feat(orchestrator): authoritative failure-count badge endpoint (DEBT-042)

New GET /api/v1/orchestrator/events/stats?since=1h&success=false&kind=...
backed by repo.count_orchestrator_failures(since_ts, kind), which
counts failed rows across both orchestrator_events and
orchestrator_emails since the cutoff.

Window parser accepts ^\d+[smhd]$, capped at 7d. Today only
success=false is accepted on this surface so the endpoint isn't
accidentally repurposed before the next consumer is properly
designed.

Orchestrator.tsx polls the endpoint on mount + every 30 s and
renders the authoritative DB-derived count instead of deriving from
the in-memory SSE buffer + one paginated page (which silently
excluded failures older than the local window).

tests/api/orchestrator/test_event_stats.py

@@ -0,0 +1,136 @@
+"""GET /api/v1/orchestrator/events/stats — failure-count badge endpoint (DEBT-042)."""
+from __future__ import annotations
+
+from datetime import datetime, timedelta, timezone
+from unittest.mock import AsyncMock, patch
+
+import httpx
+import pytest
+
+from decnet.web.api import app
+
+_V1 = "/api/v1/orchestrator"
+
+
+@pytest.mark.anyio
+async def test_stats_unauthenticated_401():
+    async with httpx.AsyncClient(
+        transport=httpx.ASGITransport(app=app), base_url="http://test",
+    ) as ac:
+        r = await ac.get(f"{_V1}/events/stats?since=1h&success=false")
+        assert r.status_code == 401
+
+
+@pytest.mark.asyncio
+async def test_stats_returns_failure_count_with_window():
+    from decnet.web.router.orchestrator.api_event_stats import (
+        orchestrator_event_stats,
+    )
+
+    with patch(
+        "decnet.web.router.orchestrator.api_event_stats.repo"
+    ) as mock_repo:
+        mock_repo.count_orchestrator_failures = AsyncMock(return_value=7)
+
+        result = await orchestrator_event_stats(
+            since="1h", success=False, kind=None,
+            user={"uuid": "u", "role": "viewer"},
+        )
+
+    assert result["count"] == 7
+    assert result["since"] == "1h"
+    assert result["success"] is False
+    assert result["kind"] is None
+
+    # Window must be "now - 1h", not 5h or 30s. Tolerance of 5 seconds
+    # for the test execution.
+    call = mock_repo.count_orchestrator_failures.await_args
+    since_ts = call.kwargs["since_ts"]
+    expected = datetime.now(timezone.utc) - timedelta(hours=1)
+    assert abs((since_ts - expected).total_seconds()) < 5
+
+
+@pytest.mark.asyncio
+async def test_stats_forwards_kind_filter():
+    from decnet.web.router.orchestrator.api_event_stats import (
+        orchestrator_event_stats,
+    )
+
+    with patch(
+        "decnet.web.router.orchestrator.api_event_stats.repo"
+    ) as mock_repo:
+        mock_repo.count_orchestrator_failures = AsyncMock(return_value=2)
+
+        await orchestrator_event_stats(
+            since="15m", success=False, kind="email",
+            user={"uuid": "u", "role": "viewer"},
+        )
+
+    assert mock_repo.count_orchestrator_failures.await_args.kwargs["kind"] == "email"
+
+
+@pytest.mark.asyncio
+async def test_stats_rejects_success_true():
+    """Only success=false is supported on this surface today; everything
+    else is rejected so the endpoint isn't accidentally repurposed
+    before the next consumer is properly designed."""
+    from fastapi import HTTPException
+
+    from decnet.web.router.orchestrator.api_event_stats import (
+        orchestrator_event_stats,
+    )
+
+    with pytest.raises(HTTPException) as exc:
+        await orchestrator_event_stats(
+            since="1h", success=True, kind=None,
+            user={"uuid": "u", "role": "viewer"},
+        )
+    assert exc.value.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_stats_rejects_success_unset():
+    from fastapi import HTTPException
+
+    from decnet.web.router.orchestrator.api_event_stats import (
+        orchestrator_event_stats,
+    )
+
+    with pytest.raises(HTTPException) as exc:
+        await orchestrator_event_stats(
+            since="1h", success=None, kind=None,
+            user={"uuid": "u", "role": "viewer"},
+        )
+    assert exc.value.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_stats_rejects_malformed_since():
+    from fastapi import HTTPException
+
+    from decnet.web.router.orchestrator.api_event_stats import (
+        orchestrator_event_stats,
+    )
+
+    with pytest.raises(HTTPException) as exc:
+        await orchestrator_event_stats(
+            since="garbage", success=False, kind=None,
+            user={"uuid": "u", "role": "viewer"},
+        )
+    assert exc.value.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_stats_rejects_window_over_max():
+    from fastapi import HTTPException
+
+    from decnet.web.router.orchestrator.api_event_stats import (
+        orchestrator_event_stats,
+    )
+
+    with pytest.raises(HTTPException) as exc:
+        await orchestrator_event_stats(
+            since="30d", success=False, kind=None,
+            user={"uuid": "u", "role": "viewer"},
+        )
+    assert exc.value.status_code == 422