diff --git a/insta-lab/app/selection.py b/insta-lab/app/selection.py
index 4edca33..80d9c41 100644
--- a/insta-lab/app/selection.py
+++ b/insta-lab/app/selection.py
@@ -55,6 +55,8 @@ def score_candidates(
     w = weights or DEFAULT_WEIGHTS
     now = _parse_iso(now_iso) if now_iso else datetime.now(timezone.utc)
     max_w = max(prefs.values()) if prefs else 1.0
+    if max_w <= 0:
+        max_w = 1.0
     out: List[Dict[str, Any]] = []
     for c in candidates:
         cat = c.get("category", "")
diff --git a/insta-lab/app/selection_judge.py b/insta-lab/app/selection_judge.py
index b745b96..0de93c7 100644
--- a/insta-lab/app/selection_judge.py
+++ b/insta-lab/app/selection_judge.py
@@ -43,7 +43,7 @@ def judge_candidates(candidates: List[Dict[str, Any]]) -> Dict[int, float]:
     try:
         client = Anthropic(api_key=ANTHROPIC_API_KEY)
         resp = client.messages.create(
-            model=ANTHROPIC_MODEL_HAIKU, max_tokens=512,
+            model=ANTHROPIC_MODEL_HAIKU, max_tokens=1024,
             messages=[{"role": "user", "content": PROMPT.format(items=items)}],
         )
         return parse_judge_response(resp.content[0].text)
diff --git a/insta-lab/tests/test_ranked_decision_api.py b/insta-lab/tests/test_ranked_decision_api.py
index 9ca95d8..ad1aa34 100644
--- a/insta-lab/tests/test_ranked_decision_api.py
+++ b/insta-lab/tests/test_ranked_decision_api.py
@@ -40,3 +40,8 @@ def test_decision_invalid_400(client):
     sid = db.add_card_slate({"keyword": "x", "category": "economy"})
     r = client.post(f"/api/insta/slates/{sid}/decision", json={"decision": "maybe"})
     assert r.status_code == 400
+
+
+def test_decision_unknown_slate_404(client):
+    r = client.post("/api/insta/slates/99999/decision", json={"decision": "approved"})
+    assert r.status_code == 404
diff --git a/insta-lab/tests/test_selection.py b/insta-lab/tests/test_selection.py
index 818e80f..3d762f2 100644
--- a/insta-lab/tests/test_selection.py
+++ b/insta-lab/tests/test_selection.py
@@ -45,3 +45,11 @@ def test_claude_included_when_provided():
     cands = [_cand(1, "A", "economy", 0.5, NOW)]
     out = score_candidates(cands, [], {"economy": 1.0}, {1: 1.0}, threshold=0.0, now_iso=NOW)
     assert out[0]["breakdown"]["claude"] == 1.0
+
+
+def test_all_zero_prefs_no_crash():
+    cands = [{"id": 1, "keyword": "A", "category": "economy", "score": 0.8,
+              "suggested_at": "2026-06-11T00:00:00Z"}]
+    prefs = {"economy": 0.0, "psychology": 0.0}
+    out = score_candidates(cands, [], prefs, None, threshold=0.0, now_iso="2026-06-11T00:00:00Z")
+    assert out[0]["breakdown"]["account_fit"] == 0.0  # 0가중 → fit 0, 크래시 없음