fix: only generate MC choices for human fights, not bot-vs-bot

Bots answer via webhook and don't need multiple choice options.
Add forHuman parameter to pickChallenge, update tests to cover both modes.

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

server/src/engine/challenges.test.ts

@@ -48,9 +48,9 @@ describe('pickChallenge', () => {
     }
   })
 
-  it('creative challenges have MC choices and a correct answer', () => {
+  it('creative challenges have MC choices and a correct answer (human mode)', () => {
     for (let i = 0; i < 100; i++) {
-      const c = pickChallenge(new Set(), null)
+      const c = pickChallenge(new Set(), null, undefined, undefined, true)
       if (c.scoring === 'creative') {
         // Creative challenges now have auto-generated MC choices with a correct answer
         expect(c.choices).toBeDefined()
@@ -63,10 +63,17 @@ describe('pickChallenge', () => {
     }
   })
 
-  it('factual challenges with choices have shuffled choices', () => {
+  it('bot challenges have no MC choices', () => {
+    for (let i = 0; i < 100; i++) {
+      const c = pickChallenge(new Set(), null)
+      expect(c.choices).toBeUndefined()
+    }
+  })
+
+  it('factual challenges with choices have shuffled choices (human mode)', () => {
     const orders = new Set<string>()
     for (let i = 0; i < 50; i++) {
-      const c = pickChallenge(new Set(), null)
+      const c = pickChallenge(new Set(), null, undefined, undefined, true)
       if (c.scoring === 'factual' && c.choices) {
         orders.add(c.choices.join(','))
       }
@@ -90,11 +97,11 @@ describe('pickChallenge', () => {
     expect(factualPct).toBeLessThan(0.85)
   })
 
-  it('True/False auto-generation for boolean answers', () => {
+  it('True/False auto-generation for boolean answers (human mode)', () => {
     // Pick many challenges, find ones with answers = ['true'] or ['false']
     let foundTFWithChoices = false
     for (let i = 0; i < 500; i++) {
-      const c = pickChallenge(new Set(), null)
+      const c = pickChallenge(new Set(), null, undefined, undefined, true)
       if (c.answers?.length === 1 && ['true', 'false'].includes(c.answers[0].toLowerCase())) {
         expect(c.choices).toBeTruthy()
         expect(c.choices!.length).toBe(2)

server/src/engine/challenges.ts

@@ -70,7 +70,7 @@ export function roundToDifficulty(round: number): PromptDifficulty {
   return 'hard'
 }
 
-export function pickChallenge(usedTypes: Set<string>, _arenaModifier: string | null, themeBias?: PromptTheme, roundNumber?: number): Challenge {
+export function pickChallenge(usedTypes: Set<string>, _arenaModifier: string | null, themeBias?: PromptTheme, roundNumber?: number, forHuman = false): Challenge {
   let available = TEMPLATES.filter(t => !usedTypes.has(t.type))
   if (available.length === 0) available = TEMPLATES
 
@@ -88,7 +88,7 @@ export function pickChallenge(usedTypes: Set<string>, _arenaModifier: string | n
   const template = pick(pool)
   const targetTheme = themeBias || pickTheme()
   const targetDifficulty = roundNumber ? roundToDifficulty(roundNumber) : undefined
-  return templateToChallenge(template, targetTheme, targetDifficulty)
+  return templateToChallenge(template, targetTheme, targetDifficulty, forHuman)
 }
 
 /** Ranked challenge: no multiple choice, only harder creative/open-ended prompts */
@@ -262,7 +262,7 @@ function generateCreativeChoices(type: string): { choices: string[]; answer: str
   }
 }
 
-function templateToChallenge(template: ChallengeTemplate, targetTheme?: PromptTheme, targetDifficulty?: PromptDifficulty): Challenge {
+function templateToChallenge(template: ChallengeTemplate, targetTheme?: PromptTheme, targetDifficulty?: PromptDifficulty, forHuman = false): Challenge {
   // Prefer prompts matching target theme if any are tagged
   let prompts = template.prompts
   if (targetTheme) {
@@ -276,19 +276,19 @@ function templateToChallenge(template: ChallengeTemplate, targetTheme?: PromptTh
   }
   const entry = pick(prompts)
 
-  // Determine choices
+  // Determine choices — only for human fights (bots answer via webhook)
   let choices: string[] | undefined
   let answers = entry.answers
-  if (entry.choices) {
-    choices = shuffleArray(entry.choices)
-  } else if (entry.answers?.length === 1 && ['true', 'false'].includes(entry.answers[0].toLowerCase())) {
-    // Auto-generate True/False choices for boolean questions
-    choices = shuffleArray(['True', 'False'])
-  } else if (template.scoring === 'creative' && CREATIVE_CHOICES[template.type]) {
-    // Auto-generate multiple choice for creative challenges
-    const generated = generateCreativeChoices(template.type)
-    choices = generated.choices
-    answers = [generated.answer]
+  if (forHuman) {
+    if (entry.choices) {
+      choices = shuffleArray(entry.choices)
+    } else if (entry.answers?.length === 1 && ['true', 'false'].includes(entry.answers[0].toLowerCase())) {
+      choices = shuffleArray(['True', 'False'])
+    } else if (template.scoring === 'creative' && CREATIVE_CHOICES[template.type]) {
+      const generated = generateCreativeChoices(template.type)
+      choices = generated.choices
+      answers = [generated.answer]
+    }
   }
 
   // For creative challenges with choices, add a "Pick the best response:" prefix