policy: fix autogroup:self propagation and optimize cache invalidation (#2807)

hscontrol/mapper/builder.go

@@ -7,7 +7,6 @@ import (
 	"time"
 
 	"github.com/juanfont/headscale/hscontrol/policy"
-	"github.com/juanfont/headscale/hscontrol/policy/matcher"
 	"github.com/juanfont/headscale/hscontrol/types"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/views"
@@ -181,6 +180,9 @@ func (b *MapResponseBuilder) WithPacketFilters() *MapResponseBuilder {
 		return b
 	}
 
+	// FilterForNode returns rules already reduced to only those relevant for this node.
+	// For autogroup:self policies, it returns per-node compiled rules.
+	// For global policies, it returns the global filter reduced for this node.
 	filter, err := b.mapper.state.FilterForNode(node)
 	if err != nil {
 		b.addError(err)
@@ -192,7 +194,7 @@ func (b *MapResponseBuilder) WithPacketFilters() *MapResponseBuilder {
 	// new PacketFilters field and "base" allows us to send a full update when we
 	// have to send an empty list, avoiding the hack in the else block.
 	b.resp.PacketFilters = map[string][]tailcfg.FilterRule{
-		"base": policy.ReduceFilterRules(node, filter),
+		"base": filter,
 	}
 
 	return b
@@ -231,18 +233,19 @@ func (b *MapResponseBuilder) buildTailPeers(peers views.Slice[types.NodeView]) (
 		return nil, errors.New("node not found")
 	}
 
-	// Use per-node filter to handle autogroup:self
-	filter, err := b.mapper.state.FilterForNode(node)
+	// Get unreduced matchers for peer relationship determination.
+	// MatchersForNode returns unreduced matchers that include all rules where the node
+	// could be either source or destination. This is different from FilterForNode which
+	// returns reduced rules for packet filtering (only rules where node is destination).
+	matchers, err := b.mapper.state.MatchersForNode(node)
 	if err != nil {
 		return nil, err
 	}
 
-	matchers := matcher.MatchesFromFilterRules(filter)
-
 	// If there are filter rules present, see if there are any nodes that cannot
 	// access each-other at all and remove them from the peers.
 	var changedViews views.Slice[types.NodeView]
-	if len(filter) > 0 {
+	if len(matchers) > 0 {
 		changedViews = policy.ReduceNodes(node, peers, matchers)
 	} else {
 		changedViews = peers