feat(layout-pagination): collapse legend, stabilize rows, real offset paginator (v0.7.3)

PR #4 of the v0.7.x GUI rework arc. Production code; central-gui restart only.

- Adapter legend: collapsed by default ("{n} adapters · Show legend ▾"). Expands
  to domain-grouped chips (same grouping as the v0.7.1 chip-picker) with uniform
  ellipsis-truncated names + full-name title tooltips. Clicking a legend chip
  toggles that adapter's filter (reuses the chip-picker's hidden CSV via
  syncField), so the legend doubles as a filter affordance.
- Row stability: time cell is single-line MM-DD HH:MM UTC (year dropped from the
  cell; full ISO in the cell tooltip + a new Time row in the expanded detail).
  Adapter cell is a chip (color swatch + short name; display_name is the
  tooltip). table-layout:fixed + per-column widths + fixed 37px row height with
  nowrap/ellipsis cells -> no per-row wrap variation.
- Real paginator: _fetch_events offset-mode returns the exact page slice plus the
  grand total via count(*) OVER() in one roundtrip. Previous/Next + windowed page
  numbers (1 ... 4 5 [6] 7 8 ... 47) + "showing X-Y of N" + a 25/50/100/250
  per-page selector. URL state persists offset + limit. events.json keeps cursor
  pagination (back-compat): offset param presence selects offset-mode, its
  absence keeps the cursor path -- cleanly separable by endpoint.

Adds TestEventsPagination (12 tests: offset/limit parse incl. max 250,
offset-vs-cursor query shape, _build_pagination windowing). Updates the time
format + adapter-cell + pagination-mode assertions in the existing frontend
tests to the new contract.

Full suite: 674 passed, 1 skipped (central and unprivileged zvx). count(*) OVER()
is ~7.5ms at current volume; vanilla JS + HTMX; CSS functional-only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_events_pagination.py

@@ -0,0 +1,113 @@
+"""Tests for v0.7.3 offset pagination: offset/limit parsing, offset-vs-cursor
+query shape, and the _build_pagination windowing math. No live DB (captured SQL).
+"""
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from central.gui import routes
+
+
+# --- offset / limit parsing -------------------------------------------------
+
+def test_offset_parse_valid():
+    parsed, err = routes._parse_events_params({"offset": "100", "limit": "50", "time": "all"})
+    assert err is None and parsed["offset"] == 100 and parsed["limit"] == 50
+
+
+def test_offset_negative_errors():
+    parsed, err = routes._parse_events_params({"offset": "-1", "time": "all"})
+    assert parsed is None and "offset" in err
+
+
+def test_offset_noninteger_errors():
+    parsed, err = routes._parse_events_params({"offset": "abc", "time": "all"})
+    assert parsed is None and "offset" in err
+
+
+def test_limit_max_is_250():
+    parsed, err = routes._parse_events_params({"limit": "250", "time": "all"})
+    assert err is None and parsed["limit"] == 250
+    over, err2 = routes._parse_events_params({"limit": "251", "time": "all"})
+    assert over is None and "250" in err2
+
+
+def test_default_offset_selects_mode():
+    """GUI passes default_offset=0 -> offset-mode; events.json omits -> cursor-mode."""
+    gui, _ = routes._parse_events_params({"time": "all"}, default_offset=0)
+    assert gui["offset"] == 0
+    api, _ = routes._parse_events_params({"time": "all"})
+    assert api["offset"] is None
+
+
+# --- query shape (captured SQL) ---------------------------------------------
+
+async def _capture(parsed):
+    captured = {}
+
+    async def fake_fetch(query, *args):
+        captured["query"] = query
+        captured["params"] = list(args)
+        return []
+
+    conn = MagicMock()
+    conn.fetch = fake_fetch
+    pool = MagicMock()
+    pool.acquire.return_value.__aenter__ = AsyncMock(return_value=conn)
+    pool.acquire.return_value.__aexit__ = AsyncMock(return_value=None)
+    with patch("central.gui.routes.get_pool", return_value=pool):
+        await routes._fetch_events(parsed)
+    return captured
+
+
+@pytest.mark.asyncio
+async def test_offset_mode_query_uses_limit_offset_and_window_count():
+    parsed, _ = routes._parse_events_params({"time": "all"}, default_offset=100)
+    cap = await _capture(parsed)
+    assert "LIMIT $" in cap["query"] and "OFFSET $" in cap["query"]
+    assert "count(*) OVER() AS total_count" in cap["query"]
+    assert 100 in cap["params"]  # offset bound as a param
+
+
+@pytest.mark.asyncio
+async def test_cursor_mode_query_has_no_offset_no_window_count():
+    parsed, _ = routes._parse_events_params({"time": "all"})  # no offset -> cursor-mode
+    cap = await _capture(parsed)
+    assert "OFFSET" not in cap["query"]
+    assert "count(*) OVER()" not in cap["query"]
+
+
+# --- _build_pagination math -------------------------------------------------
+
+def test_build_pagination_basic_windowing():
+    pg = routes._build_pagination(2341, 100, 50)
+    assert pg["page"] == 3 and pg["total_pages"] == 47
+    assert pg["start"] == 101 and pg["end"] == 150
+    assert pg["prev_offset"] == 50 and pg["next_offset"] == 150
+    nums = [p["page"] for p in pg["pages"] if "page" in p]
+    assert 1 in nums and 47 in nums and 3 in nums
+    assert any(p.get("ellipsis") for p in pg["pages"])
+    assert pg["per_page_options"] == [25, 50, 100, 250]
+
+
+def test_build_pagination_first_page_has_no_prev():
+    pg = routes._build_pagination(120, 0, 50)
+    assert pg["page"] == 1 and pg["prev_offset"] is None and pg["next_offset"] == 50
+    assert pg["start"] == 1 and pg["end"] == 50 and pg["total_pages"] == 3
+
+
+def test_build_pagination_last_page_has_no_next():
+    pg = routes._build_pagination(120, 100, 50)
+    assert pg["page"] == 3 and pg["next_offset"] is None and pg["end"] == 120
+
+
+def test_build_pagination_zero_results():
+    pg = routes._build_pagination(0, 0, 50)
+    assert pg["total"] == 0 and pg["total_pages"] == 1
+    assert pg["start"] == 0 and pg["end"] == 0
+    assert pg["prev_offset"] is None and pg["next_offset"] is None
+
+
+def test_build_pagination_single_page_no_next():
+    pg = routes._build_pagination(30, 0, 50)
+    assert pg["total_pages"] == 1 and pg["next_offset"] is None and pg["end"] == 30