refactor: extract ResolveClaw402WalletKey to store layer and expand OKX margin mode tests

- Move duplicated claw402 wallet resolution logic into store.AIModelStore.ResolveClaw402WalletKey
- api/strategy.go and manager/trader_manager.go now delegate to the shared method
- Add detailed doc comment on OKX SetMarginMode explaining the local-state-only approach
  and why the legacy /api/v5/account/set-isolated-mode endpoint is not called
- Add 3 new test cases: cross mode leverage, OpenShort tdMode, SetTakeProfit tdMode

trader/okx/trader_account.go

@@ -80,7 +80,19 @@ func (t *OKXTrader) GetBalance() (map[string]interface{}, error) {
 	return result, nil
 }
 
-// SetMarginMode sets margin mode
+// SetMarginMode configures the margin mode (cross/isolated) that will be applied
+// to all subsequent leverage and order requests for this trader instance.
+//
+// OKX V5 unified accounts do not expose a per-symbol mode-switch endpoint that
+// works reliably — the legacy /api/v5/account/set-isolated-mode endpoint returns
+// error 51000 ("Parameter isoMode error") when called on a unified account.
+// Instead, OKX applies the mode per-request via the mgnMode field on
+// /api/v5/account/set-leverage and via the tdMode field on order placement.
+//
+// This implementation therefore stores the configured mode locally and injects it
+// into each subsequent API request, rather than making an API call here.
+// NOTE: unlike Binance/Bybit implementations of this interface, no network call
+// is made — the method only updates local state.
 func (t *OKXTrader) SetMarginMode(symbol string, isCrossMargin bool) error {
 	t.isCrossMargin = isCrossMargin
 	mgnMode := t.marginMode()

trader/okx/trader_margin_mode_test.go

@@ -188,3 +188,60 @@ func TestOKXPlaceLimitOrderUsesConfiguredMarginMode(t *testing.T) {
 		t.Fatalf("expected isolated tdMode, got %#v", orderRequests[0].Body["tdMode"])
 	}
 }
+
+func TestOKXCrossMarginModeUsedInLeverage(t *testing.T) {
+	rt := &recordingTransport{}
+	trader := newTestOKXTrader(rt, true) // cross margin
+
+	if err := trader.SetLeverage("BTCUSDT", 10); err != nil {
+		t.Fatalf("SetLeverage failed: %v", err)
+	}
+
+	leverageRequests := rt.requestsForPath(okxLeveragePath)
+	if len(leverageRequests) != 2 {
+		t.Fatalf("expected 2 leverage requests, got %d", len(leverageRequests))
+	}
+
+	for _, req := range leverageRequests {
+		if req.Body["mgnMode"] != "cross" {
+			t.Fatalf("expected cross leverage mode, got %#v", req.Body["mgnMode"])
+		}
+	}
+}
+
+func TestOKXOpenShortUsesConfiguredMarginMode(t *testing.T) {
+	rt := &recordingTransport{}
+	trader := newTestOKXTrader(rt, false) // isolated
+
+	if _, err := trader.OpenShort("BTCUSDT", 0.1, 5); err != nil {
+		t.Fatalf("OpenShort failed: %v", err)
+	}
+
+	orderRequests := rt.requestsForPath(okxOrderPath)
+	if len(orderRequests) == 0 {
+		t.Fatal("expected at least one order request")
+	}
+
+	lastOrder := orderRequests[len(orderRequests)-1]
+	if lastOrder.Body["tdMode"] != "isolated" {
+		t.Fatalf("expected isolated tdMode for OpenShort, got %#v", lastOrder.Body["tdMode"])
+	}
+}
+
+func TestOKXSetTakeProfitUsesConfiguredMarginMode(t *testing.T) {
+	rt := &recordingTransport{}
+	trader := newTestOKXTrader(rt, false) // isolated
+
+	if err := trader.SetTakeProfit("BTCUSDT", "LONG", 0.1, 100000); err != nil {
+		t.Fatalf("SetTakeProfit failed: %v", err)
+	}
+
+	algoRequests := rt.requestsForPath(okxAlgoOrderPath)
+	if len(algoRequests) != 1 {
+		t.Fatalf("expected 1 algo order request, got %d", len(algoRequests))
+	}
+
+	if algoRequests[0].Body["tdMode"] != "isolated" {
+		t.Fatalf("expected isolated tdMode for SetTakeProfit, got %#v", algoRequests[0].Body["tdMode"])
+	}
+}