Personalized brief: refill to full count when a boundary hides a highlight

When a reader's boundary (avoid-term, muted topic/flavor, pause) removes a brief
item, top the highlights back up with other readable, boundary-respecting good
news instead of showing fewer cards — so 'Highlights from Today' stays full and
still honors what they don't want to see. (Reverses the earlier filter-down-only
MVP, now that the count is fixed at seven.)

- /api/brief: after filtering by prefs, refill from the accepted pool (same
  categorical SQL filters + avoid-terms) excluding already-shown items.
- Shared _prefs_sql_kw helper for feed/replacement/brief filters.
- Tests: refill stays full and respects mute + avoid-terms (89 total).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_brief_refill.py

@@ -0,0 +1,50 @@
+import json
+import pytest
+from fastapi.testclient import TestClient
+from goodnews.db import connect, init_db
+
+
+@pytest.fixture
+def client(tmp_path, monkeypatch):
+    db = tmp_path / "t.sqlite3"
+    monkeypatch.setenv("GOODNEWS_DB", str(db))
+    conn = connect(db); init_db(conn)
+    conn.execute("INSERT INTO sources (id,name,feed_url,trust_score) VALUES (1,'S','http://s/f',6)")
+
+    def add(aid, topic, in_brief_rank=None, title=None):
+        conn.execute("INSERT INTO articles (id,source_id,canonical_url,title,published_at,url_hash) "
+                     "VALUES (?,1,?,?, '2026-05-31T10:00:00+00:00', ?)",
+                     (aid, f"http://s/{aid}", title or f"t{aid}", f"h{aid}"))
+        conn.execute("INSERT INTO article_scores (article_id,constructive_score,agency_score,human_benefit_score,"
+                     "cortisol_score,ragebait_score,pr_risk_score,accepted,topic,flavor) "
+                     "VALUES (?,7,2,2,1,0,2,1,?,'solution')", (aid, topic))
+        if in_brief_rank:
+            conn.execute("INSERT INTO daily_brief_items (brief_id,article_id,rank) VALUES (1,?,?)", (aid, in_brief_rank))
+
+    conn.execute("INSERT INTO daily_briefs (id,brief_date,title) VALUES (1,'2026-05-31','B')")
+    add(1, "health", 1)        # will be muted
+    add(2, "science", 2)
+    add(3, "environment", 3)
+    add(4, "community")        # refill candidates (accepted, not in brief)
+    add(5, "animals")
+    add(6, "culture")
+    conn.commit(); conn.close()
+    from goodnews.api import create_app
+    return TestClient(create_app())
+
+
+def test_brief_refills_to_full_count_under_boundary(client):
+    full = client.get("/api/brief", params={"limit": 3}).json()
+    assert len(full["items"]) == 3
+
+    muted = client.get("/api/brief", params={"limit": 3, "prefs": json.dumps({"mute_topics": ["health"]})}).json()
+    topics = [i["topic"] for i in muted["items"]]
+    assert len(muted["items"]) == 3            # stayed full (refilled)
+    assert "health" not in topics             # boundary respected
+
+
+def test_brief_refill_respects_avoid_terms(client):
+    # avoid a word in the health item's title
+    client_resp = client.get("/api/brief", params={"limit": 3, "prefs": json.dumps({"avoid_terms": ["t1"]})}).json()
+    assert len(client_resp["items"]) == 3
+    assert all(i["id"] != 1 for i in client_resp["items"])