compileFilterRules skipped autogroup:internet destinations to keep them
out of the wire-format PacketFilter, but those same compiled rules are
the source of pm.matchers — and Node.CanAccess relies on a matcher whose
DestsIsTheInternet covers the public internet to surface exit-node peers
to ACL sources. With the skip in place no such matcher existed, exit
nodes silently dropped out of the source's peer list, and the docs'
exit-node walkthrough stopped working: `tailscale exit-node list`
returned "no exit nodes found" and `tailscale set --exit-node=<ip>`
returned "no node found in netmap with IP".
Drop the compile-time skip so autogroup:internet flows through normal
matcher derivation, and teach ReduceFilterRules to keep the resulting
client packet-filter rule on exit-route advertisers — Tailscale SaaS
sends those rules to exit nodes so the kernel filter accepts traffic
forwarded by autogroup:internet sources.
Verified against a live tailnet on 2026-04-28 via tscap; the b17/b18
captures land under testdata/issue_3212/ as a regression guard. The
captures are isolated from testdata/routes_results/ because the broader
TestRoutesCompat machinery assumes a CIDR-prefix wire format that
differs from the IPSet-range form SaaS emits for autogroup:internet —
aligning that wire format is tracked separately.
Fixes#3212
c7a0ca709f