feat(net): N1 - outbound sent-packet cache + resend on NAK

Campaign N Slice N1 (docs/plans/2026-07-29-network-transport-campaign.md
S2.1) - the direct #260 fix: every sent reliable packet is now cached and
re-emitted, header-rebuilt, when ACE NAKs a client-sequence gap. One lost
C2S datagram no longer voids every subsequent action for the session's
lifetime.

New src/AcDream.Core.Net/Transport/:
- TransportClock: injectable monotonic source + retail's 0.5 s interval
  counter (ClientFlowQueue::IncrementLocalInterval @ 0x00547F10, tail
  `intervalID_ += elapsed`; the same function's ~3 s TimeSync/Echo cadence
  stays deferred per TS-58).
- SequenceMath: wrap-safe IsNewer/Max (TimeStampUtils::lhs_newer
  @ 0x00543890, reduced to the signed-difference form).
- SentPacketStore: FIFO of ArrayPool-rented wire buffers; Add asserts
  optionalLength == 0 (NetPacket::RemoveDisposableOptionalHeaders
  @ 0x00549510 pinned as a no-op under standalone-control); FlushOlderThan
  pops strictly-older wrap-safe (SentPacketStore::AddSentPacket
  @ 0x0054AB00, Flush @ 0x0054ACD0).
- OutboundFlowQueue: owns the outbound ISAAC, highestIDSent (starts 1,
  pre-increment, wrap 0xFFFFFFFF->1, never 0), the fragment sequence, the
  store, the wrap-safe sorted dedup pending-resend list
  (FlowQueue::EnqueueAcks @ 0x005488E0), and the flushNum_ ack watermark.
  Cache commit happens AFTER a successful send
  (FlowQueue::TransmitNewPackets @ 0x00547A60, commit site 0x00547C85).
  NAK ids[0] folds into the watermark as retail's implicit cumulative ack
  (RecipientData::ProcessNaks @ 0x00547010). A resend rebuilds ONLY the
  20-byte header: flags Retransmission|EncryptedChecksum (|BlobFragments
  with fragments), Time = current interval id, Sequence/Id/Iteration/
  DataSize verbatim, checksum = fresh header hash + stored sealed checksum
  (FlowQueue::TransmitAcks @ 0x005485B0, DequeueAck @ 0x005472F0). The
  original ISAAC key rides inside the sealed value - no new keystream word
  is ever drawn (CryptoSystem::EncryptData @ 0x0065FF40 non-null-key
  path; landmines #1/#2). Resend only on explicit NAK (landmine #3).
- ReliableTransport: composition + Sweep() (interval clock, resends,
  prune). The AckNakScheduler joins in N3/N4; ack behavior is untouched
  this slice.
- TransportStats: unconditional counters (ResendsSent,
  NakRequestsReceived, UncachedNakIds, AcksConsumed) + CacheDepth.

PacketCodec.FinalizeInPlace gains an overload returning (isaacKeyUsed,
sealedChecksum) where sealedChecksum is the pre-header-hash value -
payloadHash cleartext, isaacKey ^ payloadHash encrypted (retail
NetPacket::checksum_). The old signature forwards; encode bytes are
unchanged. Decode is untouched.

WorldSession integration is minimal: the transport is constructed at
ISAAC-seeding time (first reliable packet keeps sequence 2 / fragment 1,
byte-identical to pre-N1); SendGameMessage delegates (probe fseq/pseq now
read the transport); SendAck's borrowed sequence reads HighestIdSent
(identical value, behavior EXACTLY as-is this slice); ProcessDatagram
consumes RequestRetransmit + AckSequence BEFORE the unchanged reflex ack;
the sweep runs at the end of Tick() after the budget break AND inside
both blocking handshake pump loops (Connect step 4, EnterWorld
ServerReady - landmine #8), gated on _transportNegotiated; Dispose
returns the rented cache buffers.

Bookkeeping: TS-57 filed in the divergence register (uncached NAK ids
dropped silently + counted instead of retail's RejectRetransmit - ACE
no-ops the reject and the standalone unsequenced form would trip ACE's
watermark hole); TS-27 narrowed to the inbound direction in the same
commit; the stale WorldSession class-doc gap list corrected.

N0 fold-ins from the re-review: AceSessionModel.ProcessFragment split
into ACE's two literal branches (existing-buffer checks Complete,
NetworkSession.cs:495-507; new-buffer constructs + adds + TryAdds WITHOUT
checking Complete, :509-518), and the zero-count-fragment test now pins
the parked dead buffer (PartialFragmentBufferCount 0 -> 1). e3958610
recorded in the campaign ledger's N0 row.

Tests: 15 new in Transport/OutboundReliableTransportTests.cs - store
FIFO/strict/wrap-safe flush with rent/return balance via a counting
pool, interval-clock start/advance/wrap, resend header shape (flags
exactly 3 or 7, Time = interval, verbatim fields, checksum identity,
bit-identical body), resend-consumes-no-ISAAC-word, uncached-NAK
counting, ids[0] watermark fold + strict prune, wrap-safe ack max,
conformance resend verifying under AceCryptoModel with the ORIGINAL
parked key (Headroom 256, zero orphans, ordering restored), an
end-to-end FakeAceTransport lossy run (10 game actions, C2S #5 dropped,
all 10 dispatched in order, exactly one resend, session alive), and
zero-alloc steady-state SendGameMessage.

Gates: dotnet build green; AcDream.Core.Net.Tests 702/702; full-solution
Release 9,723 passed / 5 skipped / 0 failed; connected world-lifecycle
gate vs local ACE RESULT=PASS (0 failures, both sessions exit 0; one
pre-existing expected world-edge landblock-miss warning).

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

docs/plans/2026-07-29-network-transport-campaign.md

@@ -251,8 +251,8 @@ verbatim in each implementer prompt.
 
 | Slice | Status | Commit | Notes |
 |---|---|---|---|
-| N0 | complete | `7e9134b4` + the `test(net): N0 fix-up` commit | ACE-behaviour double + virtual clock + lossy link; the review fix-up added the `Session.CheckState` inbound gate, faithful `SendBundle` coalescing/splitting, two-phase termination, an ACE-loose C2S fragment parse, and ACE's MessageBuffer edge cases. 687 Core.Net tests green. |
-| N1 | pending | — | |
+| N0 | complete | `7e9134b4` + `e3958610` | ACE-behaviour double + virtual clock + lossy link; the review fix-up added the `Session.CheckState` inbound gate, faithful `SendBundle` coalescing/splitting, two-phase termination, an ACE-loose C2S fragment parse, and ACE's MessageBuffer edge cases. 687 Core.Net tests green. N1 folded in the re-review's `ProcessFragment` two-branch split (existing-buffer checks Complete; new-buffer parks without checking — the zero-count buffer stays parked). |
+| N1 | complete | (this slice's commit; SHA recorded at N2 kickoff) | Outbound sent-packet cache + resend on NAK (`Transport/`: `TransportClock`, `SequenceMath`, `SentPacketStore`, `OutboundFlowQueue`, `ReliableTransport`, `TransportStats`); `PacketCodec.FinalizeInPlace` sealed-checksum overload; `WorldSession` sweep in Tick + both handshake pump loops; TS-57 filed, TS-27 narrowed to inbound-only. |
 | N2 | pending | — | |
 | N3 | pending | — | |
 | N4 | pending | — | |