fix: validate SSE event data before parsing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/FightPage.vue

@@ -401,32 +401,41 @@ function connectSSE() {
 
   addSSEListener(eventSource, 'spectator_count', (e) => {
     try {
+      if (!e.data) return
       const data = JSON.parse(e.data)
-      spectatorCount.value = data.count || 0
-    } catch { /* ignore */ }
+      if (typeof data.count === 'number') spectatorCount.value = data.count
+    } catch (err) {
+      console.warn('[SSE] spectator_count parse error:', err)
+    }
   })
 
   addSSEListener(eventSource, 'ping', (e) => {
     try {
-      if (e.data) {
+      if (!e.data) return
       const data = JSON.parse(e.data)
-        if (data.spectators !== undefined) spectatorCount.value = data.spectators
+      if (typeof data.spectators === 'number') spectatorCount.value = data.spectators
+    } catch (err) {
+      console.warn('[SSE] ping parse error:', err)
     }
-    } catch { /* ignore */ }
   })
 
   addSSEListener(eventSource, 'reaction', (e) => {
     try {
+      if (!e.data) return
       const data = JSON.parse(e.data)
-      if (data.emoji && data.counts) {
+      if (typeof data.emoji === 'string' && data.counts) {
         spawnLiveReactionEmoji(data.emoji)
       }
-    } catch { /* ignore */ }
+    } catch (err) {
+      console.warn('[SSE] reaction parse error:', err)
+    }
   })
 
   addSSEListener(eventSource, 'round_start', (e) => {
     try {
+      if (!e.data) return
       const data = JSON.parse(e.data)
+      if (!data.challenge || !data.round) return
       currentChallengeInfo.value = { type: data.challenge.type, label: data.challenge.label }
       liveLogItems.value.push({
         type: 'challenge',
@@ -436,12 +445,13 @@ function connectSSE() {
       })
       scrollLiveLog()
     } catch (err) {
-      console.warn('[FightPage] SSE round_start parse failed:', err)
+      console.warn('[SSE] round_start parse error:', err)
     }
   })
 
   addSSEListener(eventSource, 'human_challenge', async (e) => {
     try {
+      if (!e.data) return
       const sseData = JSON.parse(e.data)
       if (myBot.value) {
         const res = await fetch(`/api/fights/${fightId.value}/challenge/${myBot.value.id}`)
@@ -469,6 +479,7 @@ function connectSSE() {
 
   addSSEListener(eventSource, 'round_end', (e) => {
     try {
+      if (!e.data) return
       const data = JSON.parse(e.data)
       if (data.spectators !== undefined) spectatorCount.value = data.spectators
       handleRoundEnd(data).catch(() => {})
@@ -479,6 +490,7 @@ function connectSSE() {
 
   addSSEListener(eventSource, 'fight_end', (e) => {
     try {
+      if (!e.data) return
       const data = JSON.parse(e.data)
       if (data.spectators !== undefined) spectatorCount.value = data.spectators
       handleFightEnd(data).catch(() => {})