feat(pid): pid_from_spec — a whole P&ID in one transaction, graph and critique returned

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

scripts/render_readme_pid.py

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+"""Render the P&ID the README shows, using only the server's own tools.
+
+The sheet is ``EXAMPLE_SPEC`` from ``engineering/pid/spec.py`` -- the same
+document ``pid_from_spec`` draws in one transaction -- placed and routed
+through the same backend methods the MCP tools call, then rendered headlessly.
+If a symbol builder or the router regresses, the picture changes with it.
+
+Reproduce:
+
+    AUTOCAD_MCP_BACKEND=ezdxf uv run --frozen python scripts/render_readme_pid.py
+"""
+
+from __future__ import annotations
+
+import argparse
+import asyncio
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT))
+
+DEFAULT_OUTPUT = ROOT / "docs" / "assets" / "pid-showcase.png"
+
+
+async def render(output: Path) -> dict:
+    from backends.ezdxf_backend import EzdxfBackend
+    from engineering.layers import apply_layer_set
+    from engineering.pid.spec import EXAMPLE_SPEC, run_spec
+
+    backend = EzdxfBackend()
+    await backend.connect()
+    try:
+        await backend.drawing_new()
+        await apply_layer_set(backend, "pid")
+        result = await run_spec(backend, EXAMPLE_SPEC)
+        png = await backend.view_screenshot()
+        if not png:
+            raise RuntimeError("view_screenshot returned no PNG (is matplotlib installed?)")
+        output.parent.mkdir(parents=True, exist_ok=True)
+        output.write_bytes(png)
+        return {
+            "output": str(output),
+            "bytes": len(png),
+            "dangling": result["graph"]["stats"]["dangling"],
+            "critique": len(result["critique"]),
+        }
+    finally:
+        await backend.disconnect()
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--output", type=Path, default=DEFAULT_OUTPUT)
+    args = parser.parse_args()
+    print(asyncio.run(render(args.output)))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())