[management, proxy] scope agent-network model allowlist per policy/group and provider (#6905)

## Describe your changes

The model-allowlist guardrail was merged into one account-wide union and
enforced flat on every request, ignoring which policy/group/provider
authorised it. With multiple policies — especially a mix of guardrailed
and un-guardrailed ones — this caused:

- **false-allow**: a model allowlisted for one group/provider leaked to
any caller; and
- **false-deny**: an un-guardrailed policy (intended unrestricted) was
blocked by another policy's allowlist.

Enforcement is now policy/group-aware, mirroring `llm_limit_check`:

- **Management (`SelectPolicyForRequest`) is authoritative.** It uses
the request model (already carried in
`CheckLLMPolicyLimitsRequest.model`, previously ignored) to keep only
applicable policies whose guardrails permit the model; no
allowlist-enabled guardrail = unrestricted. Denies
`llm_policy.model_blocked` when policies govern the (provider, groups)
but none permits the model.
- **Proxy `llm_guardrail` becomes a per-provider fail-closed backstop.**
The synthesiser emits an allowlist only for providers every authorising
policy restricts; the middleware keys off the resolved provider id and
keeps unknown-model fail-closed.

management/internals/shared/grpc/proxy.go

@@ -285,6 +285,7 @@ func (s *ProxyServiceServer) CheckLLMPolicyLimits(ctx context.Context, req *prot
 		UserID:     req.GetUserId(),
 		GroupIDs:   req.GetGroupIds(),
 		ProviderID: req.GetProviderId(),
+		Model:      req.GetModel(),
 	})
 	if err != nil {
 		log.WithContext(ctx).Errorf("select policy for request: %v", err)

management/internals/shared/grpc/proxy_llm_policy_limits_test.go

@@ -0,0 +1,138 @@
+package grpc
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc/codes"
+	grpcstatus "google.golang.org/grpc/status"
+
+	"github.com/netbirdio/netbird/management/internals/modules/agentnetwork"
+	"github.com/netbirdio/netbird/shared/management/proto"
+)
+
+// fakeAgentNetworkLimits records the PolicySelectionInput it was invoked with
+// and returns a pre-programmed result, so tests can assert what the handler
+// forwards to the selector.
+type fakeAgentNetworkLimits struct {
+	gotInput agentnetwork.PolicySelectionInput
+	result   *agentnetwork.PolicySelectionResult
+	err      error
+}
+
+func (f *fakeAgentNetworkLimits) SelectPolicyForRequest(_ context.Context, in agentnetwork.PolicySelectionInput) (*agentnetwork.PolicySelectionResult, error) {
+	f.gotInput = in
+	if f.err != nil {
+		return nil, f.err
+	}
+	return f.result, nil
+}
+
+func (f *fakeAgentNetworkLimits) RecordUsage(_ context.Context, _ agentnetwork.RecordUsageInput) error {
+	return nil
+}
+
+// TestCheckLLMPolicyLimits_ForwardsModelToSelector proves the wiring added here:
+// the model the proxy extracted must reach the selector's Model unchanged,
+// alongside the account/user/group/provider fields.
+func TestCheckLLMPolicyLimits_ForwardsModelToSelector(t *testing.T) {
+	fake := &fakeAgentNetworkLimits{result: &agentnetwork.PolicySelectionResult{Allow: true, SelectedPolicyID: "pol-1"}}
+	s := &ProxyServiceServer{}
+	s.SetAgentNetworkLimitsService(fake)
+
+	req := &proto.CheckLLMPolicyLimitsRequest{
+		AccountId:  "acc-1",
+		UserId:     "user-1",
+		GroupIds:   []string{"grp-a", "grp-b"},
+		ProviderId: "prov-1",
+		Model:      "claude-opus-4",
+	}
+
+	resp, err := s.CheckLLMPolicyLimits(context.Background(), req)
+	require.NoError(t, err)
+	require.NotNil(t, resp)
+
+	assert.Equal(t, "acc-1", fake.gotInput.AccountID)
+	assert.Equal(t, "user-1", fake.gotInput.UserID)
+	assert.Equal(t, []string{"grp-a", "grp-b"}, fake.gotInput.GroupIDs)
+	assert.Equal(t, "prov-1", fake.gotInput.ProviderID)
+	assert.Equal(t, "claude-opus-4", fake.gotInput.Model,
+		"the request's model must be forwarded to the selector")
+}
+
+// TestCheckLLMPolicyLimits_EmptyModelForwardedAsEmpty proves an undetermined
+// model (empty string) is forwarded as-is; the selector decides how to treat it.
+func TestCheckLLMPolicyLimits_EmptyModelForwardedAsEmpty(t *testing.T) {
+	fake := &fakeAgentNetworkLimits{result: &agentnetwork.PolicySelectionResult{Allow: true}}
+	s := &ProxyServiceServer{}
+	s.SetAgentNetworkLimitsService(fake)
+
+	req := &proto.CheckLLMPolicyLimitsRequest{
+		AccountId:  "acc-1",
+		ProviderId: "prov-1",
+	}
+
+	_, err := s.CheckLLMPolicyLimits(context.Background(), req)
+	require.NoError(t, err)
+	assert.Equal(t, "", fake.gotInput.Model, "an absent model must be forwarded as empty, not fabricated")
+}
+
+// TestCheckLLMPolicyLimits_DenyResponseCarriesModelBlockedCode proves the deny
+// envelope surfaces the model-allowlist deny code + reason through the response.
+func TestCheckLLMPolicyLimits_DenyResponseCarriesModelBlockedCode(t *testing.T) {
+	fake := &fakeAgentNetworkLimits{result: &agentnetwork.PolicySelectionResult{
+		Allow:      false,
+		DenyCode:   "llm_policy.model_blocked",
+		DenyReason: `model "claude-opus-4" is not permitted by any applicable policy allowlist`,
+	}}
+	s := &ProxyServiceServer{}
+	s.SetAgentNetworkLimitsService(fake)
+
+	resp, err := s.CheckLLMPolicyLimits(context.Background(), &proto.CheckLLMPolicyLimitsRequest{
+		AccountId:  "acc-1",
+		ProviderId: "prov-1",
+		Model:      "claude-opus-4",
+	})
+	require.NoError(t, err)
+	require.NotNil(t, resp)
+	assert.Equal(t, "deny", resp.Decision)
+	assert.Equal(t, "llm_policy.model_blocked", resp.DenyCode)
+	assert.NotEmpty(t, resp.DenyReason)
+	assert.Empty(t, resp.SelectedPolicyId, "a denied request must carry no selected policy")
+}
+
+// TestCheckLLMPolicyLimits_SelectorErrorSurfacesAsInternal proves a selector
+// failure surfaces as an Internal gRPC error rather than a silent allow.
+func TestCheckLLMPolicyLimits_SelectorErrorSurfacesAsInternal(t *testing.T) {
+	fake := &fakeAgentNetworkLimits{err: errors.New("boom")}
+	s := &ProxyServiceServer{}
+	s.SetAgentNetworkLimitsService(fake)
+
+	_, err := s.CheckLLMPolicyLimits(context.Background(), &proto.CheckLLMPolicyLimitsRequest{
+		AccountId:  "acc-1",
+		ProviderId: "prov-1",
+		Model:      "gpt-4o",
+	})
+	require.Error(t, err)
+	st, ok := grpcstatus.FromError(err)
+	require.True(t, ok)
+	assert.Equal(t, codes.Internal, st.Code(), "selector errors must never fail open on the hot path")
+}
+
+// TestCheckLLMPolicyLimits_UnconfiguredServiceReturnsUnimplemented locks the
+// fallback: with no limits service wired the RPC returns Unimplemented.
+func TestCheckLLMPolicyLimits_UnconfiguredServiceReturnsUnimplemented(t *testing.T) {
+	s := &ProxyServiceServer{}
+
+	_, err := s.CheckLLMPolicyLimits(context.Background(), &proto.CheckLLMPolicyLimitsRequest{
+		AccountId:  "acc-1",
+		ProviderId: "prov-1",
+	})
+	require.Error(t, err)
+	st, ok := grpcstatus.FromError(err)
+	require.True(t, ok)
+	assert.Equal(t, codes.Unimplemented, st.Code())
+}