fix(net): FA1 review round -- zero-id tree rejection, monarch clear, 0x001F builder

Applies both MUST-FIX items and the code-facing SHOULD-FIX items from the
dual-lens FA1 review (docs/research/2026-08-12-fa1-review-mechanism.md,
docs/research/2026-08-12-fa1-review-blast.md):

Mechanism MF-1 / blast SF-2: AllegianceHierarchy::Add @0x005B6E90 wraps its
entire body in `if (_id != 0)` -- a record whose own id is zero discards
the WHOLE message, for both the monarch and a child record, and this is
also what makes treeParent == 0 unconditionally fatal for a non-monarch
record. ReadAllegianceProfileBody now rejects CharacterId == 0 on both
paths; four new boundary tests in AllegianceProfileVersionGateTests.cs
(zero-id monarch, zero-id child, zero treeParent, plus the existing
orphan/self-parent/duplicate trio).

Mechanism MF-2: added the missing 0x001F AllegianceUpdateRequest builder --
the structural twin of the fellowship 0x00A6 this slice already repaired --
with golden-vector tests for both on/off.

Mechanism SF-1 / blast SF-3: UnPack's last act before returning success
forces the monarch's MayPassupExperience to false regardless of the wire
bit or the HasPackedLevel-absent legacy-compat fallback. Ported at the end
of the record loop; the pre-existing HasPackedLevel-absent test moved off
the monarch record (which the new clear makes indistinguishable from "the
fallback never fired") onto a vassal record, and a new test proves the
monarch clear fires even when the wire bit explicitly asks for true.

Mechanism SF-2: removed ParseFellowshipDisband's invented body-length
validation -- retail's DispatchUI_Disband reads only the opcode and never
inspects a trailing body. The parser now always succeeds; the matching
test flips from asserting rejection to asserting acceptance.

Mechanism SF-3: added the D5 `<<1` shareLoot-shape test at the 0x02C0
FellowshipUpdateFellow site -- previously only pinned at 0x02BE, so a
future split of the shared ReadFellow helper could silently reintroduce a
bool read on this leg undetected.

Mechanism SF-5: renumbered the version-gate comments in
ReadAllegianceProfileBody to the true AllegianceVersion enum values
(1-11, matching acclient.h's SpokespersonAdded..ApprovedVassal) instead of
wire-appearance order, which only reached 10 and silently dropped gate 5
(BannedCharactersAdded, which is real but gates nothing in UnPack -- now
called out explicitly). Fixed the stale "lane B §12" citation in
SocialActions.cs to the actual master-table row.

Blast SF-1: pinned the two retail-faithful but user-visible behavior
changes FA1 made to the ALREADY-LIVE `@allegiance info` command --
reversed vassal print order (3-vassal test through
FormatAllegianceInfoLines) and malformed-tree silent-drop (test at the
GameEventWiring registration layer, which is `if (info is null) return;`).

Blast SF-4: fixed a doc comment citing a nonexistent `ConfirmationResponseTests`
class; the actual class is `ConfirmationTripleTests`.

Blast SF-5: cross-referenced the confirmation-triple discriminator's split
representation (ConfirmationType on the response leg only; bare uint on
the two inbound legs production actually reads) at both sites, so FA4
inherits a stated decision rather than an unexplained inconsistency.

Full Release suite: 13,158 passed / 4 skipped / 0 failed (13,162 total),
up from the pre-fix-round 13,149/4/0 (+9 tests this round).

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

src/AcDream.Core.Net/Messages/AllegianceRequests.cs

@@ -37,6 +37,24 @@ public static class AllegianceRequests
     public const uint SwearOpcode = 0x001Du;
     public const uint BreakOpcode = 0x001Eu;
 
+    /// <summary>
+    /// <c>0x001F AllegianceUpdateRequest</c> — the allegiance panel's
+    /// subscribe/unsubscribe toggle, the structural twin of the fellowship
+    /// <c>0x00A6 FellowshipUpdateRequest</c> repaired elsewhere in this
+    /// slice. Retail's <c>CM_Allegiance::Event_UpdateRequest(u32)</c>
+    /// (<c>@0x006A72BA</c>, lane C §1.2) is NOT a one-shot query — send
+    /// <c>1</c> on <c>gmAllegianceUI::PostInit</c>'s tail
+    /// (<c>@0x004911C6</c>) and on <c>RecvNotice_PlayerDescReceived</c>
+    /// (<c>@0x00490D59</c>), <c>1</c> on <c>OnVisibilityChanged</c>'s
+    /// visible branch (<c>@0x004912DD</c>), <c>0</c> on its hidden branch
+    /// (<c>@0x00491311</c>). ACE's own handler
+    /// (<c>GameActionAllegianceUpdateRequest.cs:12</c>) reads the value
+    /// and ignores it — always replying once regardless — but retail
+    /// servers do not, so this must be sent correctly (lane C §7.1
+    /// message #3).
+    /// </summary>
+    public const uint AllegianceUpdateRequestOpcode = 0x001Fu;
+
     /// <summary>Pledge yourself to the given patron.</summary>
     public static byte[] BuildSwear(uint gameActionSequence, uint patronGuid)
     {
@@ -72,6 +90,17 @@ public static class AllegianceRequests
         return Build(gameActionSequence, BreakOpcode, vassalGuid);
     }
 
+    /// <summary>
+    /// Declare the allegiance panel's visibility/subscription state to the
+    /// server (<c>0x001F AllegianceUpdateRequest</c>). See
+    /// <see cref="AllegianceUpdateRequestOpcode"/> for the four retail send
+    /// sites and their arguments.
+    /// </summary>
+    public static byte[] BuildAllegianceUpdateRequest(uint gameActionSequence, bool on)
+    {
+        return Build(gameActionSequence, AllegianceUpdateRequestOpcode, on ? 1u : 0u);
+    }
+
     private static byte[] Build(uint seq, uint sub, uint targetGuid)
     {
         byte[] body = new byte[16];