diff --git a/src/cerbero_bite/runtime/market_snapshot_cycle.py b/src/cerbero_bite/runtime/market_snapshot_cycle.py
index 244809f..854725e 100644
--- a/src/cerbero_bite/runtime/market_snapshot_cycle.py
+++ b/src/cerbero_bite/runtime/market_snapshot_cycle.py
@@ -22,7 +22,7 @@ from typing import TYPE_CHECKING, Any
 
 from cerbero_bite.clients._exceptions import McpError
 from cerbero_bite.state import connect, transaction
-from cerbero_bite.state.models import MarketSnapshotRecord
+from cerbero_bite.state.models import DvolSnapshot, MarketSnapshotRecord
 
 if TYPE_CHECKING:
     from cerbero_bite.runtime.dependencies import RuntimeContext
@@ -181,6 +181,21 @@ async def collect_market_snapshot(
             try:
                 with transaction(conn):
                     ctx.repository.record_market_snapshot(conn, record)
+                    # Mirror ETH spot+DVOL into dvol_history so monitor_cycle's
+                    # return_4h lookup has local samples even in data-only mode.
+                    if (
+                        record.asset == "ETH"
+                        and record.spot is not None
+                        and record.dvol is not None
+                    ):
+                        ctx.repository.record_dvol_snapshot(
+                            conn,
+                            DvolSnapshot(
+                                timestamp=record.timestamp,
+                                dvol=record.dvol,
+                                eth_spot=record.spot,
+                            ),
+                        )
             finally:
                 conn.close()
             persisted += 1
diff --git a/tests/unit/test_market_snapshot_cycle.py b/tests/unit/test_market_snapshot_cycle.py
index 12d6782..ec09cd5 100644
--- a/tests/unit/test_market_snapshot_cycle.py
+++ b/tests/unit/test_market_snapshot_cycle.py
@@ -164,3 +164,48 @@ async def test_returns_zero_for_empty_assets(tmp_path: Path) -> None:
     ctx = _ctx(tmp_path)
     n = await collect_market_snapshot(ctx, assets=(), now=_now())
     assert n == 0
+
+
+def _read_dvol_history(ctx: MagicMock) -> list[dict]:
+    import sqlite3
+
+    conn = connect(ctx.db_path)
+    conn.row_factory = sqlite3.Row
+    try:
+        rows = conn.execute(
+            "SELECT * FROM dvol_history ORDER BY timestamp"
+        ).fetchall()
+    finally:
+        conn.close()
+    return [dict(r) for r in rows]
+
+
+@pytest.mark.asyncio
+async def test_eth_snapshot_mirrors_into_dvol_history(tmp_path: Path) -> None:
+    ctx = _ctx(tmp_path)
+    await collect_market_snapshot(ctx, assets=("ETH", "BTC"), now=_now())
+    rows = _read_dvol_history(ctx)
+    assert len(rows) == 1
+    assert Decimal(str(rows[0]["dvol"])) == Decimal("55")
+    assert Decimal(str(rows[0]["eth_spot"])) == Decimal("3000")
+
+
+@pytest.mark.asyncio
+async def test_btc_only_snapshot_does_not_touch_dvol_history(
+    tmp_path: Path,
+) -> None:
+    ctx = _ctx(tmp_path)
+    await collect_market_snapshot(ctx, assets=("BTC",), now=_now())
+    assert _read_dvol_history(ctx) == []
+
+
+@pytest.mark.asyncio
+async def test_eth_snapshot_skips_dvol_history_when_dvol_missing(
+    tmp_path: Path,
+) -> None:
+    ctx = _ctx(tmp_path)
+    ctx.deribit.latest_dvol = AsyncMock(side_effect=RuntimeError("no dvol"))
+    await collect_market_snapshot(ctx, assets=("ETH",), now=_now())
+    # market_snapshots row still persisted, but dvol_history must stay empty
+    # because its schema enforces NOT NULL on dvol/eth_spot.
+    assert _read_dvol_history(ctx) == []