diff --git a/sharedUI/src/commonMain/kotlin/com/livrets/game/GameEngine.kt b/sharedUI/src/commonMain/kotlin/com/livrets/game/GameEngine.kt
new file mode 100644
index 0000000..d480401
--- /dev/null
+++ b/sharedUI/src/commonMain/kotlin/com/livrets/game/GameEngine.kt
@@ -0,0 +1,118 @@
+package com.livrets.game
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.launch
+import kotlin.time.Clock
+import kotlin.time.TimeSource
+
+class GameEngine(
+    private val config: GameConfig,
+    private val scope: CoroutineScope,
+    private val questionSource: QuestionSource = QuestionGenerator(),
+    private val onFinish: (GameResult) -> Unit = {},
+) {
+    private val _state = MutableStateFlow<GameState>(GameState.NotStarted)
+    val state: StateFlow<GameState> = _state.asStateFlow()
+
+    private var timerJob: Job? = null
+    private var questionStartMark: TimeSource.Monotonic.ValueTimeMark? = null
+    private val records = mutableListOf<AnswerRecord>()
+
+    fun start() {
+        records.clear()
+        beginQuestion(index = 0, previous = null)
+    }
+
+    fun onDigit(digit: Char) {
+        val playing = _state.value as? GameState.Playing ?: return
+        if (playing.entry.length < MAX_ENTRY_LENGTH) {
+            _state.value = playing.copy(entry = playing.entry + digit)
+        }
+    }
+
+    fun onDelete() {
+        val playing = _state.value as? GameState.Playing ?: return
+        _state.value = playing.copy(entry = playing.entry.dropLast(1))
+    }
+
+    fun onValidate() {
+        val playing = _state.value as? GameState.Playing ?: return
+        if (playing.entry.isEmpty()) return
+        submit(playing.entry.toInt())
+    }
+
+    fun onTimeout() {
+        val playing = _state.value as? GameState.Playing ?: return
+        submit(playing.entry.takeIf { it.isNotEmpty() }?.toInt())
+    }
+
+    private fun submit(givenAnswer: Int?) {
+        val playing = _state.value as? GameState.Playing ?: return
+        timerJob?.cancel()
+        val record = AnswerRecord(
+            question = playing.question,
+            givenAnswer = givenAnswer,
+            correctAnswer = playing.question.correctAnswer,
+            isCorrect = givenAnswer == playing.question.correctAnswer,
+            durationMs = questionStartMark?.elapsedNow()?.inWholeMilliseconds ?: 0L,
+        )
+        records += record
+        _state.value = GameState.Feedback(record, playing.questionIndex)
+        scope.launch {
+            delay(FEEDBACK_DURATION_MS)
+            if (_state.value is GameState.Feedback) {
+                val next = playing.questionIndex + 1
+                if (next >= config.questionCount) finish()
+                else beginQuestion(index = next, previous = playing.question)
+            }
+        }
+    }
+
+    private fun beginQuestion(index: Int, previous: Question?) {
+        val question = questionSource.next(previous, config.maxTable)
+        questionStartMark = TimeSource.Monotonic.markNow()
+        _state.value = GameState.Playing(
+            question = question,
+            questionIndex = index,
+            totalQuestions = config.questionCount,
+            remainingMs = config.secondsPerQuestion * 1000L,
+            entry = "",
+        )
+        timerJob?.cancel()
+        timerJob = scope.launch { runTimer(question) }
+    }
+
+    private suspend fun runTimer(question: Question) {
+        val totalMs = config.secondsPerQuestion * 1000L
+        var elapsedMs = 0L
+        while (elapsedMs < totalMs) {
+            delay(TICK_MS)
+            elapsedMs += TICK_MS
+            val current = _state.value
+            if (current !is GameState.Playing || current.question != question) return
+            _state.value = current.copy(remainingMs = (totalMs - elapsedMs).coerceAtLeast(0L))
+        }
+        onTimeout()
+    }
+
+    private fun finish() {
+        val result = GameResult(
+            date = Clock.System.now(),
+            config = config,
+            records = records.toList(),
+        )
+        _state.value = GameState.Finished(result)
+        onFinish(result)
+    }
+
+    companion object {
+        const val TICK_MS = 100L
+        const val FEEDBACK_DURATION_MS = 1500L
+        const val MAX_ENTRY_LENGTH = 4
+    }
+}
diff --git a/sharedUI/src/commonMain/kotlin/com/livrets/game/GameState.kt b/sharedUI/src/commonMain/kotlin/com/livrets/game/GameState.kt
new file mode 100644
index 0000000..dfc4650
--- /dev/null
+++ b/sharedUI/src/commonMain/kotlin/com/livrets/game/GameState.kt
@@ -0,0 +1,20 @@
+package com.livrets.game
+
+sealed interface GameState {
+    data object NotStarted : GameState
+
+    data class Playing(
+        val question: Question,
+        val questionIndex: Int,     // à partir de 0
+        val totalQuestions: Int,
+        val remainingMs: Long,
+        val entry: String,
+    ) : GameState
+
+    data class Feedback(
+        val record: AnswerRecord,
+        val questionIndex: Int,
+    ) : GameState
+
+    data class Finished(val result: GameResult) : GameState
+}
diff --git a/sharedUI/src/commonTest/kotlin/com/livrets/game/GameEngineTest.kt b/sharedUI/src/commonTest/kotlin/com/livrets/game/GameEngineTest.kt
new file mode 100644
index 0000000..18584fa
--- /dev/null
+++ b/sharedUI/src/commonTest/kotlin/com/livrets/game/GameEngineTest.kt
@@ -0,0 +1,136 @@
+package com.livrets.game
+
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.advanceTimeBy
+import kotlinx.coroutines.test.runTest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class GameEngineTest {
+
+    private val fixedQuestion = Question.Direct(7, 8)   // bonne réponse : 56
+
+    private fun GameEngine.playing(): GameState.Playing =
+        state.value as GameState.Playing
+
+    private fun GameEngine.feedback(): GameState.Feedback =
+        state.value as GameState.Feedback
+
+    @Test
+    fun `bonne réponse - feedback puis question suivante`() = runTest {
+        val engine = GameEngine(GameConfig(2, 10, 12), backgroundScope, QuestionSource { _, _ -> fixedQuestion })
+        engine.start()
+
+        engine.onDigit('5'); engine.onDigit('6'); engine.onValidate()
+
+        val fb = engine.feedback()
+        assertTrue(fb.record.isCorrect)
+        assertEquals(56, fb.record.givenAnswer)
+
+        advanceTimeBy(1600)
+        val next = engine.playing()
+        assertEquals(1, next.questionIndex)
+        assertEquals("", next.entry)
+    }
+
+    @Test
+    fun `mauvaise réponse - enregistre la réponse donnée et la bonne réponse`() = runTest {
+        val engine = GameEngine(GameConfig(2, 10, 12), backgroundScope, QuestionSource { _, _ -> fixedQuestion })
+        engine.start()
+
+        engine.onDigit('9'); engine.onValidate()
+
+        val fb = engine.feedback()
+        assertFalse(fb.record.isCorrect)
+        assertEquals(9, fb.record.givenAnswer)
+        assertEquals(56, fb.record.correctAnswer)
+    }
+
+    @Test
+    fun `validation avec saisie vide est ignorée`() = runTest {
+        val engine = GameEngine(GameConfig(2, 10, 12), backgroundScope, QuestionSource { _, _ -> fixedQuestion })
+        engine.start()
+
+        engine.onValidate()
+
+        assertTrue(engine.state.value is GameState.Playing)
+        engine.onDelete()  // suppression sur saisie vide : sans effet
+        assertEquals("", engine.playing().entry)
+    }
+
+    @Test
+    fun `timeout sans saisie compte comme faux avec réponse nulle`() = runTest {
+        val engine = GameEngine(GameConfig(2, 5, 12), backgroundScope, QuestionSource { _, _ -> fixedQuestion })
+        engine.start()
+
+        advanceTimeBy(5100)
+
+        val fb = engine.feedback()
+        assertFalse(fb.record.isCorrect)
+        assertEquals(null, fb.record.givenAnswer)
+    }
+
+    @Test
+    fun `timeout avec saisie en cours auto-valide la saisie`() = runTest {
+        val engine = GameEngine(GameConfig(1, 5, 12), backgroundScope, QuestionSource { _, _ -> fixedQuestion })
+        engine.start()
+
+        engine.onDigit('5'); engine.onDigit('6')
+        advanceTimeBy(5100)
+
+        val fb = engine.feedback()
+        assertEquals(56, fb.record.givenAnswer)
+        assertTrue(fb.record.isCorrect)
+
+        advanceTimeBy(1600)
+        assertTrue(engine.state.value is GameState.Finished)
+    }
+
+    @Test
+    fun `fin de partie après N questions avec résultat complet`() = runTest {
+        var finished: GameResult? = null
+        val engine = GameEngine(
+            GameConfig(2, 10, 12),
+            backgroundScope,
+            QuestionSource { _, _ -> fixedQuestion },
+        ) { finished = it }
+
+        engine.start()
+        repeat(2) {
+            engine.onDigit('5'); engine.onDigit('6'); engine.onValidate()
+            advanceTimeBy(1600)
+        }
+
+        val finishedState = engine.state.value as GameState.Finished
+        assertEquals(2, finishedState.result.records.size)
+        assertEquals(2, finishedState.result.correctCount)
+        assertEquals(2, finished?.records?.size)
+    }
+
+    @Test
+    fun `le chrono est en pause pendant le feedback`() = runTest {
+        val engine = GameEngine(GameConfig(50, 1, 12), backgroundScope, QuestionSource { _, _ -> fixedQuestion })
+        engine.start()
+
+        engine.onDigit('5'); engine.onDigit('6'); engine.onValidate()
+        advanceTimeBy(1499)
+        assertTrue(engine.state.value is GameState.Feedback)
+
+        advanceTimeBy(2)
+        assertTrue(engine.state.value is GameState.Playing)
+    }
+
+    @Test
+    fun `événements pendant le feedback sont ignorés`() = runTest {
+        val engine = GameEngine(GameConfig(2, 10, 12), backgroundScope, QuestionSource { _, _ -> fixedQuestion })
+        engine.start()
+
+        engine.onDigit('5'); engine.onDigit('6'); engine.onValidate()
+        engine.onDigit('1'); engine.onDigit('2'); engine.onValidate()  // pendant Feedback : ignorés
+
+        assertEquals(0, engine.feedback().questionIndex)
+    }
+}