fix(task-8): actuators stack on the body's real top and every stem meets its glyph

Two authoring slips in the valve x actuator composition:

- The diaphragm actuator's stem stopped at y=4 while the dome's flat base
  sat at y=6, so the canonical control-valve symbol (PID_VALVE_*_DIAPHRAGM,
  9 catalogue entries) shipped with its dome floating 2 mm above the stem.
- Actuators were placed at a fixed y=4 regardless of the body, so on the
  needle body (top 5.6) the piston/motor/solenoid glyphs were drawn over
  the knob and the hand bar across the needle's stem; the stem line(0,0,0,4)
  also duplicated the needle's own axial line (and the butterfly disc).

Placement is now body-relative: `_body` reports `axis_top` (where its own
geometry on x=0 ends) and the stem runs from there to the glyph base at
`body_top + STEM_CLEARANCE`; the diaphragm dome's base is the stem top
(base + DIAPHRAGM_YOKE), and the FAIL attribute follows the glyph base.
The reference 8x4 bodies keep their published numbers (globe+diaphragm
signal at y=9.0, bbox top 9.0).

Tests: per-combination check that the stem starts at the body's derived
axis top, the glyph's lowest edge equals the stem top, the glyph clears
the body, and the signal port is the topmost edge; plus a catalogue-wide
no-duplicate-primitives gate. 33 combinations fail on the old geometry.
The plan's Step 3 snippet is synced with the fixed module.

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

tests/test_pid_symbols.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import json
 import math
 import re
 
@@ -208,7 +209,13 @@ def test_list_symbols_reports_variants_and_ports():
 
 # ── valves (Task 8) ──────────────────────────────────────────────────────────
 
-from engineering.pid.symbols_valves import ACTUATORS, VALVE_BODIES, build_valve  # noqa: E402
+from engineering.pid.symbols_valves import (  # noqa: E402
+    ACTUATORS,
+    NO_ACTUATOR,
+    STEM_CLEARANCE,
+    VALVE_BODIES,
+    build_valve,
+)
 
 
 def test_valve_bodies_and_actuators_enumerate():
@@ -247,3 +254,76 @@ def test_three_way_angle_and_relief_ports():
     assert {p.name: p.direction_deg for p in angle.ports} == {"in": 180.0, "out": 270.0}
     relief = build_valve("relief")
     assert {p.name: p.direction_deg for p in relief.ports} == {"in": 270.0, "out": 0.0}
+
+
+def _axis_top(primitives) -> float:
+    """Highest y at which a body's own geometry touches the x = 0 axis."""
+    ys = [0.0]
+    for p in primitives:
+        kind = p["type"]
+        if kind == "line" and p["x1"] == 0.0 == p["x2"]:
+            ys += [p["y1"], p["y2"]]
+        elif kind == "circle" and p["cx"] == 0.0:
+            ys.append(p["cy"] + p["r"])
+        elif kind == "arc" and p["cx"] == 0.0:
+            if (90.0 - p["start_deg"]) % 360.0 <= (p["end_deg"] - p["start_deg"]) % 360.0:
+                ys.append(p["cy"] + p["r"])
+        elif kind == "polyline":
+            pts = list(p["points"]) + ([p["points"][0]] if p["closed"] else [])
+            for (x1, y1), (x2, y2) in zip(pts, pts[1:], strict=False):
+                if x1 == 0.0 == x2:
+                    ys += [y1, y2]
+                elif min(x1, x2) <= 0.0 <= max(x1, x2):
+                    ys.append(y1 + (y2 - y1) * (0.0 - x1) / (x2 - x1))
+    return max(ys)
+
+
+def _actuated():
+    return [
+        (body, actuator)
+        for body in VALVE_BODIES
+        if body not in NO_ACTUATOR
+        for actuator in ACTUATORS
+        if actuator != "none"
+    ]
+
+
+@pytest.mark.parametrize("body,actuator", _actuated(), ids=lambda v: v)
+def test_actuator_glyph_is_connected_to_its_stem_and_clear_of_the_body(body, actuator):
+    bare = build_valve(body)
+    composed = build_valve(body, actuator)
+    extra = list(composed.primitives[len(bare.primitives) :])
+    assert composed.primitives[: len(bare.primitives)] == bare.primitives
+    stem, glyph = extra[0], extra[1:]
+    assert stem["type"] == "line" and stem["x1"] == 0.0 == stem["x2"]
+    stem_bottom, stem_top = sorted((stem["y1"], stem["y2"]))
+    # The stem starts where the body's own axial geometry ends — never
+    # coincident with a body line (butterfly disc, needle stem) or inside a
+    # body circle / dome.
+    assert stem_bottom == pytest.approx(_axis_top(bare.primitives))
+    # The glyph's lowest edge sits on the stem's top (no floating dome) ...
+    assert bbox_of(glyph)[1] == pytest.approx(stem_top)
+    # ... and the whole glyph is above the body, with the standard clearance.
+    assert bbox_of(glyph)[1] >= bare.bbox[3] + STEM_CLEARANCE - EPS
+    # The FAIL attribute sits beside the glyph, not on the body.
+    if actuator != "hand":
+        fail = next(a for a in composed.attdefs if a["tag"] == "FAIL")
+        assert fail["y"] > bare.bbox[3]
+    if actuator != "hand":
+        signal = next(p for p in composed.ports if p.name == "signal")
+        assert signal.y == pytest.approx(composed.bbox[3])
+
+
+def test_hand_actuator_has_no_fail_attribute_or_signal_port():
+    for body in VALVE_BODIES:
+        if body in NO_ACTUATOR:
+            continue
+        hand = build_valve(body, "hand")
+        assert all(a["tag"] != "FAIL" for a in hand.attdefs)
+        assert all(p.name != "signal" for p in hand.ports)
+
+
+@pytest.mark.parametrize("spec", all_specs(), ids=_ids())
+def test_no_duplicate_primitives(spec):
+    seen = [json.dumps(p, sort_keys=True) for p in spec.primitives]
+    assert len(seen) == len(set(seen)), "duplicate overlapping geometry inside the block"