Align console behavior with operator routing and image workflow expectations

Constraint: Must preserve current exchange-rate logic, same-group routing boundary, and temporary image-file behavior while fixing UX-visible inconsistencies.
Rejected: Large frontend chunk refactor | introduced risky circular chunking and did not improve deliverability for this rollout.
Confidence: medium
Scope-risk: moderate
Directive: Keep channel failover constrained to the selected group and preserve Beijing-day semantics for user cache dashboard metrics.
Tested: go test ./controller ./model ./service ./common -count=1; npm run build; remote smoke on source deployment at http://38.76.218.56:18081/ plus /api/status and /api/image-studio/settings.
Not-tested: Browser-driven end-to-end verification of every console page interaction.

model/channel_cache_selection_test.go

@@ -0,0 +1,57 @@
+package model
+
+import (
+	"testing"
+
+	"github.com/QuantumNous/new-api/common"
+)
+
+func TestGetRandomSatisfiedChannelOrderedByPriorityThenWeight(t *testing.T) {
+	origMemoryCacheEnabled := common.MemoryCacheEnabled
+	origCacheEnabled := group2model2channels
+	origChannels := channelsIDM
+	defer func() {
+		common.MemoryCacheEnabled = origMemoryCacheEnabled
+		group2model2channels = origCacheEnabled
+		channelsIDM = origChannels
+	}()
+
+	common.MemoryCacheEnabled = true
+	group2model2channels = map[string]map[string][]int{
+		"image": {
+			"gpt-image-2": {1, 2, 3},
+		},
+	}
+	channelsIDM = map[int]*Channel{
+		1: {Id: 1, Priority: int64Ptr(10), Weight: uintPtr(50)},
+		2: {Id: 2, Priority: int64Ptr(10), Weight: uintPtr(20)},
+		3: {Id: 3, Priority: int64Ptr(5), Weight: uintPtr(99)},
+	}
+
+	first, err := GetRandomSatisfiedChannel("image", "gpt-image-2", 0)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if first == nil || first.Id != 1 {
+		t.Fatalf("expected first channel id 1, got %+v", first)
+	}
+
+	second, err := GetRandomSatisfiedChannel("image", "gpt-image-2", 1)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if second == nil || second.Id != 2 {
+		t.Fatalf("expected second channel id 2, got %+v", second)
+	}
+
+	third, err := GetRandomSatisfiedChannel("image", "gpt-image-2", 2)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if third == nil || third.Id != 3 {
+		t.Fatalf("expected third channel id 3, got %+v", third)
+	}
+}
+
+func int64Ptr(v int64) *int64 { return &v }
+func uintPtr(v uint) *uint    { return &v }