feat(api): GET /api/products/export — streamed canonical CSV, 409 empty_catalog (§6.4, PUC-9)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/main.py

@@ -17,7 +17,7 @@ from typing import Any
 
 import psycopg
 from fastapi import Depends, FastAPI, File, Query, Response, UploadFile
-from fastapi.responses import JSONResponse, PlainTextResponse
+from fastapi.responses import JSONResponse, PlainTextResponse, StreamingResponse
 from fastapi.staticfiles import StaticFiles
 from pydantic import BaseModel
 
@@ -374,6 +374,27 @@ def create_app(database_url: str | None = None, static_dir: str | Path | None =
         _account, sf = gate
         return products.summary(conn, sf.id)
 
+    @app.get("/api/products/export")
+    def export_products(
+        status: str = Query(default="all", pattern="^(all|active|draft|archived)$"),
+        conn: psycopg.Connection = Depends(get_conn),
+        sess: dict | None = Depends(get_session),
+    ):
+        """Stream the catalog as canonical CSV, optionally status-filtered (§6.4; PUC-9)."""
+        gate = _merchant_gate(conn, sess)
+        if isinstance(gate, JSONResponse):
+            return gate
+        _account, sf = gate
+        try:
+            stream = products.export_catalog(conn, sf.id, status)
+        except products.EmptyCatalog:
+            return _error(409, "empty_catalog", "There are no products to export.")
+        return StreamingResponse(
+            stream,
+            media_type="text/csv",
+            headers={"content-disposition": 'attachment; filename="ecomm-products-export.csv"'},
+        )
+
     @app.get("/api/products/sample.csv")
     def products_sample_csv():
         """The DOC-3 worked-example CSV. Documentation, so no auth gate (§6.4)."""

backend/tests/test_products_endpoints.py

@@ -93,3 +93,43 @@ def test_sample_csv_imports_clean(fresh_db_url):
         sample = client.get("/api/products/sample.csv").content
         body = _upload(client, sample, "sample.csv").json()
         assert body["summary"]["errors"] == 0 and body["summary"]["adds"] == 2
+
+
+def test_export_returns_canonical_csv(fresh_db_url):
+    with _merchant_client(fresh_db_url) as client:
+        draft = _upload(client).json()
+        client.post(f"/api/products/imports/drafts/{draft['id']}/confirm")
+        resp = client.get("/api/products/export")
+        assert resp.status_code == 200
+        assert resp.headers["content-type"].startswith("text/csv")
+        assert "attachment" in resp.headers["content-disposition"]
+        body = resp.text
+        assert body.splitlines()[0].startswith("Handle,")
+        assert "moon-mug" in body
+
+
+def test_export_status_filter_respected(fresh_db_url):
+    with _merchant_client(fresh_db_url) as client:
+        # GOOD_CSV's moon-mug has no Status column → defaults to active.
+        draft = _upload(client).json()
+        client.post(f"/api/products/imports/drafts/{draft['id']}/confirm")
+        assert "moon-mug" in client.get("/api/products/export?status=active").text
+        # No archived products → 409.
+        assert client.get("/api/products/export?status=archived").status_code == 409
+
+
+def test_export_empty_catalog_409(fresh_db_url):
+    with _merchant_client(fresh_db_url) as client:
+        resp = client.get("/api/products/export")
+        assert resp.status_code == 409
+        assert resp.json()["error"]["code"] == "empty_catalog"
+
+
+def test_export_requires_merchant(fresh_db_url):
+    with TestClient(create_app(database_url=fresh_db_url)) as client:
+        assert client.get("/api/products/export").status_code == 401
+
+
+def test_export_bad_status_422(fresh_db_url):
+    with _merchant_client(fresh_db_url) as client:
+        assert client.get("/api/products/export?status=bogus").status_code == 422