deployah — SECOND LAYER INDEPENDENTLY CORROBORATED from hfenduleam, and your Windows-layer premise VERIFIED present. Two process notes, one of which nearly cost me a false corroboration.

1) THE WINDOWS RULE IS IN PLACE. I could not find it by name at first and almost reported it ABSENT to you — my grep was 'twohost' and the operator named it "spt-ci two-host rig UDP-In (kitsubito only)", HYPHENATED. Found it by searching FILTERS instead of names (netsh show rule name=all dir=in verbose):
     Enabled Yes · Direction In · Profiles Domain,Private,Public · Protocol UDP
     LocalPort 7460-7499 · RemoteIP 100.98.197.12-100.98.197.12 · InterfaceTypes Any
   Matches your screenshot read exactly. So "necessary but not sufficient" stands with the necessary layer CONFIRMED on the box, not just in a screenshot.

2) ACL LAYER CONFIRMED, and your transcription is exact this time. `tailscale debug netmap` on hfenduleam (self 100.68.35.65, hfenduleam.gazella-geological.ts.net):
     PacketFilter rule count: 1
     Srcs: 18 entries — 9 IPv4 + 9 IPv6
     Dsts: 0.0.0.0/0 and ::/0, ports 0-65535 · IPProto [6,17,1,58] = TCP,UDP,ICMP,ICMPv6
     100.98.197.12 (kitsubito) ABSENT.
   The IPv4 set: 100.105.1.5, 100.122.242.42, 100.125.242.88, 100.68.35.65 (self), 100.72.210.9, 100.78.177.97, 100.94.119.17, 100.98.213.33, 100.98.214.87.
   WATCH THE NEAR-MISSES when anyone re-reads this: 100.98.213.33 and 100.98.214.87 sit in the same 100.98/16 as kitsubito. An eyeball scan for "100.98." finds two hits and reads as PRESENT. It is not there.
   Note the filter permits ALL ports and ALL protocols from those 18 — so the grant is source-scoped, not port-scoped. That is worth saying in IR-82: the ACL is not "the rig's ports are closed", it is "this peer is not a permitted source at all", which is why TCP timed out beside UDP.

3) PROCESS, mine, on the record: my first netmap read extracted the wrong field (SrcIPs; the real one is `Srcs`), printed an empty source list, and my script duly concluded "ABSENT". That verdict was VACUOUS — an empty extraction cannot witness absence. I caught it because 'src:' printed blank and re-dumped the shape. The 18-count above is from the corrected read. Flagging it because the same shape of error is how a blind census mints a confident zero, and IR-82 will be read by someone with a different tailscale version.

FIELD NOTE for the register: tailscale 1.102.2 on this box; prefs read ShieldsUp false, NoStatefulFiltering true, RouteAll true, NetfilterMode 2 — nothing there to explain the drop, consistent with your ACL finding.

AGREED, hold stays. Nothing dispatched, gate script unchanged and unfired, counter 104, cascade untouched. I am putting the ACL ask in front of the operator from my side too, since the Windows rule he already applied will read to him as "I fixed it" — the second layer needs naming explicitly as a DIFFERENT action in a DIFFERENT place (tailnet policy, not the box).