Merge pull request #1903 from nrobi144/fix/chess-interop

fix(chess): normalize SAN for cross-client Jester interop

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/chess/ChessConfig.kt

@@ -30,14 +30,16 @@ import com.vitorpamplona.quartz.nip01Core.relay.normalizer.normalizeRelayUrl
  */
 object ChessConfig {
     /**
-     * The 3 main relays for chess events.
-     * These are used for both fetching and publishing chess events.
+     * Relays for chess events.
+     * Includes relays used by jester.nyo.dev (relay.damus.io, offchain.pub)
+     * and popular community relays for broader reach.
      */
     val CHESS_RELAYS =
         listOf(
             "wss://relay.damus.io",
             "wss://nos.lol",
             "wss://relay.primal.net",
+            "wss://offchain.pub",
         )
 
     /**
@@ -48,6 +50,7 @@ object ChessConfig {
             "relay.damus.io".normalizeRelayUrl(),
             "nos.lol".normalizeRelayUrl(),
             "relay.primal.net".normalizeRelayUrl(),
+            "offchain.pub".normalizeRelayUrl(),
         )
 
     /**

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/chess/ChessLobbyLogic.kt

@@ -756,6 +756,9 @@ class ChessLobbyLogic(
                     if (!result.liveState.isSpectator) {
                         state.addActiveGame(startEventId, result.liveState)
                         pollingDelegate.addGameId(startEventId)
+                    } else {
+                        state.addSpectatingGame(startEventId, result.liveState)
+                        pollingDelegate.addGameId(startEventId)
                     }
                 }
 

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip64Chess/jester/JesterContent.kt

@@ -20,18 +20,26 @@
  */
 package com.vitorpamplona.quartz.nip64Chess.jester
 
+import kotlinx.serialization.EncodeDefault
+import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.Serializable
 
 /**
- * JSON content structure for Jester events
+ * JSON content structure for Jester events.
+ *
+ * Fields marked @EncodeDefault are always serialized even when they match
+ * the default value. This is required for jester.nyo.dev compatibility —
+ * jester's isStartGameEvent checks arrayEquals(json.history, []) which
+ * fails if the field is absent.
  */
+@OptIn(ExperimentalSerializationApi::class)
 @Serializable
 data class JesterContent(
-    val version: String = "0",
+    @EncodeDefault val version: String = "0",
     val kind: Int,
-    val fen: String = JesterProtocol.FEN_START,
+    @EncodeDefault val fen: String = JesterProtocol.FEN_START,
     val move: String? = null,
-    val history: List<String> = emptyList(),
+    @EncodeDefault val history: List<String> = emptyList(),
     val nonce: String? = null,
     // Extended fields for Amethyst (backward compatible - jesterui ignores unknown fields)
     val playerColor: String? = null, // "white" or "black" - challenger's color choice

quartz/src/jvmAndroid/kotlin/com/vitorpamplona/quartz/nip64Chess/ChessEngine.jvmAndroid.kt

@@ -50,12 +50,13 @@ actual class ChessEngine {
 
     actual fun makeMove(san: String): MoveResult =
         try {
-            if (board.doMove(san)) {
-                // Input is already SAN from Nostr events, store directly
-                sanHistory.add(san)
+            val normalized = normalizeSan(san)
+            if (board.doMove(normalized)) {
+                // Store the normalized SAN, not the original
+                sanHistory.add(normalized)
                 MoveResult(
                     success = true,
-                    san = san,
+                    san = normalized,
                     position = boardToPosition(),
                 )
             } else {
@@ -71,6 +72,31 @@ actual class ChessEngine {
             )
         }
 
+    /**
+     * Normalize SAN notation for interoperability with different chess clients.
+     *
+     * Handles:
+     * - Castling with zeros: 0-0 → O-O, 0-0-0 → O-O-O (preserving +/# suffix)
+     * - Annotation symbols: strips trailing !, ?, !!, ??, !?, ?!
+     */
+    private fun normalizeSan(san: String): String {
+        var s = san.trim()
+
+        // Strip trailing annotation characters (!, ?, and combinations)
+        while (s.isNotEmpty() && (s.last() == '!' || s.last() == '?')) {
+            s = s.dropLast(1)
+        }
+
+        // Normalize castling with zeros to letters
+        // Handle 0-0-0 before 0-0 to avoid partial match
+        s =
+            s
+                .replace("0-0-0", "O-O-O")
+                .replace("0-0", "O-O")
+
+        return s
+    }
+
     actual fun makeMove(
         from: String,
         to: String,

quartz/src/jvmAndroidTest/kotlin/com/vitorpamplona/quartz/nip64Chess/ChessInteropBugTest.kt

@@ -0,0 +1,645 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.nip64Chess
+
+import com.vitorpamplona.quartz.nip64Chess.jester.JesterEvent
+import com.vitorpamplona.quartz.nip64Chess.jester.JesterGameEvents
+import com.vitorpamplona.quartz.nip64Chess.jester.JesterProtocol
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+/**
+ * Tests for interoperability bugs when playing chess against other clients.
+ *
+ * Category 1: SAN Format Mismatch — different engines produce different SAN notation
+ * Category 2: Reconstruction with variant SAN
+ * Category 3: Open Challenge Spectator Detection
+ * Category 4: Missing Start Event
+ */
+class ChessInteropBugTest {
+    private val whitePubkey = "white_pubkey_abc123"
+    private val blackPubkey = "black_pubkey_def456"
+    private val spectatorPubkey = "spectator_pubkey_xyz789"
+    private val startEventId = "start-event-001"
+
+    // Italian Game opening to reach castling position:
+    // 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5
+    private val italianGameMoves = listOf("e4", "e5", "Nf3", "Nc6", "Bc4", "Bc5")
+
+    // Queenside castling setup: 1. d4 d5 2. Nc3 Nf6 3. Bf4 e6 4. Qd2 Be7
+    private val queensideCastlingSetup = listOf("d4", "d5", "Nc3", "Nf6", "Bf4", "e6", "Qd2", "Be7")
+
+    // ==========================================================================
+    // CATEGORY 1: SAN NORMALIZATION (ChessEngine)
+    // ==========================================================================
+
+    @Test
+    fun `engine handles 0-0 kingside castling notation`() {
+        val engine = ChessEngine()
+        for (move in italianGameMoves) {
+            val result = engine.makeMove(move)
+            assertTrue(result.success, "Setup move $move should succeed")
+        }
+        val result = engine.makeMove("0-0")
+        assertTrue(
+            result.success,
+            "0-0 (zeros) should be accepted for kingside castling",
+        )
+    }
+
+    @Test
+    fun `engine handles 0-0-0 queenside castling notation`() {
+        val engine = ChessEngine()
+        for (move in queensideCastlingSetup) {
+            val result = engine.makeMove(move)
+            assertTrue(result.success, "Setup move $move should succeed")
+        }
+        val result = engine.makeMove("0-0-0")
+        assertTrue(
+            result.success,
+            "0-0-0 (zeros) should be accepted for queenside castling",
+        )
+    }
+
+    @Test
+    fun `engine handles 0-0 with check suffix`() {
+        // Setup a position where kingside castling gives check
+        // Use FEN to create a contrived position where O-O gives check
+        // Easier: just verify 0-0+ is normalized to O-O (check suffix preserved)
+        val engine = ChessEngine()
+        for (move in italianGameMoves) {
+            engine.makeMove(move)
+        }
+        // 0-0+ — the + may or may not be relevant depending on position,
+        // but normalization should convert 0-0+ → O-O and strip +
+        // In Italian Game position, O-O doesn't give check, so we just verify
+        // the move is accepted (the engine ignores spurious +)
+        val result = engine.makeMove("0-0+")
+        assertTrue(
+            result.success,
+            "0-0+ should be normalized and accepted",
+        )
+    }
+
+    @Test
+    fun `engine handles 0-0-0 with check suffix`() {
+        val engine = ChessEngine()
+        for (move in queensideCastlingSetup) {
+            engine.makeMove(move)
+        }
+        val result = engine.makeMove("0-0-0+")
+        assertTrue(
+            result.success,
+            "0-0-0+ should be normalized and accepted",
+        )
+    }
+
+    @Test
+    fun `engine handles move with annotation !`() {
+        val engine = ChessEngine()
+        val result = engine.makeMove("e4!")
+        assertTrue(result.success, "e4! should be accepted after stripping annotation")
+    }
+
+    @Test
+    fun `engine handles move with annotation !!`() {
+        val engine = ChessEngine()
+        val result = engine.makeMove("e4")
+        assertTrue(result.success)
+        val result2 = engine.makeMove("e5")
+        assertTrue(result2.success)
+        val result3 = engine.makeMove("Nf3!!")
+        assertTrue(result3.success, "Nf3!! should be accepted after stripping annotation")
+    }
+
+    @Test
+    fun `engine handles move with annotation questionmark-bang`() {
+        val engine = ChessEngine()
+        val result = engine.makeMove("e4?!")
+        assertTrue(result.success, "e4?! should be accepted after stripping annotation")
+    }
+
+    @Test
+    fun `engine handles standard O-O still works`() {
+        val engine = ChessEngine()
+        for (move in italianGameMoves) {
+            engine.makeMove(move)
+        }
+        val result = engine.makeMove("O-O")
+        assertTrue(result.success, "Standard O-O should still work (regression check)")
+    }
+
+    @Test
+    fun `engine handles standard O-O-O still works`() {
+        val engine = ChessEngine()
+        for (move in queensideCastlingSetup) {
+            engine.makeMove(move)
+        }
+        val result = engine.makeMove("O-O-O")
+        assertTrue(result.success, "Standard O-O-O should still work (regression check)")
+    }
+
+    @Test
+    fun `engine handles Qxf7# checkmate notation`() {
+        val engine = ChessEngine()
+        val setup = listOf("e4", "e5", "Qh5", "Nc6", "Bc4", "Nf6")
+        for (move in setup) {
+            engine.makeMove(move)
+        }
+        val result = engine.makeMove("Qxf7#")
+        assertTrue(result.success, "Qxf7# should be accepted")
+        assertTrue(engine.isCheckmate(), "Position should be checkmate")
+    }
+
+    @Test
+    fun `engine handles Qh5 check notation`() {
+        val engine = ChessEngine()
+        // 1. e4 e5 2. Qh5 — Qh5 doesn't give check here but let's verify it works
+        engine.makeMove("e4")
+        engine.makeMove("e5")
+        val result = engine.makeMove("Qh5")
+        assertTrue(result.success, "Qh5 should be accepted")
+    }
+
+    @Test
+    fun `engine stores normalized SAN in history`() {
+        val engine = ChessEngine()
+        for (move in italianGameMoves) {
+            engine.makeMove(move)
+        }
+        // Castle with zero notation
+        engine.makeMove("0-0")
+        val history = engine.getMoveHistory()
+        assertEquals(
+            "O-O",
+            history.last(),
+            "History should store normalized O-O, not 0-0",
+        )
+    }
+
+    @Test
+    fun `engine stores normalized SAN without annotations in history`() {
+        val engine = ChessEngine()
+        engine.makeMove("e4!")
+        val history = engine.getMoveHistory()
+        assertEquals(
+            "e4",
+            history.last(),
+            "History should store e4, not e4!",
+        )
+    }
+
+    // ==========================================================================
+    // CATEGORY 2: RECONSTRUCTION WITH VARIANT SAN
+    // ==========================================================================
+
+    @Test
+    fun `reconstructor handles castling with 0-0 in history`() {
+        val historyWithZeros = italianGameMoves + "0-0"
+        val finalMove =
+            createMoveEvent(
+                id = "move-007",
+                pubKey = whitePubkey,
+                startEventId = startEventId,
+                headEventId = "move-006",
+                move = "0-0",
+                fen = "r1bqk1nr/pppp1ppp/2n5/2b1p3/2B1P3/5N2/PPPP1PPP/RNBQ1RK1 b kq - 5 4",
+                history = historyWithZeros,
+                opponentPubkey = blackPubkey,
+            )
+
+        val events =
+            JesterGameEvents(
+                startEvent = createStartEvent(startEventId, whitePubkey, Color.WHITE, blackPubkey),
+                moves = listOf(finalMove),
+            )
+
+        val result = ChessStateReconstructor.reconstruct(events, whitePubkey)
+        assertTrue(
+            result.isSuccess(),
+            "Reconstruction with 0-0 in history should succeed",
+        )
+
+        val state = result.getOrNull()!!
+        assertEquals(7, state.moveHistory.size)
+        assertFalse(state.isDesynced, "Should not be desynced")
+    }
+
+    @Test
+    fun `reconstructor handles castling with 0-0-0 in history`() {
+        val historyWithZeros = queensideCastlingSetup + "0-0-0"
+        val finalMove =
+            createMoveEvent(
+                id = "move-009",
+                pubKey = whitePubkey,
+                startEventId = startEventId,
+                headEventId = "move-008",
+                move = "0-0-0",
+                fen = "rnbqk2r/ppp1bppp/4pn2/3p4/3P1B2/2N5/PPPQPPPP/2KR1BNR b kq - 6 5",
+                history = historyWithZeros,
+                opponentPubkey = blackPubkey,
+            )
+
+        val events =
+            JesterGameEvents(
+                startEvent = createStartEvent(startEventId, whitePubkey, Color.WHITE, blackPubkey),
+                moves = listOf(finalMove),
+            )
+
+        val result = ChessStateReconstructor.reconstruct(events, whitePubkey)
+        assertTrue(
+            result.isSuccess(),
+            "Reconstruction with 0-0-0 in history should succeed",
+        )
+
+        val state = result.getOrNull()!!
+        assertEquals(9, state.moveHistory.size)
+        assertFalse(state.isDesynced, "Should not be desynced")
+    }
+
+    @Test
+    fun `reconstructor handles mixed SAN formats in history`() {
+        val mixedHistory = listOf("e4", "e5", "Nf3!", "Nc6", "Bc4", "Bc5", "0-0")
+        val finalMove =
+            createMoveEvent(
+                id = "move-007",
+                pubKey = whitePubkey,
+                startEventId = startEventId,
+                headEventId = "move-006",
+                move = "0-0",
+                fen = "r1bqk1nr/pppp1ppp/2n5/2b1p3/2B1P3/5N2/PPPP1PPP/RNBQ1RK1 b kq - 5 4",
+                history = mixedHistory,
+                opponentPubkey = blackPubkey,
+            )
+
+        val events =
+            JesterGameEvents(
+                startEvent = createStartEvent(startEventId, whitePubkey, Color.WHITE, blackPubkey),
+                moves = listOf(finalMove),
+            )
+
+        val result = ChessStateReconstructor.reconstruct(events, whitePubkey)
+        assertTrue(
+            result.isSuccess(),
+            "Reconstruction with mixed SAN formats should succeed",
+        )
+
+        val state = result.getOrNull()!!
+        assertEquals(7, state.moveHistory.size)
+        assertFalse(state.isDesynced, "Should not be desynced")
+    }
+
+    @Test
+    fun `reconstructor handles jester-style content without playerColor`() {
+        val events =
+            JesterGameEvents(
+                startEvent = createOpenChallengeStartEventNoColor(startEventId, whitePubkey),
+                moves = emptyList(),
+            )
+
+        val result = ChessStateReconstructor.reconstruct(events, whitePubkey)
+        assertTrue(result.isSuccess())
+
+        val state = result.getOrNull()!!
+        assertEquals(
+            whitePubkey,
+            state.whitePubkey,
+            "Challenger should default to WHITE when playerColor is absent",
+        )
+    }
+
+    // ==========================================================================
+    // CATEGORY 3: OPEN CHALLENGE SPECTATOR DETECTION
+    // ==========================================================================
+
+    @Test
+    fun `open challenge with no p-tag no playerColor - only challenger moves - viewer is spectator`() {
+        val move1 =
+            createMoveEvent(
+                id = "move-001",
+                pubKey = whitePubkey,
+                startEventId = startEventId,
+                headEventId = startEventId,
+                move = "e4",
+                fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1",
+                history = listOf("e4"),
+                opponentPubkey = blackPubkey,
+            )
+
+        val events =
+            JesterGameEvents(
+                startEvent = createOpenChallengeStartEvent(startEventId, whitePubkey),
+                moves = listOf(move1),
+            )
+
+        val result = ChessStateReconstructor.reconstruct(events, spectatorPubkey)
+        assertTrue(result.isSuccess())
+
+        val state = result.getOrNull()!!
+        assertEquals(ViewerRole.SPECTATOR, state.viewerRole, "Third party should be SPECTATOR")
+        assertFalse(state.isPlayerTurn(), "Spectators never have a turn")
+    }
+
+    @Test
+    fun `open challenge with no p-tag - acceptor made moves - viewer is player`() {
+        val move1 =
+            createMoveEvent(
+                id = "move-001",
+                pubKey = whitePubkey,
+                startEventId = startEventId,
+                headEventId = startEventId,
+                move = "e4",
+                fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1",
+                history = listOf("e4"),
+                opponentPubkey = blackPubkey,
+            )
+        val move2 =
+            createMoveEvent(
+                id = "move-002",
+                pubKey = blackPubkey,
+                startEventId = startEventId,
+                headEventId = "move-001",
+                move = "e5",
+                fen = "rnbqkbnr/pppp1ppp/8/4p3/4P3/8/PPPP1PPP/RNBQKBNR w KQkq e6 0 2",
+                history = listOf("e4", "e5"),
+                opponentPubkey = whitePubkey,
+            )
+
+        val events =
+            JesterGameEvents(
+                startEvent = createOpenChallengeStartEvent(startEventId, whitePubkey),
+                moves = listOf(move1, move2),
+            )
+
+        val result = ChessStateReconstructor.reconstruct(events, blackPubkey)
+        assertTrue(result.isSuccess())
+
+        val state = result.getOrNull()!!
+        assertEquals(
+            ViewerRole.BLACK_PLAYER,
+            state.viewerRole,
+            "Acceptor who made a move should be BLACK_PLAYER",
+        )
+        assertEquals(Color.BLACK, state.playerColor)
+        assertEquals(whitePubkey, state.opponentPubkey)
+    }
+
+    @Test
+    fun `open challenge - challenger chose black via content - roles swap correctly`() {
+        // Challenger chose black, so the acceptor will be white
+        val move1 =
+            createMoveEvent(
+                id = "move-001",
+                pubKey = blackPubkey, // Acceptor plays as white (first move)
+                startEventId = startEventId,
+                headEventId = startEventId,
+                move = "e4",
+                fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1",
+                history = listOf("e4"),
+                opponentPubkey = whitePubkey,
+            )
+
+        val events =
+            JesterGameEvents(
+                // Challenger (whitePubkey) chose BLACK
+                startEvent = createStartEvent(startEventId, whitePubkey, Color.BLACK, null),
+                moves = listOf(move1),
+            )
+
+        val challengerResult = ChessStateReconstructor.reconstruct(events, whitePubkey)
+        assertTrue(challengerResult.isSuccess())
+        val challengerState = challengerResult.getOrNull()!!
+        assertEquals(ViewerRole.BLACK_PLAYER, challengerState.viewerRole, "Challenger chose black")
+        assertEquals(Color.BLACK, challengerState.playerColor)
+
+        val acceptorResult = ChessStateReconstructor.reconstruct(events, blackPubkey)
+        assertTrue(acceptorResult.isSuccess())
+        val acceptorState = acceptorResult.getOrNull()!!
+        assertEquals(ViewerRole.WHITE_PLAYER, acceptorState.viewerRole, "Acceptor should be white")
+        assertEquals(Color.WHITE, acceptorState.playerColor)
+    }
+
+    @Test
+    fun `jester-style content with version as integer`() {
+        val content = """{"version":0,"kind":0,"fen":"${JesterProtocol.FEN_START}","history":[]}"""
+        val event =
+            JesterEvent(
+                id = startEventId,
+                pubKey = whitePubkey,
+                createdAt = 1000,
+                tags =
+                    arrayOf(
+                        arrayOf("e", JesterProtocol.START_POSITION_HASH),
+                    ),
+                content = content,
+                sig = "sig-start",
+            )
+
+        assertTrue(event.isStartEvent(), "Event with version as integer should parse as start event")
+        assertEquals(JesterProtocol.FEN_START, event.fen())
+        assertTrue(event.history().isEmpty())
+    }
+
+    // ==========================================================================
+    // CATEGORY 4: MISSING START EVENT
+    // ==========================================================================
+
+    @Test
+    fun `reconstruction fails clearly with no start event`() {
+        val events = JesterGameEvents(startEvent = null, moves = emptyList())
+
+        val result = ChessStateReconstructor.reconstruct(events, whitePubkey)
+        assertTrue(result is ReconstructionResult.Error)
+        assertEquals("No start event found", result.message)
+    }
+
+    @Test
+    fun `reconstruction with moves but no start event`() {
+        val move1 =
+            createMoveEvent(
+                id = "move-001",
+                pubKey = whitePubkey,
+                startEventId = startEventId,
+                headEventId = startEventId,
+                move = "e4",
+                fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1",
+                history = listOf("e4"),
+                opponentPubkey = blackPubkey,
+            )
+
+        val events =
+            JesterGameEvents(
+                startEvent = null,
+                moves = listOf(move1),
+            )
+
+        val result = ChessStateReconstructor.reconstruct(events, whitePubkey)
+        assertTrue(result is ReconstructionResult.Error, "Should return Error, not crash")
+        assertEquals("No start event found", result.message)
+    }
+
+    // ==========================================================================
+    // HELPER FUNCTIONS
+    // ==========================================================================
+
+    private fun createStartEvent(
+        id: String,
+        challengerPubkey: String,
+        challengerColor: Color,
+        opponentPubkey: String?,
+        createdAt: Long = 1000,
+    ): JesterEvent {
+        val tags =
+            mutableListOf(
+                arrayOf("e", JesterProtocol.START_POSITION_HASH),
+            )
+        opponentPubkey?.let { tags.add(arrayOf("p", it)) }
+
+        val colorString = if (challengerColor == Color.WHITE) "white" else "black"
+        val content = """{"version":"0","kind":0,"fen":"${JesterProtocol.FEN_START}","history":[],"nonce":"test123","playerColor":"$colorString"}"""
+
+        return JesterEvent(
+            id = id,
+            pubKey = challengerPubkey,
+            createdAt = createdAt,
+            tags = tags.toTypedArray(),
+            content = content,
+            sig = "sig-start",
+        )
+    }
+
+    private fun createOpenChallengeStartEvent(
+        id: String,
+        challengerPubkey: String,
+        createdAt: Long = 1000,
+    ): JesterEvent {
+        val content = """{"version":"0","kind":0,"fen":"${JesterProtocol.FEN_START}","history":[],"nonce":"test123","playerColor":"white"}"""
+
+        return JesterEvent(
+            id = id,
+            pubKey = challengerPubkey,
+            createdAt = createdAt,
+            tags =
+                arrayOf(
+                    arrayOf("e", JesterProtocol.START_POSITION_HASH),
+                ),
+            content = content,
+            sig = "sig-start",
+        )
+    }
+
+    private fun createOpenChallengeStartEventNoColor(
+        id: String,
+        challengerPubkey: String,
+        createdAt: Long = 1000,
+    ): JesterEvent {
+        val content = """{"version":"0","kind":0,"fen":"${JesterProtocol.FEN_START}","history":[],"nonce":"test123"}"""
+
+        return JesterEvent(
+            id = id,
+            pubKey = challengerPubkey,
+            createdAt = createdAt,
+            tags =
+                arrayOf(
+                    arrayOf("e", JesterProtocol.START_POSITION_HASH),
+                ),
+            content = content,
+            sig = "sig-start",
+        )
+    }
+
+    // ==========================================================================
+    // CATEGORY 5: JESTER CONTENT SERIALIZATION
+    // ==========================================================================
+
+    @Test
+    fun `serialized start content includes version fen and history fields`() {
+        // Jester's isStartGameEvent checks arrayEquals(json.history, [])
+        // which fails if history field is absent from JSON
+        val content =
+            com.vitorpamplona.quartz.nip64Chess.jester.JesterContent(
+                kind = 0,
+                nonce = "test1234",
+                playerColor = "white",
+            )
+        val json =
+            com.vitorpamplona.quartz.nip01Core.core.JsonMapper
+                .toJson(content)
+
+        assertTrue(json.contains("\"version\""), "JSON must include version field: $json")
+        assertTrue(json.contains("\"fen\""), "JSON must include fen field: $json")
+        assertTrue(json.contains("\"history\""), "JSON must include history field: $json")
+        assertTrue(json.contains("\"history\":[]"), "history must be empty array: $json")
+    }
+
+    @Test
+    fun `serialized move content includes version fen and history fields`() {
+        val content =
+            com.vitorpamplona.quartz.nip64Chess.jester.JesterContent(
+                kind = 1,
+                fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1",
+                move = "e4",
+                history = listOf("e4"),
+            )
+        val json =
+            com.vitorpamplona.quartz.nip01Core.core.JsonMapper
+                .toJson(content)
+
+        assertTrue(json.contains("\"version\""), "JSON must include version field: $json")
+        assertTrue(json.contains("\"fen\""), "JSON must include fen field: $json")
+        assertTrue(json.contains("\"history\""), "JSON must include history field: $json")
+    }
+
+    // ==========================================================================
+    // HELPERS
+    // ==========================================================================
+
+    private fun createMoveEvent(
+        id: String,
+        pubKey: String,
+        startEventId: String,
+        headEventId: String,
+        move: String,
+        fen: String,
+        history: List<String>,
+        opponentPubkey: String,
+        createdAt: Long = 2000,
+    ): JesterEvent {
+        val historyJson = history.joinToString(",") { "\"$it\"" }
+        val content = """{"version":"0","kind":1,"fen":"$fen","move":"$move","history":[$historyJson]}"""
+
+        return JesterEvent(
+            id = id,
+            pubKey = pubKey,
+            createdAt = createdAt,
+            tags =
+                arrayOf(
+                    arrayOf("e", startEventId),
+                    arrayOf("e", headEventId),
+                    arrayOf("p", opponentPubkey),
+                ),
+            content = content,
+            sig = "sig-move",
+        )
+    }
+}