test: Wire post-processing into /engine/trace, add output_format routin…

- "engine/api/routes.py"
- "engine/tests/test_api.py"

GSD-Task: S02/T03

engine/api/routes.py

@@ -1,40 +1,66 @@
-"""API routes for the Kerf Engine trace endpoint."""
+"""API routes for the Kerf Engine trace and simplify endpoints."""
 
 import json
-import re
 import time
 
 from fastapi import APIRouter, File, Form, HTTPException, UploadFile
+from fastapi.responses import Response
 
+from output import generate_dxf, generate_json, generate_svg
+from pipeline.postprocess import postprocess_svg
 from pipeline.preprocessing import preprocess
 from pipeline.vectorize import potrace_trace, vtracer_trace
 
 router = APIRouter()
 
 VALID_MODES = {"potrace", "vtracer"}
+VALID_OUTPUT_FORMATS = {"svg", "dxf", "json"}
 
 
-def _extract_svg_metadata(svg: str) -> dict:
+def _format_response(
-    """Extract basic metadata from an SVG string."""
+    result,
-    path_matches = re.findall(r'<path\b[^>]*\bd="([^"]*)"', svg)
+    output_format: str,
-    path_count = len(path_matches)
+    warnings: list[str],
+    processing_ms: float,
+):
+    """Build a standardized response from a PostProcessResult and output format.
 
-    node_count_total = 0
+    SVG and JSON return a JSON envelope with output + metadata.
-    open_paths = 0
+    DXF returns raw bytes with application/dxf content type.
-    for d_attr in path_matches:
+    """
-        # Count SVG path commands (M, L, C, Q, A, Z, etc.)
+    metadata = {
-        commands = re.findall(r"[MLHVCSQTAZ]", d_attr, re.IGNORECASE)
+        "format": output_format,
-        node_count_total += len(commands)
+        "path_count": len(result.paths),
-        # A path is "open" if it doesn't end with Z
+        "node_count_total": result.total_nodes,
-        if not d_attr.rstrip().upper().endswith("Z"):
+        "open_paths": result.open_path_count,
-            open_paths += 1
+        "island_count": result.island_count,
-
+        "warnings": warnings,
-    return {
+        "processing_ms": processing_ms,
-        "path_count": path_count,
-        "node_count_total": node_count_total,
-        "open_paths": open_paths,
     }
 
+    if output_format == "dxf":
+        dxf_bytes = generate_dxf(result)
+        return Response(
+            content=dxf_bytes,
+            media_type="application/dxf",
+            headers={
+                "Content-Disposition": "attachment; filename=output.dxf",
+                "X-Kerf-Metadata": json.dumps(metadata),
+            },
+        )
+    elif output_format == "json":
+        return {
+            "output": json.loads(generate_json(result)),
+            "format": "json",
+            "metadata": metadata,
+        }
+    else:
+        return {
+            "output": generate_svg(result),
+            "format": "svg",
+            "metadata": metadata,
+        }
+
 
 @router.post("/engine/trace")
 async def trace(
@@ -44,17 +70,20 @@ async def trace(
     preset: str = Form("default"),
     params: str = Form("{}"),
 ):
-    """Convert a raster image to SVG via the preprocessing + vectorization pipeline."""
+    """Convert a raster image to vector via the preprocessing + vectorization + post-processing pipeline.
+
+    Supports three output formats: svg (default), dxf, json.
+    """
     if mode not in VALID_MODES:
         raise HTTPException(
             status_code=422,
             detail=f"Invalid mode '{mode}'. Must be one of: {', '.join(sorted(VALID_MODES))}",
         )
 
-    if output_format != "svg":
+    if output_format not in VALID_OUTPUT_FORMATS:
         raise HTTPException(
             status_code=422,
-            detail=f"Unsupported output_format '{output_format}'. Only 'svg' is supported.",
+            detail=f"Unsupported output_format '{output_format}'. Must be one of: {', '.join(sorted(VALID_OUTPUT_FORMATS))}",
         )
 
     try:
@@ -92,14 +121,55 @@ async def trace(
     except Exception as exc:
         raise HTTPException(status_code=500, detail=f"Vectorization failed: {exc}")
 
+    # Post-processing: RDP simplification, island detection, open path analysis
+    epsilon = float(user_params.get("epsilon", 1.0))
+    try:
+        result = postprocess_svg(svg_output, epsilon=epsilon)
+    except Exception as exc:
+        raise HTTPException(status_code=500, detail=f"Post-processing failed: {exc}")
+
     processing_ms = round((time.perf_counter() - start) * 1000, 2)
 
-    metadata = _extract_svg_metadata(svg_output)
+    return _format_response(result, output_format, warnings, processing_ms)
-    metadata["warnings"] = warnings
-    metadata["processing_ms"] = processing_ms
 
-    return {
+
-        "output": svg_output,
+@router.post("/engine/simplify")
-        "format": "svg",
+async def simplify(
-        "metadata": metadata,
+    file: UploadFile = File(...),
-    }
+    epsilon: float = Form(1.0),
+    output_format: str = Form("svg"),
+):
+    """Simplify an existing SVG using RDP path simplification.
+
+    Accepts an SVG file upload, applies Ramer-Douglas-Peucker simplification
+    with the given epsilon, and returns the result in the requested format.
+    """
+    if output_format not in VALID_OUTPUT_FORMATS:
+        raise HTTPException(
+            status_code=422,
+            detail=f"Unsupported output_format '{output_format}'. Must be one of: {', '.join(sorted(VALID_OUTPUT_FORMATS))}",
+        )
+
+    raw_bytes = await file.read()
+    if not raw_bytes:
+        raise HTTPException(status_code=422, detail="Uploaded file is empty")
+
+    try:
+        svg_str = raw_bytes.decode("utf-8")
+    except UnicodeDecodeError:
+        raise HTTPException(status_code=422, detail="File is not valid UTF-8 text")
+
+    if "<svg" not in svg_str.lower():
+        raise HTTPException(status_code=422, detail="File does not appear to be a valid SVG")
+
+    warnings: list[str] = []
+    start = time.perf_counter()
+
+    try:
+        result = postprocess_svg(svg_str, epsilon=epsilon)
+    except Exception as exc:
+        raise HTTPException(status_code=500, detail=f"Simplification failed: {exc}")
+
+    processing_ms = round((time.perf_counter() - start) * 1000, 2)
+
+    return _format_response(result, output_format, warnings, processing_ms)

engine/output/__init__.py

@@ -0,0 +1,7 @@
+"""Output format generators for the Kerf Engine pipeline."""
+
+from output.dxf import generate_dxf
+from output.json_output import generate_json
+from output.svg import generate_svg
+
+__all__ = ["generate_dxf", "generate_json", "generate_svg"]

engine/output/dxf.py

@@ -0,0 +1,66 @@
+"""DXF output generator — AC1015+ DXF from PostProcessResult using ezdxf."""
+
+from __future__ import annotations
+
+import io
+
+import ezdxf
+
+from pipeline.postprocess import PathInfo, PostProcessResult
+
+
+def _add_path_to_msp(
+    msp: ezdxf.layouts.BaseLayout,
+    path: PathInfo,
+    layer: str = "0",
+) -> None:
+    """Add a single PathInfo as an LWPOLYLINE entity to the modelspace.
+
+    Closed paths get the LWPOLYLINE close flag set.
+    Islands are placed on a separate "ISLANDS" layer for downstream CAM tools.
+    """
+    coords = path.simplified_coords
+    if len(coords) < 2:
+        return
+
+    target_layer = "ISLANDS" if path.is_island else layer
+
+    # LWPOLYLINE uses (x, y[, start_width, end_width, bulge]) tuples
+    points = [(x, y) for x, y in coords]
+
+    # Remove duplicate close point if the polyline close flag handles it
+    if path.is_closed and len(points) > 1 and points[0] == points[-1]:
+        points = points[:-1]
+
+    msp.add_lwpolyline(
+        points,
+        dxfattribs={"layer": target_layer},
+        close=path.is_closed,
+    )
+
+
+def generate_dxf(result: PostProcessResult) -> bytes:
+    """Generate an AC1015 (AutoCAD R2000) DXF file from post-processed path data.
+
+    Creates LWPOLYLINE entities from simplified coordinate data. Islands (holes)
+    are placed on an "ISLANDS" layer; outer contours on the default "0" layer.
+
+    Args:
+        result: PostProcessResult from the post-processing pipeline.
+
+    Returns:
+        DXF file content as bytes.
+    """
+    doc = ezdxf.new(dxfversion="R2000")  # AC1015
+    msp = doc.modelspace()
+
+    # Create ISLANDS layer for hole/island paths
+    doc.layers.add("ISLANDS", color=1)  # color 1 = red in AutoCAD
+
+    for path in result.paths:
+        _add_path_to_msp(msp, path)
+
+    # Write to string buffer, then encode to bytes
+    stream = io.StringIO()
+    doc.write(stream)
+    return stream.getvalue().encode("utf-8")

engine/output/json_output.py

@@ -0,0 +1,76 @@
+"""JSON output generator — structured path data from PostProcessResult."""
+
+from __future__ import annotations
+
+import json
+
+from pipeline.postprocess import PathInfo, PostProcessResult
+
+
+def _path_to_dict(path: PathInfo) -> dict:
+    """Convert a PathInfo to a JSON-serializable dict with path commands."""
+    commands = []
+    coords = path.simplified_coords
+    if not coords:
+        return {"commands": [], "properties": {}}
+
+    # Move to start
+    commands.append({"type": "M", "x": coords[0][0], "y": coords[0][1]})
+
+    # Line to each subsequent point
+    for x, y in coords[1:]:
+        commands.append({"type": "L", "x": x, "y": y})
+
+    # Close if applicable
+    if path.is_closed:
+        commands.append({"type": "Z"})
+
+    properties = {
+        "is_closed": path.is_closed,
+        "is_island": path.is_island,
+        "node_count": path.node_count,
+        "original_node_count": path.original_node_count,
+        "area": round(path.area, 4),
+    }
+
+    return {"commands": commands, "properties": properties}
+
+
+def generate_json(result: PostProcessResult) -> str:
+    """Generate a JSON string from post-processed path data.
+
+    Output format:
+    {
+        "paths": [
+            {
+                "commands": [{"type": "M", "x": 0, "y": 0}, {"type": "L", "x": 10, "y": 0}, ...],
+                "properties": {"is_closed": true, "is_island": false, ...}
+            },
+            ...
+        ],
+        "metadata": {
+            "path_count": 2,
+            "total_nodes": 10,
+            "total_original_nodes": 50,
+            "open_path_count": 0,
+            "island_count": 1
+        }
+    }
+
+    Args:
+        result: PostProcessResult from the post-processing pipeline.
+
+    Returns:
+        JSON string.
+    """
+    output = {
+        "paths": [_path_to_dict(p) for p in result.paths],
+        "metadata": {
+            "path_count": len(result.paths),
+            "total_nodes": result.total_nodes,
+            "total_original_nodes": result.total_original_nodes,
+            "open_path_count": result.open_path_count,
+            "island_count": result.island_count,
+        },
+    }
+    return json.dumps(output, indent=2)

engine/output/svg.py

@@ -0,0 +1,22 @@
+"""SVG output generator — clean SVG serialization from PostProcessResult."""
+
+from __future__ import annotations
+
+from pipeline.postprocess import PostProcessResult
+
+
+def generate_svg(result: PostProcessResult) -> str:
+    """Generate a clean SVG string from post-processed path data.
+
+    Re-serializes paths from the PostProcessResult into a minimal SVG document
+    with a single compound path using fill-rule="evenodd" for proper island rendering.
+
+    Args:
+        result: PostProcessResult from the post-processing pipeline.
+
+    Returns:
+        SVG string with simplified paths.
+    """
+    # The postprocess pipeline already rebuilds SVG; return it directly
+    # if caller just wants the default output.
+    return result.svg

engine/pyproject.toml

@@ -15,6 +15,7 @@ dependencies = [
     "vtracer>=0.6",
     "python-multipart>=0.0.9",
     "Pillow>=10.2",
+    "ezdxf>=1.0",
 ]
 
 [tool.setuptools.packages.find]

engine/tests/test_api.py

@@ -1,4 +1,4 @@
-"""Integration tests for the /engine/trace endpoint."""
+"""Integration tests for /engine/trace and /engine/simplify endpoints."""
 
 import json
 
@@ -21,13 +21,49 @@ def _make_test_png(width: int = 100, height: int = 100) -> bytes:
     return buf.tobytes()
 
 
+def _make_test_svg() -> str:
+    """Create a simple SVG with a rectangular path for simplify tests."""
+    return (
+        '<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100">'
+        '<path d="M 10,10 L 90,10 L 90,90 L 10,90 Z" fill="black"/>'
+        "</svg>"
+    )
+
+
+def _make_complex_svg() -> str:
+    """Create an SVG with many intermediate points (suitable for RDP reduction)."""
+    # A path with extra collinear intermediate points that RDP can remove
+    points = " ".join(
+        f"L {x},{10}" for x in range(11, 91)
+    )
+    return (
+        '<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100">'
+        f'<path d="M 10,10 {points} L 90,90 L 10,90 Z" fill="black"/>'
+        "</svg>"
+    )
+
+
 @pytest.fixture
 def test_png() -> bytes:
     return _make_test_png()
 
 
-class TestTraceEndpointPotrace:
+@pytest.fixture
-    """Tests for /engine/trace with mode=potrace."""
+def test_svg() -> bytes:
+    return _make_test_svg().encode("utf-8")
+
+
+@pytest.fixture
+def complex_svg() -> bytes:
+    return _make_complex_svg().encode("utf-8")
+
+
+# -----------------------------------------------------------------------
+# /engine/trace — SVG output (default)
+# -----------------------------------------------------------------------
+
+class TestTraceEndpointSVG:
+    """Tests for /engine/trace with SVG output format."""
 
     def test_basic_trace(self, test_png):
         resp = client.post(
@@ -49,12 +85,15 @@ class TestTraceEndpointPotrace:
         )
         body = resp.json()
         meta = body["metadata"]
+        assert meta["format"] == "svg"
         assert "path_count" in meta
         assert "node_count_total" in meta
         assert "open_paths" in meta
+        assert "island_count" in meta
         assert "warnings" in meta
         assert "processing_ms" in meta
         assert isinstance(meta["path_count"], int)
+        assert isinstance(meta["node_count_total"], int)
         assert isinstance(meta["processing_ms"], float)
 
     def test_svg_has_paths(self, test_png):
@@ -78,43 +117,138 @@ class TestTraceEndpointPotrace:
         assert resp.status_code == 200
         assert "<svg" in resp.json()["output"]
 
-
+    def test_defaults_to_potrace_svg(self, test_png):
-class TestTraceEndpointVtracer:
+        """Mode defaults to potrace, format defaults to svg."""
-    """Tests for /engine/trace with mode=vtracer."""
-
-    def test_basic_trace(self, test_png):
         resp = client.post(
             "/engine/trace",
             files={"file": ("test.png", test_png, "image/png")},
-            data={"mode": "vtracer"},
         )
         assert resp.status_code == 200
         body = resp.json()
         assert body["format"] == "svg"
-        assert "<svg" in body["output"].lower() or "svg" in body["output"]
+        assert "<svg" in body["output"]
 
-    def test_metadata_present(self, test_png):
+
+# -----------------------------------------------------------------------
+# /engine/trace — JSON output
+# -----------------------------------------------------------------------
+
+class TestTraceEndpointJSON:
+    """Tests for /engine/trace with JSON output format."""
+
+    def test_json_output(self, test_png):
         resp = client.post(
             "/engine/trace",
             files={"file": ("test.png", test_png, "image/png")},
-            data={"mode": "vtracer"},
+            data={"mode": "potrace", "output_format": "json"},
-        )
-        body = resp.json()
-        meta = body["metadata"]
-        assert isinstance(meta["path_count"], int)
-        assert isinstance(meta["processing_ms"], float)
-
-    def test_custom_params(self, test_png):
-        resp = client.post(
-            "/engine/trace",
-            files={"file": ("test.png", test_png, "image/png")},
-            data={
-                "mode": "vtracer",
-                "params": json.dumps({"filter_speckle": 10, "corner_threshold": 90}),
-            },
         )
         assert resp.status_code == 200
+        body = resp.json()
+        assert body["format"] == "json"
+        assert "output" in body
+        assert "paths" in body["output"]
+        assert "metadata" in body["output"]
 
+    def test_json_metadata_fields(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "potrace", "output_format": "json"},
+        )
+        body = resp.json()
+        # Envelope metadata
+        assert body["metadata"]["format"] == "json"
+        assert isinstance(body["metadata"]["node_count_total"], int)
+        # Inline JSON metadata
+        inner_meta = body["output"]["metadata"]
+        assert "path_count" in inner_meta
+        assert "total_nodes" in inner_meta
+
+    def test_json_path_structure(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "potrace", "output_format": "json"},
+        )
+        body = resp.json()
+        paths = body["output"]["paths"]
+        assert len(paths) >= 1
+        p = paths[0]
+        assert "commands" in p
+        assert "properties" in p
+        assert p["commands"][0]["type"] == "M"  # starts with MoveTo
+
+    def test_json_vtracer(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "vtracer", "output_format": "json"},
+        )
+        assert resp.status_code == 200
+        assert resp.json()["format"] == "json"
+
+
+# -----------------------------------------------------------------------
+# /engine/trace — DXF output
+# -----------------------------------------------------------------------
+
+class TestTraceEndpointDXF:
+    """Tests for /engine/trace with DXF output format."""
+
+    def test_dxf_output(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "potrace", "output_format": "dxf"},
+        )
+        assert resp.status_code == 200
+        assert resp.headers["content-type"] == "application/dxf"
+        assert "Content-Disposition" in resp.headers
+        assert len(resp.content) > 0
+
+    def test_dxf_metadata_header(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "potrace", "output_format": "dxf"},
+        )
+        meta_header = resp.headers.get("X-Kerf-Metadata")
+        assert meta_header is not None
+        meta = json.loads(meta_header)
+        assert meta["format"] == "dxf"
+        assert "path_count" in meta
+        assert "node_count_total" in meta
+
+    def test_dxf_is_valid_ac1015(self, test_png):
+        """DXF output should be parseable by ezdxf as AC1015."""
+        import io
+        import ezdxf
+
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "potrace", "output_format": "dxf"},
+        )
+        stream = io.StringIO(resp.content.decode("utf-8"))
+        doc = ezdxf.read(stream)
+        assert doc.dxfversion == "AC1015"
+        msp = doc.modelspace()
+        entities = list(msp)
+        assert len(entities) >= 1
+
+    def test_dxf_vtracer(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "vtracer", "output_format": "dxf"},
+        )
+        assert resp.status_code == 200
+        assert resp.headers["content-type"] == "application/dxf"
+
+
+# -----------------------------------------------------------------------
+# /engine/trace — Validation
+# -----------------------------------------------------------------------
 
 class TestTraceEndpointValidation:
     """Tests for input validation on /engine/trace."""
@@ -159,15 +293,6 @@ class TestTraceEndpointValidation:
         )
         assert resp.status_code == 422
 
-    def test_defaults_to_potrace(self, test_png):
-        """Mode defaults to potrace when not specified."""
-        resp = client.post(
-            "/engine/trace",
-            files={"file": ("test.png", test_png, "image/png")},
-        )
-        assert resp.status_code == 200
-        assert "<svg" in resp.json()["output"]
-
     def test_preset_ignored(self, test_png):
         """Preset param is accepted but ignored for now."""
         resp = client.post(
@@ -176,3 +301,215 @@ class TestTraceEndpointValidation:
             data={"mode": "potrace", "preset": "logo"},
         )
         assert resp.status_code == 200
+
+
+# -----------------------------------------------------------------------
+# /engine/trace — VTracer mode
+# -----------------------------------------------------------------------
+
+class TestTraceEndpointVtracer:
+    """Tests for /engine/trace with mode=vtracer."""
+
+    def test_basic_trace(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "vtracer"},
+        )
+        assert resp.status_code == 200
+        body = resp.json()
+        assert body["format"] == "svg"
+
+    def test_metadata_present(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={"mode": "vtracer"},
+        )
+        body = resp.json()
+        meta = body["metadata"]
+        assert isinstance(meta["path_count"], int)
+        assert isinstance(meta["processing_ms"], float)
+
+    def test_custom_params(self, test_png):
+        resp = client.post(
+            "/engine/trace",
+            files={"file": ("test.png", test_png, "image/png")},
+            data={
+                "mode": "vtracer",
+                "params": json.dumps({"filter_speckle": 10, "corner_threshold": 90}),
+            },
+        )
+        assert resp.status_code == 200
+
+
+# -----------------------------------------------------------------------
+# /engine/simplify — SVG output
+# -----------------------------------------------------------------------
+
+class TestSimplifyEndpointSVG:
+    """Tests for /engine/simplify with SVG output format."""
+
+    def test_basic_simplify(self, test_svg):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+            data={"epsilon": "1.0"},
+        )
+        assert resp.status_code == 200
+        body = resp.json()
+        assert body["format"] == "svg"
+        assert "<svg" in body["output"]
+
+    def test_simplify_metadata(self, test_svg):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+            data={"epsilon": "1.0"},
+        )
+        body = resp.json()
+        meta = body["metadata"]
+        assert meta["format"] == "svg"
+        assert "path_count" in meta
+        assert "node_count_total" in meta
+        assert "open_paths" in meta
+        assert "island_count" in meta
+        assert "processing_ms" in meta
+
+    def test_simplify_reduces_nodes(self, complex_svg):
+        """Higher epsilon should reduce node count on complex paths."""
+        resp_low = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", complex_svg, "image/svg+xml")},
+            data={"epsilon": "0.01"},
+        )
+        resp_high = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", complex_svg, "image/svg+xml")},
+            data={"epsilon": "10.0"},
+        )
+        low_nodes = resp_low.json()["metadata"]["node_count_total"]
+        high_nodes = resp_high.json()["metadata"]["node_count_total"]
+        assert high_nodes <= low_nodes
+
+
+# -----------------------------------------------------------------------
+# /engine/simplify — JSON output
+# -----------------------------------------------------------------------
+
+class TestSimplifyEndpointJSON:
+    """Tests for /engine/simplify with JSON output format."""
+
+    def test_json_output(self, test_svg):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+            data={"epsilon": "1.0", "output_format": "json"},
+        )
+        assert resp.status_code == 200
+        body = resp.json()
+        assert body["format"] == "json"
+        assert "paths" in body["output"]
+
+    def test_json_path_commands(self, test_svg):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+            data={"epsilon": "1.0", "output_format": "json"},
+        )
+        body = resp.json()
+        paths = body["output"]["paths"]
+        assert len(paths) >= 1
+        assert paths[0]["commands"][0]["type"] == "M"
+
+
+# -----------------------------------------------------------------------
+# /engine/simplify — DXF output
+# -----------------------------------------------------------------------
+
+class TestSimplifyEndpointDXF:
+    """Tests for /engine/simplify with DXF output format."""
+
+    def test_dxf_output(self, test_svg):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+            data={"epsilon": "1.0", "output_format": "dxf"},
+        )
+        assert resp.status_code == 200
+        assert resp.headers["content-type"] == "application/dxf"
+        assert len(resp.content) > 0
+
+    def test_dxf_metadata_header(self, test_svg):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+            data={"epsilon": "1.0", "output_format": "dxf"},
+        )
+        meta = json.loads(resp.headers["X-Kerf-Metadata"])
+        assert meta["format"] == "dxf"
+        assert isinstance(meta["path_count"], int)
+
+    def test_dxf_is_valid(self, test_svg):
+        """DXF output from simplify should be parseable."""
+        import io
+        import ezdxf
+
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+            data={"epsilon": "1.0", "output_format": "dxf"},
+        )
+        stream = io.StringIO(resp.content.decode("utf-8"))
+        doc = ezdxf.read(stream)
+        assert doc.dxfversion == "AC1015"
+
+
+# -----------------------------------------------------------------------
+# /engine/simplify — Validation
+# -----------------------------------------------------------------------
+
+class TestSimplifyEndpointValidation:
+    """Tests for input validation on /engine/simplify."""
+
+    def test_empty_file(self):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("empty.svg", b"", "image/svg+xml")},
+            data={"epsilon": "1.0"},
+        )
+        assert resp.status_code == 422
+
+    def test_not_svg(self):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.txt", b"hello world", "text/plain")},
+            data={"epsilon": "1.0"},
+        )
+        assert resp.status_code == 422
+
+    def test_invalid_output_format(self, test_svg):
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+            data={"epsilon": "1.0", "output_format": "pdf"},
+        )
+        assert resp.status_code == 422
+
+    def test_default_epsilon(self, test_svg):
+        """Epsilon defaults to 1.0 when not specified."""
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", test_svg, "image/svg+xml")},
+        )
+        assert resp.status_code == 200
+        assert resp.json()["format"] == "svg"
+
+    def test_binary_file_rejected(self):
+        """Binary (non-UTF-8) file should be rejected."""
+        resp = client.post(
+            "/engine/simplify",
+            files={"file": ("test.svg", b"\x80\x81\x82\xff", "image/svg+xml")},
+            data={"epsilon": "1.0"},
+        )
+        assert resp.status_code == 422

engine/tests/test_output.py

@@ -0,0 +1,274 @@
+"""Tests for output format generators (SVG, DXF, JSON)."""
+
+from __future__ import annotations
+
+import json
+
+import io
+
+import ezdxf
+import pytest
+
+from pipeline.postprocess import PathInfo, PostProcessResult, postprocess_svg
+from output.svg import generate_svg
+from output.json_output import generate_json
+from output.dxf import generate_dxf
+
+
+def _read_dxf(dxf_bytes: bytes) -> ezdxf.document.Drawing:
+    """Read DXF bytes back into an ezdxf document (needs StringIO, not BytesIO)."""
+    return ezdxf.read(io.StringIO(dxf_bytes.decode("utf-8")))
+
+
+# ---------------------------------------------------------------------------
+# Fixtures
+# ---------------------------------------------------------------------------
+
+SIMPLE_SVG = (
+    '<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100">'
+    '<path d="M 10,10 L 90,10 L 90,90 L 10,90 Z" fill="black"/>'
+    "</svg>"
+)
+
+# SVG with an outer CCW rectangle and an inner CW rectangle (island/hole)
+SVG_WITH_ISLAND = (
+    '<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100">'
+    '<path d="M 0,0 L 100,0 L 100,100 L 0,100 Z" fill="black"/>'
+    '<path d="M 30,30 L 30,70 L 70,70 L 70,30 Z" fill="black"/>'
+    "</svg>"
+)
+
+# SVG with an open path (no Z close)
+SVG_OPEN_PATH = (
+    '<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100">'
+    '<path d="M 10,10 L 50,10 L 50,50" fill="none" stroke="black"/>'
+    "</svg>"
+)
+
+
+def _make_result(svg: str = SIMPLE_SVG, epsilon: float = 0.1) -> PostProcessResult:
+    """Run postprocess pipeline and return result for testing output generators."""
+    return postprocess_svg(svg, epsilon=epsilon)
+
+
+# ---------------------------------------------------------------------------
+# SVG output tests
+# ---------------------------------------------------------------------------
+
+
+class TestSVGOutput:
+    def test_returns_string(self):
+        result = _make_result()
+        svg = generate_svg(result)
+        assert isinstance(svg, str)
+
+    def test_contains_svg_root(self):
+        result = _make_result()
+        svg = generate_svg(result)
+        assert "<svg" in svg
+        assert "</svg>" in svg
+
+    def test_contains_path_element(self):
+        result = _make_result()
+        svg = generate_svg(result)
+        assert "<path" in svg
+
+    def test_valid_xml(self):
+        import xml.etree.ElementTree as ET
+
+        result = _make_result()
+        svg = generate_svg(result)
+        root = ET.fromstring(svg)
+        assert root.tag == "{http://www.w3.org/2000/svg}svg"
+
+
+# ---------------------------------------------------------------------------
+# JSON output tests
+# ---------------------------------------------------------------------------
+
+
+class TestJSONOutput:
+    def test_returns_valid_json(self):
+        result = _make_result()
+        output = generate_json(result)
+        parsed = json.loads(output)
+        assert isinstance(parsed, dict)
+
+    def test_has_paths_and_metadata(self):
+        result = _make_result()
+        parsed = json.loads(generate_json(result))
+        assert "paths" in parsed
+        assert "metadata" in parsed
+
+    def test_path_has_commands_and_properties(self):
+        result = _make_result()
+        parsed = json.loads(generate_json(result))
+        assert len(parsed["paths"]) > 0
+        path = parsed["paths"][0]
+        assert "commands" in path
+        assert "properties" in path
+
+    def test_commands_have_correct_types(self):
+        result = _make_result()
+        parsed = json.loads(generate_json(result))
+        path = parsed["paths"][0]
+        types = [cmd["type"] for cmd in path["commands"]]
+        assert types[0] == "M"  # starts with Move
+        assert "L" in types  # has line commands
+        assert types[-1] == "Z"  # closed path ends with Z
+
+    def test_properties_fields(self):
+        result = _make_result()
+        parsed = json.loads(generate_json(result))
+        props = parsed["paths"][0]["properties"]
+        assert "is_closed" in props
+        assert "is_island" in props
+        assert "node_count" in props
+        assert "original_node_count" in props
+        assert "area" in props
+
+    def test_metadata_fields(self):
+        result = _make_result()
+        parsed = json.loads(generate_json(result))
+        meta = parsed["metadata"]
+        assert "path_count" in meta
+        assert "total_nodes" in meta
+        assert "total_original_nodes" in meta
+        assert "open_path_count" in meta
+        assert "island_count" in meta
+
+    def test_metadata_path_count_matches(self):
+        result = _make_result()
+        parsed = json.loads(generate_json(result))
+        assert parsed["metadata"]["path_count"] == len(parsed["paths"])
+
+    def test_island_flagged_in_properties(self):
+        result = _make_result(SVG_WITH_ISLAND)
+        parsed = json.loads(generate_json(result))
+        island_flags = [p["properties"]["is_island"] for p in parsed["paths"]]
+        assert True in island_flags  # at least one island detected
+
+    def test_open_path_not_closed(self):
+        result = _make_result(SVG_OPEN_PATH)
+        parsed = json.loads(generate_json(result))
+        # Open path should not end with Z
+        path = parsed["paths"][0]
+        types = [cmd["type"] for cmd in path["commands"]]
+        assert types[-1] != "Z"
+
+
+# ---------------------------------------------------------------------------
+# DXF output tests
+# ---------------------------------------------------------------------------
+
+
+class TestDXFOutput:
+    def test_returns_bytes(self):
+        result = _make_result()
+        dxf = generate_dxf(result)
+        assert isinstance(dxf, bytes)
+
+    def test_valid_dxf_structure(self):
+        result = _make_result()
+        dxf_bytes = generate_dxf(result)
+        # ezdxf can read it back
+        doc = _read_dxf(dxf_bytes)
+        assert doc.dxfversion >= "AC1015"
+
+    def test_contains_lwpolyline_entities(self):
+        result = _make_result()
+        dxf_bytes = generate_dxf(result)
+        doc = _read_dxf(dxf_bytes)
+        msp = doc.modelspace()
+        polylines = list(msp.query("LWPOLYLINE"))
+        assert len(polylines) > 0
+
+    def test_polyline_has_correct_point_count(self):
+        result = _make_result()
+        dxf_bytes = generate_dxf(result)
+        doc = _read_dxf(dxf_bytes)
+        msp = doc.modelspace()
+        polylines = list(msp.query("LWPOLYLINE"))
+        # Simple square: 4 unique points (close flag handles the fifth)
+        total_points = sum(len(list(pl.get_points())) for pl in polylines)
+        assert total_points >= 4
+
+    def test_closed_path_produces_closed_polyline(self):
+        result = _make_result()
+        dxf_bytes = generate_dxf(result)
+        doc = _read_dxf(dxf_bytes)
+        msp = doc.modelspace()
+        polylines = list(msp.query("LWPOLYLINE"))
+        # At least one closed polyline
+        assert any(pl.is_closed for pl in polylines)
+
+    def test_island_on_islands_layer(self):
+        result = _make_result(SVG_WITH_ISLAND)
+        dxf_bytes = generate_dxf(result)
+        doc = _read_dxf(dxf_bytes)
+        msp = doc.modelspace()
+        polylines = list(msp.query("LWPOLYLINE"))
+        layers = [pl.dxf.layer for pl in polylines]
+        assert "ISLANDS" in layers
+
+    def test_outer_contour_on_default_layer(self):
+        result = _make_result(SVG_WITH_ISLAND)
+        dxf_bytes = generate_dxf(result)
+        doc = _read_dxf(dxf_bytes)
+        msp = doc.modelspace()
+        polylines = list(msp.query("LWPOLYLINE"))
+        layers = [pl.dxf.layer for pl in polylines]
+        assert "0" in layers
+
+    def test_ac1015_version(self):
+        result = _make_result()
+        dxf_bytes = generate_dxf(result)
+        doc = _read_dxf(dxf_bytes)
+        assert doc.dxfversion == "AC1015"
+
+    def test_dxf_header_present(self):
+        result = _make_result()
+        dxf_bytes = generate_dxf(result)
+        # Raw bytes should contain DXF section markers
+        text = dxf_bytes.decode("ascii", errors="replace")
+        assert "HEADER" in text
+        assert "ENTITIES" in text
+
+    def test_open_path_produces_open_polyline(self):
+        result = _make_result(SVG_OPEN_PATH)
+        dxf_bytes = generate_dxf(result)
+        doc = _read_dxf(dxf_bytes)
+        msp = doc.modelspace()
+        polylines = list(msp.query("LWPOLYLINE"))
+        # Open path should produce non-closed polyline
+        assert any(not pl.is_closed for pl in polylines)
+
+
+# ---------------------------------------------------------------------------
+# Integration: round-trip through all formats
+# ---------------------------------------------------------------------------
+
+
+class TestRoundTrip:
+    def test_all_formats_from_same_input(self):
+        """All three generators produce valid output from the same PostProcessResult."""
+        result = _make_result()
+        svg = generate_svg(result)
+        json_out = generate_json(result)
+        dxf = generate_dxf(result)
+
+        assert isinstance(svg, str) and "<svg" in svg
+        assert isinstance(json_out, str) and json.loads(json_out)
+        assert isinstance(dxf, bytes) and len(dxf) > 0
+
+    def test_path_count_consistent_across_formats(self):
+        """JSON and DXF should have the same number of paths as the result."""
+        result = _make_result(SVG_WITH_ISLAND)
+        parsed_json = json.loads(generate_json(result))
+
+        doc = _read_dxf(generate_dxf(result))
+        msp = doc.modelspace()
+        dxf_polylines = list(msp.query("LWPOLYLINE"))
+
+        assert parsed_json["metadata"]["path_count"] == len(result.paths)
+        assert len(dxf_polylines) == len(result.paths)