feat(pagesetup): page_setup_list/apply on both engines — the PDF's own /MediaBox is the evidence

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

engineering/standards/pdfinfo.py

@@ -0,0 +1,59 @@
+"""Read a PDF's page size back from the file — no dependency, no rendering.
+
+The evidence rule for page setup (spec §8.3): the sheet size a plot produced is
+what the PDF says it is, not what the layout was asked for. ``/MediaBox`` is the
+one PDF object that carries it. matplotlib and AutoCAD's DWG To PDF driver both
+write it in clear text; a PDF 1.5+ writer may put the page dictionary inside a
+FlateDecode object stream, so when the plain scan finds nothing every stream is
+inflated and searched. Anything else raises rather than guessing.
+"""
+
+from __future__ import annotations
+
+import re
+import zlib
+from pathlib import Path
+
+__all__ = ["PT_TO_MM", "read_mediabox"]
+
+#: PostScript points to millimetres.
+PT_TO_MM = 25.4 / 72.0
+
+_NUMBER = rb"([-+]?\d*\.?\d+)"
+_MEDIABOX_RE = re.compile(
+    rb"/MediaBox\s*\[\s*"
+    + _NUMBER
+    + rb"\s+"
+    + _NUMBER
+    + rb"\s+"
+    + _NUMBER
+    + rb"\s+"
+    + _NUMBER
+    + rb"\s*\]"
+)
+_STREAM_RE = re.compile(rb"stream\r?\n(.*?)\r?\nendstream", re.DOTALL)
+
+
+def read_mediabox(path: str) -> tuple[float, float]:
+    """Return the first page ``/MediaBox`` as ``(width_mm, height_mm)``.
+
+    Raises ``ValueError`` when the file is not a PDF or carries no MediaBox.
+    ``/Rotate`` is not applied: the box is reported as written.
+    """
+    data = Path(path).read_bytes()
+    if not data.startswith(b"%PDF"):
+        raise ValueError(f"read_mediabox: {path} is not a PDF (no %PDF header)")
+    match = _MEDIABOX_RE.search(data)
+    if match is None:
+        for stream in _STREAM_RE.finditer(data):
+            try:
+                inflated = zlib.decompress(stream.group(1))
+            except zlib.error:
+                continue
+            match = _MEDIABOX_RE.search(inflated)
+            if match is not None:
+                break
+    if match is None:
+        raise ValueError(f"read_mediabox: no /MediaBox found in {path}")
+    x0, y0, x1, y1 = (float(value) for value in match.groups())
+    return (round(abs(x1 - x0) * PT_TO_MM, 3), round(abs(y1 - y0) * PT_TO_MM, 3))