c2-core: Archive "Load more" skipped 150 of every 200 calls

/calls/search scans a 200-row window and returns 50, but the next cursor
was always the last SCANNED row — so with an unfiltered list each page
jumped past the 150 matches it had already read and not shown. Resume
after the last RETURNED row when matches overflow the page; keep the
last-scanned cursor only when the page holds every match (the sparse-
filter case that cursor exists for). Same fix for /calls/eval-queue.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-c2-core/app/routers/calls.py

@@ -40,6 +40,25 @@ def _parse_ts(value: Optional[str], field: str) -> Optional[datetime]:
     return dt if dt.tzinfo else dt.replace(tzinfo=timezone.utc)
 
 
+def _next_cursor(rows: list[dict], matches: list[dict], page: list[dict], window: int) -> Optional[str]:
+    """Where the next page of a bounded-window scan starts.
+
+    More matches than fit on the page → resume right after the last row
+    returned, or every match between it and the end of the window is skipped
+    (a 200-row window shown 50 at a time lost 150 calls per "Load more").
+    Otherwise resume after the last row SCANNED, not the last match — a page
+    whose last match sits early in the window would re-scan everything after
+    it and loop forever on a sparse filter. A short window is the end.
+    """
+    if len(matches) > len(page):
+        last = page[-1].get("started_at")
+    elif len(rows) == window:
+        last = rows[-1].get("started_at")
+    else:
+        return None
+    return last.isoformat() if hasattr(last, "isoformat") else last
+
+
 @router.get("")
 async def list_calls(
     node_id: Optional[str] = Query(None),
@@ -153,13 +172,7 @@ async def search_calls(
     matches = [c for c in rows if _keep(c)]
     page = matches[:limit]
 
-    # Cursor advances over the SCANNED window, not the filtered page — otherwise
-    # a page whose last match sits early in the window would re-scan everything
-    # after it on the next request and loop forever on a sparse filter.
-    next_cursor = None
-    if len(rows) == window:
-        last_scanned = rows[-1].get("started_at")
-        next_cursor = last_scanned.isoformat() if hasattr(last_scanned, "isoformat") else last_scanned
+    next_cursor = _next_cursor(rows, matches, page, window)
 
     return {
         "calls": [with_playback_url(c) for c in page],
@@ -216,10 +229,7 @@ async def eval_queue(
     matches = [c for c in rows if _eligible(c)]
     page = matches[:limit]
 
-    next_cursor = None
-    if len(rows) == window:
-        last_scanned = rows[-1].get("started_at")
-        next_cursor = last_scanned.isoformat() if hasattr(last_scanned, "isoformat") else last_scanned
+    next_cursor = _next_cursor(rows, matches, page, window)
 
     return {
         "calls": [with_playback_url(c) for c in page],

drb-c2-core/tests/test_calls_parse_ts.py

@@ -8,7 +8,7 @@ from datetime import datetime, timezone
 import pytest
 from fastapi import HTTPException
 
-from app.routers.calls import _parse_ts
+from app.routers.calls import _next_cursor, _parse_ts
 
 
 def test_empty_is_none():
@@ -33,3 +33,27 @@ def test_garbage_is_400():
     with pytest.raises(HTTPException) as exc:
         _parse_ts("yesterday", "date_from")
     assert exc.value.status_code == 400
+
+
+# ── _next_cursor ──────────────────────────────────────────────────────────
+
+
+def _rows(n):
+    return [{"started_at": datetime(2026, 9, 20, 12, i // 60, i % 60, tzinfo=timezone.utc)} for i in range(n)]
+
+
+def test_cursor_resumes_after_last_returned_row_when_matches_overflow():
+    rows = _rows(200)
+    page = rows[:50]
+    assert _next_cursor(rows, rows, page, 200) == page[-1]["started_at"].isoformat()
+
+
+def test_cursor_resumes_after_window_when_page_holds_every_match():
+    rows = _rows(200)
+    matches = rows[:3]
+    assert _next_cursor(rows, matches, matches, 200) == rows[-1]["started_at"].isoformat()
+
+
+def test_short_window_is_the_end():
+    rows = _rows(20)
+    assert _next_cursor(rows, rows[:5], rows[:5], 200) is None