feat(net): N5 - loss observability, lossy decorator, the connected loss gate

Campaign N Slice N5 (docs/plans/2026-07-29-network-transport-campaign.md
section 8 rung 3): the permanent removal of the loopback blindness that let
#260 ship. Local ACE never drops a datagram, so every historical connected
gate was structurally incapable of exercising the N1-N4 recovery machinery;
from this slice on, tools/run-connected-loss-gate.ps1 runs the standard
lifecycle route through deterministic seeded loss and passes only on proven
non-zero recovery.

Observability:
- [net-tick] gains resend/s nak-out/s nak-in/s rej-in/s dup-drop/s parked/s
  reclaim/s cache= nakset= - TransportStats window deltas mirroring the
  acks/s cumulative-delta pattern, plus the two instantaneous depths (the
  unbounded-like-retail sent-packet cache watchdog and the inbound NAK set).
  TransportStats gains RejectsReceived (inbound RejectRetransmit packets).
  Counters increment unconditionally; every string is behind
  NetDiagnostics.ProbeNet (Code Structure Rule 5).
- WorldSession.Dispose emits one cumulative [net-final] totals line so the
  loss gate asserts exact counters instead of reconstructing them from
  rounded per-second rates.
- LinkStatusSnapshot.PacketLossPercentage is deliberately NOT wired: filed
  #261 - retail's CLinkStatusAverages formula
  (LinkStatusHolder::GetPacketLossPercentage @ 0x00411370) must be located
  first; inventing a ratio is forbidden.

N4-review F3 fold-in:
- Fresh reliable sends stamp Header.Iteration = the session iteration
  through the same shared retail header build already cited for Time (N3)
  and the N4 control packets: FlowQueue::TransmitNewPackets @ 0x00547A60,
  the stack build at 0x00547A84/0x00547AA8. The control-header rule now
  holds across all three send shapes (fresh reliable, ack, NAK). ACE reads
  neither Time nor Iteration inbound (campaign section 3) - wire-safe, and
  resends keep the stamp verbatim per the N1 rebuild rule.

Loss injection (Transport/LossyTransportDecorator):
- IWorldSessionTransport wrapper with deterministic seeded per-direction
  loss. Config via NetDiagnostics typed env properties read once:
  ACDREAM_NET_DROP_PCT (0 = off = default), ACDREAM_NET_DROP_SEED (default
  1), ACDREAM_NET_DROP_DIR (out|in|both, default both).
- Arming gate: NOTHING drops in either direction until the decorator has
  FORWARDED the first ENCRYPTED outbound datagram - parse-free check on
  length > 20 with EncryptedChecksum set in the LE flags word at bytes
  4..8. The cleartext handshake always survives and the arming datagram is
  never a casualty; handshake-loss testing belongs to N6's ConnectResponse
  0.333 s retransmit.
- Structurally absent at 0%: WrapIfConfigured returns the raw transport -
  WorldSession's default factory is the only production seam and a normal
  run never constructs the decorator.

Root-cause fix the gate immediately exposed:
- The logoff-confirmation wait in Dispose processed inbound datagrams but
  never pumped the transport, so a lost S2C logoff confirmation was
  gap-detected but its healing NAK never went out. Retail's pump
  (Client::UseTime @ 0x00411C40 -> PacketController::UseTime @ 0x005410D0)
  runs until LogOffServer; the wait now sweeps per processed datagram,
  making the logoff wait the third covered blocking pump (after Tick and
  the handshake loops). A lost C2S logoff REQUEST remains unrecoverable by
  ACE design (arrival-driven NAK; a quiet client is never NAKed - campaign
  section 3 row 1), recorded in the gate header.

Gates:
- tools/run-connected-loss-gate.ps1 (-DropPct 2 -Seed 1): PASS vs local
  ACE - the first automated observation of packet loss in project history.
  Decorator ledger: dropped out=3 in=10 of forwarded out=183 in=496.
  [net-final] resends=2 nak-in=2 nak-out=6 rej-in=0 acks-out=114
  acks-in=119 dup-drop=0 sanity-drop=0 cksum-fail=0 parked=9 reclaimed=0
  uncached-nak=0 cache=1 nakset=0. Every injected loss healed: both
  ACE-driven C2S resend recovery (nak-in=2 -> resends=2) and client-driven
  S2C NAK recovery (parked=9 -> nak-out=6) fired on a real connected
  route, all six checkpoints validated, graceful logout confirmed, ACE
  recorded the transport Disconnect.
- tools/run-connected-world-lifecycle-gate.ps1 (decorator absent): PASS -
  zero behavior change on the no-loss baseline; the gate now defensively
  clears the drop env vars.
- Core.Net Release: 747/747 (737 + 10 N5: decorator determinism/direction/
  arming/structural-absence/env parsing, the 5% seeded WorldSession lossy
  lifecycle with zero message loss both ways + ACE Headroom 256, the
  [net-tick] field pins, the Iteration stamps).
- Full solution Release: 9,763 passed / 5 skipped / 0 failed.

Test-fixture note: FakeAceTransport gains AutoAdvanceOnBlockingReceive so
virtual time can move during the blocking Connect()/EnterWorld() pumps -
with the clock frozen there, a dropped handshake-window datagram could
never be NAK-healed (a fixture artifact, not a transport property).

Campaign section 9 ledger row added (SHA recorded at N6 kickoff).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/ISSUES.md

@@ -97,6 +97,28 @@ Copy this block when adding a new issue:
 
 ---
 
+## #261 — Wire LinkStatusSnapshot.PacketLossPercentage from retail's formula
+
+**Status:** OPEN
+**Severity:** LOW
+**Filed:** 2026-07-29
+**Component:** net (link-status presentation)
+
+**Description:** `LinkStatusSnapshot.PacketLossPercentage`
+(`src/AcDream.Core.Net/LinkStatusSnapshot.cs:11`) is a permanent default 0 —
+the indicator UI renders it but nothing computes it. Campaign N Slice N5's
+`TransportStats` now counts every input a loss figure could want (resends,
+NAKs both directions, duplicate drops, parked words), but **locate retail's
+`CLinkStatusAverages` loss formula (see
+`LinkStatusHolder::GetPacketLossPercentage @ 0x00411370`) before wiring
+PacketLossPercentage; inventing a ratio is forbidden** — the displayed number
+must be retail's windowed average, not an acdream-invented counter quotient.
+
+**Acceptance:** the ported formula cites the named-retail symbol + address,
+and the indicator shows non-zero loss under `tools/run-connected-loss-gate.ps1`.
+
+---
+
 ## #260 — Portal-network wedge: outbound actions die + native/GPU memory climbs
 
 **Status:** ROOT-CAUSED 2026-07-29 — **fix in flight as Campaign N**