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>

goodnews/api.py

@@ -32,11 +32,11 @@ from pathlib import Path
 
 from fastapi import BackgroundTasks, FastAPI, HTTPException, Query, Request, Response
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import HTMLResponse, RedirectResponse
+from fastapi.responses import FileResponse, HTMLResponse, RedirectResponse
 from fastapi.staticfiles import StaticFiles
 from pydantic import BaseModel
 
-from . import auth, bloom, email_send, feeds, games, oauth_google, publishing, queries, share, sources, summarize
+from . import art, auth, bloom, email_send, feeds, games, oauth_google, publishing, queries, share, sources, summarize
 from .localtime import local_today
 from .markup import reply_html_to_text, sanitize_reply_html
 from .db import connect
@@ -2258,6 +2258,30 @@ def create_app() -> FastAPI:
         with get_conn() as conn:
             return queries.available_dates(conn, limit=limit)
 
+    # --- Daily Art (the /art room) -----------------------------------------
+    @app.get("/api/art/today")
+    def art_today(response: Response) -> dict:
+        with get_conn() as conn:
+            a = art.get_today(conn)
+        if not a:
+            response.headers["Cache-Control"] = _PRIVATE
+            raise HTTPException(status_code=404, detail="No art yet.")
+        response.headers["Cache-Control"] = _EDGE_FEED   # one piece a day, same for everyone
+        return {
+            "date": a["art_date"], "object_id": a["object_id"], "title": a["title"],
+            "artist": a["artist"], "date_text": a["date_text"], "medium": a["medium"],
+            "department": a["department"], "credit": a["credit"], "source_url": a["source_url"],
+            "source": a["source"], "image_url": f"/api/art/image/{a['object_id']}",
+        }
+
+    @app.get("/api/art/image/{object_id}")
+    def art_image(object_id: int) -> FileResponse:
+        matches = sorted(art.cache_dir().glob(f"{object_id}.*"))
+        if not matches:
+            raise HTTPException(status_code=404, detail="Not cached.")
+        # Cached museum image: immutable for a given object id.
+        return FileResponse(str(matches[0]), headers={"Cache-Control": "public, max-age=31536000, immutable"})
+
     @app.get("/api/replacement", response_model=Article | None)
     def replacement(
         exclude: str = Query("", description="comma-separated article ids already shown"),