docs(net): N4 accepted - Opus review PASS; AP-125 filed; F1/F5 fixed

The N4 review confirmed the draw-order reclaim design (invariant attacked
from five angles, held) and NAK fidelity down to the decomp''s x87
comparison masks. This acceptance commit settles the two process debts it
found: AP-125 (standalone control packets vs retail''s CoalesceData
piggyback - the ACE-safety divergence that has shipped since N3''s ack and
N4''s NAK) now has its register row; the false rounding-bug justification
in AckNakScheduler (0.6 x 1e7 rounds UP under IEEE-754, truncation never
lost a tick) is rewritten as the defensive hardening it actually is; and
Admission.Process''s defaulted draw-ordinal is now ulong.MaxValue so an
accidental cleartext repark can never head a bubble-shift chain. Core.Net
737/737 green.

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

src/AcDream.Core.Net/Transport/AckNakScheduler.cs

@@ -136,9 +136,13 @@ internal sealed class AckNakScheduler
         _sessionIteration = sessionIteration;
         _stats = stats;
         _send = send;
-        // Round, don't truncate: 0.6 has no exact double form and
-        // 0.6 × 10^7 truncates to 5,999,999 ticks — one tick short, which
-        // would open the STRICT gate at exactly 0.6 s elapsed.
+        // Round rather than truncate — defensive hardening only. At the
+        // frequencies in play (10 MHz Stopwatch/VirtualClock, 1 GHz Linux)
+        // 0.6 × Frequency rounds to the exact integer under IEEE-754 double
+        // multiplication (the 0.6 representation error is below the half-ulp
+        // at that magnitude), so truncation would be equivalent; Math.Round
+        // keeps the gate exact for any hypothetical frequency where the
+        // product lands below the integer. (N4 review F1.)
         _ackGateTicks = (long)Math.Round(AckGateSeconds * clock.Frequency);
         _nakGateTicks = (long)Math.Round(NakGateSeconds * clock.Frequency);
         // ReceiverData::SharedInit @ 0x00548EF0 (from Init @ 0x00548FA0)

src/AcDream.Core.Net/Transport/InboundSequenceTracker.cs

@@ -194,9 +194,16 @@ internal sealed class InboundSequenceTracker
     {
         public static Admission Dropped => new(true, null, 0);
 
+        /// <summary>
+        /// The default draw-order is <see cref="ulong.MaxValue"/>, NOT 0:
+        /// the one-arg form is the cleartext path (no word, no ordinal), and
+        /// an accidental repark of a defaulted admission must sort ABOVE
+        /// every real parked word instead of silently heading every
+        /// bubble-shift chain (N4 review F5 — ordinal 0 would).
+        /// </summary>
         public static Admission Process(
             uint? verifyKey,
-            ulong verifyKeyDrawOrder = 0) =>
+            ulong verifyKeyDrawOrder = ulong.MaxValue) =>
             new(false, verifyKey, verifyKeyDrawOrder);
     }