[proxy,management] Bound model discovery to the caller's own policies

The listing was narrowed by the provider record's enumerated models, which is
the right bound only while one policy reaches a provider. Where two teams
share a provider under different allowlists, every caller was offered the
union: each model outside their own policy is a request the guardrail refuses
a moment later, which is the empty-or-wrong picker this endpoint exists to
avoid, moved one level up. A gateway record enumerating nothing was worse
still — it offered the upstream's entire catalogue however narrow the policy.

The synthesiser already knows which policies authorise a provider and which
groups each binds, so the router can answer this at request time where it
knows the caller's groups. Each route now carries one rule per authorising
policy — its source groups and the models it permits — and the listing is
bounded to the union across the rules matching the caller, intersected with
what the provider serves.

This is deliberately finer than the guardrail's own per-provider allowlist,
which stays as it is: that list is a fail-closed backstop and cannot tell who
is asking, so discovery is now narrower than the backstop rather than wider.
A policy setting no allowlist lifts the restriction for the groups it binds,
so nil and empty model lists stay distinct end to end — collapsing them would
let a listing that should offer nothing fall open to everything.

e2e/agentnetwork/discovery_multipolicy_test.go

@@ -0,0 +1,122 @@
+//go:build e2e
+
+package agentnetwork
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/netbirdio/netbird/e2e/harness"
+	"github.com/netbirdio/netbird/shared/management/http/api"
+)
+
+// TestDiscoveryBoundToCallersPolicies covers a model listing on a provider two
+// teams reach under different allowlists.
+//
+// Bounding the listing by the provider's enumerated models alone is not enough
+// once more than one policy is in play: the caller would be offered every model
+// any team may use, and each one outside their own policy is a request the
+// guardrail refuses a moment later — the empty-or-wrong picker this endpoint
+// exists to avoid, just moved one level up.
+//
+// The client joins the main group only. Both models are enumerated by the same
+// provider and both are advertised by the upstream, so a listing that leaked
+// the other team's model would visibly contain it.
+func TestDiscoveryBoundToCallersPolicies(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Minute)
+	defer cancel()
+
+	vllm, err := harness.StartVLLM(ctx, srv)
+	require.NoError(t, err, "start mock upstream")
+	t.Cleanup(func() { _ = vllm.Terminate(context.Background()) })
+
+	grpMain, err := srv.API().Groups.Create(ctx, api.PostApiGroupsJSONRequestBody{Name: "e2e-disc-mp-main"})
+	require.NoError(t, err, "create main group")
+	t.Cleanup(func() { _ = srv.API().Groups.Delete(context.Background(), grpMain.Id) })
+
+	grpOther, err := srv.API().Groups.Create(ctx, api.PostApiGroupsJSONRequestBody{Name: "e2e-disc-mp-other"})
+	require.NoError(t, err, "create other group")
+	t.Cleanup(func() { _ = srv.API().Groups.Delete(context.Background(), grpOther.Id) })
+
+	ephemeral := false
+	sk, err := srv.API().SetupKeys.Create(ctx, api.PostApiSetupKeysJSONRequestBody{
+		Name:       "e2e-disc-mp-client",
+		Type:       "reusable",
+		ExpiresIn:  86400,
+		UsageLimit: 0,
+		AutoGroups: []string{grpMain.Id}, // the client joins grpMain only
+		Ephemeral:  &ephemeral,
+	})
+	require.NoError(t, err, "mint setup key")
+	require.NotEmpty(t, sk.Key, "setup key plaintext")
+
+	// One provider enumerating both models the upstream advertises, so the
+	// listing is narrowed by policy rather than by what the provider serves.
+	staticKey := "static-e2e-token"
+	prov, err := srv.CreateProvider(ctx, api.AgentNetworkProviderRequest{
+		Name:        "e2e-disc-mp",
+		ProviderId:  "openai_api",
+		UpstreamUrl: vllm.URL,
+		ApiKey:      &staticKey,
+		Enabled:     ptr(true),
+		Models: &[]api.AgentNetworkProviderModel{
+			{Id: harness.VLLMModel, InputPer1k: 0.001, OutputPer1k: 0.001},
+			{Id: harness.VLLMUnlistedModel, InputPer1k: 0.001, OutputPer1k: 0.001},
+		},
+	})
+	require.NoError(t, err, "create provider")
+	t.Cleanup(func() { _ = srv.DeleteProvider(context.Background(), prov.Id) })
+
+	mkGuardrail := func(name, model string) api.AgentNetworkGuardrail {
+		var gr api.AgentNetworkGuardrailRequest
+		gr.Name = name
+		gr.Checks.ModelAllowlist.Enabled = true
+		gr.Checks.ModelAllowlist.Models = []string{model}
+		g, gerr := srv.CreateGuardrail(ctx, gr)
+		require.NoError(t, gerr, "create guardrail %s", name)
+		t.Cleanup(func() { _ = srv.DeleteGuardrail(context.Background(), g.Id) })
+		return g
+	}
+	gMain := mkGuardrail("e2e-disc-mp-main", harness.VLLMModel)
+	gOther := mkGuardrail("e2e-disc-mp-other", harness.VLLMUnlistedModel)
+
+	enabled := true
+	polMain, err := srv.CreatePolicy(ctx, api.AgentNetworkPolicyRequest{
+		Name:                   "e2e-disc-mp-main",
+		Enabled:                &enabled,
+		SourceGroups:           []string{grpMain.Id},
+		DestinationProviderIds: []string{prov.Id},
+		GuardrailIds:           &[]string{gMain.Id},
+	})
+	require.NoError(t, err, "create main policy")
+	t.Cleanup(func() { _ = srv.DeletePolicy(context.Background(), polMain.Id) })
+
+	// The other team's policy, on the same provider, permitting the model the
+	// client must never be offered.
+	polOther, err := srv.CreatePolicy(ctx, api.AgentNetworkPolicyRequest{
+		Name:                   "e2e-disc-mp-other",
+		Enabled:                &enabled,
+		SourceGroups:           []string{grpOther.Id},
+		DestinationProviderIds: []string{prov.Id},
+		GuardrailIds:           &[]string{gOther.Id},
+	})
+	require.NoError(t, err, "create other policy")
+	t.Cleanup(func() { _ = srv.DeletePolicy(context.Background(), polOther.Id) })
+
+	endpoint, proxyIP, cl, px := connectClient(t, ctx, "disc-mp", sk.Key)
+	_ = px
+
+	code, body := callUntil(t, func() (int, string, error) {
+		return cl.Get(ctx, endpoint, proxyIP, "/v1/models?limit=1000", nil)
+	}, 200)
+	require.Equal(t, 200, code, "discovery must be served; body: %s", body)
+
+	assert.Contains(t, body, harness.VLLMModel,
+		"the model the caller's own policy permits must reach the picker")
+	assert.NotContains(t, body, harness.VLLMUnlistedModel,
+		"a model only another group's policy permits must not be offered to this caller")
+}

management/internals/modules/agentnetwork/synthesizer.go

@@ -211,7 +211,19 @@ func SynthesizeServices(ctx context.Context, s store.Store, accountID string) ([
 
 	groupIndex := indexProviderGroups(enabledPolicies)
 
-	routerCfgJSON, err := buildRouterConfigJSON(enabledProviders, groupIndex)
+	// The proxy guardrail is a per-provider fail-closed backstop; the
+	// authoritative per-policy/group decision is management's
+	// SelectPolicyForRequest. A provider lands in that map only when every
+	// authorising policy restricts models.
+	providerAllowlists := buildProviderAllowlists(enabledPolicies, guardrailsByID)
+
+	// Discovery gets the finer view: per policy rather than flattened per
+	// provider, so a listing can be bounded to what the calling groups may
+	// actually use instead of the union across everyone who reaches the
+	// provider.
+	modelPolicies := buildModelPolicies(enabledPolicies, guardrailsByID)
+
+	routerCfgJSON, err := buildRouterConfigJSON(enabledProviders, groupIndex, modelPolicies)
 	if err != nil {
 		return nil, err
 	}
@@ -228,11 +240,6 @@ func SynthesizeServices(ctx context.Context, s store.Store, accountID string) ([
 
 	mergedGuardrails := mergeGuardrails(enabledPolicies, guardrailsByID)
 	applyAccountCollectionControls(&mergedGuardrails, settings)
-	// The proxy guardrail is a per-provider fail-closed backstop; the
-	// authoritative per-policy/group decision is management's
-	// SelectPolicyForRequest. A provider lands in this map only when every
-	// authorising policy restricts models.
-	providerAllowlists := buildProviderAllowlists(enabledPolicies, guardrailsByID)
 	guardrailJSON, err := marshalGuardrailConfig(providerAllowlists, mergedGuardrails.PromptCapture)
 	if err != nil {
 		return nil, err
@@ -351,6 +358,11 @@ type routerProviderRoute struct {
 	AuthHeaderName  string   `json:"auth_header_name"`
 	AuthHeaderValue string   `json:"auth_header_value"`
 	AllowedGroupIDs []string `json:"allowed_group_ids,omitempty"`
+	// ModelPolicies is one entry per enabled policy authorising this provider,
+	// carrying that policy's source groups and the models it permits. The
+	// router bounds a model listing with it, so a provider two groups reach
+	// under different allowlists offers each only its own.
+	ModelPolicies []routerModelPolicy `json:"model_policies,omitempty"`
 	// Vertex marks a Google Vertex AI provider, whose requests carry the
 	// model in the URL path. The router selects it by path, bypassing the
 	// model/vendor table.
@@ -422,7 +434,7 @@ func indexProviderGroups(policies []*types.Policy) map[string][]string {
 // path-prefix tiebreak. Providers no enabled policy authorises
 // (orphans) are intentionally OMITTED so the router never observes a
 // route with an empty ACL.
-func buildRouterConfigJSON(providers []*types.Provider, groupIndex map[string][]string) ([]byte, error) {
+func buildRouterConfigJSON(providers []*types.Provider, groupIndex map[string][]string, modelPolicies map[string][]routerModelPolicy) ([]byte, error) {
 	cfg := routerConfig{Providers: make([]routerProviderRoute, 0, len(providers))}
 	for _, p := range providers {
 		groups, hasPolicy := groupIndex[p.ID]
@@ -449,6 +461,7 @@ func buildRouterConfigJSON(providers []*types.Provider, groupIndex map[string][]
 			AuthHeaderName:          headerName,
 			AuthHeaderValue:         headerValue,
 			AllowedGroupIDs:         groups,
+			ModelPolicies:           modelPolicies[p.ID],
 			Vertex:                  catalog.IsVertexPathStyle(p.ProviderID),
 			Bedrock:                 catalog.IsBedrockPathStyle(p.ProviderID),
 			GCPServiceAccountKeyB64: gcpSAKeyB64,
@@ -1098,3 +1111,46 @@ func mergeGuardrail(g *types.Guardrail, merged *MergedGuardrails) {
 		}
 	}
 }
+
+// routerModelPolicy mirrors the router's ModelPolicyRule: one authorising
+// policy's source groups plus the models it permits. Models is nil for a
+// policy that sets no model allowlist, which lifts the restriction for the
+// groups it binds — so nil and empty must survive the round trip distinctly.
+type routerModelPolicy struct {
+	GroupIDs []string `json:"group_ids"`
+	Models   []string `json:"models"`
+}
+
+// buildModelPolicies indexes, per provider, one rule for each enabled policy
+// authorising it: the policy's source groups and the models its guardrail
+// permits.
+//
+// This is deliberately finer than buildProviderAllowlists, which flattens the
+// same inputs into one list per provider for the proxy's fail-closed guardrail.
+// A flattened list cannot answer "what may THIS caller see", so a provider two
+// teams reach under different allowlists would offer each team the other's
+// models — a picker full of entries the next request refuses. Keeping the
+// source groups alongside the models lets the router answer it at request time,
+// where it knows the caller's groups.
+func buildModelPolicies(policies []*types.Policy, byID map[string]*types.Guardrail) map[string][]routerModelPolicy {
+	out := make(map[string][]routerModelPolicy)
+	for _, p := range policies {
+		if p == nil || len(p.SourceGroups) == 0 {
+			continue
+		}
+		restricted, models := policyModelAllowlist(p, byID)
+		rule := routerModelPolicy{GroupIDs: append([]string(nil), p.SourceGroups...)}
+		if restricted {
+			// Never nil when restricted: an allowlist permitting nothing must
+			// stay distinguishable from no allowlist at all.
+			rule.Models = append([]string{}, models...)
+		}
+		for _, providerID := range p.DestinationProviderIDs {
+			if providerID == "" {
+				continue
+			}
+			out[providerID] = append(out[providerID], rule)
+		}
+	}
+	return out
+}

management/internals/modules/agentnetwork/synthesizer_provider_allowlist_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/netbirdio/netbird/management/internals/modules/agentnetwork/types"
 )
@@ -93,3 +94,75 @@ func TestBuildProviderAllowlists(t *testing.T) {
 			"an enabled-but-empty allowlist is restricted with an empty set, not unrestricted")
 	})
 }
+
+// policyForGroups builds an enabled policy binding the given source groups to
+// the given providers under an optional guardrail.
+func policyForGroups(id string, groups []string, guardrailIDs []string, providerIDs ...string) *types.Policy {
+	return &types.Policy{
+		ID:                     id,
+		Enabled:                true,
+		SourceGroups:           groups,
+		DestinationProviderIDs: providerIDs,
+		GuardrailIDs:           guardrailIDs,
+	}
+}
+
+// TestBuildModelPolicies covers the finer index discovery needs. Where
+// buildProviderAllowlists flattens every authorising policy into one list per
+// provider — enough for a fail-closed backstop, but blind to who is asking —
+// this keeps each policy's source groups beside its models so the router can
+// bound a listing to the calling groups.
+func TestBuildModelPolicies(t *testing.T) {
+	byID := map[string]*types.Guardrail{
+		"g-4o":       allowlistGuardrail("g-4o", "acc-1", "gpt-4o"),
+		"g-opus":     allowlistGuardrail("g-opus", "acc-1", "claude-opus-4"),
+		"g-disabled": {ID: "g-disabled", Checks: types.GuardrailChecks{ModelAllowlist: types.GuardrailModelAllowlist{Enabled: false, Models: []string{"gpt-4o"}}}},
+	}
+
+	t.Run("each policy keeps its own groups and models", func(t *testing.T) {
+		policies := []*types.Policy{
+			policyForGroups("p1", []string{"grp-eng"}, []string{"g-4o"}, "prov-x"),
+			policyForGroups("p2", []string{"grp-sales"}, []string{"g-opus"}, "prov-x"),
+		}
+		got := buildModelPolicies(policies, byID)
+		assert.Equal(t, []routerModelPolicy{
+			{GroupIDs: []string{"grp-eng"}, Models: []string{"gpt-4o"}},
+			{GroupIDs: []string{"grp-sales"}, Models: []string{"claude-opus-4"}},
+		}, got["prov-x"],
+			"the two policies must stay separable so neither group is offered the other's models")
+	})
+
+	t.Run("an unrestricted policy carries nil models", func(t *testing.T) {
+		policies := []*types.Policy{
+			policyForGroups("p1", []string{"grp-eng"}, []string{"g-4o"}, "prov-x"),
+			policyForGroups("p2", []string{"grp-admin"}, nil, "prov-x"),
+		}
+		got := buildModelPolicies(policies, byID)
+		assert.Nil(t, got["prov-x"][1].Models,
+			"no allowlist must reach the router as nil, which lifts the restriction for its groups")
+	})
+
+	t.Run("a disabled allowlist is not a restriction", func(t *testing.T) {
+		policies := []*types.Policy{policyForGroups("p1", []string{"grp-eng"}, []string{"g-disabled"}, "prov-x")}
+		got := buildModelPolicies(policies, byID)
+		assert.Nil(t, got["prov-x"][0].Models,
+			"a guardrail with the allowlist check off restricts nothing")
+	})
+
+	t.Run("an enabled allowlist with no models permits nothing", func(t *testing.T) {
+		byIDEmpty := map[string]*types.Guardrail{
+			"g-empty": {ID: "g-empty", Checks: types.GuardrailChecks{ModelAllowlist: types.GuardrailModelAllowlist{Enabled: true}}},
+		}
+		policies := []*types.Policy{policyForGroups("p1", []string{"grp-eng"}, []string{"g-empty"}, "prov-x")}
+		got := buildModelPolicies(policies, byIDEmpty)
+		require.NotNil(t, got["prov-x"][0].Models,
+			"an empty allowlist must not arrive as nil — that would read as unrestricted")
+		assert.Empty(t, got["prov-x"][0].Models)
+	})
+
+	t.Run("a policy binding no groups is skipped", func(t *testing.T) {
+		policies := []*types.Policy{policyForGroups("p1", nil, []string{"g-4o"}, "prov-x")}
+		assert.Empty(t, buildModelPolicies(policies, byID),
+			"a policy with no source groups authorises nobody, so it bounds nobody's listing")
+	})
+}

proxy/internal/middleware/builtin/llm_router/factory.go

@@ -44,6 +44,12 @@ type ProviderRoute struct {
 	AuthHeaderName  string   `json:"auth_header_name"`
 	AuthHeaderValue string   `json:"auth_header_value"`
 	AllowedGroupIDs []string `json:"allowed_group_ids"`
+	// ModelPolicies carries, per authorising policy, the source groups it
+	// binds and the models it permits. The router uses it to bound a model
+	// listing to what THIS caller may use: a provider reachable by two groups
+	// under different allowlists must not offer either group the other's
+	// models. Empty means no policy restricts models on this route.
+	ModelPolicies []ModelPolicyRule `json:"model_policies,omitempty"`
 	// Vertex marks a Google Vertex AI provider. Vertex requests carry the
 	// model in the URL path, so the router selects this route by path
 	// (isVertexPath) and bypasses the model/vendor table entirely.
@@ -65,6 +71,18 @@ type ProviderRoute struct {
 	SkipTLSVerify bool `json:"skip_tls_verify,omitempty"`
 }
 
+// ModelPolicyRule is one authorising policy's contribution to what a caller
+// may use on a route: the source groups it binds, and the models it permits.
+//
+// Models is nil when the policy sets no model allowlist — an unrestricted
+// policy, which lifts the restriction for the groups it binds. That is why
+// nil and empty must stay distinct: an empty list is a guardrail that permits
+// nothing, and collapsing the two would let a listing fail open.
+type ModelPolicyRule struct {
+	GroupIDs []string `json:"group_ids"`
+	Models   []string `json:"models"`
+}
+
 // Config is the on-wire configuration accepted by the factory. An
 // empty Providers slice yields a router that denies every request as
 // not-routable; the synthesiser is responsible for stamping the

proxy/internal/middleware/builtin/llm_router/middleware.go

@@ -242,12 +242,13 @@ func (m *Middleware) routeModelless(reqPath, surface, method string, userGroups
 		if _, hadPrefix := splitBedrockNamespace(reqPath); hadPrefix {
 			stripBedrockNamespace(out)
 		}
-		// A route that enumerates its models bounds what the caller may use,
-		// so the picker must not offer the rest: every entry outside the list
-		// is a request the chain will deny.
-		if reqPath == modelListingPath && len(route.Models) > 0 &&
-			out.Mutations != nil && out.Mutations.RewriteUpstream != nil {
-			out.Mutations.RewriteUpstream.DiscoveryModels = append([]string(nil), route.Models...)
+		// What the caller may actually use bounds what the picker may offer:
+		// every entry outside it is a request the chain will deny a moment
+		// later.
+		if reqPath == modelListingPath && out.Mutations != nil && out.Mutations.RewriteUpstream != nil {
+			if models, bounded := discoverableModels(route, userGroups); bounded {
+				out.Mutations.RewriteUpstream.DiscoveryModels = models
+			}
 		}
 		return out
 	case matchOutcomeUnauthorised:
@@ -271,6 +272,96 @@ func isNonInferenceMethod(method string) bool {
 	return method == http.MethodGet || method == http.MethodHead
 }
 
+// discoverableModels returns the model ids a caller in userGroups may actually
+// use on this route, and whether the listing should be bounded to them at all.
+//
+// Two things narrow a listing, and both must apply or the picker offers models
+// the very next request refuses:
+//
+//   - the provider's own enumerated models, when it lists any (a gateway record
+//     enumerates nothing and claims everything);
+//   - the model allowlists of the policies that authorise THIS caller. A
+//     provider reachable by two groups under different allowlists must not
+//     offer either group the other's models, which is why the rules carry their
+//     source groups rather than arriving pre-flattened.
+//
+// A policy that sets no allowlist lifts the restriction for the groups it
+// binds, so a caller holding one unrestricted policy sees the provider's full
+// list. bounded is false when nothing narrows the listing — an unrestricted
+// caller on a route that enumerates nothing — in which case the upstream's own
+// answer passes through untouched.
+func discoverableModels(route ProviderRoute, userGroups []string) ([]string, bool) {
+	permitted, restricted := policyPermittedModels(route, userGroups)
+
+	switch {
+	case !restricted && len(route.Models) == 0:
+		return nil, false
+	case !restricted:
+		return append([]string(nil), route.Models...), true
+	case len(route.Models) == 0:
+		// A gateway record enumerates nothing, so the allowlist is the whole
+		// bound — previously such a record offered the upstream's entire
+		// catalogue however narrow the policy was.
+		return sortedModels(permitted), true
+	}
+
+	// Both bound: only what the provider serves and the policy permits.
+	intersection := make(map[string]struct{}, len(route.Models))
+	for _, m := range route.Models {
+		if _, ok := permitted[m]; ok {
+			intersection[m] = struct{}{}
+		}
+	}
+	return sortedModels(intersection), true
+}
+
+// policyPermittedModels folds the rules whose groups intersect the caller's
+// into the set of models they permit. restricted is false when the caller
+// holds at least one authorising policy that sets no allowlist, or when no
+// rule binds them at all.
+func policyPermittedModels(route ProviderRoute, userGroups []string) (map[string]struct{}, bool) {
+	permitted := make(map[string]struct{})
+	restricted := false
+	for _, rule := range route.ModelPolicies {
+		if !groupsIntersect(rule.GroupIDs, userGroups) {
+			continue
+		}
+		if rule.Models == nil {
+			// An unrestricted policy the caller holds lifts the restriction
+			// entirely, whatever the others say.
+			return nil, false
+		}
+		restricted = true
+		for _, m := range rule.Models {
+			permitted[m] = struct{}{}
+		}
+	}
+	return permitted, restricted
+}
+
+// groupsIntersect reports whether the two group-id sets share a member.
+func groupsIntersect(a, b []string) bool {
+	for _, x := range a {
+		for _, y := range b {
+			if x == y {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// sortedModels flattens a model set into a stable slice so the bound the proxy
+// applies — and any test asserting on it — does not depend on map order.
+func sortedModels(set map[string]struct{}) []string {
+	out := make([]string, 0, len(set))
+	for m := range set {
+		out = append(out, m)
+	}
+	sort.Strings(out)
+	return out
+}
+
 // markNonInference tags an allow as a request that spends no tokens, so the
 // limit check skips the management pre-flight it would charge nothing against.
 func markNonInference(out *middleware.Output) {

proxy/internal/middleware/builtin/llm_router/middleware_test.go

@@ -1145,3 +1145,144 @@ func TestRouter_PinnedDatedModelStaysDistinct(t *testing.T) {
 			"declaration order must not decide between two deliberately pinned builds")
 	})
 }
+
+// TestRouter_DiscoveryBoundToCallersPolicies pins that a model listing is
+// bounded by the policies that authorise the caller, not by the union across
+// everyone who can reach the provider. Two teams sharing one provider record
+// under different allowlists is the case that makes the difference visible: a
+// flattened per-provider list would offer each team the other's models, and
+// every one of those entries is a request the guardrail then refuses.
+func TestRouter_DiscoveryBoundToCallersPolicies(t *testing.T) {
+	const (
+		eng   = "grp-eng"
+		sales = "grp-sales"
+	)
+	route := ProviderRoute{
+		ID:              "shared-gateway",
+		Models:          []string{"claude-sonnet-5", "claude-haiku-4-5", "gpt-4o"},
+		AllowedGroupIDs: []string{eng, sales},
+		UpstreamScheme:  "https",
+		UpstreamHost:    "gateway.example.com",
+		ModelPolicies: []ModelPolicyRule{
+			{GroupIDs: []string{eng}, Models: []string{"claude-sonnet-5"}},
+			{GroupIDs: []string{sales}, Models: []string{"gpt-4o"}},
+		},
+	}
+
+	listingFor := func(t *testing.T, group string) []string {
+		t.Helper()
+		mw := New(Config{Providers: []ProviderRoute{route}})
+		in := newModellessInput(modelListingPath)
+		in.UserGroups = []string{group}
+
+		out, err := mw.Invoke(context.Background(), in)
+		require.NoError(t, err)
+		require.Equal(t, middleware.DecisionAllow, out.Decision)
+		require.NotNil(t, out.Mutations)
+		require.NotNil(t, out.Mutations.RewriteUpstream)
+		return out.Mutations.RewriteUpstream.DiscoveryModels
+	}
+
+	t.Run("each group sees only its own policy's models", func(t *testing.T) {
+		assert.Equal(t, []string{"claude-sonnet-5"}, listingFor(t, eng),
+			"engineering must not be offered the model only sales may use")
+		assert.Equal(t, []string{"gpt-4o"}, listingFor(t, sales),
+			"sales must not be offered the model only engineering may use")
+	})
+
+	t.Run("a model no policy allows is offered to nobody", func(t *testing.T) {
+		for _, group := range []string{eng, sales} {
+			assert.NotContains(t, listingFor(t, group), "claude-haiku-4-5",
+				"the provider serves it, but no policy permits it")
+		}
+	})
+}
+
+// TestRouter_DiscoveryUnrestrictedPolicy covers the lifting rule: a caller
+// holding one policy without a model allowlist sees everything the provider
+// enumerates, whatever the other policies say.
+func TestRouter_DiscoveryUnrestrictedPolicy(t *testing.T) {
+	const (
+		eng   = "grp-eng"
+		admin = "grp-admin"
+	)
+	route := ProviderRoute{
+		ID:              "shared-gateway",
+		Models:          []string{"claude-sonnet-5", "gpt-4o"},
+		AllowedGroupIDs: []string{eng, admin},
+		UpstreamScheme:  "https",
+		UpstreamHost:    "gateway.example.com",
+		ModelPolicies: []ModelPolicyRule{
+			{GroupIDs: []string{eng}, Models: []string{"claude-sonnet-5"}},
+			// nil Models: a policy that sets no allowlist at all.
+			{GroupIDs: []string{admin}},
+		},
+	}
+	mw := New(Config{Providers: []ProviderRoute{route}})
+
+	in := newModellessInput(modelListingPath)
+	in.UserGroups = []string{eng, admin}
+
+	out, err := mw.Invoke(context.Background(), in)
+	require.NoError(t, err)
+	require.NotNil(t, out.Mutations.RewriteUpstream)
+	assert.ElementsMatch(t, []string{"claude-sonnet-5", "gpt-4o"},
+		out.Mutations.RewriteUpstream.DiscoveryModels,
+		"an unrestricted policy the caller holds lifts the restriction")
+}
+
+// TestRouter_DiscoveryOnGatewayRecord covers a record that enumerates no
+// models. It previously offered the upstream's whole catalogue however narrow
+// the policy was, because there was nothing to intersect against; the policy
+// allowlist is now the bound on its own.
+func TestRouter_DiscoveryOnGatewayRecord(t *testing.T) {
+	const eng = "grp-eng"
+	base := ProviderRoute{
+		ID:              "litellm",
+		AllowedGroupIDs: []string{eng},
+		UpstreamScheme:  "https",
+		UpstreamHost:    "litellm.internal",
+	}
+
+	t.Run("a policy allowlist bounds it", func(t *testing.T) {
+		route := base
+		route.ModelPolicies = []ModelPolicyRule{{GroupIDs: []string{eng}, Models: []string{"gpt-4o"}}}
+		mw := New(Config{Providers: []ProviderRoute{route}})
+
+		in := newModellessInput(modelListingPath)
+		in.UserGroups = []string{eng}
+
+		out, err := mw.Invoke(context.Background(), in)
+		require.NoError(t, err)
+		assert.Equal(t, []string{"gpt-4o"}, out.Mutations.RewriteUpstream.DiscoveryModels,
+			"a catch-all record must still be bounded by what policy permits")
+	})
+
+	t.Run("an allowlist permitting nothing offers nothing", func(t *testing.T) {
+		route := base
+		route.ModelPolicies = []ModelPolicyRule{{GroupIDs: []string{eng}, Models: []string{}}}
+		mw := New(Config{Providers: []ProviderRoute{route}})
+
+		in := newModellessInput(modelListingPath)
+		in.UserGroups = []string{eng}
+
+		out, err := mw.Invoke(context.Background(), in)
+		require.NoError(t, err)
+		require.NotNil(t, out.Mutations.RewriteUpstream)
+		assert.Empty(t, out.Mutations.RewriteUpstream.DiscoveryModels,
+			"an empty allowlist permits nothing, and must not be read as unrestricted")
+	})
+
+	t.Run("no policy restriction leaves the listing alone", func(t *testing.T) {
+		mw := New(Config{Providers: []ProviderRoute{base}})
+
+		in := newModellessInput(modelListingPath)
+		in.UserGroups = []string{eng}
+
+		out, err := mw.Invoke(context.Background(), in)
+		require.NoError(t, err)
+		require.NotNil(t, out.Mutations.RewriteUpstream)
+		assert.Nil(t, out.Mutations.RewriteUpstream.DiscoveryModels,
+			"nothing narrows the listing, so the upstream's own answer passes through")
+	})
+}