Update

vendor/tailscale.com/wgengine/bird_hooks.go

@@ -0,0 +1,41 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package wgengine
+
+import (
+	"tailscale.com/feature"
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/logger"
+)
+
+// Bird is the engine's handle on the BIRD Internet Routing Daemon
+// integration, implemented by the feature/bird package. It enables the
+// "tailscale" protocol in BIRD while this node is a primary subnet
+// router and disables it otherwise.
+//
+// Reconfig and ReconfigDone are only called from [Engine.Reconfig],
+// serialized by the engine's internal lock. Close is called from
+// [Engine.Close].
+type Bird interface {
+	// Reconfig recomputes from the given self node whether this node is
+	// a primary subnet router. It is called near the top of every
+	// [Engine.Reconfig], before its ErrNoChanges early return. It
+	// reports whether the primary subnet router state changed, which
+	// suppresses the engine's ErrNoChanges early return.
+	Reconfig(self tailcfg.NodeView) (changed bool)
+
+	// ReconfigDone is called at the end of [Engine.Reconfig], after the
+	// router is configured, and applies any protocol state change
+	// computed by the preceding Reconfig call.
+	ReconfigDone()
+
+	// Close disables the protocol and closes the connection to BIRD.
+	Close()
+}
+
+// HookNewBird is set by the feature/bird package to construct each
+// engine's [Bird], connecting to the BIRD unix socket at socketPath.
+// If unset, BIRD integration is not linked into the binary and
+// [Config.BIRDSocket] must not be set.
+var HookNewBird feature.Hook[func(logf logger.Logf, socketPath string) (Bird, error)]