From 88581912ba8fad4e48ba9303f811bbf3fd9a248f Mon Sep 17 00:00:00 2001
From: Wesley Liddick <dev@sub2api.org>
Date: Wed, 8 Jul 2026 19:23:38 +0000
Subject: [PATCH] test: add regression tests for fallback pricing pollution

---
 .../service/model_pricing_resolver_test.go    | 60 +++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/backend/internal/service/model_pricing_resolver_test.go b/backend/internal/service/model_pricing_resolver_test.go
index 3b49b15556..d4169e5f0e 100644
--- a/backend/internal/service/model_pricing_resolver_test.go
+++ b/backend/internal/service/model_pricing_resolver_test.go
@@ -727,3 +727,63 @@ func TestApplyTokenOverrides_IntervalSetsImageOutputPriceExplicit(t *testing.T)
 	require.True(t, pricing.ImageOutputPriceExplicit)
 	require.Equal(t, 0.0, pricing.ImageOutputPricePerToken)
 }
+
+// ===========================================================================
+// 10. Regression: channel overrides must not pollute fallbackPrices
+// ===========================================================================
+
+// TestApplyTokenOverrides_FlatDoesNotPolluteFallbackPrices verifies that the
+// flat-override path in applyTokenOverrides clones the BasePricing struct
+// before mutation, so the shared fallbackPrices map entry is not written through.
+func TestApplyTokenOverrides_FlatDoesNotPolluteFallbackPrices(t *testing.T) {
+	r := newResolverWithChannel(t, []ChannelModelPricing{{
+		Platform:    "anthropic",
+		Models:      []string{"claude-sonnet-4"},
+		BillingMode: BillingModeToken,
+		InputPrice:  testPtrFloat64(10e-6), // base is 3e-6
+		OutputPrice: testPtrFloat64(50e-6), // base is 15e-6
+	}})
+
+	resolved := r.Resolve(context.Background(), PricingInput{
+		Model:   "claude-sonnet-4",
+		GroupID: groupIDPtr(),
+	})
+
+	// Resolved pricing should reflect the channel override
+	require.NotNil(t, resolved)
+	require.InDelta(t, 10e-6, resolved.BasePricing.InputPricePerToken, 1e-12)
+	require.InDelta(t, 50e-6, resolved.BasePricing.OutputPricePerToken, 1e-12)
+
+	// Global fallbackPrices must NOT be polluted
+	fp := r.billingService.fallbackPrices["claude-sonnet-4"]
+	require.InDelta(t, 3e-6, fp.InputPricePerToken, 1e-12, "fallback InputPricePerToken polluted")
+	require.InDelta(t, 15e-6, fp.OutputPricePerToken, 1e-12, "fallback OutputPricePerToken polluted")
+	require.False(t, fp.ImageOutputPriceExplicit, "fallback ImageOutputPriceExplicit polluted")
+}
+
+// TestApplyTokenOverrides_IntervalDoesNotPolluteFallbackPrices verifies that
+// the interval-override path also clones before mutation.
+func TestApplyTokenOverrides_IntervalDoesNotPolluteFallbackPrices(t *testing.T) {
+	r := newResolverWithChannel(t, []ChannelModelPricing{{
+		Platform:    "anthropic",
+		Models:      []string{"claude-sonnet-4"},
+		BillingMode: BillingModeToken,
+		Intervals: []PricingInterval{
+			{MinTokens: 0, MaxTokens: testPtrInt(100000), InputPrice: testPtrFloat64(2e-6), OutputPrice: testPtrFloat64(8e-6)},
+		},
+	}})
+
+	resolved := r.Resolve(context.Background(), PricingInput{
+		Model:   "claude-sonnet-4",
+		GroupID: groupIDPtr(),
+	})
+
+	require.NotNil(t, resolved)
+	require.True(t, resolved.BasePricing.ImageOutputPriceExplicit)
+
+	// Global fallbackPrices must NOT be polluted
+	fp := r.billingService.fallbackPrices["claude-sonnet-4"]
+	require.InDelta(t, 3e-6, fp.InputPricePerToken, 1e-12, "fallback InputPricePerToken polluted")
+	require.InDelta(t, 15e-6, fp.OutputPricePerToken, 1e-12, "fallback OutputPricePerToken polluted")
+	require.False(t, fp.ImageOutputPriceExplicit, "fallback ImageOutputPriceExplicit polluted")
+}