feat(quest): QT6 — plugins can read the contract tracker

The last piece of QT6's own scope: r10-quest-dialogs.md §11.6's contract half.
IGameState.Contracts exposes what the client structurally knows about quests,
which — per that same research — is the tracker and nothing else. The rest of
§11.6 (chat stream, tells, give, use, confirmations) is other features and
stays out of this campaign.

A pull-through source rather than a pushed mirror. Contracts change rarely and
are already owned canonically, so a second copy would only be a thing to keep
in step; reading through means a plugin cannot observe a stale list.

Both hosts implement it. The headless one carries contract id, stage and
progress but no names — a bot has no dat access — because losing the TEXT is
expected while losing the QUEST would leave a bot silently unable to see what
it is on. Same rule covers a contract the installed dat has never heard of: it
still projects, with empty text and a correct status, rather than vanishing.

The interface member is defaulted so a host predating this campaign still
satisfies IGameState.

Two lazy catalog loads exist (the panel's and this one) rather than one shared
instance. That is deliberate: threading a shared ContractCatalog through three
composition records to avoid reading a 322-row immutable table at most twice
per session would be plumbing for no correctness or performance gain, and the
comment at the call site says so.

Campaign QT is complete; the connected user gate is owed.

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

src/AcDream.Plugin.Abstractions/ContractSnapshot.cs

@@ -0,0 +1,41 @@
+namespace AcDream.Plugin.Abstractions;
+
+/// <summary>
+/// One tracked contract, as a plugin sees it.
+/// </summary>
+/// <remarks>
+/// <para>
+/// This is the ONLY structured view of quest state a client ever has. The
+/// retail client stores no quest flags and is never told one changed; it learns
+/// about quests through NPC dialogue, generic error text, and this tracker. A
+/// plugin asking "what quests am I on?" is asking this and nothing else.
+/// </para>
+/// <para>
+/// <paramref name="Name"/>, <paramref name="Description"/> and
+/// <paramref name="Status"/> come from the installed dat and may be empty on a
+/// host with no dat access (a headless bot), or for a contract the installed
+/// dat build has never heard of. The numeric fields are always present.
+/// </para>
+/// </remarks>
+/// <param name="ContractId">Key into the dat's ContractTable.</param>
+/// <param name="Stage">
+/// Raw wire stage: 1 available, 2 in progress, 3 done-or-pending-repeat, and
+/// <c>4 + n</c> for a progress counter with n steps done — see
+/// <paramref name="Progress"/>.
+/// </param>
+/// <param name="Progress">Completed steps, or 0 when the stage carries no counter.</param>
+/// <param name="IsDisplayed">Whether the server nominated this as the shown contract.</param>
+/// <param name="Name">Authored contract name.</param>
+/// <param name="Description">Authored long-form description.</param>
+/// <param name="Status">
+/// The progress text retail's own panel shows — "Available", "In Progress",
+/// "5/20 Tuskers", "Done (1h 30s to Repeat)".
+/// </param>
+public readonly record struct ContractSnapshot(
+    uint ContractId,
+    uint Stage,
+    uint Progress,
+    bool IsDisplayed,
+    string Name = "",
+    string Description = "",
+    string Status = "");

src/AcDream.Plugin.Abstractions/IGameState.cs

@@ -4,4 +4,15 @@ namespace AcDream.Plugin.Abstractions;
 public interface IGameState
 {
     IReadOnlyList<WorldEntitySnapshot> Entities { get; }
+
+    /// <summary>
+    /// The player's tracked contracts — the client's only structured view of
+    /// quest state (<c>r10-quest-dialogs.md</c> §1.3). Empty when the server
+    /// has sent none.
+    /// </summary>
+    /// <remarks>
+    /// Defaulted so a host predating Campaign QT still satisfies the interface;
+    /// both in-tree hosts implement it.
+    /// </remarks>
+    IReadOnlyList<ContractSnapshot> Contracts => [];
 }