M12: model3d_render, a 3D annotation's PRC model drawn to a PNG

pdfcraft-annot reads a page's 3D annotations and the model each shows:
the /3DD stream, or the stream a /3DRef names (at most four deep, so a
cycle ends), decoded within 256 MB and typed PRC or U3D by /Subtype.
pdfcraft-engine exposes both on Document.

The automation tool model3d_render picks a page's Nth 3D model, parses
PRC with pdfcraft-prc, assembles and frames it with pdfcraft-prc-render
from a chosen direction (default an isometric-style view, Z up), and
returns the image as a PNG. U3D gives an error until a decoder lands.
parity misc.3d-view moves to partial.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SqmHYx8FiWM5PcsoiErgp9

parity/acrobat-features.toml

@@ -9896,11 +9896,11 @@ title = "View 3D (U3D/PRC) content"
 area = "N"
 tier = "P3"
 milestone = "M12"
-status = "planned"
+status = "partial"
 commands = []
-tools = []
-evidence = []
-notes = ""
+tools = ["model3d_render"]
+evidence = ["crates/automation/tests/it/model3d_render.rs::a_prc_model_is_drawn_over_the_background", "crates/annot/src/model3d/tests.rs::a_3dref_leads_to_the_stream_it_names", "crates/prc-render/tests/model.rs::a_synthetic_prc_renders_its_nearer_triangle_over_the_farther"]
+notes = "headless only: model3d_render draws a page's PRC model (through a /3DRef too) to a PNG, framed from a chosen direction, with headlight shading. Missing: the 3D view in the app (no activation, no navigation), U3D (an error), the annotation's /3DV views, lighting schemes and /RM render modes, materials and textures, compressed tessellation, picking, cross sections, the model tree, and measurements"
 
 [[feature]]
 id = "misc.legacy-multimedia"