feat: prevent duplicate cards, merge contexts, and display star badge when word is in library

tests/test_api.py

@@ -811,3 +811,60 @@ def test_gzip_compression():
     resp_raw = client.get("/static/js/app.js", headers={"Accept-Encoding": "identity"})
     assert resp_raw.status_code == 200
     assert resp_raw.headers.get("content-encoding") is None
+
+
+def test_duplicate_prevention_and_in_library_flag():
+    # Login as testadmin
+    client.post("/api/login", json={"username": "testadmin", "password": "testpass12345"})
+
+    # 1. Create initial card for 'admired'
+    resp1 = client.post("/api/cards", json={
+        "term": "admired",
+        "translation": "восхищались",
+        "context_sentence": "People admired his courage.",
+        "tags": "jfk, book:kennedy",
+        "collection": "Literature",
+    })
+    assert resp1.status_code == 200
+    card1 = resp1.json()
+    card_id = card1["id"]
+
+    # 2. Try adding same term with different case ('Admired') and new context
+    resp2 = client.post("/api/cards", json={
+        "term": "Admired",
+        "translation": "восхищались",
+        "context_sentence": "He admired his older brother.",
+        "tags": "history, reader",
+        "collection": "General",
+    })
+    assert resp2.status_code == 200
+    card2 = resp2.json()
+
+    # Must be same card ID (no duplicate created!)
+    assert card2["id"] == card_id
+    assert card2.get("already_exists") is True
+
+    # Both contexts should be present and tags merged
+    assert "People admired his courage." in card2["context_sentence"]
+    assert "He admired his older brother." in card2["context_sentence"]
+    assert "book:kennedy" in card2["tags"]
+    assert "history" in card2["tags"]
+
+    # Verify database count has only 1 card for 'admired'
+    cards_list = client.get("/api/cards?search=admired").json()["cards"]
+    assert len(cards_list) == 1
+    assert cards_list[0]["id"] == card_id
+
+    # 3. Test /api/lookup returns in_library: True for existing word
+    resp_lookup_existing = client.get("/api/lookup?term=admired")
+    assert resp_lookup_existing.status_code == 200
+    data_existing = resp_lookup_existing.json()
+    assert data_existing["in_library"] is True
+    assert data_existing["library_card"]["id"] == card_id
+
+    # Test /api/lookup returns in_library: False for word not in user library
+    resp_lookup_new = client.get("/api/lookup?term=xylophone_unseen_xyz")
+    assert resp_lookup_new.status_code == 200
+    data_new = resp_lookup_new.json()
+    assert data_new["in_library"] is False
+    assert data_new["library_card"] is None