bench: matrix v5 adds mech_assembly; the correctness suite grows with the mechanical and sheet checks

The evidence for tracks B and G, in the shape tracks A and E used.

- benchmarks/tasks_v5.py: 18 tasks, DEFAULT_MATRIX = "v5"; v4, v3 and v2 stay
  addressable so an earlier report reproduces exactly rather than being only
  described. mech_assembly is roadmap criterion 3 - a flange-coupling sheet
  built from the part model and the sheet standard, through the code the
  tools call (apply_titleblock, draw_part/add_view/dimension_part,
  insert_std_part, extract_records -> draw_bom_table, add_balloon), gated on
  two numbers that cannot be negotiated: drawing_critique(focus=None) returns
  zero issues and the finalize score is at least 90 (it scores 100, 18/18 on
  the v5 matrix). The adapter returns the focuses that fired, so a
  regression names itself, and a test drops one balloon to prove the gate
  fails and names mech_bom_balloon_mismatch.
- Seven correctness checks (32 -> 39). mech_section_hatch_area is the one
  that cannot be faked: a sleeve of length 60, outside diameter 40 and bore
  20 cuts two faces totalling 1200 mm^2 exactly, read back out of the drawing
  through entity_measure. sheet_frame_iso5457_a3 pins the A3 frame (20,10 to
  410,287 inside the 420 x 297 trimmed sheet); mech_iso286_on_dimension pins
  40 H7 at +0.025/0 through the layout; std_part_iso4014_m12 pins s = 18 and
  k = 7.5 by value; mech_thread_unrepresented_is_caught is the seventh: a
  quality gate that never fires is not a gate.
- scripts/smoke_mech_com.py executed every new COM path once on AutoCAD 2026
  (25.1s): frame, title block, a sectioned shaft with 12 dimensions, an ISO
  4014 block with 1 ACADMCP_MECH chunk, a weld symbol, the parts list read off
  the drawing, a linked balloon, an xref attached / listed / detached, a
  31687-byte .dwg (AC1032) through ActiveX SaveAs, critique 0 issues, exit 0,
  every scratch document closed. It retries RPC_E_CALL_REJECTED (measured:
  the first call after Documents.Add is refused) and tracks its documents by
  the document list, since SaveAs renames them.
- Defects the evidence found, each fixed with a test that fails on the old
  code:
  * ezdxf dimension_diameter put the text beyond the SECOND chord point;
    ActiveX AddDimDiametric puts it beyond the first (measured live: a d50
    from (x,170) to (x,220), leader 10, text at (x,160)). Headlessly every
    front-view diameter stood on its own chain dimension. ezdxf now follows
    ActiveX.
  * draw_part's anchor goes on MECH; ActiveX refuses entity.Layer on a
    missing layer (measured -0x7ffdfff7 'Key not found'). draw.py ensures
    every target layer before the first entity.
  * bom.extract_records filtered on INSERT; ActiveX names it BLOCKREFERENCE
    (ObjectName AcDbBlockReference) - the live parts list was empty.
  * COM _entity_info reported no dimension text_position: ModelSpace.Item
    narrows to IAcadEntity, which has no TextPosition (measured
    AttributeError); read through _com_unnarrow (TextPosition measured on
    AcDbDiametricDimension, WCS). dim_overlap compared bbox centres and a
    diameter collided with its own bore.
  * pid graph raised KeyError 'start' mid-critique on a LINE whose point read
    AutoCAD refused while busy; such a line is left out.
  * the validator read "ISO 4014 - M12x60" as fake dimension text.
- The published A/B report is re-run over the grown suite rather than
  re-typed (26/39 -> 39/39, 13 fixed, 0 regressed), check_doc_numbers derives
  the task count from the v5 matrix, the token table is remeasured with a
  TOOL_PACKS=core,mech row (193 tools / 61,673 tokens), and the README's
  collected-tests figure is retaken (3990).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

engineering/validator.py

@@ -27,6 +27,22 @@ DIMENSION_LIKE_TEXT = re.compile(
     re.IGNORECASE,
 )
 
+# A standard-part designation (ISO 4014 - M12x60, DIN 912 - M8x20) names a
+# part, it does not measure one: the "12x60" in it is the thread and the
+# nominal length the standard's designation grammar spells that way. A parts
+# list drawn as text carries one per row, so the designation is taken out
+# before DIMENSION_LIKE_TEXT looks - a hand-typed "Ø78" beside it still flags.
+STANDARD_DESIGNATION = re.compile(
+    r"\b(?:ISO|DIN|EN)\s*\d+(?:-\d+)?\s*-\s*M\d+(?:\.\d+)?(?:\s*[x×]\s*\d+(?:\.\d+)?)?",
+    re.IGNORECASE,
+)
+
+
+def looks_like_dimension(text: str) -> bool:
+    """Is this TEXT/MTEXT content masquerading as a dimension?"""
+    return bool(DIMENSION_LIKE_TEXT.search(STANDARD_DESIGNATION.sub(" ", text or "")))
+
+
 # R27 — match SPUR / HELICAL as whole words (not substrings of e.g.
 # "SPURIOUS") when checking title/helix consistency.
 _SPUR_RE = re.compile(r"\bSPUR\b", re.IGNORECASE)
@@ -92,7 +108,7 @@ class DrawingValidator:
                 e
                 for e in ents
                 if e.type in ("TEXT", "MTEXT")
-                and DIMENSION_LIKE_TEXT.search(getattr(e, "properties", {}).get("text", "") or "")
+                and looks_like_dimension(getattr(e, "properties", {}).get("text", "") or "")
             ]
             real_dims = [e for e in ents if e.type in REAL_DIMENSION_TYPES]
             if text_likes: