feat(runtime): FA2 -- RuntimeFellowshipState + RuntimeAllegianceState sibling J-owners

Two new sibling Runtime owners under GameRuntime per the Slice-J
pattern (D2): RuntimeFellowshipState is session-scoped (a new
RuntimeGenerationResetStage.Fellowship clears it at every generation
reset, matching the ExternalContainer precedent); RuntimeAllegianceState
survives reconnect behind a HasServerSeed-style one-way latch and
participates in NO reset stage (its data persists like a real
disconnect does not sever allegiance membership).

Fellowship: full-update REPLACE, incremental-fellow UPSERT, self-vs-
other quit/dismiss removal (self clears the whole snapshot), disband
clear, and retail's leader hand-off rule for the Quit button
(RequiresLeaderHandoffBeforeQuit -- the current leader quitting WITHOUT
disbanding must send 0x0290 AssignNewLeader before 0x00A3, lane B
§2.5/§3.6).

Allegiance: seeded by AllegianceUpdate (0x0020, always self) and,
self-gated on TargetGuid == playerGuid(), by AllegianceInfoResponse
(0x027C); wraps the FA1-assembled flat AllegianceMemberRecord list
directly (AllegianceTree was deleted at FA1 -- nothing left to wrap).

Both apply the full 8-edit J-owner template: construction + fault
points + Owner/View properties + CaptureOwnership + a new
GameRuntimeTeardownStage pair (FellowshipDisposed/AllegianceDisposed,
stage count 11->13) + RuntimeGameplayOwnershipSnapshot inclusion +
RuntimeStateCheckpoint/trace fields. IRuntimeFellowshipCommands/
IRuntimeAllegianceCommands added to IGameRuntimeCommands and
implemented on DirectGameRuntimeCommandAdapter. No IRuntimeEventObserver
member added (D2) -- consumers poll Snapshot.Revision.

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

src/AcDream.Runtime/RuntimeGenerationReset.cs

@@ -32,15 +32,23 @@ public enum RuntimeGenerationResetStage
     Friends = 9,
     Squelch = 10,
     NegotiatedChannels = 11,
-    BeginEntityRetirement = 12,
-    RetireEntities = 13,
-    DrainHostProjection = 14,
-    CompleteCanonicalEntities = 15,
-    CompleteHostProjection = 16,
-    ChatIdentity = 17,
-    PlayerSnapshots = 18,
-    PlayerIdentity = 19,
-    Complete = 20,
+    /// <summary>
+    /// Campaign FA slice FA2 (2026-08-12): the fellowship roster is
+    /// session-scoped (a disconnect drops you from the fellowship
+    /// server-side) — clear it here, alongside the other social-list
+    /// stages. Allegiance is deliberately NOT a reset stage — it survives
+    /// reconnect (see <see cref="RuntimeAllegianceState"/>'s class doc).
+    /// </summary>
+    Fellowship = 12,
+    BeginEntityRetirement = 13,
+    RetireEntities = 14,
+    DrainHostProjection = 15,
+    CompleteCanonicalEntities = 16,
+    CompleteHostProjection = 17,
+    ChatIdentity = 18,
+    PlayerSnapshots = 19,
+    PlayerIdentity = 20,
+    Complete = 21,
 }
 
 public readonly record struct RuntimeGenerationResetSnapshot(
@@ -88,6 +96,7 @@ public sealed class RuntimeGenerationReset
     private readonly RuntimeEntityObjectLifetime _entityObjects;
     private readonly RuntimeCharacterState _character;
     private readonly RuntimeLocalPlayerIdentityState _identity;
+    private readonly RuntimeFellowshipState _fellowship;
     private ResetState? _state;
     private RuntimeGenerationToken _lastCompletedGeneration;
     private bool _hasCompletedGeneration;
@@ -102,7 +111,8 @@ public sealed class RuntimeGenerationReset
         RuntimeLocalPlayerMovementState movement,
         RuntimeEntityObjectLifetime entityObjects,
         RuntimeCharacterState character,
-        RuntimeLocalPlayerIdentityState identity)
+        RuntimeLocalPlayerIdentityState identity,
+        RuntimeFellowshipState fellowship)
     {
         _transit = transit ?? throw new ArgumentNullException(nameof(transit));
         _communication = communication
@@ -118,6 +128,8 @@ public sealed class RuntimeGenerationReset
             ?? throw new ArgumentNullException(nameof(character));
         _identity = identity
             ?? throw new ArgumentNullException(nameof(identity));
+        _fellowship = fellowship
+            ?? throw new ArgumentNullException(nameof(fellowship));
     }
 
     public RuntimeGenerationToken? ActiveRetiringGeneration =>
@@ -285,6 +297,9 @@ public sealed class RuntimeGenerationReset
                         state,
                         _communication.ResetNegotiatedChannels);
                     break;
+                case RuntimeGenerationResetStage.Fellowship:
+                    Advance(state, _fellowship.ResetSession);
+                    break;
                 case RuntimeGenerationResetStage.BeginEntityRetirement:
                     _ = _entityObjects.BeginSessionClear();
                     state.Retirements = _entityObjects