Task 2: Research Locking - prevent switching topics while study in progress

src/components/game/SkillsTab.tsx

@@ -267,7 +267,10 @@ export function SkillsTab() {
                   const baseCost = def.base * (level + 1) * currentTier;
                   const cost = Math.floor(baseCost * studyCostMult);
                   
-                  const canStudy = !maxed && prereqMet && store.rawMana >= cost && !isStudying;
+                  // Check if any study is in progress (prevent switching topics)
+                  const isAnyStudyInProgress = store.currentAction === 'study' && store.currentStudyTarget;
+                  // Can only study if: not maxed, prereqs met, has mana, and either no study in progress or already studying this skill
+                  const canStudy = !maxed && prereqMet && store.rawMana >= cost && (!isAnyStudyInProgress || isStudying);
                   
                   const milestoneInfo = hasMilestoneUpgrade(tieredSkillId, level);
                   const nextTierSkill = getNextTierSkill(tieredSkillId);
@@ -369,6 +372,9 @@ export function SkillsTab() {
                           <Badge className="bg-green-900/50 text-green-300">Maxed</Badge>
                         ) : (
                           <div className="flex gap-1">
+                            <TooltipProvider>
+                              <Tooltip>
+                                <TooltipTrigger asChild>
                                   <Button
                                     size="sm"
                                     variant={canStudy ? 'default' : 'outline'}
@@ -378,6 +384,14 @@ export function SkillsTab() {
                                   >
                                     Study ({fmt(cost)})
                                   </Button>
+                                </TooltipTrigger>
+                                {!canStudy && isAnyStudyInProgress && !isStudying && (
+                                  <TooltipContent>
+                                    <p>Cannot switch topics while studying {SKILLS_DEF[store.currentStudyTarget?.id || '']?.name || 'another skill'}</p>
+                                  </TooltipContent>
+                                )}
+                              </Tooltip>
+                            </TooltipProvider>
                             {/* Parallel Study button */}
                             {hasParallelStudy && 
                              store.currentStudyTarget &&