Add AutoCAD MCP premium skill and backend APIs

Introduce the autocad-mcp-premium skill with workflow docs, examples, and references (.claude/skills/autocad-mcp-premium/*). Add PlanSpec/critique plumbing and engineering helpers (engineering/plan_spec.py, engineering/critique.py) plus tests and a smoke script. Extend backend API (backends/base.py) with corner operations and premium meta-tools (trim/extend/fillet/chamfer, drawing_plan, drawing_critique, point_from_snap, construction_xline/clear, drawing_apply_iso_layers, dimension_auto, entity_select_smart) and implement COM backend corner ops (backends/com_backend.py) with placeholders for meta-tools. Update CLAUDE.md to document the premium drawing rules and standard workflow. Misc: add examples, references, and tests for premium features, and minor server/backend adjustments.

engineering/layers.py

@@ -25,6 +25,49 @@ ENGINEERING_LAYERS: list[tuple[str, int, str, float, str]] = [
     ("CONSTRUCTION", 250, "Continuous", 0.05, "scratch / construction"),
 ]
 
+
+# P&ID standard layer set (de-facto, distilled from ISO 10628 + common practice).
+PID_LAYERS: list[tuple[str, int, str, float, str]] = [
+    ("0",                          7,  "Continuous", 0.25, "default"),
+    ("PROCESS-PIPING-MAIN",        1,  "Continuous", 0.70, "main process line (heavy)"),
+    ("PROCESS-PIPING-SECONDARY",   2,  "Continuous", 0.50, "secondary process line"),
+    ("PROCESS-EQUIPMENT",          7,  "Continuous", 0.50, "vessels / pumps / drums"),
+    ("PROCESS-VALVES",             3,  "Continuous", 0.35, "valves / fittings"),
+    ("INSTRUMENT-SYMBOL",          4,  "Continuous", 0.35, "instrument bubbles / FCFs"),
+    ("INSTRUMENT-LINE-SIGNAL",     4,  "DASHED",     0.18, "pneumatic / electrical signal"),
+    ("INSTRUMENT-TAG-TEXT",        7,  "Continuous", 0.25, "tag labels"),
+    ("ELECTRICAL-LINE",            6,  "DASHDOT",    0.18, "electrical line"),
+    ("UTILITY-LINE",               5,  "PHANTOM",    0.25, "utility (steam, water, air)"),
+    ("INSULATION-HATCH",           8,  "Continuous", 0.13, "insulation hatch"),
+    ("DIM",                        2,  "Continuous", 0.18, "dimensions"),
+    ("TEXT-NOTES",                 7,  "Continuous", 0.25, "free-form notes"),
+    ("TITLEBLOCK",                 7,  "Continuous", 0.50, "drawing border + title"),
+    ("CONSTRUCTION",               250, "Continuous", 0.05, "scratch / construction"),
+]
+
+
+# ISO 13567-style layer naming kit (Agent2-Element6-Presentation2-Status1).
+# This is a *starter* set — extend as needed per discipline.
+ISO13567_LAYERS: list[tuple[str, int, str, float, str]] = [
+    ("0",            7,  "Continuous", 0.25, "default"),
+    ("M-GEOMET-E-N", 7,  "Continuous", 0.50, "Mechanical / geometry / edge / new"),
+    ("M-HIDDEN-E-N", 3,  "HIDDEN",     0.25, "Mechanical / hidden edge"),
+    ("M-CENTL-E-N",  1,  "CENTER",     0.18, "Mechanical / centerlines"),
+    ("M-PHANT-E-N",  6,  "PHANTOM",    0.18, "Mechanical / phantom"),
+    ("M-DIMEN-T-N",  2,  "Continuous", 0.18, "Mechanical / dimension text"),
+    ("M-TEXT-T-N",   7,  "Continuous", 0.25, "Mechanical / annotation text"),
+    ("M-HATCH-H-N",  8,  "Continuous", 0.13, "Mechanical / hatch"),
+    ("M-TITLE-T-N",  7,  "Continuous", 0.50, "Title block"),
+    ("M-CONST-E-N",  250, "Continuous", 0.05, "Construction (scratch)"),
+]
+
+
+LAYER_SET_REGISTRY: dict[str, list[tuple[str, int, str, float, str]]] = {
+    "mech": ENGINEERING_LAYERS,
+    "pid": PID_LAYERS,
+    "iso13567": ISO13567_LAYERS,
+}
+
 STANDARD_LINETYPES: list[str] = ["CENTER", "HIDDEN", "PHANTOM", "DASHED", "DASHDOT"]
 
 
@@ -51,6 +94,19 @@ async def ensure_standard_linetypes(backend: "AutoCADBackend") -> dict[str, str]
 
 async def ensure_engineering_layers(backend: "AutoCADBackend") -> dict[str, str]:
     """Idempotently create every layer in ENGINEERING_LAYERS via backend.layer_create."""
+    return await apply_layer_set(backend, "mech")
+
+
+async def apply_layer_set(
+    backend: "AutoCADBackend", standard: str = "mech",
+) -> dict[str, str]:
+    """Idempotently apply a named layer set ('mech', 'pid', 'iso13567')."""
+    layer_set = LAYER_SET_REGISTRY.get(standard)
+    if layer_set is None:
+        raise RuntimeError(
+            f"Unknown layer set '{standard}'. "
+            f"Choose one of: {sorted(LAYER_SET_REGISTRY)}"
+        )
     await ensure_standard_linetypes(backend)
 
     try:
@@ -60,7 +116,7 @@ async def ensure_engineering_layers(backend: "AutoCADBackend") -> dict[str, str]
         existing = set()
 
     results: dict[str, str] = {}
-    for name, color, linetype, lineweight, _desc in ENGINEERING_LAYERS:
+    for name, color, linetype, lineweight, _desc in layer_set:
         if name.lower() in existing:
             results[name] = "exists"
             continue