Less Is More: Android 앱에 On-Device Small Language Model 통합할 때 실제로 겪는 엔지니어링 문제들

// 1. 5단계 방어적 파싱 파이프라인
private fun parseHints(rawText: String): List<String>? {
    val sanitized = rawText.replace("\uFFFD", "") // UTF-8 정제
    val stripped = sanitized
        .replace(Regex("```json\\s*"), "")
        .replace(Regex("```\\s*"), "") // 코드펜스 제거
    
    // 직접 JSON 파싱 시도
    tryDirectParse(stripped)?.let { return it }
    
    // 정규식으로 JSON 추출
    val jsonMatch = Regex("\\{[^{}]*(?:\\{[^{}]*\\}[^{}]*)*\\}")
        .find(stripped)?.value
    jsonMatch?.let { tryDirectParse(it) }?.let { return it }
    
    // 키 이름 무시하고 값 타입으로 추론
    return tryStructuralParse(stripped)
}

// 다국어 힌트 키 지원
val hintsKeys = setOf("hints", "dicas", "pistas", "clues", "indices", "consejos")

// 2. 세션 로테이션으로 KV 캐시 포화 방지
const val SESSION_ROTATION = 5
var puzzleIndex = 0
while (puzzleIndex < count) {
    val chunkSize = (count - puzzleIndex).coerceAtMost(SESSION_ROTATION)
    engineManager.createChatSession(systemPrompt).use { session ->
        repeat(chunkSize) {
            generateSinglePuzzle(session, lastFailureReason)
            puzzleIndex++
        }
    }
}

// 3. 실패 이유 포함한 컨텍스트 재시도
val retryPrompt = """
    Your previous response was rejected:
    word has ${rejectedWord.length} letters but we asked for $targetLength.
    The word MUST have exactly $targetLength letters.
    Try again with a DIFFERENT word.
""".trimIndent()

// 4. 최종 힌트 전용 프롬프트 (Day 5)
val systemPrompt = """
    You write short, clear word-game hints in $lang.
    Rules:
    - ALL hints MUST be written in $lang. Never write hints in English or any other language.
    - Do NOT include the word in any hint.
    - Each hint should be one short sentence.
    - Return ONLY a JSON object: {"hints": ["hint1", "hint2", "hint3"]}
""".trimIndent()

val userPrompt = """
    Write 3 hints for this word IN $lang.
    Do NOT write hints in English unless the language is English.
    Word: "$word"
""".trimIndent()

// 5. 결정론적 폴백 (LLM 실패 시 게임 중단 방지)
fun fallbackHints(word: String, language: String): List<String> = when (language) {
    "pt" -> listOf(
        "É algo que as pessoas conhecem",
        "Pode ser encontrado no dia a dia",
        "Tem ${word.length} letras"
    )
    "es" -> listOf(
        "Es algo que la gente conoce",
        "Se puede encontrar en la vida cotidiana",
        "Tiene ${word.length} letras"
    )
    else -> listOf(
        "It is something people know",
        "It can be found in everyday life",
        "It has ${word.length} letters"
    )
}