Disable treasure buttons when they cannot apply

Pick Up Treasure is disabled unless an uncarried treasure sits on your
square (and your actions haven't ended); Drop Treasure unless you are
actually carrying one. The warp-step button reuses the same derived
state. Buttons stay visible for stable layout — they just stop
inviting impossible clicks.

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

packages/web/src/App.svelte

@@ -351,6 +351,20 @@
   function drop() { net.command({ type: "dropTreasure" }); }
   function pass() { net.command({ type: "pass" }); }
 
+  const me = $derived(view?.players.find((p) => p.id === view?.you) ?? null);
+  const carryingTreasure = $derived(me?.carriedTreasureId != null);
+  const treasureHere = $derived(
+    view != null && me != null &&
+    view.treasures.some((t) => t.position && t.position.x === me.position.x &&
+                               t.position.y === me.position.y && !t.carriedBy),
+  );
+  const onWarpToken = $derived(
+    view != null && me != null &&
+    view.dimWarps.some((w) =>
+      (w.a.x === me.position.x && w.a.y === me.position.y) ||
+      (w.b.x === me.position.x && w.b.y === me.position.y)),
+  );
+
   let chronicleEl = $state<HTMLElement | null>(null);
   $effect(() => {
     void net.log.length;
@@ -556,16 +570,13 @@
       {/if}
 
       <div class="actions">
-        {#if isYourTurn && view.dimWarps.some((w) => {
+        {#if isYourTurn && onWarpToken}
-          const me = view.players.find((p) => p.id === view.you)!;
-          return (w.a.x === me.position.x && w.a.y === me.position.y) ||
-                 (w.b.x === me.position.x && w.b.y === me.position.y);
-        })}
           <button class="stamp" onclick={() => net.command({ type: "warpStep" })}>Step through the warp</button>
         {/if}
         {#if isYourTurn}
-          <button class="stamp" onclick={pickUp}>Pick up treasure</button>
+          <button class="stamp" disabled={!treasureHere || carryingTreasure || view.turn.actionsEnded}
-          <button class="stamp" onclick={drop}>Drop treasure</button>
+            onclick={pickUp}>Pick up treasure</button>
+          <button class="stamp" disabled={!carryingTreasure} onclick={drop}>Drop treasure</button>
           <label class="inline draw-pick">
             draw
             <select bind:value={drawCount}>