Daily Art backend: curated Met pool, daily cached pick, /api/art (prototype)

The engine for the /art room (design-independent; deploy held for Codex review).

- goodnews/art.py: harvest a curated pool of public-domain HIGHLIGHT artworks from the
  Met (isHighlight+isPublicDomain+hasImages -> masterworks, never potsherds; CC0). Daily
  deterministic pick from the least-recently-shown (no soon-repeats, same for everyone),
  fetch metadata + download the image to OUR cache (data/art_cache) so the homepage never
  waits on or hotlinks the museum. Bulletproof: bad object/image falls through candidates;
  a failed day keeps the last piece (room never empty). Injectable HTTP for tests.
- Schema: art_pool + daily_art. /api/art/today (edge-cacheable) + /api/art/image/{id}
  (served from cache, immutable). CLI `art [--harvest] [--force]` + a non-fatal cycle step.
- Tests (5, mocked HTTP) + verified live against the Met: harvested 1641 works,
  picked/cached "Repose" by John White Alexander. 371 tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_art.py

@@ -0,0 +1,75 @@
+"""Daily Art: curated harvest, bulletproof daily pick (skips non-public-domain / bad
+images, falls through candidates), local image cache, and never-empty get_today."""
+import pytest
+
+from goodnews import art
+from goodnews.db import connect, init_db
+
+OBJECTS = {
+    1: {"objectID": 1, "isPublicDomain": True, "title": "Sunflowers", "artistDisplayName": "Van Gogh",
+        "objectDate": "1887", "medium": "Oil on canvas", "department": "European Paintings",
+        "creditLine": "Gift", "objectURL": "https://met/1",
+        "primaryImageSmall": "https://img/1-web.jpg", "primaryImage": "https://img/1.jpg"},
+    2: {"objectID": 2, "isPublicDomain": False, "primaryImageSmall": "https://img/2.jpg"},  # not CC0 -> skip
+    3: {"objectID": 3, "isPublicDomain": True, "title": "Irises", "artistDisplayName": "Van Gogh",
+        "primaryImageSmall": "https://img/3-web.jpg"},
+}
+
+
+def _fake_json(url, timeout=20):
+    if "/search" in url:
+        return {"total": 3, "objectIDs": [1, 2, 3]}
+    if "/objects/" in url:
+        return OBJECTS[int(url.rstrip("/").split("/")[-1])]
+    raise AssertionError(url)
+
+
+def _fake_bytes(url, timeout=30):
+    return (b"\xff\xd8\xff" + b"x" * 5000, "image/jpeg")   # a valid-looking jpeg
+
+
+@pytest.fixture
+def conn(tmp_path, monkeypatch):
+    monkeypatch.setenv("GOODNEWS_ART_CACHE", str(tmp_path / "art"))
+    monkeypatch.setattr(art, "_http_json", _fake_json)
+    monkeypatch.setattr(art, "_http_bytes", _fake_bytes)
+    c = connect(":memory:"); init_db(c)
+    yield c
+    c.close()
+
+
+def test_harvest_dedupes_into_pool(conn):
+    r = art.harvest_pool(conn)
+    assert r["pool"] == 3 and r["added"] == 3
+    assert art.harvest_pool(conn)["added"] == 0          # idempotent
+
+
+def test_pick_caches_image_metadata_and_marks_shown(conn):
+    art.harvest_pool(conn)
+    a = art.pick_daily(conn, art_date="2026-06-21")
+    assert a and a["object_id"] in (1, 3) and a["title"] in ("Sunflowers", "Irises")
+    assert a["artist"] == "Van Gogh" and a["image_file"]
+    assert list(art.cache_dir().glob(f"{a['object_id']}.*"))        # image cached locally
+    shown = conn.execute("SELECT shown_at FROM art_pool WHERE object_id=?", (a["object_id"],)).fetchone()[0]
+    assert shown == "2026-06-21"
+
+
+def test_pick_skips_non_public_domain(conn):
+    conn.execute("INSERT INTO art_pool (source, object_id) VALUES ('met', 2)")  # only the non-CC0 one
+    conn.commit()
+    assert art.pick_daily(conn, art_date="2026-06-21") is None     # nothing fetched, not an error
+
+
+def test_pick_is_idempotent_and_get_today_never_empty(conn):
+    art.harvest_pool(conn)
+    a1 = art.pick_daily(conn, art_date="2026-06-21")
+    a2 = art.pick_daily(conn, art_date="2026-06-21")               # same day -> unchanged
+    assert a1["object_id"] == a2["object_id"]
+    assert art.get_today(conn, "2026-06-21")["object_id"] == a1["object_id"]
+    # an unknown date falls back to the most recent cached piece (room never empty)
+    assert art.get_today(conn, "2099-01-01")["object_id"] == a1["object_id"]
+
+
+def test_run_daily_bootstraps_pool_then_picks(conn):
+    r = art.run_daily(conn)
+    assert r["pool"] == 3 and r["picked_object"] in (1, 3)