[management] Cover the gateway-pin claim against a real store

Belongs with 1b6a9d8 — the file was new and untracked, so the commit that
added the query it exercises went out without it.

Drives HasGatewayPinnedByOtherAccount through sqlite: another account is
refused the host, the pinning account may still claim it (pin first,
deploy the proxy after), an unpinned host stays free, and a labeled pin
claims the cluster address rather than the labeled endpoint beneath it.

management/server/store/sql_store_agentnetwork_gatewaypin_test.go

@@ -0,0 +1,73 @@
+package store
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	agentNetworkTypes "github.com/netbirdio/netbird/management/internals/modules/agentnetwork/types"
+)
+
+// TestHasGatewayPinnedByOtherAccount_RealStore drives the query a proxy
+// registration asks before claiming a cluster address, against a real sqlite
+// store.
+//
+// A gateway pin is a claim on the host: it is immutable, it is served by
+// whichever proxy declares that address, and an account-scoped proxy only ever
+// receives its own account's mappings — so a proxy from a different account
+// taking the address strands the pin. The account's own pin is the opposite
+// case and must stay claimable, because pinning first and deploying the proxy
+// after is the documented order.
+func TestHasGatewayPinnedByOtherAccount_RealStore(t *testing.T) {
+	ctx := context.Background()
+	s, cleanup, err := NewTestStoreFromSQL(ctx, "", t.TempDir())
+	require.NoError(t, err, "real sqlite test store must come up")
+	defer cleanup()
+
+	const (
+		pinnedHost = "gw.account1.example.com"
+		freeHost   = "nobody.example.com"
+	)
+
+	settings := agentNetworkTypes.DefaultSettings("account1")
+	settings.Domain = pinnedHost
+	settings.ProxyAddress = pinnedHost
+	require.NoError(t, s.CreateAgentNetworkSettings(ctx, settings), "seeding the pin must succeed")
+
+	t.Run("another account is refused the host", func(t *testing.T) {
+		pinned, err := s.HasGatewayPinnedByOtherAccount(ctx, pinnedHost, "account2")
+		require.NoError(t, err)
+		assert.True(t, pinned, "a host another account pinned its gateway to is claimed")
+	})
+
+	t.Run("the pinning account may still claim it", func(t *testing.T) {
+		pinned, err := s.HasGatewayPinnedByOtherAccount(ctx, pinnedHost, "account1")
+		require.NoError(t, err)
+		assert.False(t, pinned, "an account must be able to deploy the proxy for its own pin")
+	})
+
+	t.Run("an unpinned host is free", func(t *testing.T) {
+		pinned, err := s.HasGatewayPinnedByOtherAccount(ctx, freeHost, "account2")
+		require.NoError(t, err)
+		assert.False(t, pinned, "a host no gateway is pinned to stays claimable")
+	})
+
+	t.Run("a labeled pin claims the cluster, not just the endpoint", func(t *testing.T) {
+		// A labeled bootstrap hangs <label>.<cluster> beneath the address while
+		// pinning the cluster itself, so the claim follows proxy_address.
+		labeled := agentNetworkTypes.DefaultSettings("account3")
+		labeled.ProxyAddress = "byop.account3.example.com"
+		labeled.Domain = "violet." + labeled.ProxyAddress
+		require.NoError(t, s.CreateAgentNetworkSettings(ctx, labeled))
+
+		pinned, err := s.HasGatewayPinnedByOtherAccount(ctx, labeled.ProxyAddress, "account2")
+		require.NoError(t, err)
+		assert.True(t, pinned, "the pinned cluster address is the claim, not the labeled endpoint")
+
+		pinned, err = s.HasGatewayPinnedByOtherAccount(ctx, labeled.Domain, "account2")
+		require.NoError(t, err)
+		assert.False(t, pinned, "the labeled endpoint itself is not a cluster claim")
+	})
+}