Sox int writes

- Tidy Layout lays linked boxes out left to right by signal flow, in as few
  columns as the longest chain allows; feedback loops are cut where they run
  backwards, and sources sit just before the boxes they feed.
- Boxes with no link on the open sheet go to the bottom of the first column,
  alphabetically.
- A box that wires skipping its column would cross is pushed down below them.
- The wiresheet is fixed at meta's 255-step reach; outside it is light grey.
  Dragging keeps a box's top-left corner on the sheet.
- Sox write_i4 wraps to signed, so meta with x >= 128 reaches the device.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app_state.py

@@ -8,7 +8,7 @@ so later rebinding would only ever be seen by the module that did it.
 import configparser
 import os
 
-VERSION = "0.0.0.173"
+VERSION = "0.0.0.174"
 PROPERTIES_FILE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "editor.properties")
 DEFAULT_GRID_SIZE = 10
 DEFAULT_ADD_TIMESTAMP = True

main.py

@@ -933,7 +933,7 @@ def do_tidy_layout(event=None):
     multiplier = app_state.meta_scale // app_state.GRID_SIZE
 
     if moved == 0:
-        messagebox.showinfo("Tidy Layout", "Nothing to move — no boxes overlap.")
+        messagebox.showinfo("Tidy Layout", "Nothing to move — the sheet is already tidy.")
     elif clamped:
         messagebox.showwarning(
             "Tidy Layout",
@@ -991,14 +991,8 @@ def zoom_to(level, anchor=None):
     if after == before:
         return
 
-    # Scroll the repainted sheet back under the held point. The scrollregion starts at
+    # Scroll the repainted sheet back under the held point.
-    # the origin, so its far corner is the span the view fractions are measured against.
+    wiresheet.scroll_view_to(sheet_x * after - anchor[0], sheet_y * after - anchor[1])
-    region = str(canvas.cget("scrollregion")).split()
-    if len(region) == 4:
-        span_x = float(region[2]) or 1.0
-        span_y = float(region[3]) or 1.0
-        canvas.xview_moveto(max(0.0, (sheet_x * after - anchor[0]) / span_x))
-        canvas.yview_moveto(max(0.0, (sheet_y * after - anchor[1]) / span_y))
 
 
 def do_zoom_in(event=None):
@@ -1054,12 +1048,8 @@ def do_zoom_fit(event=None):
     applied = wiresheet.set_zoom(level)
     update_zoom_label()
 
-    region = str(canvas.cget("scrollregion")).split()
+    wiresheet.scroll_view_to(bounds[0] * applied - wiresheet.FIT_PADDING,
-    if len(region) == 4:
+                             bounds[1] * applied - wiresheet.FIT_PADDING)
-        span_x = float(region[2]) or 1.0
-        span_y = float(region[3]) or 1.0
-        canvas.xview_moveto(max(0.0, (bounds[0] * applied - wiresheet.FIT_PADDING) / span_x))
-        canvas.yview_moveto(max(0.0, (bounds[1] * applied - wiresheet.FIT_PADDING) / span_y))
     return "break"
 
 
@@ -1256,16 +1246,11 @@ def scroll_canvas_to(tag):
     """Scrolls the sheet so the tagged items sit in the middle of the view."""
     canvas = app_state.canvas
     box = canvas.bbox(tag)
-    region = str(canvas.cget("scrollregion")).split()
+    if box is None:
-    if box is None or len(region) != 4:
         return
 
-    span_x = float(region[2]) or 1.0
+    wiresheet.scroll_view_to((box[0] + box[2]) / 2 - canvas.winfo_width() / 2,
-    span_y = float(region[3]) or 1.0
+                             (box[1] + box[3]) / 2 - canvas.winfo_height() / 2)
-    middle_x = (box[0] + box[2]) / 2 - canvas.winfo_width() / 2
-    middle_y = (box[1] + box[3]) / 2 - canvas.winfo_height() / 2
-    canvas.xview_moveto(max(0.0, middle_x / span_x))
-    canvas.yview_moveto(max(0.0, middle_y / span_y))
 
 
 def select_link_element(link_elem):
@@ -2111,8 +2096,10 @@ def on_canvas_drag(event):
     # out of the margin strip along the top and left canvas edges.
     wanted_x = box_x + (cx - app_state.drag_data["x"])
     wanted_y = app_state.drag_data["box_y"] + (cy - app_state.drag_data["y"])
-    target_x = max(margin, round(wanted_x / step) * step)
+    # The box's corner also stays on the sheet, the furthest meta can store it.
-    target_y = max(margin, round(wanted_y / step) * step)
+    limit = wiresheet.META_COORD_MAX * step
+    target_x = min(limit, max(margin, round(wanted_x / step) * step))
+    target_y = min(limit, max(margin, round(wanted_y / step) * step))
 
     shift_x = target_x - origin[0]
     shift_y = target_y - origin[1]
@@ -2137,8 +2124,9 @@ def on_canvas_release(event):
         current_x, current_y = origin
 
         margin = wiresheet.layout_margin(app_state.meta_scale) * app_state.zoom
-        snapped_x = max(margin, round(current_x / step) * step)
+        limit = wiresheet.META_COORD_MAX * step
-        snapped_y = max(margin, round(current_y / step) * step)
+        snapped_x = min(limit, max(margin, round(current_x / step) * step))
+        snapped_y = min(limit, max(margin, round(current_y / step) * step))
 
         shift_x = snapped_x - current_x
         shift_y = snapped_y - current_y
@@ -3755,11 +3743,11 @@ canvas_hscroll.pack(side=tk.BOTTOM, fill=tk.X)
 
 canvas = tk.Canvas(
     frame_editor,
-    bg="white",
+    bg=wiresheet.OFF_SHEET_COLOUR,
     highlightthickness=0,
     xscrollcommand=canvas_hscroll.set,
     yscrollcommand=canvas_vscroll.set,
-    scrollregion=(0, 0, 2000, 2000),
+    scrollregion=(0, 0, *wiresheet.sheet_extent()),
 )
 app_state.canvas = canvas
 canvas.pack(fill=tk.BOTH, expand=True)

sax_file.py

@@ -180,7 +180,7 @@ def reset_to_startup_state():
 
     if app_state.canvas is not None:
         app_state.canvas.delete("all")
-        wiresheet.draw_grid()
+        wiresheet.fit_sheet_region()
 
     if app_state.window is not None:
         app_state.window.title(app_state.base_window_title())
@@ -223,7 +223,7 @@ def open_file():
         for item in tree.get_children():
             tree.delete(item)
         canvas.delete("all")
-        wiresheet.draw_grid()
+        wiresheet.fit_sheet_region()
 
         xml_tree = ET.parse(file_path)
         app_state.xml_root_element = xml_tree.getroot()

sox.py

@@ -134,7 +134,9 @@ class SoxMsg:
 
     def write_i4(self, v):
         self._grow(4)
-        struct.pack_into(">i", self._buf, self._pos, v)
+        # Wrapped to signed: meta packs x into the top byte, so x >= 128 reads as an
+        # unsigned 32-bit value although the device stores the same bits as sys::int.
+        struct.pack_into(">i", self._buf, self._pos, ((v + 2**31) % 2**32) - 2**31)
         self._pos += 4
 
     def write_i8(self, v):

wiresheet.py

@@ -122,6 +122,8 @@ FIT_PADDING = 20
 # Below this a grid line is closer to its neighbour than the line is wide, which reads
 # as a grey wash rather than a grid, so the grid is left off instead.
 MIN_GRID_STEP = 3
+SHEET_MARGIN_GRIDS = 3  # grid squares of grey kept past anything that overflows the sheet
+OFF_SHEET_COLOUR = "#f3f3f3"  # canvas outside the area a box's origin can be stored in
 
 
 def snap_up(value, grid_size):
@@ -238,28 +240,40 @@ def measure_box(comp, fonts, linked_slot_index):
 
 
 def draw_grid():
-    """Draws a grid onto the Canvas based on the scrollable region.
+    """Paints the sheet white and grids it; the canvas around it stays OFF_SHEET_COLOUR.
 
-    Drawn at the sheet's zoom, so a box still lands on a line at every scale. The area
+    Drawn at the sheet's zoom, so a box still lands on a line at every scale.
-    covered is the same patch of sheet whatever the zoom, which is why the span is
-    scaled along with the step.
     """
     canvas = app_state.canvas
     canvas.delete("grid")
 
+    x1, y1 = 0, 0
+    x2, y2 = (coord * app_state.zoom for coord in sheet_extent())
+    canvas.create_rectangle(x1, y1, x2, y2, fill="white", outline="#c8c8c8", tags="grid")
+
     step = app_state.GRID_SIZE * app_state.zoom
-    if step < MIN_GRID_STEP:
+    if step >= MIN_GRID_STEP:
-        return
+        draw_grid_lines(canvas, step, x1, y1, x2, y2)
-
-    span = 3000 * app_state.zoom
-    for index in range(int(span // step) + 1):
-        offset = index * step
-        canvas.create_line(offset, 0, offset, span, fill="#e0e0e0", tags="grid")
-        canvas.create_line(0, offset, span, offset, fill="#e0e0e0", tags="grid")
-
     canvas.tag_lower("grid")
 
 
+def sheet_extent():
+    """1:1 (width, height) of the sheet: the furthest position meta can store a box at.
+
+    Only a box's top-left corner has to fit; a box reaching past the edge is drawn over
+    the grey, and keeping it inside is left to the author.
+    """
+    side = META_COORD_MAX * (app_state.meta_scale or app_state.GRID_SIZE)
+    return side, side
+
+
+def draw_grid_lines(canvas, step, x1, y1, x2, y2):
+    for index in range(math.ceil(x1 / step - 1e-6), math.floor(x2 / step + 1e-6) + 1):
+        canvas.create_line(index * step, y1, index * step, y2, fill="#e0e0e0", tags="grid")
+    for index in range(math.ceil(y1 / step - 1e-6), math.floor(y2 / step + 1e-6) + 1):
+        canvas.create_line(x1, index * step, x2, index * step, fill="#e0e0e0", tags="grid")
+
+
 def create_round_rectangle(canvas, x1, y1, x2, y2, radius=4, **kwargs):
     """Draws a visually smooth rounded rectangle using native canvas arcs and polygons."""
     points = [
@@ -1160,9 +1174,6 @@ def render_components(components_to_render):
     meta_scale = sheet_meta_scale(components_to_render)
     app_state.meta_scale = meta_scale
 
-    max_reached_x = 1000
-    max_reached_y = 1000
-
     for comp in components_to_render:
         meta_prop = comp.find("prop[@name='meta']")
         meta_str = meta_prop.get("val") if meta_prop is not None else None
@@ -1175,22 +1186,17 @@ def render_components(components_to_render):
         app_state.canvas_comp_map[comp_tag] = comp
         app_state.canvas_tag_by_element[comp] = comp_tag
 
-        box_width, box_height, slot_offsets = draw_component_box(
+        _, _, slot_offsets = draw_component_box(
             canvas, comp, coord_x, coord_y, fonts, linked_slot_index,
             ("component", comp_tag), outline_tags=("block_outline",)
         )
         app_state.component_slot_offsets[comp_tag] = slot_offsets
 
-        if coord_x + box_width > max_reached_x:
-            max_reached_x = coord_x + box_width
-        if coord_y + box_height > max_reached_y:
-            max_reached_y = coord_y + box_height
-
     draw_links()
-    apply_sheet_zoom(fonts, max_reached_x + 200, max_reached_y + 200)
+    apply_sheet_zoom(fonts)
 
 
-def apply_sheet_zoom(fonts, extent_x, extent_y):
+def apply_sheet_zoom(fonts):
     """Scales the finished sheet to app_state.zoom and sizes the canvas to match.
 
     Painting and routing both work at 1:1, because that is where every metric here is
@@ -1212,10 +1218,46 @@ def apply_sheet_zoom(fonts, extent_x, extent_y):
 
         scale_knob_ends(zoom)
 
-    canvas.config(scrollregion=(0, 0, extent_x * zoom, extent_y * zoom))
+    fit_sheet_region()
+
+
+def fit_sheet_region():
+    """Sets the scrollable area: the whole sheet, plus whatever hangs off its edges.
+
+    The sheet itself never grows (see sheet_extent). A box near the right or bottom
+    edge can still reach past it, or a wire loop past the top, so the scrollable area
+    takes those in too, with SHEET_MARGIN_GRIDS of grey beyond them.
+    """
+    canvas = app_state.canvas
+    zoom = app_state.zoom
+    margin = SHEET_MARGIN_GRIDS * app_state.GRID_SIZE
+    width, height = sheet_extent()
+    x1, y1, x2, y2 = 0, 0, width, height
+    bounds = sheet_content_bounds()
+    if bounds is not None:
+        if bounds[0] < 0:
+            x1 = bounds[0] - margin
+        if bounds[1] < 0:
+            y1 = bounds[1] - margin
+        if bounds[2] > width:
+            x2 = bounds[2] + margin
+        if bounds[3] > height:
+            y2 = bounds[3] + margin
+    canvas.config(scrollregion=(x1 * zoom, y1 * zoom, x2 * zoom, y2 * zoom))
     draw_grid()
 
 
+def scroll_view_to(x, y):
+    """Scrolls so canvas point (x, y) sits at the view's top-left, as near as the sheet allows."""
+    canvas = app_state.canvas
+    region = str(canvas.cget("scrollregion")).split()
+    if len(region) != 4:
+        return
+    x1, y1, x2, y2 = (float(v) for v in region)
+    canvas.xview_moveto(max(0.0, (x - x1) / ((x2 - x1) or 1.0)))
+    canvas.yview_moveto(max(0.0, (y - y1) / ((y2 - y1) or 1.0)))
+
+
 def scale_knob_ends(zoom):
     """Brings the cached knob-to-knob ends onto the painted scale.
 
@@ -1237,6 +1279,7 @@ def redraw_links():
     zoom = app_state.zoom
     if zoom == 1.0:
         draw_links()
+        fit_sheet_region()   # a box dragged over the edge brings the grey past it into view
         return
 
     canvas = app_state.canvas
@@ -1245,6 +1288,7 @@ def redraw_links():
     canvas.scale("component", 0, 0, zoom, zoom)
     canvas.scale("link", 0, 0, zoom, zoom)
     scale_knob_ends(zoom)
+    fit_sheet_region()
 
 
 def zoom_step(direction):
@@ -1307,14 +1351,8 @@ def fit_zoom_level():
     if bounds is None:
         return None
 
-    # A canvas cannot scroll left of or above its origin, so anything out there cannot
+    content_width = bounds[2] - bounds[0]
-    # be brought into view however far the sheet is zoomed out. The fit is measured from
+    content_height = bounds[3] - bounds[1]
-    # the origin in that case rather than from the content's own corner.
-    left = max(0.0, bounds[0])
-    top = max(0.0, bounds[1])
-
-    content_width = bounds[2] - left
-    content_height = bounds[3] - top
     view_width = canvas.winfo_width() - 2 * FIT_PADDING
     view_height = canvas.winfo_height() - 2 * FIT_PADDING
 
@@ -1411,59 +1449,225 @@ def column_gap_for(run_count):
                + max(0, run_count - 1) * clear.lane)
 
 
-def plan_columns(columns, column_keys, demand, scale):
+def plan_columns(columns, column_keys, demand, scale, spans=()):
     """Walks the columns at `scale` px per meta step, without touching the DOM.
 
     Returns (placements, clamped) where a placement is (item, step_x, step_y). Boxes are
     positioned in pixels exactly as they will be painted, then divided down into meta
     steps, so a coarser scale reaches further across the sheet for the same 0..255 range.
+
+    `spans` are the wires that skip columns, as (src_column, dst_column, dst_item,
+    dst_slot). The router turns such a wire down beside its source, so it crosses every
+    column in between level with its target slot; a box in its way is pushed down below
+    it instead of making the wire detour. Columns are filled right to left for that,
+    since a wire's height is set by its target, which always lies further right.
     """
     margin = snap_up(TIDY_MARGIN, scale)
-    placements = []
+    clear_end = grid_clearance().end
     clamped = 0
-    cursor_x = margin  # the left-most column clears the canvas edge by the margin
 
+    # Column x positions depend only on widths and wire lanes, so they come first.
+    column_x = []
+    cursor_x = margin  # the left-most column clears the canvas edge by the margin
     for index, grid_x in enumerate(column_keys):
-        column = sorted(columns[grid_x], key=lambda i: i["grid_y"])
+        column_x.append(cursor_x)
+        gap = column_gap_for(demand.get(index, 0))
+        cursor_x = snap_up(cursor_x + max(i["width"] for i in columns[grid_x]) + gap,
+                           scale)
+
+    top_of = {}   # id(item) -> pixel y its box was given
+    placed = {}   # id(item) -> (step_x, step_y)
+    for index in reversed(range(len(column_keys))):
+        rows = sorted(
+            top_of[id(dst_item)] + dst_item["slot_offsets"].get(
+                dst_slot, dst_item["height"] / 2)
+            for src_col, dst_col, dst_item, dst_slot in spans
+            if src_col < index < dst_col
+        )
         cursor_y = margin
 
-        for item in column:
+        for item in columns[column_keys[index]]:   # already in top-to-bottom order
-            step_x = min(META_COORD_MAX, round(cursor_x / scale))
+            top = cursor_y
-            step_y = min(META_COORD_MAX, round(cursor_y / scale))
+            # Step below every passing wire the box would sit across, keeping the
+            # clearance the router wants between a horizontal run and a box edge.
+            moved = True
+            while moved:
+                moved = False
+                for row in rows:
+                    if top - clear_end < row < top + item["height"] + clear_end:
+                        top = snap_up(row + clear_end, scale)
+                        moved = True
+
+            top_of[id(item)] = top
+            step_x = min(META_COORD_MAX, round(column_x[index] / scale))
+            step_y = min(META_COORD_MAX, round(top / scale))
             if step_x == META_COORD_MAX or step_y == META_COORD_MAX:
                 clamped += 1
-            placements.append((item, step_x, step_y))
+            placed[id(item)] = (step_x, step_y)
 
             # Clear the box just placed by at least TIDY_GAP, then step to the next
             # whole meta step so the box still lands on a storable position.
-            cursor_y = snap_up(cursor_y + item["height"] + TIDY_GAP, scale)
+            cursor_y = snap_up(top + item["height"] + TIDY_GAP, scale)
-
-        gap = column_gap_for(demand.get(index, 0))
-        cursor_x = snap_up(cursor_x + max(i["width"] for i in column) + gap, scale)
 
+    placements = [
+        (item, *placed[id(item)])
+        for grid_x in column_keys
+        for item in columns[grid_x]
+    ]
     return placements, clamped
 
 
+def sheet_link_pairs(components):
+    """(source, target) for each link between two different components on this sheet."""
+    root = app_state.xml_root_element
+    pairs = []
+    if root is None:
+        return pairs
+    links_elem = root.find("links")
+    if links_elem is None:
+        return pairs
+
+    comp_by_path = {get_component_path(comp, root): comp for comp in components}
+    for link in links_elem.findall("link"):
+        from_ref, to_ref = link.get("from", ""), link.get("to", "")
+        if "." not in from_ref or "." not in to_ref:
+            continue
+        src = comp_by_path.get(from_ref.rsplit(".", 1)[0])
+        dst = comp_by_path.get(to_ref.rsplit(".", 1)[0])
+        if src is not None and dst is not None and src is not dst:
+            pairs.append((src, dst))
+    return pairs
+
+
+def flow_columns(items, pairs):
+    """Lays linked boxes out as a left-to-right signal flow, in as few columns as it can.
+
+    Returns a list of columns, each listed top to bottom. A box goes one column right of
+    the furthest box feeding it, so the column count is the length of the longest chain
+    and cannot be smaller. A box nothing feeds is then pulled right to sit just before
+    the first box it feeds, which keeps its wires short. Feedback loops are cut where
+    they run backwards relative to the boxes' current positions, so a loop keeps the
+    direction the author drew it in.
+    """
+    def position(item):
+        return item["grid_x"], item["grid_y"], item["comp"].get("name", "")
+
+    item_of = {item["comp"]: item for item in items}
+    succs = {id(item): [] for item in items}
+    for src, dst in pairs:
+        if item_of[dst] not in succs[id(item_of[src])]:
+            succs[id(item_of[src])].append(item_of[dst])
+    for out in succs.values():
+        out.sort(key=position)
+
+    # Depth-first from the left-most boxes; an edge back onto the current path is
+    # feedback and is left out of the layering.
+    forward = {id(item): [] for item in items}
+    state = {}                       # id -> 1 on the current path, 2 finished
+    for start in sorted(items, key=position):
+        if id(start) in state:
+            continue
+        state[id(start)] = 1
+        stack = [(start, iter(succs[id(start)]))]
+        while stack:
+            node, pending = stack[-1]
+            nxt = next(pending, None)
+            if nxt is None:
+                state[id(node)] = 2
+                stack.pop()
+            elif state.get(id(nxt)) == 1:
+                continue             # feedback
+            else:
+                forward[id(node)].append(nxt)
+                if id(nxt) not in state:
+                    state[id(nxt)] = 1
+                    stack.append((nxt, iter(succs[id(nxt)])))
+
+    preds = {id(item): [] for item in items}
+    for item in items:
+        for nxt in forward[id(item)]:
+            preds[id(nxt)].append(item)
+
+    # Longest path from the sources, in topological order.
+    layer = {}
+    indegree = {id(item): len(preds[id(item)]) for item in items}
+    ready = sorted((i for i in items if not indegree[id(i)]), key=position)
+    order = []
+    while ready:
+        node = ready.pop(0)
+        order.append(node)
+        layer[id(node)] = max((layer[id(p)] + 1 for p in preds[id(node)]), default=0)
+        for nxt in forward[id(node)]:
+            indegree[id(nxt)] -= 1
+            if not indegree[id(nxt)]:
+                ready.append(nxt)
+    for node in reversed(order):
+        if not preds[id(node)] and forward[id(node)]:
+            layer[id(node)] = min(layer[id(n)] for n in forward[id(node)]) - 1
+
+    columns = [[] for _ in range(max(layer.values(), default=-1) + 1)]
+    for item in sorted(items, key=lambda i: (i["grid_y"], i["grid_x"])):
+        columns[layer[id(item)]].append(item)
+
+    # Order each column after the boxes feeding it, so wires run as level as they can;
+    # then once back right to left, settling the boxes nothing feeds beside the boxes
+    # they feed. Ties keep the author's top-to-bottom order.
+    row = {}
+
+    def settle(column, neighbours):
+        def key(item):
+            near = [row[id(n)] for n in neighbours(item) if id(n) in row]
+            return sum(near) / len(near) if near else row.get(id(item), float("inf"))
+        column.sort(key=key)
+        for index, item in enumerate(column):
+            row[id(item)] = index
+
+    for column in columns:
+        settle(column, lambda i: preds[id(i)])
+    for column in reversed(columns):
+        settle(column, lambda i: forward[id(i)] if not preds[id(i)] else ())
+    return columns
+
+
 def build_layout_items(components):
     """Column-grouped layout items for a sheet, measured rather than read off the canvas.
 
-    Returns (columns, column_keys, demand). Called both while painting -- to settle the
+    Returns (columns, column_keys, demand, spans), each column listed top to bottom.
-    scale before anything is drawn -- and by tidy, so the two agree.
+    Linked boxes are arranged by flow_columns. A box with no link to another box on this
+    sheet -- unlinked, or linked only off-sheet -- goes to the bottom of the first
+    column, alphabetically by name.
+    Called both while painting -- to settle the scale before anything is drawn -- and by
+    tidy, so the two agree.
     """
     fonts = sheet_fonts()
     linked_slot_index = build_linked_slot_index()
+    pairs = sheet_link_pairs(components)
+    on_sheet = {comp for pair in pairs for comp in pair}
 
-    columns = {}
+    linked = []
+    loose = []
     for comp in components:
         meta_prop = comp.find("prop[@name='meta']")
         meta_val = meta_prop.get("val") if meta_prop is not None else None
         grid_x, grid_y = read_meta_property(meta_val)[:2]
-        width, height = measure_box(comp, fonts, linked_slot_index)[:2]
+        width, height, slot_rows = measure_box(comp, fonts, linked_slot_index)[:3]
-        columns.setdefault(grid_x, []).append({
+        item = {
             "comp": comp, "meta": meta_val,
             "grid_x": grid_x, "grid_y": grid_y,
             "width": width, "height": height,
-        })
+            # Where each slot's wire meets the box, as painted by draw_component_box.
+            "slot_offsets": {
+                raw_name: HEADER_HEIGHT + row * SLOT_ROW_HEIGHT + SLOT_ROW_HEIGHT // 2
+                for row, (raw_name, _, _) in enumerate(slot_rows)
+            },
+        }
+        (linked if comp in on_sheet else loose).append(item)
+
+    columns = dict(enumerate(flow_columns(linked, pairs)))
+    if loose:
+        loose.sort(key=lambda i: (i["comp"].get("name", "").casefold(),
+                                  i["comp"].get("name", "")))
+        columns.setdefault(0, []).extend(loose)
 
     column_keys = sorted(columns)
     column_of_comp = {
@@ -1471,7 +1675,40 @@ def build_layout_items(components):
         for index, key in enumerate(column_keys)
         for item in columns[key]
     }
-    return columns, column_keys, wire_demand_by_boundary(column_of_comp)
+    return (columns, column_keys, wire_demand_by_boundary(column_of_comp),
+            column_skipping_spans(columns, column_of_comp))
+
+
+def column_skipping_spans(columns, column_of_comp):
+    """Wires running left to right past at least one column, for plan_columns.
+
+    Each is (src_column, dst_column, dst_item, dst_slot).
+    """
+    spans = []
+    root = app_state.xml_root_element
+    links_elem = root.find("links") if root is not None else None
+    if links_elem is None:
+        return spans
+
+    item_by_path = {
+        get_component_path(item["comp"], root): item
+        for column in columns.values()
+        for item in column
+    }
+    for link in links_elem.findall("link"):
+        from_ref, to_ref = link.get("from", ""), link.get("to", "")
+        if "." not in from_ref or "." not in to_ref:
+            continue
+        src_item = item_by_path.get(from_ref.rsplit(".", 1)[0])
+        dst_path, dst_slot = to_ref.rsplit(".", 1)
+        dst_item = item_by_path.get(dst_path)
+        if src_item is None or dst_item is None:
+            continue
+        src_col = column_of_comp[src_item["comp"]]
+        dst_col = column_of_comp[dst_item["comp"]]
+        if dst_col - src_col >= 2:
+            spans.append((src_col, dst_col, dst_item, dst_slot))
+    return spans
 
 
 def sheet_meta_scale(components):
@@ -1485,22 +1722,24 @@ def sheet_meta_scale(components):
     if not components:
         return grid_size
 
-    columns, column_keys, demand = build_layout_items(components)
+    columns, column_keys, demand, spans = build_layout_items(components)
     if not column_keys:
         return grid_size
 
     for multiplier in range(1, META_SCALE_MAX + 1):
-        _, clamped = plan_columns(columns, column_keys, demand, grid_size * multiplier)
+        _, clamped = plan_columns(columns, column_keys, demand, grid_size * multiplier,
+                                  spans)
         if not clamped:
             return grid_size * multiplier
     return grid_size * META_SCALE_MAX
 
 
 def tidy_layout():
-    """Re-flows the open sheet so no two boxes overlap, preserving the author's columns.
+    """Re-flows the open sheet as a left-to-right signal flow with no two boxes overlapping.
 
-    Boxes keep their column grouping and their top-to-bottom order; only the spacing is
+    Columns follow the wiring (see flow_columns), using as few as the longest chain of
-    rebuilt, from the sizes actually painted. Every placement lands on a whole meta step,
+    links allows; spacing is rebuilt from the sizes actually painted. Boxes with no link to another box on the
+    sheet are gathered at the bottom of the first column, A to Z. Every placement lands on a whole meta step,
     the first column and row clear the canvas edge by at least TIDY_MARGIN, and
     neighbours are left at least TIDY_GAP apart, widened where wires need lanes. A sheet
     too wide for meta's 0..255 range is laid out at a coarser multiple of the grid rather
@@ -1511,12 +1750,12 @@ def tidy_layout():
         return 0, 0
 
     components = list(app_state.canvas_comp_map.values())
-    columns, column_keys, demand = build_layout_items(components)
+    columns, column_keys, demand, spans = build_layout_items(components)
     if not column_keys:
         return 0, 0
 
     scale = sheet_meta_scale(components)
-    placements, clamped = plan_columns(columns, column_keys, demand, scale)
+    placements, clamped = plan_columns(columns, column_keys, demand, scale, spans)
 
     changes = [
         (item["comp"], item["meta"], step_x, step_y)