fix(pid): existing line payloads are read tolerantly and crossings follow arcs, not chords

A foreign or hand-edited ACADMCP_PID payload (from: 'garbage', seq: True)
made the next pid_line_draw raise TypeError; payload_port_refs /
payload_seq now accept only well-formed values and a reader result never
raises. An existing polyline with a bulge was tested as its chord, so a
line through the arc reported crossings 0; flatten_bulges (pure, pinned
against ezdxf.math's flattening) feeds count_crossings on both engines.

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

engineering/pid/drawlines.py

@@ -13,6 +13,7 @@ from .lines import (
     PID_LINE_LAYERS,
     aim_points,
     count_crossings,
+    flatten_bulges,
     format_line_number,
     label_placement,
     marker_positions,
@@ -106,13 +107,57 @@ def _vertices(info) -> list[tuple[float, float]]:
     return [(float(p[0]), float(p[1])) for p in info.properties.get("points") or []]
 
 
+def _bulges(info, count: int) -> list[float]:
+    """Per-vertex bulges as the engine reports them (both engines put a
+    ``bulges`` list next to ``points``); straight when it reports none."""
+    raw = info.properties.get("bulges") or []
+    out = []
+    for value in raw[:count]:
+        try:
+            out.append(float(value or 0.0))
+        except (TypeError, ValueError):
+            out.append(0.0)
+    return out + [0.0] * (count - len(out))
+
+
+def payload_port_refs(payload) -> list[tuple[str, str]]:
+    """``(handle, port)`` for each well-formed ``from``/``to`` in a line payload.
+
+    A foreign or hand-edited payload can carry anything under those keys
+    (``"garbage"``, ``None``, a number); reading it used to raise
+    ``TypeError`` out of ``draw_line``. Reader results never raise: a
+    malformed end is simply not a reference.
+    """
+    refs = []
+    if not isinstance(payload, dict):
+        return refs
+    for key in ("from", "to"):
+        ref = payload.get(key)
+        if not isinstance(ref, dict):
+            continue
+        handle, port = ref.get("handle"), ref.get("port")
+        if isinstance(handle, str) and isinstance(port, str):
+            refs.append((handle, port))
+    return refs
+
+
+def payload_seq(payload) -> int | None:
+    """The payload's sequence number when it is a genuine int (``True`` is not)."""
+    if not isinstance(payload, dict):
+        return None
+    seq = payload.get("seq")
+    return seq if type(seq) is int else None
+
+
 async def existing_pid_lines(backend: AutoCADBackend) -> list[dict]:
     """Every LINE/polyline on a P&ID line layer, with its payload when it has one.
 
     Listed without a type filter: the two engines name a lightweight polyline
     differently (``_POLY_TYPES``), and a filter spelled for one of them is blind
     on the other — every auto-built number would restart at 1 and no crossing
-    or port reuse would ever be reported there.
+    or port reuse would ever be reported there. ``vertices`` are the raw
+    vertices; ``bulges`` (one per vertex, DXF convention) let the crossing test
+    follow an arc instead of its chord.
     """
     out = []
     offset = 0
@@ -124,7 +169,15 @@ async def existing_pid_lines(backend: AutoCADBackend) -> list[dict]:
             if info.layer.upper() not in PID_LINE_LAYERS:
                 continue
             payload = await read_payload(backend, info.handle) if info.type in _POLY_TYPES else None
-            out.append({"handle": info.handle, "vertices": _vertices(info), "payload": payload})
+            vertices = _vertices(info)
+            out.append(
+                {
+                    "handle": info.handle,
+                    "vertices": vertices,
+                    "bulges": _bulges(info, len(vertices)),
+                    "payload": payload,
+                }
+            )
         if len(page) < _PAGE:
             break
         offset += _PAGE
@@ -184,17 +237,16 @@ async def draw_line(
     path = route(s_point, s_dir, e_point, e_dir, stub=stub, mode=route_mode)
 
     existing = await existing_pid_lines(backend)
-    crossings = count_crossings(path, [ln["vertices"] for ln in existing])
+    crossings = count_crossings(
+        path, [flatten_bulges(ln["vertices"], ln["bulges"]) for ln in existing]
+    )
     used: set[tuple[str, str]] = set()
     max_seq = 0
     for ln in existing:
-        payload = ln["payload"] or {}
-        for key in ("from", "to"):
-            ref = payload.get(key)
-            if ref:
-                used.add((ref["handle"], ref["port"]))
-        if isinstance(payload.get("seq"), int):
-            max_seq = max(max_seq, payload["seq"])
+        used.update(payload_port_refs(ln["payload"]))
+        seq = payload_seq(ln["payload"])
+        if seq is not None:
+            max_seq = max(max_seq, seq)
     port_reuse = [
         {"handle": ep["handle"], "port": ep["port"]}
         for ep in (start, end)

engineering/pid/lines.py

@@ -238,6 +238,53 @@ def marker_positions(vertices, min_len: float = 15.0) -> list[tuple[float, float
     return out
 
 
+#: Max chord deviation (mm) when a bulged polyline edge is flattened for the
+#: crossing test — a tenth of the thinnest ISO 128 lineweight.
+FLATTEN_SAGITTA = 0.05
+
+
+def flatten_bulges(points, bulges, sagitta: float = FLATTEN_SAGITTA) -> list[Point]:
+    """The polyline as straight segments, every bulged edge replaced by chords
+    that deviate from the arc by at most ``sagitta``.
+
+    Same arc arithmetic as ``engineering/measure.py`` (sweep ``4·atan(bulge)``,
+    radius ``chord / 2·sin(|sweep|/2)``) and ``graph._point_segment_distance``
+    (centre on the chord's left normal, ``radius - sagitta`` carrying it across
+    the chord past a semicircle). Checked against ``ezdxf.math.bulge_to_arc``
+    + ``ConstructionArc.flattening`` in ``tests/test_pid_lines.py``: identical
+    vertex count and positions to 1e-12 for bulges 0.2 … 2.0 of either sign.
+    A straight edge (bulge 0) is passed through; ``bulges`` shorter than the
+    edge count is padded with zeros.
+    """
+    pts = [(float(x), float(y)) for x, y in points]
+    if len(pts) < 2:
+        return pts
+    out: list[Point] = []
+    for i, (a, b) in enumerate(zip(pts, pts[1:], strict=False)):
+        out.append(a)
+        bulge = float(bulges[i]) if i < len(bulges) and bulges[i] else 0.0
+        chord = _dist(a, b)
+        if abs(bulge) < 1e-12 or chord < 1e-12:
+            continue
+        theta = 4.0 * math.atan(bulge)  # signed sweep, radians
+        radius = chord / (2.0 * math.sin(abs(theta) / 2.0))
+        sag = abs(bulge) * chord / 2.0
+        nx, ny = -(b[1] - a[1]) / chord, (b[0] - a[0]) / chord  # left of a→b
+        offset = (radius - sag) * (1.0 if bulge > 0 else -1.0)
+        cx = (a[0] + b[0]) / 2.0 + offset * nx
+        cy = (a[1] + b[1]) / 2.0 + offset * ny
+        start = math.atan2(a[1] - cy, a[0] - cx)
+        if sagitta >= radius:
+            segments = 1
+        else:
+            segments = max(1, math.ceil(abs(theta) / (2.0 * math.acos(1.0 - sagitta / radius))))
+        for k in range(1, segments):
+            angle = start + theta * k / segments
+            out.append((cx + radius * math.cos(angle), cy + radius * math.sin(angle)))
+    out.append(pts[-1])
+    return out
+
+
 def _orient(a: Point, b: Point, c: Point) -> float:
     return (b[0] - a[0]) * (c[1] - a[1]) - (b[1] - a[1]) * (c[0] - a[0])