feat(multiplayer): propagate allocated launch configuration

server/supervisor/supervisor.go

@@ -23,7 +23,8 @@ import (
 type GameServer struct {
 	// ObjectMeta.Annotations carries per-allocation data the agones package
 	// requests on the GameServerAllocation (server/agones/allocation.go) --
-	// currently cosmic-clash.io/match-id and cosmic-clash.io/allocation-id.
+	// currently cosmic-clash.io/match-id, cosmic-clash.io/allocation-id, and
+	// allocator-selected compatibility fields.
 	// This is the only channel for match-specific config to reach an
 	// already-Ready pod: env vars are fixed at pod creation, before Agones
 	// assigns a match to it. NOTE: the exact JSON key for this field
@@ -187,6 +188,10 @@ func (s *Supervisor) Start(ctx context.Context) error {
 			return err
 		}
 		command := withAllocatedConfig(s.config.Command, s.matchID(), s.config.ServerID, s.config.ImageDigest, rosterExpiry)
+		command, err = withAllocatedCompatibility(command, s.lastGameServer)
+		if err != nil {
+			return err
+		}
 		command = withPort(command, port)
 		s.cmd = exec.CommandContext(ctx, command[0], command[1:]...)
 	} else {
@@ -328,6 +333,55 @@ func withAllocatedConfig(command []string, matchID, serverID, imageDigest string
 	return result
 }
 
+// withAllocatedCompatibility overlays fields selected by the allocator onto
+// child flags. These values arrive through Agones allocation annotations after
+// the pod was created, so static Fleet defaults must never win over them.
+func withAllocatedCompatibility(command []string, gameServer GameServer) ([]string, error) {
+	values := map[string]string{}
+	annotations := gameServer.ObjectMeta.Annotations
+	if annotations == nil {
+		return command, nil
+	}
+	for annotation, flag := range map[string]string{
+		"cosmic-clash.io/region":    "region",
+		"cosmic-clash.io/build":     "client-build",
+		"cosmic-clash.io/protocol":  "protocol-version",
+		"cosmic-clash.io/transport": "transport",
+	} {
+		value := annotations[annotation]
+		if value == "" {
+			continue
+		}
+		if strings.ContainsAny(value, "\r\n\t") {
+			return nil, fmt.Errorf("allocated annotation %q contains control characters", annotation)
+		}
+		values[flag] = value
+	}
+	return withAllocatedValues(command, values), nil
+}
+
+func withAllocatedValues(command []string, values map[string]string) []string {
+	result := append([]string(nil), command...)
+	for key, value := range values {
+		if value == "" {
+			continue
+		}
+		prefix := "--" + key + "="
+		replaced := false
+		for i, arg := range result {
+			if strings.HasPrefix(arg, prefix) {
+				result[i] = prefix + value
+				replaced = true
+				break
+			}
+		}
+		if !replaced {
+			result = append(result, prefix+value)
+		}
+	}
+	return result
+}
+
 // reportAssignmentReady is best-effort: process-ready has already succeeded,
 // so the process is legitimately usable either way. A persistent failure is
 // written to stderr rather than returned, since treating it as fatal would

server/supervisor/supervisor_test.go

@@ -34,6 +34,36 @@ func TestWithAllocatedConfigOverridesAuthoritativeChildFlags(t *testing.T) {
 	}
 }
 
+func TestWithAllocatedCompatibilityOverridesStaleFlagsAndRejectsUnsafeValues(t *testing.T) {
+	command := []string{"game-server", "--region=EU", "--client-build=stale", "--protocol-version=1", "--transport=enet", "--custom=keep"}
+	gameServer := GameServer{}
+	gameServer.ObjectMeta.Annotations = map[string]string{
+		"cosmic-clash.io/region": "NA", "cosmic-clash.io/build": "build-live",
+		"cosmic-clash.io/protocol": "12", "cosmic-clash.io/transport": "steam_sdr",
+	}
+	got, err := withAllocatedCompatibility(command, gameServer)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{"--region=NA", "--client-build=build-live", "--protocol-version=12", "--transport=steam_sdr", "--custom=keep"} {
+		found := false
+		for _, arg := range got {
+			if arg == want {
+				found = true
+				break
+			}
+		}
+		if !found {
+			t.Fatalf("dynamic flag %q missing from %#v", want, got)
+		}
+	}
+	unsafe := gameServer
+	unsafe.ObjectMeta.Annotations = map[string]string{"cosmic-clash.io/region": "NA\nforged"}
+	if _, err := withAllocatedCompatibility(command, unsafe); err == nil {
+		t.Fatal("unsafe annotation did not fail closed")
+	}
+}
+
 func TestAllocatedStartInjectsDynamicEndpointAndCallsReadyAfterProbe(t *testing.T) {
 	ready := false
 	readyCalled := false