diff --git a/backend/app/domains/pipeline/tasks/extract_metadata.py b/backend/app/domains/pipeline/tasks/extract_metadata.py
index 01fc022..fa53489 100644
--- a/backend/app/domains/pipeline/tasks/extract_metadata.py
+++ b/backend/app/domains/pipeline/tasks/extract_metadata.py
@@ -17,59 +17,17 @@ logger = logging.getLogger(__name__)
 
 
 def _bbox_from_glb(glb_path: str) -> dict | None:
-    """Extract bounding box from a GLB file (meters → converted to mm).
+    """Backward-compatible wrapper for GLB bbox extraction."""
+    from app.domains.rendering.workflow_runtime_services import extract_bbox_from_glb
 
-    Returns {"dimensions_mm": {x,y,z}, "bbox_center_mm": {x,y,z}} or None on failure.
-    OCC GLB output is in meters; multiply by 1000 to get mm.
-    """
-    try:
-        import trimesh
-        p = Path(glb_path)
-        if not p.exists():
-            return None
-        scene = trimesh.load(str(p), force="scene")
-        bounds = getattr(scene, "bounds", None)
-        if bounds is None:
-            return None
-        mins, maxs = bounds
-        dims = maxs - mins
-        return {
-            "dimensions_mm": {
-                "x": round(float(dims[0]) * 1000, 2),
-                "y": round(float(dims[1]) * 1000, 2),
-                "z": round(float(dims[2]) * 1000, 2),
-            },
-            "bbox_center_mm": {
-                "x": round(float((mins[0] + maxs[0]) / 2) * 1000, 2),
-                "y": round(float((mins[1] + maxs[1]) / 2) * 1000, 2),
-                "z": round(float((mins[2] + maxs[2]) / 2) * 1000, 2),
-            },
-        }
-    except Exception as exc:
-        logger.debug(f"_bbox_from_glb failed for {glb_path}: {exc}")
-        return None
+    return extract_bbox_from_glb(glb_path)
 
 
 def _bbox_from_step_cadquery(step_path: str) -> dict | None:
-    """Fallback: extract bounding box by re-parsing STEP via cadquery."""
-    try:
-        import cadquery as cq
-        bb = cq.importers.importStep(step_path).val().BoundingBox()
-        return {
-            "dimensions_mm": {
-                "x": round(bb.xlen, 2),
-                "y": round(bb.ylen, 2),
-                "z": round(bb.zlen, 2),
-            },
-            "bbox_center_mm": {
-                "x": round((bb.xmin + bb.xmax) / 2, 2),
-                "y": round((bb.ymin + bb.ymax) / 2, 2),
-                "z": round((bb.zmin + bb.zmax) / 2, 2),
-            },
-        }
-    except Exception as exc:
-        logger.debug(f"_bbox_from_step_cadquery failed for {step_path}: {exc}")
-        return None
+    """Backward-compatible wrapper for STEP bbox fallback extraction."""
+    from app.domains.rendering.workflow_runtime_services import extract_bbox_from_step_cadquery
+
+    return extract_bbox_from_step_cadquery(step_path)
 
 
 @celery_app.task(bind=True, name="app.tasks.step_tasks.process_step_file", queue="step_processing")
@@ -267,6 +225,7 @@ def reextract_cad_metadata(cad_file_id: str):
     from sqlalchemy.orm import Session
     from app.config import settings as app_settings
     from app.models.cad_file import CadFile
+    from app.domains.rendering.workflow_runtime_services import resolve_cad_bbox
 
     pl = PipelineLogger(task_id=None)
     pl.step_start("reextract_cad_metadata", {"cad_file_id": cad_file_id})
@@ -289,7 +248,8 @@ def reextract_cad_metadata(cad_file_id: str):
     try:
         p = Path(step_path)
         glb_path = p.parent / f"{p.stem}_thumbnail.glb"
-        patch = _bbox_from_glb(str(glb_path)) or _bbox_from_step_cadquery(step_path)
+        bbox_result = resolve_cad_bbox(step_path, glb_path=str(glb_path))
+        patch = bbox_result.bbox_data
         if patch:
             with Session(eng) as session:
                 set_tenant_context_sync(session, _tenant_id)
diff --git a/backend/app/domains/pipeline/tasks/render_thumbnail.py b/backend/app/domains/pipeline/tasks/render_thumbnail.py
index a5ac633..633c548 100644
--- a/backend/app/domains/pipeline/tasks/render_thumbnail.py
+++ b/backend/app/domains/pipeline/tasks/render_thumbnail.py
@@ -117,7 +117,7 @@ def render_step_thumbnail(self, cad_file_id: str):
     # ── Post-render: bbox + sharp edges + materials (single session) ──────
     try:
         from app.models.cad_file import CadFile
-        from app.domains.pipeline.tasks.extract_metadata import _bbox_from_glb, _bbox_from_step_cadquery
+        from app.domains.rendering.workflow_runtime_services import resolve_cad_bbox
 
         with _pipeline_session(_tenant_id) as session:
             cad = session.get(CadFile, cad_file_id)
@@ -131,7 +131,7 @@ def render_step_thumbnail(self, cad_file_id: str):
                 if step_path and not attrs.get("dimensions_mm"):
                     _step = Path(step_path)
                     _glb = _step.parent / f"{_step.stem}_thumbnail.glb"
-                    bbox_data = _bbox_from_glb(str(_glb)) or _bbox_from_step_cadquery(step_path)
+                    bbox_data = resolve_cad_bbox(step_path, glb_path=str(_glb)).bbox_data
                     if bbox_data:
                         cad.mesh_attributes = {**attrs, **bbox_data}
                         attrs = cad.mesh_attributes
diff --git a/backend/app/domains/rendering/workflow_runtime_services.py b/backend/app/domains/rendering/workflow_runtime_services.py
index dbb5534..828800a 100644
--- a/backend/app/domains/rendering/workflow_runtime_services.py
+++ b/backend/app/domains/rendering/workflow_runtime_services.py
@@ -87,6 +87,18 @@ class AutoPopulateMaterialsResult:
     cad_parts: list[str] = field(default_factory=list)
 
 
+@dataclass(slots=True)
+class BBoxResolutionResult:
+    bbox_data: dict[str, dict[str, float]] | None
+    source_kind: Literal["glb", "step", "none"]
+    step_path: str
+    glb_path: str | None = None
+
+    @property
+    def has_bbox(self) -> bool:
+        return self.bbox_data is not None
+
+
 def _emit(emit: EmitFn, order_line_id: str, message: str, level: str | None = None) -> None:
     if emit is None:
         return
@@ -105,6 +117,86 @@ def _resolve_asset_path(storage_key: str | None) -> Path | None:
     return None
 
 
+def extract_bbox_from_glb(glb_path: str) -> dict[str, dict[str, float]] | None:
+    """Extract a bounding box from a GLB file in meters and convert to mm."""
+    try:
+        import trimesh
+
+        path = Path(glb_path)
+        if not path.exists():
+            return None
+        scene = trimesh.load(str(path), force="scene")
+        bounds = getattr(scene, "bounds", None)
+        if bounds is None:
+            return None
+        mins, maxs = bounds
+        dims = maxs - mins
+        return {
+            "dimensions_mm": {
+                "x": round(float(dims[0]) * 1000, 2),
+                "y": round(float(dims[1]) * 1000, 2),
+                "z": round(float(dims[2]) * 1000, 2),
+            },
+            "bbox_center_mm": {
+                "x": round(float((mins[0] + maxs[0]) / 2) * 1000, 2),
+                "y": round(float((mins[1] + maxs[1]) / 2) * 1000, 2),
+                "z": round(float((mins[2] + maxs[2]) / 2) * 1000, 2),
+            },
+        }
+    except Exception as exc:
+        logger.debug("extract_bbox_from_glb failed for %s: %s", glb_path, exc)
+        return None
+
+
+def extract_bbox_from_step_cadquery(step_path: str) -> dict[str, dict[str, float]] | None:
+    """Fallback: extract a bounding box by re-parsing the STEP file via cadquery."""
+    try:
+        import cadquery as cq
+
+        bb = cq.importers.importStep(step_path).val().BoundingBox()
+        return {
+            "dimensions_mm": {
+                "x": round(bb.xlen, 2),
+                "y": round(bb.ylen, 2),
+                "z": round(bb.zlen, 2),
+            },
+            "bbox_center_mm": {
+                "x": round((bb.xmin + bb.xmax) / 2, 2),
+                "y": round((bb.ymin + bb.ymax) / 2, 2),
+                "z": round((bb.zmin + bb.zmax) / 2, 2),
+            },
+        }
+    except Exception as exc:
+        logger.debug("extract_bbox_from_step_cadquery failed for %s: %s", step_path, exc)
+        return None
+
+
+def resolve_cad_bbox(
+    step_path: str,
+    *,
+    glb_path: str | None = None,
+) -> BBoxResolutionResult:
+    """Resolve CAD bounding-box data with the legacy GLB-first fallback order."""
+    bbox_data = None
+    source_kind: Literal["glb", "step", "none"] = "none"
+    if glb_path:
+        bbox_data = extract_bbox_from_glb(glb_path)
+        if bbox_data:
+            source_kind = "glb"
+
+    if bbox_data is None:
+        bbox_data = extract_bbox_from_step_cadquery(step_path)
+        if bbox_data:
+            source_kind = "step"
+
+    return BBoxResolutionResult(
+        bbox_data=bbox_data,
+        source_kind=source_kind,
+        step_path=step_path,
+        glb_path=glb_path,
+    )
+
+
 def prepare_order_line_render_context(
     session: Session,
     order_line_id: str,
diff --git a/backend/tests/domains/test_workflow_runtime_services.py b/backend/tests/domains/test_workflow_runtime_services.py
index d511654..d6d8891 100644
--- a/backend/tests/domains/test_workflow_runtime_services.py
+++ b/backend/tests/domains/test_workflow_runtime_services.py
@@ -17,6 +17,7 @@ from app.domains.products.models import CadFile, Product
 from app.domains.rendering.models import OutputType, RenderTemplate
 from app.domains.rendering.workflow_runtime_services import (
     auto_populate_materials_for_cad,
+    resolve_cad_bbox,
     prepare_order_line_render_context,
     resolve_order_line_material_map,
     resolve_order_line_template_context,
@@ -365,3 +366,68 @@ def test_auto_populate_materials_for_cad_skips_when_materials_already_present(sy
         {"part_name": "InnerRing", "material": "Steel raw"},
         {"part_name": "OuterRing", "material": "Steel raw"},
     ]
+
+
+def test_resolve_cad_bbox_prefers_glb_over_step(monkeypatch):
+    monkeypatch.setattr(
+        "app.domains.rendering.workflow_runtime_services.extract_bbox_from_glb",
+        lambda path: {
+            "dimensions_mm": {"x": 10.0, "y": 20.0, "z": 30.0},
+            "bbox_center_mm": {"x": 1.0, "y": 2.0, "z": 3.0},
+        },
+    )
+    monkeypatch.setattr(
+        "app.domains.rendering.workflow_runtime_services.extract_bbox_from_step_cadquery",
+        lambda path: {
+            "dimensions_mm": {"x": 100.0, "y": 200.0, "z": 300.0},
+            "bbox_center_mm": {"x": 10.0, "y": 20.0, "z": 30.0},
+        },
+    )
+
+    result = resolve_cad_bbox("/tmp/model.step", glb_path="/tmp/model_thumbnail.glb")
+
+    assert result.source_kind == "glb"
+    assert result.bbox_data == {
+        "dimensions_mm": {"x": 10.0, "y": 20.0, "z": 30.0},
+        "bbox_center_mm": {"x": 1.0, "y": 2.0, "z": 3.0},
+    }
+
+
+def test_resolve_cad_bbox_falls_back_to_step(monkeypatch):
+    monkeypatch.setattr(
+        "app.domains.rendering.workflow_runtime_services.extract_bbox_from_glb",
+        lambda path: None,
+    )
+    monkeypatch.setattr(
+        "app.domains.rendering.workflow_runtime_services.extract_bbox_from_step_cadquery",
+        lambda path: {
+            "dimensions_mm": {"x": 100.0, "y": 200.0, "z": 300.0},
+            "bbox_center_mm": {"x": 10.0, "y": 20.0, "z": 30.0},
+        },
+    )
+
+    result = resolve_cad_bbox("/tmp/model.step", glb_path="/tmp/model_thumbnail.glb")
+
+    assert result.source_kind == "step"
+    assert result.bbox_data == {
+        "dimensions_mm": {"x": 100.0, "y": 200.0, "z": 300.0},
+        "bbox_center_mm": {"x": 10.0, "y": 20.0, "z": 30.0},
+    }
+
+
+def test_extract_metadata_bbox_wrappers_delegate_to_runtime_services(monkeypatch):
+    from app.domains.pipeline.tasks.extract_metadata import _bbox_from_glb, _bbox_from_step_cadquery
+
+    monkeypatch.setattr(
+        "app.domains.rendering.workflow_runtime_services.extract_bbox_from_glb",
+        lambda path: {"dimensions_mm": {"x": 1.0, "y": 2.0, "z": 3.0}},
+    )
+    monkeypatch.setattr(
+        "app.domains.rendering.workflow_runtime_services.extract_bbox_from_step_cadquery",
+        lambda path: {"dimensions_mm": {"x": 4.0, "y": 5.0, "z": 6.0}},
+    )
+
+    assert _bbox_from_glb("/tmp/a.glb") == {"dimensions_mm": {"x": 1.0, "y": 2.0, "z": 3.0}}
+    assert _bbox_from_step_cadquery("/tmp/a.step") == {
+        "dimensions_mm": {"x": 4.0, "y": 5.0, "z": 6.0}
+    }
diff --git a/docs/workflows/WORKFLOW_DELIVERY_CHECKLIST.md b/docs/workflows/WORKFLOW_DELIVERY_CHECKLIST.md
index 9687955..fe95aed 100644
--- a/docs/workflows/WORKFLOW_DELIVERY_CHECKLIST.md
+++ b/docs/workflows/WORKFLOW_DELIVERY_CHECKLIST.md
@@ -22,7 +22,7 @@
 - [ ] Missing legacy steps extracted into reusable executors
 - [ ] Extracted node behavior matches legacy services
 - [ ] Node-level tests cover success and failure paths
-- Progress: `order_line_setup`, `resolve_template`, `material_map_resolve`, and `auto_populate_materials` are extracted and covered by targeted backend tests; remaining parity nodes are still open.
+- Progress: `order_line_setup`, `resolve_template`, `material_map_resolve`, `auto_populate_materials`, and `glb_bbox` are extracted and covered by targeted backend tests; remaining parity nodes are still open.
 
 ### Phase 4
 
diff --git a/docs/workflows/WORKFLOW_IMPLEMENTATION_BACKLOG.md b/docs/workflows/WORKFLOW_IMPLEMENTATION_BACKLOG.md
index e015ce4..b4e645d 100644
--- a/docs/workflows/WORKFLOW_IMPLEMENTATION_BACKLOG.md
+++ b/docs/workflows/WORKFLOW_IMPLEMENTATION_BACKLOG.md
@@ -55,7 +55,7 @@
 - `E3-T3` Extract `resolve_template`. `completed`
 - `E3-T4` Extract `material_map_resolve`. `completed`
 - `E3-T5` Extract `auto_populate_materials`. `completed`
-- `E3-T6` Extract `glb_bbox`.
+- `E3-T6` Extract `glb_bbox`. `completed`
 - `E3-T7` Extract `output_save`.
 - `E3-T8` Extract `notify`.
 - `E3-T9` Add executor tests for all extracted nodes.