fix(task-14): a border INSERT is not a port, and a turned symbol's box is its geometry

Two verified blocking findings on pid_graph.

A foreign block's inferred ports were any line end within tolerance of
its drawn box *or strictly inside it*. A sheet border or title block is
an INSERT too, and its box encloses the whole drawing, so every end that
missed a port attached to the border instead of becoming the junction
or dangling end the tool exists to report: on a border sheet the plan's
own small P&ID read back with no junction, no dangling end and its open
signal line "connected" to A3_BORDER. The test is the boundary again, as
spec 9.2 step 3 says (within tolerance of the block's bounding-box
boundary); overshoot into a body is the tolerance's business. The
nearest-insertion tie-break stays for two boundaries that share an end.

The COM engine's `geometry_bbox` carried each definition member's own
axis-aligned box through the INSERT corner by corner, which is exact at
a right-angle rotation and too large everywhere else: a 45-degree-turned
circle of radius 5 read as 7.07, a diagonal line stood upright read 7.07
wide, and the two engines disagreed on the same drawing with no marker.
Off a right angle the member's real geometry is now measured - a LINE,
POINT and straight polyline by their vertices, a CIRCLE by the
closed-form extents of the scaled-and-turned ellipse, an ARC and a
bulged polyline by their ends and the quadrant points the sweep passes
(uniform scale, reflection reversing the sense) - and cross-checked
against ezdxf's `virtual_entities` extents at 37 and 45 degrees, scaled
and mirrored. A member that cannot be measured (text, hatch, a nested
reference, an elliptical arc) is still carried by its corners and the
box then says `approximate: true`; the graph takes the tighter wall of
that box and the attribute-inclusive `bounding_box`, both of which hold
the drawn geometry.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

backends/com_backend.py

@@ -348,16 +348,113 @@ def _com_bulges(entity, coords, closed: bool, length) -> list[float]:
     return [_com_bulge(entity, i) for i in range(count)]
 
 
+def _is_right_angle(rotation: float) -> bool:
+    """True when ``rotation`` (radians) is a multiple of a quarter turn."""
+    quarter = rotation / (math.pi / 2.0)
+    return abs(quarter - round(quarter)) <= 1e-9
+
+
+def _arc_extent_points(cx, cy, radius, start, end):
+    """The points that bound a counter-clockwise circular arc: its two ends
+    and every quadrant point (0, 90, 180, 270 degrees) the sweep passes."""
+    sweep = (end - start) % (2.0 * math.pi)
+    pts = [
+        (cx + radius * math.cos(start), cy + radius * math.sin(start)),
+        (cx + radius * math.cos(end), cy + radius * math.sin(end)),
+    ]
+    for q in range(4):
+        angle = q * math.pi / 2.0
+        if (angle - start) % (2.0 * math.pi) <= sweep:
+            pts.append((cx + radius * math.cos(angle), cy + radius * math.sin(angle)))
+    return pts
+
+
+def _com_member_extent_points(member, xform, sx, sy, rotation):
+    """WCS points whose extents are exactly the transformed member's extents,
+    for the members a P&ID symbol is drawn from; None when the member's
+    geometry is not one this reads (text, hatch, spline, ellipse, a nested
+    reference) so the caller falls back to its box and says so.
+
+    A LINE, a POINT and a straight polyline are bounded by their vertices
+    under any affine map. A CIRCLE becomes an ellipse under an axis scale, and
+    its extents after a rotation are closed-form. An ARC and a bulged
+    polyline segment stay circular only under a uniform scale; a reflection
+    (``sx * sy < 0``) reverses their sense.
+    """
+    name = member.ObjectName
+    uniform = abs(abs(sx) - abs(sy)) <= 1e-12
+    mirrored = sx * sy < 0
+    if name == "AcDbLine":
+        s, e = member.StartPoint, member.EndPoint
+        return [xform(s[0], s[1]), xform(e[0], e[1])]
+    if name == "AcDbPoint":
+        c = member.Coordinates
+        return [xform(c[0], c[1])]
+    if name == "AcDbCircle":
+        c = member.Center
+        r = float(member.Radius)
+        cx, cy = xform(c[0], c[1])
+        a, b = r * abs(sx), r * abs(sy)
+        cos_r, sin_r = math.cos(rotation), math.sin(rotation)
+        hx = math.hypot(a * cos_r, b * sin_r)
+        hy = math.hypot(a * sin_r, b * cos_r)
+        return [(cx - hx, cy - hy), (cx + hx, cy + hy)]
+    if name == "AcDbArc":
+        if not uniform:
+            return None
+        c = member.Center
+        r = float(member.Radius)
+        cx, cy = xform(c[0], c[1])
+        ends = []
+        for angle in (float(member.StartAngle), float(member.EndAngle)):
+            px, py = xform(c[0] + r * math.cos(angle), c[1] + r * math.sin(angle))
+            ends.append(math.atan2(py - cy, px - cx))
+        if mirrored:
+            ends.reverse()
+        return _arc_extent_points(cx, cy, r * abs(sx), ends[0], ends[1])
+    if name in _COM_LWPOLYLINE_NAMES:
+        coords = list(member.Coordinates)
+        closed = bool(member.Closed)
+        bulges = _com_bulges(member, coords, closed, member.Length)
+        pts = [xform(coords[i], coords[i + 1]) for i in range(0, len(coords) - 1, 2)]
+        if not any(bulges):
+            return pts
+        if not uniform:
+            return None
+        from ezdxf.math import Vec2, bulge_to_arc
+
+        segments = list(zip(pts, pts[1:], bulges, strict=False))
+        if closed and len(pts) > 1:
+            segments.append((pts[-1], pts[0], bulges[len(pts) - 1]))
+        out = list(pts)
+        for a, b, bulge in segments:
+            if not bulge or math.dist(a, b) < 1e-12:
+                continue
+            centre, start, end, radius = bulge_to_arc(
+                Vec2(a), Vec2(b), -bulge if mirrored else bulge
+            )
+            out.extend(_arc_extent_points(centre.x, centre.y, radius, start, end))
+        return out
+    return None
+
+
 def _com_geometry_bbox(entity) -> dict | None:
     """WCS extents of a block reference's *drawn* geometry, attributes excluded.
 
     ``GetBoundingBox`` on an INSERT takes its ATTRIBs with it, so a TAG lettered
     above a valve pushes the box past the body — a line ending on the body's
     real edge then lies *inside* the box. The definition's members are read in
-    block space (skipping ``AcDbAttributeDefinition``), each member's box is
+    block space (skipping ``AcDbAttributeDefinition``) and carried through the
-    carried through the INSERT (origin, scale, rotation) corner by corner, and
+    INSERT (origin, scale, rotation).
-    the extents of those corners is the answer. None when there is nothing
+
-    drawn or ActiveX refuses any step — the caller then omits the key.
+    At a right-angle rotation (the P&ID case) each member's own box maps to
+    an axis-aligned box, so carrying its corners is exact. Off a right angle
+    the box of a rotated box is too large — a 45-degree-turned circle of
+    radius 5 would read as 7.07 — so each member's real geometry is measured
+    (`_com_member_extent_points`); a member that cannot be, or refuses, is
+    carried by its corners and the result is marked ``approximate: True`` so
+    no reader mistakes it for the extents the ezdxf engine reports. None when
+    there is nothing drawn or ActiveX refuses — the caller then omits the key.
     """
     try:
         try:
@@ -373,24 +470,46 @@ def _com_geometry_bbox(entity) -> dict | None:
         sx, sy = float(entity.XScaleFactor), float(entity.YScaleFactor)
         rot = float(entity.Rotation)
         cos_r, sin_r = math.cos(rot), math.sin(rot)
+        right_angle = _is_right_angle(rot)
+
+        def xform(bx, by):
+            lx = (float(bx) - float(origin[0])) * sx
+            ly = (float(by) - float(origin[1])) * sy
+            return (
+                float(ins[0]) + lx * cos_r - ly * sin_r,
+                float(ins[1]) + lx * sin_r + ly * cos_r,
+            )
+
         xs: list[float] = []
         ys: list[float] = []
+        approximate = False
         for i in range(blk.Count):
             member = blk.Item(i)
             if member.ObjectName == "AcDbAttributeDefinition":
                 continue
+            pts = None
+            if not right_angle:
+                try:
+                    pts = _com_member_extent_points(member, xform, sx, sy, rot)
+                except Exception as exc:
+                    log.debug("exact extents of block member failed: %s", exc)
+                    pts = None
+            if pts is None:
                 try:
                     lo, hi = member.GetBoundingBox()
                 except Exception:
                     continue
-            for bx, by in ((lo[0], lo[1]), (hi[0], lo[1]), (lo[0], hi[1]), (hi[0], hi[1])):
+                corners = ((lo[0], lo[1]), (hi[0], lo[1]), (lo[0], hi[1]), (hi[0], hi[1]))
-                lx = (float(bx) - float(origin[0])) * sx
+                pts = [xform(bx, by) for bx, by in corners]
-                ly = (float(by) - float(origin[1])) * sy
+                approximate = approximate or not right_angle
-                xs.append(float(ins[0]) + lx * cos_r - ly * sin_r)
+            xs.extend(x for x, _ in pts)
-                ys.append(float(ins[1]) + lx * sin_r + ly * cos_r)
+            ys.extend(y for _, y in pts)
         if not xs:
             return None
-        return {"min": [min(xs), min(ys)], "max": [max(xs), max(ys)]}
+        box = {"min": [min(xs), min(ys)], "max": [max(xs), max(ys)]}
+        if approximate:
+            box["approximate"] = True
+        return box
     except Exception as exc:
         log.debug("geometry bbox failed for block reference: %s", exc)
         return None

engineering/pid/graph.py

@@ -263,23 +263,51 @@ def _bbox(info: EntityInfo):
     edge on that side lies *inside* the box. Both engines report
     ``geometry_bbox`` (attributes excluded) for an INSERT that draws anything;
     the attribute-inclusive box is the fallback for a reader that lacks it.
+
+    An engine may mark ``geometry_bbox`` ``approximate`` (the COM engine does
+    for an INSERT rotated off a right angle whose members it cannot measure
+    exactly): the box then encloses the drawn geometry but may overshoot it,
+    and a line ending on the body's true edge would sit *inside* that box
+    and dangle. The drawn geometry lies inside the attribute-inclusive box
+    too, so the tighter wall of the two is taken on every side.
     """
-    bb = info.properties.get("geometry_bbox") or info.properties.get("bounding_box")
+    geometry = info.properties.get("geometry_bbox")
-    if not bb:
+    outer = info.properties.get("bounding_box")
+    boxes = [
+        (float(bb["min"][0]), float(bb["min"][1]), float(bb["max"][0]), float(bb["max"][1]))
+        for bb in (geometry, outer)
+        if bb
+    ]
+    if not boxes:
         return None
-    return (float(bb["min"][0]), float(bb["min"][1]), float(bb["max"][0]), float(bb["max"][1]))
+    if geometry and outer and geometry.get("approximate"):
+        return (
+            max(boxes[0][0], boxes[1][0]),
+            max(boxes[0][1], boxes[1][1]),
+            min(boxes[0][2], boxes[1][2]),
+            min(boxes[0][3], boxes[1][3]),
+        )
+    return boxes[0]
 
 
-def _touches_bbox(p, bbox, tolerance) -> bool:
+def _on_bbox_boundary(p, bbox, tolerance) -> bool:
-    """Within ``tolerance`` of the box's boundary, or strictly inside it.
+    """Within ``tolerance`` of the box's boundary (spec §9.2 step 3).
 
-    A line drawn into the symbol is a connection just as one that stops on
+    The boundary, not the interior: a foreign block's box is only a proxy for
-    its edge is: foreign P&IDs overshoot into the body as often as they meet
+    where its ports are, and its edges are the only place a port can be. An
-    it, and a box tested on its boundary alone called those ends dangling.
+    end strictly inside was once accepted as "drawn into the body" — but a
+    sheet border or title block is an INSERT too, its box encloses the whole
+    drawing, and every end that missed a port then attached to the border
+    instead of becoming the junction or dangling end the tool exists to
+    report. Overshoot into a body is the tolerance's business.
     """
     x, y = p
     xmin, ymin, xmax, ymax = bbox
-    return xmin - tolerance <= x <= xmax + tolerance and ymin - tolerance <= y <= ymax + tolerance
+    inside_x = xmin - tolerance <= x <= xmax + tolerance
+    inside_y = ymin - tolerance <= y <= ymax + tolerance
+    near_vertical = min(abs(x - xmin), abs(x - xmax)) <= tolerance and inside_y
+    near_horizontal = min(abs(y - ymin), abs(y - ymax)) <= tolerance and inside_x
+    return near_vertical or near_horizontal
 
 
 async def _collect(backend: AutoCADBackend, scope: str) -> list[tuple[EntityInfo, str]]:
@@ -461,9 +489,9 @@ async def build_graph(
         return edge.vertices[0] if end == "from" else edge.vertices[-1]
 
     def _attach(edge: _Edge, end: str) -> dict | None:
-        """``{node, port}`` when this end sits on a port, or on or inside a
+        """``{node, port}`` when this end sits on a port, or on the boundary of
-        foreign block's drawn box; None otherwise. Only a successful match has
+        a foreign block's drawn box; None otherwise. Only a successful match
-        side effects."""
+        has side effects."""
         x, y = _end(edge, end)
         for node_id, pname, cx, cy, r in radial_ports:
             if abs(math.hypot(x - cx, y - cy) - r) <= tolerance:
@@ -477,15 +505,15 @@ async def build_graph(
             _, (_kind, node_id, pname) = best
             nodes[node_id].ports[pname]["edges"].append(edge.id)
             return {"node": node_id, "port": pname}
-        # Several foreign boxes can hold the same end (a valve drawn inside a
+        # Two foreign boundaries can share the end (a valve drawn flush with
-        # vessel's outline, a nested detail); the one inserted nearest wins.
+        # a vessel's outline, a nested detail); the one inserted nearest wins.
         node = min(
             (
                 n
                 for n in list(nodes.values()) + list(candidates.values())
                 if n.source in ("heuristic", "inferred")
                 and n.bbox
-                and _touches_bbox((x, y), n.bbox, tolerance)
+                and _on_bbox_boundary((x, y), n.bbox, tolerance)
             ),
             key=lambda n: math.hypot(x - n.x, y - n.y),
             default=None,

tests/test_com_backend.py

@@ -604,3 +604,171 @@ def test_com_geometry_bbox_is_omitted_when_the_block_draws_nothing_or_activex_re
     assert _com_geometry_bbox(ent) is None
     props = _entity_info(ent).properties
     assert "geometry_bbox" not in props and props["rotation_deg"] == 0.0
+
+
+# ── geometry_bbox off a right angle: the geometry, not the box of a box ──────
+#
+# Rotating a member's axis-aligned box and taking the extents of the corners
+# is exact only at multiples of 90 degrees. A circle of radius 5 turned 45
+# degrees is still x in [-5, 5]; its box's corners reach 7.07. The ezdxf
+# engine measures the real geometry, so the live engine must too — or say
+# that it could not.
+
+
+def _circle(cx, cy, r):
+    return _Entity(
+        "AcDbCircle",
+        Center=(cx, cy, 0.0),
+        Radius=r,
+        GetBoundingBox=lambda: ((cx - r, cy - r, 0.0), (cx + r, cy + r, 0.0)),
+    )
+
+
+def _line(x0, y0, x1, y1):
+    return _Entity(
+        "AcDbLine",
+        StartPoint=(x0, y0, 0.0),
+        EndPoint=(x1, y1, 0.0),
+        GetBoundingBox=lambda: ((min(x0, x1), min(y0, y1), 0.0), (max(x0, x1), max(y0, y1), 0.0)),
+    )
+
+
+def _arc(cx, cy, r, start_deg, end_deg):
+    import math
+
+    return _Entity(
+        "AcDbArc",
+        Center=(cx, cy, 0.0),
+        Radius=r,
+        StartAngle=math.radians(start_deg),
+        EndAngle=math.radians(end_deg),
+        GetBoundingBox=lambda: ((cx - r, cy - r, 0.0), (cx + r, cy + r, 0.0)),
+    )
+
+
+def _polyline(points, bulges, closed=False):
+    import math
+
+    coords = [c for p in points for c in p]
+    chord = sum(math.dist(a, b) for a, b in zip(points, points[1:], strict=False))
+    if closed:
+        chord += math.dist(points[-1], points[0])
+    length = chord + (1.0 if any(bulges) else 0.0)  # "longer than its chord" is all that matters
+    xs = [p[0] for p in points]
+    ys = [p[1] for p in points]
+    return _Entity(
+        "AcDbPolyline",
+        Coordinates=coords,
+        Closed=closed,
+        Length=length,
+        GetBulge=lambda i: bulges[i],
+        GetBoundingBox=lambda: ((min(xs), min(ys), 0.0), (max(xs), max(ys), 0.0)),
+    )
+
+
+def test_com_geometry_bbox_of_a_rotated_circle_and_diagonal_line_is_exact():
+    import math
+
+    from backends.com_backend import _com_geometry_bbox
+
+    ent = _blockref(
+        "PUMP_C",
+        {"PUMP_C": _Block([_circle(0.0, 0.0, 5.0)])},
+        insertion=(100.0, 100.0, 0.0),
+        rotation=math.radians(45.0),
+    )
+    box = _com_geometry_bbox(ent)
+    assert box["min"] == pytest.approx([95.0, 95.0]) and box["max"] == pytest.approx([105.0, 105.0])
+    assert "approximate" not in box
+    # a diagonal line turned 45 degrees stands upright: x is exactly 0
+    ent = _blockref(
+        "DIAG", {"DIAG": _Block([_line(0.0, 0.0, 10.0, 10.0)])}, rotation=math.radians(45.0)
+    )
+    box = _com_geometry_bbox(ent)
+    assert box["min"] == pytest.approx([0.0, 0.0], abs=1e-9)
+    assert box["max"] == pytest.approx([0.0, math.sqrt(200.0)], abs=1e-9)
+    assert "approximate" not in box
+
+
+@pytest.mark.parametrize(
+    ("rotation_deg", "sx", "sy"),
+    [(37.0, 1.0, 1.0), (45.0, 1.5, 1.5), (-120.0, 1.0, -1.0), (37.0, 2.0, -2.0)],
+)
+def test_com_geometry_bbox_off_a_right_angle_matches_the_ezdxf_engine(rotation_deg, sx, sy):
+    """Same block, same INSERT, both engines: a circle, an arc, a bulged
+    polyline and a diagonal line, turned and scaled and mirrored."""
+    import math
+
+    import ezdxf
+    from ezdxf import bbox as _bbox
+
+    from backends.com_backend import _com_geometry_bbox
+
+    doc = ezdxf.new()
+    blk = doc.blocks.new("MIXED")
+    blk.add_circle((3.0, 0.0), 5.0)
+    blk.add_arc((0.0, 8.0), 4.0, 200.0, 330.0)
+    blk.add_lwpolyline([(-6, -6, 0.0), (0, -6, 0.8), (0, -12, 0.0)], format="xyb")
+    blk.add_line((-2.0, 1.0), (7.0, 9.0))
+    blk.add_attdef("TAG", insert=(0, 15), text="", dxfattribs={"height": 2.5})
+    ref = doc.modelspace().add_blockref(
+        "MIXED",
+        (50.0, 20.0),
+        dxfattribs={"rotation": rotation_deg, "xscale": sx, "yscale": sy},
+    )
+    expected = _bbox.extents(
+        e for e in ref.virtual_entities() if e.dxftype() not in ("ATTRIB", "ATTDEF")
+    )
+
+    members = [
+        _circle(3.0, 0.0, 5.0),
+        _arc(0.0, 8.0, 4.0, 200.0, 330.0),
+        _polyline([(-6.0, -6.0), (0.0, -6.0), (0.0, -12.0)], [0.0, 0.8, 0.0]),
+        _line(-2.0, 1.0, 7.0, 9.0),
+        _Entity(
+            "AcDbAttributeDefinition", GetBoundingBox=lambda: ((0.0, 15.0, 0.0), (8.0, 17.5, 0.0))
+        ),
+    ]
+    ent = _blockref(
+        "MIXED",
+        {"MIXED": _Block(members)},
+        insertion=(50.0, 20.0, 0.0),
+        sx=sx,
+        sy=sy,
+        rotation=math.radians(rotation_deg),
+    )
+    box = _com_geometry_bbox(ent)
+    assert "approximate" not in box
+    # ezdxf flattens the curves (default 0.01), so agreement is to that
+    assert box["min"] == pytest.approx([expected.extmin.x, expected.extmin.y], abs=0.02)
+    assert box["max"] == pytest.approx([expected.extmax.x, expected.extmax.y], abs=0.02)
+
+
+def test_com_geometry_bbox_is_marked_approximate_when_a_rotated_member_cannot_be_measured():
+    import math
+
+    from backends.com_backend import _com_geometry_bbox, _entity_info
+
+    hatch = _Entity("AcDbHatch", GetBoundingBox=lambda: ((-5.0, -5.0, 0.0), (5.0, 5.0, 0.0)))
+    blocks = {"FILLED": _Block([_circle(0.0, 0.0, 5.0), hatch])}
+    # at a right angle the corners are exact — no marker, no geometry reads
+    ent = _blockref("FILLED", blocks, insertion=(100.0, 100.0, 0.0), rotation=math.pi)
+    box = _com_geometry_bbox(ent)
+    assert box == {"min": [95.0, 95.0], "max": [105.0, 105.0]}
+    # off one, the hatch is carried by its corners and the box says so
+    ent = _blockref("FILLED", blocks, insertion=(100.0, 100.0, 0.0), rotation=math.radians(45.0))
+    props = _entity_info(ent).properties
+    box = props["geometry_bbox"]
+    assert box["approximate"] is True
+    half = 5.0 * math.sqrt(2.0)
+    assert box["min"] == pytest.approx([100.0 - half, 100.0 - half])
+    assert box["max"] == pytest.approx([100.0 + half, 100.0 + half])
+    # a non-uniformly scaled arc is an elliptical arc: not measured, said so
+    ent = _blockref(
+        "ARC",
+        {"ARC": _Block([_arc(0.0, 0.0, 4.0, 0.0, 90.0)])},
+        sx=2.0,
+        sy=1.0,
+        rotation=math.radians(30.0),
+    )
+    assert _com_geometry_bbox(ent)["approximate"] is True

tests/test_pid_graph.py

@@ -185,22 +185,94 @@ async def test_a_foreign_vessel_takes_lines_on_every_edge_regardless_of_where_it
     assert {(d["edge"], d["end"]) for d in graph["dangling"]} == {(top, "from"), (side, "from")}
 
 
-async def test_a_line_drawn_into_a_foreign_body_attaches_to_the_nearest_block(backend):
+async def test_a_line_drawn_into_a_foreign_body_is_dangling_unless_tolerance_reaches_the_edge(
-    """An end strictly inside the drawn symbol is a connection, and when two
+    backend,
-    foreign boxes hold it the one inserted nearest wins."""
+):
+    """Spec §9.2 step 3: a foreign port is an end within ``tolerance`` of the
+    block's bounding-box *boundary*. The interior is not a port — a border
+    INSERT's interior is the whole sheet."""
+    small = backend._doc.blocks.new(name="GATE_VALVE")
+    small.add_lwpolyline([(-4, -2), (4, -2), (4, 2), (-4, 2)], close=True)
+    valve = (await backend.block_insert("GATE_VALVE", 20, 0, attributes={"TAG": "HV-2"})).handle
+    # body x in [16, 24]; the line overshoots 2 mm into it
+    line = (await backend.entity_create_line(60, 0, 22, 0, layer="PROCESS-PIPING-MAIN")).handle
+    graph = await build_graph(backend, tolerance=0.5)
+    edge = next(e for e in graph["edges"] if e["id"] == line)
+    assert edge["to"] is None
+    assert {(d["edge"], d["end"]) for d in graph["dangling"]} == {(line, "from"), (line, "to")}
+    assert next(n for n in graph["nodes"] if n["id"] == valve)["ports"] == {}
+    graph = await build_graph(backend, tolerance=2.0)
+    edge = next(e for e in graph["edges"] if e["id"] == line)
+    assert edge["to"] == {"node": valve, "port": "p1"}
+    assert {(d["edge"], d["end"]) for d in graph["dangling"]} == {(line, "from")}
+
+
+async def test_two_foreign_boundaries_sharing_an_end_go_to_the_nearest_insertion(backend):
     big = backend._doc.blocks.new(name="VESSEL_BIG")
     big.add_lwpolyline([(-30, -30), (30, -30), (30, 30), (-30, 30)], close=True)
     small = backend._doc.blocks.new(name="GATE_VALVE")
     small.add_lwpolyline([(-4, -2), (4, -2), (4, 2), (-4, 2)], close=True)
     vessel = (await backend.block_insert("VESSEL_BIG", 0, 0, attributes={"TAG": "V-2"})).handle
-    valve = (await backend.block_insert("GATE_VALVE", 20, 0, attributes={"TAG": "HV-2"})).handle
+    # the valve sits flush with the vessel's right wall: both boundaries hold (30, 0)
-    line = (await backend.entity_create_line(60, 0, 22, 0, layer="PROCESS-PIPING-MAIN")).handle
+    valve = (await backend.block_insert("GATE_VALVE", 26, 0, attributes={"TAG": "HV-2"})).handle
+    line = (await backend.entity_create_line(60, 0, 30, 0, layer="PROCESS-PIPING-MAIN")).handle
     graph = await build_graph(backend)
     edge = next(e for e in graph["edges"] if e["id"] == line)
-    assert edge["to"]["node"] == valve
+    assert edge["to"] == {"node": valve, "port": "p1"}
     assert next(n for n in graph["nodes"] if n["id"] == vessel)["ports"] == {}
 
 
+async def test_a_sheet_border_insert_never_swallows_junctions_or_dangling_ends(backend):
+    """The border is an INSERT whose box encloses the whole sheet. Accepting
+    ends strictly inside a foreign box made every end that missed a port a
+    port of the border: no junction, no dangling end, the signal line
+    'connected' to A3_BORDER."""
+    border = backend._doc.blocks.new(name="A3_BORDER")
+    border.add_lwpolyline([(0, 0), (420, 0), (420, 297), (0, 297)], close=True)
+    sheet = (await backend.block_insert("A3_BORDER", 0, 0)).handle
+    ids = await _small_pid(backend)
+    branch = await draw_line(
+        backend, {"x": 130, "y": 111}, {"x": 130, "y": 60}, line_class="process_minor"
+    )
+    graph = await build_graph(backend)
+    assert graph["unclassified"] == [{"handle": sheet, "block_name": "A3_BORDER"}]
+    assert sheet not in {n["id"] for n in graph["nodes"]}
+    assert [(j["id"], j["x"], j["y"]) for j in graph["junctions"]] == [("J1", 130.0, 111.0)]
+    assert set(graph["junctions"][0]["edges"]) == {branch["handle"], ids["l1"]["handle"]}
+    dangling = {(d["edge"], d["end"]) for d in graph["dangling"]}
+    assert dangling == {(ids["sig"]["handle"], "to"), (branch["handle"], "to")}
+    assert graph["stats"]["dangling"] == 2 and graph["stats"]["unclassified"] == 1
+    edges = {e["id"]: e for e in graph["edges"]}
+    assert edges[ids["sig"]["handle"]]["to"] is None
+    assert edges[branch["handle"]]["from"] == {"junction": "J1"}
+
+
+async def test_a_foreign_title_block_does_not_connect_the_valve_or_adopt_loose_lines(backend):
+    title = backend._doc.blocks.new(name="TITLEBLOCK_A3")
+    title.add_lwpolyline([(0, 0), (420, 0), (420, 297), (0, 297)], close=True)
+    title.add_lwpolyline([(240, 0), (240, 60), (420, 60)])
+    blk = backend._doc.blocks.new(name="GATE_VALVE")
+    blk.add_lwpolyline([(-4, -2), (-4, 2), (0, 0)], close=True)
+    blk.add_lwpolyline([(4, -2), (4, 2), (0, 0)], close=True)
+    blk.add_attdef("TAG", insert=(0, 4), text="", dxfattribs={"height": 2.5})
+    sheet = (await backend.block_insert("TITLEBLOCK_A3", 0, 0)).handle
+    valve = (await backend.block_insert("GATE_VALVE", 50, 50, attributes={"TAG": "HV-9"})).handle
+    left = (await backend.entity_create_line(10, 50, 46, 50, layer="PROCESS-PIPING-MAIN")).handle
+    right = (await backend.entity_create_line(54, 50, 120, 50, layer="PROCESS-PIPING-MAIN")).handle
+    loose = (await backend.entity_create_line(200, 200, 260, 200, layer="0")).handle
+    graph = await build_graph(backend)
+    edges = {e["id"]: e for e in graph["edges"]}
+    assert set(edges) == {left, right}
+    assert loose not in edges and "unknown" not in graph["stats"]["edges_by_class"]
+    assert edges[left]["to"] == {"node": valve, "port": "p1"}
+    assert edges[right]["from"] == {"node": valve, "port": "p2"}
+    assert edges[left]["from"] is None and edges[right]["to"] is None
+    assert {(d["edge"], d["end"]) for d in graph["dangling"]} == {(left, "from"), (right, "to")}
+    assert graph["stats"]["dangling"] == 2
+    assert graph["unclassified"] == [{"handle": sheet, "block_name": "TITLEBLOCK_A3"}]
+    assert {n["id"] for n in graph["nodes"]} == {valve}
+
+
 async def test_include_foreign_false_ignores_untagged_blocks(backend):
     blk = backend._doc.blocks.new(name="GATE_VALVE")
     blk.add_line((0, 0), (1, 0))
@@ -499,3 +571,38 @@ def test_com_polyline_bulges_are_read_only_when_length_says_an_arc_exists():
     curved, calls = fake((0.0, 0.0, 10.0, 0.0, 10.0, 10.0), 10 + 5 * math.pi, [0.0, 1.0, 0.0])
     assert _entity_info(curved).properties["bulges"] == [0.0, 1.0, 0.0]
     assert calls == [0, 1, 2]
+
+
+def test_an_approximate_geometry_bbox_is_tightened_by_the_attribute_inclusive_box():
+    """The COM engine marks a rotated INSERT's box ``approximate`` when a
+    member could only be carried by its corners: the box then overshoots the
+    body, and a line ending on the body's true edge would sit *inside* it and
+    dangle. The drawn geometry lies inside ``bounding_box`` too, so every
+    wall takes the tighter of the two; an exact box is used as it is."""
+    from backends.base import EntityInfo
+    from engineering.pid.graph import _bbox, _on_bbox_boundary
+
+    def info(**props):
+        return EntityInfo(
+            handle="1",
+            type="INSERT",
+            layer="0",
+            color=256,
+            linetype="ByLayer",
+            visible=True,
+            properties=props,
+        )
+
+    exact = {"min": [95.0, 95.0], "max": [105.0, 105.0]}
+    outer = {"min": [95.0, 95.0], "max": [105.0, 118.0]}  # the TAG above the body
+    assert _bbox(info(geometry_bbox=exact, bounding_box=outer)) == (95.0, 95.0, 105.0, 105.0)
+    loose = {"min": [92.93, 92.93], "max": [107.07, 107.07], "approximate": True}
+    assert _bbox(info(geometry_bbox=loose, bounding_box=outer)) == (95.0, 95.0, 105.0, 107.07)
+    assert _bbox(info(geometry_bbox=loose)) == (92.93, 92.93, 107.07, 107.07)
+    assert _bbox(info(bounding_box=outer)) == (95.0, 95.0, 105.0, 118.0)
+    assert _bbox(info()) is None
+    # a line ending on the body's true left edge attaches through the tightened box
+    assert _on_bbox_boundary(
+        (95.0, 100.0), _bbox(info(geometry_bbox=loose, bounding_box=outer)), 0.5
+    )
+    assert not _on_bbox_boundary((95.0, 100.0), _bbox(info(geometry_bbox=loose)), 0.5)