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

tests/test_pid_line_draw.py

@@ -424,3 +424,72 @@ async def test_dry_run_plans_the_same_bubble_exit_as_the_real_run(backend):
     drawn = await run_spec(backend, spec)
     edge = drawn["graph"]["edges"][0]
     assert edge["line_number"] is None, "signal lines from a spec are unnumbered too"
+
+
+# ── Track A hardening (track E wave 0, Task 7) ───────────────────────────────
+
+
+async def test_foreign_line_payloads_are_tolerated_not_raised(backend):
+    """A hand-edited payload with a non-dict ``from``, a ``None`` ``to`` and a
+    bool ``seq`` used to escape as ``TypeError: string indices must be
+    integers``; reader results never raise."""
+    poly = await backend.entity_create_polyline([[0, 0], [10, 0]], layer="PROCESS-PIPING-MAIN")
+    await write_payload(
+        backend,
+        poly.handle,
+        {"v": 1, "kind": "line", "seq": True, "from": "garbage", "to": None, "number": 7},
+    )
+    other = await backend.entity_create_polyline([[0, 5], [10, 5]], layer="PROCESS-PIPING-MAIN")
+    await write_payload(
+        backend,
+        other.handle,
+        {"v": 1, "kind": "line", "seq": "9", "from": {"handle": 3, "port": "x"}, "to": 4},
+    )
+    result = await draw_line(
+        backend, {"x": 0, "y": 50}, {"x": 50, "y": 50}, size="100", service="P"
+    )
+    assert result["line_number"] == "100-P-1", "neither True nor '9' counts as a sequence number"
+    assert result["port_reuse"] == []
+
+
+def test_payload_helpers_accept_only_well_formed_values():
+    from engineering.pid.drawlines import payload_port_refs, payload_seq
+
+    good = {"from": {"handle": "2A", "port": "discharge"}, "to": {"handle": "2B", "port": None}}
+    assert payload_port_refs(good) == [("2A", "discharge")]
+    assert payload_port_refs("garbage") == [] and payload_port_refs(None) == []
+    assert payload_port_refs({"from": "x", "to": 5}) == []
+    assert payload_seq({"seq": 7}) == 7
+    assert payload_seq({"seq": True}) is None and payload_seq({"seq": "9"}) is None
+    assert payload_seq({"seq": 7.0}) is None and payload_seq(None) is None
+
+
+async def test_crossings_follow_a_bulged_line_not_its_chord(backend):
+    """A foreign P&ID line with a semicircular jump (bulge -1 from (0,0) to
+    (100,0) bows to +Y, apex (50,50)): a vertical utility line at x=30 from
+    y=20 to y=60 crosses the arc once at y≈45.8 and its chord never."""
+    msp = backend._msp()
+    msp.add_lwpolyline(
+        [(0, 0, 0, 0, -1.0), (100, 0, 0, 0, 0)],
+        format="xyseb",
+        dxfattribs={"layer": "PROCESS-PIPING-MAIN"},
+    )
+    backend._mark_dirty()
+    lines = await existing_pid_lines(backend)
+    assert lines[0]["vertices"] == [(0.0, 0.0), (100.0, 0.0)]
+    assert lines[0]["bulges"] == [-1.0, 0.0]
+    result = await draw_line(backend, {"x": 30, "y": 20}, {"x": 30, "y": 60}, line_class="utility")
+    assert result["crossings"] == 1
+    below = await draw_line(backend, {"x": 70, "y": -20}, {"x": 70, "y": -60}, line_class="utility")
+    assert below["crossings"] == 0, "the chord side of the arc is empty"
+
+
+async def test_com_existing_lines_carry_bulges(monkeypatch):
+    payload = line_payload("process_major", "100-P-7", "100", "P", None, None, 7, None, None)
+    poly = _com_pid_polyline("3E", (0.0, 0.0, 100.0, 0.0), payload)
+    poly.Length = 157.0796  # a semicircle: longer than the 100 mm chord walk
+    poly.GetBulge = lambda index: -1.0 if index == 0 else 0.0
+    backend = _fake_com(monkeypatch, [poly])
+    lines = await existing_pid_lines(backend)
+    assert lines[0]["vertices"] == [(0.0, 0.0), (100.0, 0.0)]
+    assert lines[0]["bulges"] == [-1.0, 0.0]

tests/test_pid_lines.py

@@ -3,6 +3,8 @@
 
 from __future__ import annotations
 
+import math
+
 import pytest
 
 from engineering.pid.lines import (
@@ -176,3 +178,41 @@ def test_route_refuses_non_axis_port_directions_with_a_value_error():
     # Equivalent angles and engine float drift still resolve to the axis.
     assert route((0, 0), -360.0, (50, 0), 540.0) == [(0.0, 0.0), (50.0, 0.0)]
     assert route((0, 0), 1e-9, (50, 0), 180.0 - 1e-9) == [(0.0, 0.0), (50.0, 0.0)]
+
+
+# ── Track A hardening (track E wave 0, Task 7): bulge flattening ─────────────
+
+
+@pytest.mark.parametrize("bulge", [1.0, -1.0, 0.5, -0.3, 2.0, 0.2])
+def test_flatten_bulges_matches_ezdxf_flattening(bulge):
+    """Pinned against ezdxf's own arc flattening: same vertex count, same points."""
+    from ezdxf.math import ConstructionArc, Vec2, bulge_to_arc
+
+    from engineering.pid.lines import FLATTEN_SAGITTA, flatten_bulges
+
+    a, b = (0.0, 0.0), (10.0, 0.0)
+    mine = flatten_bulges([a, b], [bulge])
+    centre, start_rad, end_rad, radius = bulge_to_arc(Vec2(a), Vec2(b), bulge)
+    arc = ConstructionArc(
+        center=centre,
+        radius=radius,
+        start_angle=math.degrees(start_rad),
+        end_angle=math.degrees(end_rad),
+    )
+    reference = [(p.x, p.y) for p in arc.flattening(FLATTEN_SAGITTA)]
+    assert len(mine) == len(reference)
+    assert mine[0] == a and mine[-1] == b
+    assert all(math.hypot(p[0] - centre.x, p[1] - centre.y) == pytest.approx(radius) for p in mine)
+    assert mine[len(mine) // 2] == pytest.approx(reference[len(reference) // 2])
+
+
+def test_flatten_bulges_passes_straight_edges_through_and_pads_short_bulge_lists():
+    from engineering.pid.lines import flatten_bulges
+
+    pts = [(0.0, 0.0), (10.0, 0.0), (10.0, 10.0)]
+    assert flatten_bulges(pts, []) == pts
+    assert flatten_bulges(pts, [0.0, 0.0, 0.0]) == pts
+    flat = flatten_bulges(pts, [0.0, 1.0])
+    assert flat[0] == (0.0, 0.0) and flat[1] == (10.0, 0.0) and flat[-1] == (10.0, 10.0)
+    assert len(flat) > 3, "the second edge became a semicircle of chords"
+    assert flatten_bulges([(1.0, 1.0)], [1.0]) == [(1.0, 1.0)]