Persist replacements across refresh (device-local, no account)

A reader who swaps a story away should keep that swap after a refresh; before,
the server re-served the original brief.
- localStorage now persists seen / dismissed / history (loadJSON/saveJSON).
- /api/brief accepts an exclude list; dismissed (replaced-away) ids are dropped
  and the highlights refill around them, so swaps stick and stay full.
- Replace records the swap to dismissed+seen and persists; the seen-set
  (persisted) keeps Replace from recycling across refreshes too.
- History panel survives refresh and gains 'Clear what I've seen (start fresh)'
  so it never feels suffocating. Saved history/favorites still come with sign-in.

Tests: brief exclude + refill (90 total).

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

goodnews/api.py

@@ -313,28 +313,32 @@ def create_app() -> FastAPI:
         date: str | None = Query(None),
         limit: int = Query(10, ge=1, le=50),
         prefs: str | None = Query(None),
+        exclude: str = Query("", description="comma-separated article ids the reader has dismissed"),
     ) -> BriefResponse:
         fp = prefs_from_json(prefs)
         now = datetime.now(timezone.utc)
+        excl = {int(x) for x in exclude.split(",") if x.strip().lstrip("-").isdigit()}
         with get_conn() as conn:
             data = queries.brief(conn, brief_date=date, limit=limit)
-            items = data["items"]
+            # Drop dismissed (replaced-away) items and anything the reader's
+            # boundaries hide; avoid-terms take precedence over curation.
+            items = [a for a in data["items"] if a["id"] not in excl]
             if not fp.is_empty():
-                # Apply personal boundaries (avoid-terms take precedence over curation).
                 items = filter_articles(items, fp, now)
-                # Keep the highlights full: if a boundary hid a story, top up with
-                # other readable, boundary-respecting good news rather than show fewer.
-                if len(items) < limit:
-                    have = {a["id"] for a in items}
-                    pool = queries.feed(
-                        conn, accepted_only=True, limit=limit * 5 + 20, offset=0, **_prefs_sql_kw(fp, now)
-                    )
-                    for a in filter_articles(pool, fp, now):
-                        if len(items) >= limit:
-                            break
-                        if a["id"] not in have:
-                            items.append(a)
-                            have.add(a["id"])
+            # Keep the highlights full: if a boundary or a dismissal removed a
+            # story, top up with other readable, boundary-respecting good news
+            # rather than show fewer.
+            if len(items) < limit:
+                have = {a["id"] for a in items} | excl
+                pool = queries.feed(
+                    conn, accepted_only=True, limit=limit * 5 + 40, offset=0, **_prefs_sql_kw(fp, now)
+                )
+                for a in filter_articles(pool, fp, now):
+                    if len(items) >= limit:
+                        break
+                    if a["id"] not in have:
+                        items.append(a)
+                        have.add(a["id"])
         # Lead with a gentle, readable story (charged or paywalled stories stay
         # in the set, just not as the first thing seen).
         items = _pick_lead(items)