diff --git a/lib/screens/settings/logs_screen.dart b/lib/screens/settings/logs_screen.dart
index 43c4d8f1..447f7751 100644
--- a/lib/screens/settings/logs_screen.dart
+++ b/lib/screens/settings/logs_screen.dart
@@ -24,6 +24,38 @@ import '../../utils/snackbar_helper.dart';
 import '../../widgets/desktop_app_bar.dart';
 import '../../widgets/ios_status_bar_tap_scroll_to_top.dart';
 
+/// Relay `/logs` accepts 1 MiB. The in-memory buffer intentionally remains
+/// larger for local viewing and copying; uploads retain the device header and
+/// newest log lines within this transport contract.
+const int maxLogUploadBytes = 1 * 1024 * 1024;
+
+String constrainLogUploadPayload({required String header, required String logs, int maxBytes = maxLogUploadBytes}) {
+  if (maxBytes <= 0) return '';
+
+  final headerBytes = utf8.encode(header);
+  if (headerBytes.length >= maxBytes) {
+    var end = maxBytes;
+    while (end > 0 && end < headerBytes.length && (headerBytes[end] & 0xC0) == 0x80) {
+      end--;
+    }
+    return utf8.decode(headerBytes.sublist(0, end));
+  }
+
+  final logBytes = utf8.encode(logs);
+  final availableLogBytes = maxBytes - headerBytes.length;
+  if (logBytes.length <= availableLogBytes) return '$header$logs';
+
+  var start = logBytes.length - availableLogBytes;
+  while (start < logBytes.length && (logBytes[start] & 0xC0) == 0x80) {
+    start++;
+  }
+  final nextLine = logBytes.indexOf(0x0A, start);
+  if (nextLine >= 0 && nextLine + 1 < logBytes.length) {
+    start = nextLine + 1;
+  }
+  return header + utf8.decode(logBytes.sublist(start));
+}
+
 class LogsScreen extends StatefulWidget {
   const LogsScreen({super.key});
 
@@ -114,28 +146,28 @@ class _LogsScreenState extends State<LogsScreen> with MountedSetStateMixin {
     showSuccessSnackBar(context, t.messages.logsCleared);
   }
 
-  String _formatAllLogs() {
-    final buffer = StringBuffer();
-    if (_deviceInfo.isNotEmpty) {
-      buffer.writeln(_deviceInfo);
-      buffer.writeln('---');
-    }
-    bool isFirst = true;
+  String _formatAllLogs({int? maxBytes}) {
+    final header = _deviceInfo.isEmpty ? '' : '$_deviceInfo\n---\n';
+    final logs = StringBuffer();
+    var isFirst = true;
     for (final log in _logs.reversed) {
       if (!isFirst) {
-        buffer.write('\n');
+        logs.write('\n');
       }
       isFirst = false;
 
-      buffer.write('[${_formatTime(log.timestamp)}] [${log.level.name.toUpperCase()}] ${log.message}');
+      logs.write('[${_formatTime(log.timestamp)}] [${log.level.name.toUpperCase()}] ${log.message}');
       if (log.error != null) {
-        buffer.write('\nError: ${log.error}');
+        logs.write('\nError: ${log.error}');
       }
       if (log.stackTrace != null) {
-        buffer.write('\nStack trace:\n${log.stackTrace}');
+        logs.write('\nStack trace:\n${log.stackTrace}');
       }
     }
-    return buffer.toString();
+    final logText = logs.toString();
+    return maxBytes == null
+        ? '$header$logText'
+        : constrainLogUploadPayload(header: header, logs: logText, maxBytes: maxBytes);
   }
 
   void _copyAllLogs() {
@@ -144,7 +176,7 @@ class _LogsScreenState extends State<LogsScreen> with MountedSetStateMixin {
   }
 
   Future<void> _uploadLogs() async {
-    final logText = _formatAllLogs();
+    final logText = _formatAllLogs(maxBytes: maxLogUploadBytes);
 
     showLoadingDialog(context);
 
diff --git a/lib/services/discord_rpc_service.dart b/lib/services/discord_rpc_service.dart
index 3d59abea..1cdb5ae3 100644
--- a/lib/services/discord_rpc_service.dart
+++ b/lib/services/discord_rpc_service.dart
@@ -12,6 +12,30 @@ import '../utils/platform_detector.dart';
 import '../utils/media_server_http_client.dart';
 import 'settings_service.dart';
 
+const Duration _defaultPosterCacheTtl = Duration(hours: 3);
+const Duration _maxPosterCacheTtl = Duration(days: 365);
+
+DateTime posterCacheExpiryFromResponse(Object? responseData, {required DateTime receivedAt}) {
+  final expiresIn = switch (responseData) {
+    {'expiresIn': final int seconds} => seconds,
+    _ => null,
+  };
+  if (expiresIn == null) {
+    return receivedAt.add(_defaultPosterCacheTtl);
+  }
+  if (expiresIn <= 0) {
+    return receivedAt;
+  }
+  if (expiresIn > _maxPosterCacheTtl.inSeconds) {
+    return receivedAt.add(_defaultPosterCacheTtl);
+  }
+  try {
+    return receivedAt.add(Duration(seconds: expiresIn));
+  } on RangeError {
+    return receivedAt.add(_defaultPosterCacheTtl);
+  }
+}
+
 /// Cached poster URL with expiry timestamp.
 class _CachedUrl {
   final String url;
@@ -29,7 +53,6 @@ class _CachedUrl {
 class DiscordRPCService {
   static const String _applicationId = '1453773470306402439';
   static const String _posterUploadUrl = 'https://ice.plezy.app/posters';
-  static const Duration _posterCacheTtl = Duration(hours: 3);
   static const int _maxPosterUploadBytes = 5 * 1024 * 1024;
 
   /// Cache of thumbnail paths to hosted poster URLs. Keyed by
@@ -320,14 +343,21 @@ class DiscordRPCService {
         timeout: const Duration(seconds: 15),
       );
 
-      final uploadedUrl = switch (uploadResponse.data) {
+      final responseData = uploadResponse.data;
+      final uploadedUrl = switch (responseData) {
         {'url': final String url} when uploadResponse.statusCode >= 200 && uploadResponse.statusCode < 300 => url,
         _ => null,
       };
       final hostedUrl = _absolutePosterUrl(uploadedUrl);
       if (hostedUrl != null) {
-        _posterUrlCache[cacheKey] = _CachedUrl(hostedUrl, DateTime.now().add(_posterCacheTtl));
-        appLogger.d('Uploaded and cached thumbnail: $hostedUrl');
+        final receivedAt = DateTime.now();
+        final expiresAt = posterCacheExpiryFromResponse(responseData, receivedAt: receivedAt);
+        if (expiresAt.isAfter(receivedAt)) {
+          _posterUrlCache[cacheKey] = _CachedUrl(hostedUrl, expiresAt);
+          appLogger.d('Uploaded and cached thumbnail until $expiresAt: $hostedUrl');
+        } else {
+          appLogger.d('Uploaded thumbnail without caching expired URL: $hostedUrl');
+        }
         return hostedUrl;
       }
     } catch (e) {
diff --git a/lib/watch_together/services/relay_protocol.g.dart b/lib/watch_together/services/relay_protocol.g.dart
new file mode 100644
index 00000000..c815dc52
--- /dev/null
+++ b/lib/watch_together/services/relay_protocol.g.dart
@@ -0,0 +1,36 @@
+// Generated by scripts/generate_relay_protocol.py. Do not edit.
+
+abstract final class RelayProtocol {
+  static const String create = 'create';
+  static const String join = 'join';
+  static const String broadcast = 'broadcast';
+  static const String sendTo = 'sendTo';
+  static const String ping = 'ping';
+  static const String created = 'created';
+  static const String joined = 'joined';
+  static const String peerJoined = 'peerJoined';
+  static const String peerLeft = 'peerLeft';
+  static const String message = 'message';
+  static const String error = 'error';
+  static const String pong = 'pong';
+  static const String rateLimitedCode = 'rate_limited';
+  static const String invalidMessageCode = 'invalid_message';
+  static const String roomExistsCode = 'room_exists';
+  static const String roomNotFoundCode = 'room_not_found';
+  static const String roomFullCode = 'room_full';
+  static const String notInRoomCode = 'not_in_room';
+  static const String alreadyInRoomCode = 'already_in_room';
+
+  static const int maxRoomSize = 8;
+  static const int maxMessageSize = 65536;
+  static const int maxSessionIdLength = 64;
+  static const int maxPeerIdLength = 128;
+
+  static final RegExp _idPattern = RegExp(r'^[A-Za-z0-9_-]+$');
+
+  static bool isValidSessionId(String value) =>
+      value.isNotEmpty && value.length <= maxSessionIdLength && _idPattern.hasMatch(value);
+
+  static bool isValidPeerId(String value) =>
+      value.isNotEmpty && value.length <= maxPeerIdLength && _idPattern.hasMatch(value);
+}
diff --git a/lib/watch_together/services/watch_together_peer_service.dart b/lib/watch_together/services/watch_together_peer_service.dart
index a9128236..a0dd4b45 100644
--- a/lib/watch_together/services/watch_together_peer_service.dart
+++ b/lib/watch_together/services/watch_together_peer_service.dart
@@ -11,6 +11,7 @@ import '../../services/base_peer_service.dart';
 import '../../utils/app_logger.dart';
 import '../models/sync_message.dart';
 import '../primitives.dart';
+import 'relay_protocol.g.dart';
 
 // Re-export so existing callers that import from here keep working.
 export '../../services/base_peer_service.dart' show PeerError, PeerErrorType;
@@ -185,7 +186,7 @@ class WatchTogetherPeerService with KeepaliveMixin {
       final type = msg['type'] as String?;
 
       switch (type) {
-        case 'created':
+        case RelayProtocol.created:
           appLogger.d('WatchTogether: Room created: ${msg['sessionId']}');
           _safeAdd(_connectionStateController, true);
           if (_setupCompleter case final completer? when !completer.isCompleted) {
@@ -193,7 +194,7 @@ class WatchTogetherPeerService with KeepaliveMixin {
             _setupCompleter = null;
           }
 
-        case 'joined':
+        case RelayProtocol.joined:
           final peers = (msg['peers'] as List<dynamic>?)?.cast<String>() ?? [];
           appLogger.d('WatchTogether: Joined room ${msg['sessionId']} with peers: $peers');
           for (final peerId in peers) {
@@ -206,14 +207,14 @@ class WatchTogetherPeerService with KeepaliveMixin {
             _setupCompleter = null;
           }
 
-        case 'peerJoined':
+        case RelayProtocol.peerJoined:
           final peerId = msg['peerId'] as String;
           appLogger.d('WatchTogether: Peer joined: $peerId');
           _connectedPeers.add(peerId);
           _safeAdd(_peerConnectedController, peerId);
           _safeAdd(_connectionStateController, true);
 
-        case 'peerLeft':
+        case RelayProtocol.peerLeft:
           final peerId = msg['peerId'] as String;
           appLogger.d('WatchTogether: Peer left: $peerId');
           _connectedPeers.remove(peerId);
@@ -222,7 +223,7 @@ class WatchTogetherPeerService with KeepaliveMixin {
             _safeAdd(_connectionStateController, false);
           }
 
-        case 'message':
+        case RelayProtocol.message:
           final payload = msg['payload'];
           final serverFrom = msg['from'] as String?;
           if (payload != null) {
@@ -240,7 +241,7 @@ class WatchTogetherPeerService with KeepaliveMixin {
             }
           }
 
-        case 'error':
+        case RelayProtocol.error:
           final code = msg['code'] as String? ?? 'unknown';
           final message = msg['message'] as String? ?? t.common.unknown;
           appLogger.e('WatchTogether: Server error: $code - $message');
@@ -251,7 +252,7 @@ class WatchTogetherPeerService with KeepaliveMixin {
             _setupCompleter = null;
           }
 
-        case 'pong':
+        case RelayProtocol.pong:
           // Handled by resetPongTimer() already
           break;
 
@@ -264,7 +265,7 @@ class WatchTogetherPeerService with KeepaliveMixin {
   }
 
   @override
-  void sendPing() => _sendRaw({'type': 'ping'});
+  void sendPing() => _sendRaw({'type': RelayProtocol.ping});
 
   @override
   void onPongTimeout() {
@@ -329,14 +330,14 @@ class WatchTogetherPeerService with KeepaliveMixin {
         // Always try join first — the room may still have peers (e.g. host
         // reconnecting while guests remain). Fall back to create only if
         // the room no longer exists and we were the host.
-        final completer = await _connectAndAnnounce('join');
+        final completer = await _connectAndAnnounce(RelayProtocol.join);
 
         try {
           await completer.future.namedTimeout(const Duration(seconds: 10), operation: 'WatchTogether reconnect');
         } on PeerError catch (e) {
-          if (_isHost && e.serverCode == 'room_not_found') {
+          if (_isHost && e.serverCode == RelayProtocol.roomNotFoundCode) {
             appLogger.d('WatchTogether: Room gone, re-creating as host');
-            final createCompleter = _announce('create');
+            final createCompleter = _announce(RelayProtocol.create);
             await createCompleter.future.namedTimeout(
               const Duration(seconds: 10),
               operation: 'WatchTogether reconnect create',
@@ -369,13 +370,21 @@ class WatchTogetherPeerService with KeepaliveMixin {
       await disconnect();
     }
 
+    final resolvedSessionId = sessionId?.toUpperCase() ?? _generateSessionId();
+    if (!RelayProtocol.isValidSessionId(resolvedSessionId)) {
+      throw ArgumentError.value(
+        sessionId,
+        'sessionId',
+        'Must be 1–${RelayProtocol.maxSessionIdLength} letters, digits, _ or -',
+      );
+    }
     _isHost = true;
-    _sessionId = sessionId?.toUpperCase() ?? _generateSessionId();
-    _myPeerId = watchTogetherHostPeerId(_sessionId!);
+    _sessionId = resolvedSessionId;
+    _myPeerId = watchTogetherHostPeerId(resolvedSessionId);
     _reconnectAttempts = 0;
 
     try {
-      final completer = await _connectAndAnnounce('create');
+      final completer = await _connectAndAnnounce(RelayProtocol.create);
 
       await completer.future.timeout(
         const Duration(seconds: 10),
@@ -399,13 +408,21 @@ class WatchTogetherPeerService with KeepaliveMixin {
       await disconnect();
     }
 
+    final resolvedSessionId = sessionId.toUpperCase();
+    if (!RelayProtocol.isValidSessionId(resolvedSessionId)) {
+      throw ArgumentError.value(
+        sessionId,
+        'sessionId',
+        'Must be 1–${RelayProtocol.maxSessionIdLength} letters, digits, _ or -',
+      );
+    }
     _isHost = false;
-    _sessionId = sessionId.toUpperCase();
+    _sessionId = resolvedSessionId;
     _myPeerId = const Uuid().v4();
     _reconnectAttempts = 0;
 
     try {
-      final completer = await _connectAndAnnounce('join');
+      final completer = await _connectAndAnnounce(RelayProtocol.join);
 
       await completer.future.timeout(
         const Duration(seconds: 10),
@@ -425,13 +442,16 @@ class WatchTogetherPeerService with KeepaliveMixin {
   /// Broadcast a message to all connected peers
   void broadcast(SyncMessage message) {
     final payload = message.toJson();
-    _sendRaw({'type': 'broadcast', 'payload': payload});
+    _sendRaw({'type': RelayProtocol.broadcast, 'payload': payload});
   }
 
   /// Send a message to a specific peer
   void sendTo(String peerId, SyncMessage message) {
+    if (!RelayProtocol.isValidPeerId(peerId)) {
+      throw ArgumentError.value(peerId, 'peerId', 'Must be 1–${RelayProtocol.maxPeerIdLength} letters, digits, _ or -');
+    }
     final payload = message.toJson();
-    _sendRaw({'type': 'sendTo', 'to': peerId, 'payload': payload});
+    _sendRaw({'type': RelayProtocol.sendTo, 'to': peerId, 'payload': payload});
   }
 
   /// Disconnect from all peers and close the session
diff --git a/relay_protocol.json b/relay_protocol.json
new file mode 100644
index 00000000..8a9a8b8c
--- /dev/null
+++ b/relay_protocol.json
@@ -0,0 +1,34 @@
+{
+  "clientMessageTypes": {
+    "create": "create",
+    "join": "join",
+    "broadcast": "broadcast",
+    "sendTo": "sendTo",
+    "ping": "ping"
+  },
+  "serverMessageTypes": {
+    "created": "created",
+    "joined": "joined",
+    "peerJoined": "peerJoined",
+    "peerLeft": "peerLeft",
+    "message": "message",
+    "error": "error",
+    "pong": "pong"
+  },
+  "errorCodes": {
+    "rateLimited": "rate_limited",
+    "invalidMessage": "invalid_message",
+    "roomExists": "room_exists",
+    "roomNotFound": "room_not_found",
+    "roomFull": "room_full",
+    "notInRoom": "not_in_room",
+    "alreadyInRoom": "already_in_room"
+  },
+  "limits": {
+    "maxRoomSize": 8,
+    "maxMessageSize": 65536,
+    "maxSessionIdLength": 64,
+    "maxPeerIdLength": 128
+  },
+  "idPattern": "^[A-Za-z0-9_-]+$"
+}
diff --git a/scripts/codegen.sh b/scripts/codegen.sh
index 86c84f87..e64e65d8 100755
--- a/scripts/codegen.sh
+++ b/scripts/codegen.sh
@@ -8,16 +8,18 @@ if [[ "${1:-}" == "--check" ]]; then
   shift
 fi
 
+python3 scripts/generate_relay_protocol.py
 dart run slang
 dart run build_runner build --delete-conflicting-outputs "$@"
 
 if $check; then
   generated_changes="$({
-    git diff --name-only -- lib
+    git diff --name-only -- lib server/relay_protocol_gen.go
     git ls-files --others --exclude-standard -- \
       ':(glob)lib/**/*.g.dart' \
-      ':(glob)lib/**/*.freezed.dart'
-  } | grep -E '\.(g|freezed)\.dart$' || true)"
+      ':(glob)lib/**/*.freezed.dart' \
+      server/relay_protocol_gen.go
+  } | grep -E '(\.(g|freezed)\.dart|relay_protocol_gen\.go)$' || true)"
 
   if [[ -n "$generated_changes" ]]; then
     echo "Generated files are out of date:" >&2
diff --git a/scripts/generate_relay_protocol.py b/scripts/generate_relay_protocol.py
new file mode 100755
index 00000000..f08845c5
--- /dev/null
+++ b/scripts/generate_relay_protocol.py
@@ -0,0 +1,117 @@
+#!/usr/bin/env python3
+"""Generate Dart and Go relay protocol constants from relay_protocol.json."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+SPEC_PATH = ROOT / "relay_protocol.json"
+DART_PATH = ROOT / "lib/watch_together/services/relay_protocol.g.dart"
+GO_PATH = ROOT / "server/relay_protocol_gen.go"
+
+
+def camel_to_pascal(value: str) -> str:
+    return value[:1].upper() + value[1:]
+
+
+def dart_source(spec: dict) -> str:
+    lines = [
+        "// Generated by scripts/generate_relay_protocol.py. Do not edit.",
+        "",
+        "abstract final class RelayProtocol {",
+    ]
+    for group in ("clientMessageTypes", "serverMessageTypes"):
+        for name, value in spec[group].items():
+            lines.append(f"  static const String {name} = {value!r};")
+    for name, value in spec["errorCodes"].items():
+        lines.append(f"  static const String {name}Code = {value!r};")
+    lines.append("")
+    for name, value in spec["limits"].items():
+        lines.append(f"  static const int {name} = {value};")
+    lines.extend(
+        [
+            "",
+            "  static final RegExp _idPattern = RegExp(r'^[A-Za-z0-9_-]+$');",
+            "",
+            "  static bool isValidSessionId(String value) =>",
+            "      value.isNotEmpty && value.length <= maxSessionIdLength && _idPattern.hasMatch(value);",
+            "",
+            "  static bool isValidPeerId(String value) =>",
+            "      value.isNotEmpty && value.length <= maxPeerIdLength && _idPattern.hasMatch(value);",
+            "}",
+            "",
+        ]
+    )
+    return "\n".join(lines)
+
+
+def go_source(spec: dict) -> str:
+    lines = [
+        "// Code generated by scripts/generate_relay_protocol.py. DO NOT EDIT.",
+        "",
+        "package main",
+        "",
+        "const (",
+    ]
+    protocol_constants = []
+    for group in ("clientMessageTypes", "serverMessageTypes"):
+        protocol_constants.extend(
+            (f"relayType{camel_to_pascal(name)}", f'"{value}"')
+            for name, value in spec[group].items()
+        )
+    protocol_constants.extend(
+        (f"relayError{camel_to_pascal(name)}", f'"{value}"')
+        for name, value in spec["errorCodes"].items()
+    )
+    protocol_name_width = max(len(name) for name, _ in protocol_constants)
+    lines.extend(
+        f"\t{name:<{protocol_name_width}} = {value}"
+        for name, value in protocol_constants
+    )
+    lines.append("")
+    go_limit_names = {
+        "maxRoomSize": "maxRoomSize",
+        "maxMessageSize": "maxMessageSize",
+        "maxSessionIdLength": "maxSessionIDLength",
+        "maxPeerIdLength": "maxPeerIDLength",
+    }
+    limit_constants = [
+        (go_limit_names[name], str(value)) for name, value in spec["limits"].items()
+    ]
+    limit_name_width = max(len(name) for name, _ in limit_constants)
+    lines.extend(
+        f"\t{name:<{limit_name_width}} = {value}"
+        for name, value in limit_constants
+    )
+    lines.extend(
+        [
+            ")",
+            "",
+            "func validRelayID(value string, maxLength int) bool {",
+            "\tif len(value) == 0 || len(value) > maxLength {",
+            "\t\treturn false",
+            "\t}",
+            "\tfor _, ch := range value {",
+            "\t\tif (ch < 'a' || ch > 'z') && (ch < 'A' || ch > 'Z') &&",
+            "\t\t\t(ch < '0' || ch > '9') && ch != '_' && ch != '-' {",
+            "\t\t\treturn false",
+            "\t\t}",
+            "\t}",
+            "\treturn true",
+            "}",
+            "",
+        ]
+    )
+    return "\n".join(lines)
+
+
+def main() -> None:
+    spec = json.loads(SPEC_PATH.read_text(encoding="utf-8"))
+    DART_PATH.write_text(dart_source(spec), encoding="utf-8")
+    GO_PATH.write_text(go_source(spec), encoding="utf-8")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/server/main.go b/server/main.go
index 487f4775..a0c78d96 100644
--- a/server/main.go
+++ b/server/main.go
@@ -25,7 +25,6 @@ import (
 )
 
 const (
-	maxRoomSize        = 8
 	rateBurst          = 30
 	rateSustained      = 10
 	cleanupInterval    = 5 * time.Minute
@@ -34,7 +33,6 @@ const (
 	writeWait          = 10 * time.Second
 	pongWait           = 60 * time.Second
 	pingInterval       = 30 * time.Second
-	maxMessageSize     = 64 * 1024
 	maxLogSize         = 1 * 1024 * 1024 // 1MB
 	logMaxAge          = 3 * 24 * time.Hour
 	logIDLength        = 5
@@ -62,142 +60,6 @@ var upgrader = websocket.Upgrader{
 	CheckOrigin:     func(r *http.Request) bool { return true },
 }
 
-// --- Rate limiter (token bucket) ---
-
-type rateLimiter struct {
-	tokens     float64
-	maxTokens  float64
-	refillRate float64
-	lastTime   time.Time
-	mu         sync.Mutex
-}
-
-func newRateLimiter(burst, sustained int) *rateLimiter {
-	return &rateLimiter{
-		tokens:     float64(burst),
-		maxTokens:  float64(burst),
-		refillRate: float64(sustained),
-		lastTime:   time.Now(),
-	}
-}
-
-func (rl *rateLimiter) allow() bool {
-	rl.mu.Lock()
-	defer rl.mu.Unlock()
-
-	now := time.Now()
-	elapsed := now.Sub(rl.lastTime).Seconds()
-	rl.lastTime = now
-
-	rl.tokens += elapsed * rl.refillRate
-	if rl.tokens > rl.maxTokens {
-		rl.tokens = rl.maxTokens
-	}
-
-	if rl.tokens < 1 {
-		return false
-	}
-	rl.tokens--
-	return true
-}
-
-// stale reports whether a limiter hasn't been touched in over 10 minutes —
-// safe to GC from a per-IP map.
-func (rl *rateLimiter) stale(now time.Time) bool {
-	rl.mu.Lock()
-	defer rl.mu.Unlock()
-	return now.Sub(rl.lastTime) > 10*time.Minute
-}
-
-// --- Connection tracker (per-IP limits) ---
-
-type connTracker struct {
-	mu          sync.Mutex
-	perIP       map[string]int
-	ipRate      map[string]*rateLimiter
-	roomsPerIP  map[string]int
-	globalCount int
-}
-
-func newConnTracker() *connTracker {
-	return &connTracker{
-		perIP:      make(map[string]int),
-		ipRate:     make(map[string]*rateLimiter),
-		roomsPerIP: make(map[string]int),
-	}
-}
-
-func (ct *connTracker) tryConnect(ip string) bool {
-	ct.mu.Lock()
-	defer ct.mu.Unlock()
-
-	if ct.globalCount >= maxGlobalConns {
-		return false
-	}
-	if ct.perIP[ip] >= maxConnsPerIP {
-		return false
-	}
-
-	rl, ok := ct.ipRate[ip]
-	if !ok {
-		rl = newRateLimiter(connRateBurst, connRateSustained)
-		ct.ipRate[ip] = rl
-	}
-	// Unlock ct.mu before calling rl.allow() would be cleaner,
-	// but since rl has its own mutex this is safe (no deadlock).
-	if !rl.allow() {
-		return false
-	}
-
-	ct.perIP[ip]++
-	ct.globalCount++
-	return true
-}
-
-func (ct *connTracker) disconnect(ip string) {
-	ct.mu.Lock()
-	defer ct.mu.Unlock()
-
-	if ct.perIP[ip] > 0 {
-		ct.perIP[ip]--
-		ct.globalCount--
-	}
-	if ct.perIP[ip] == 0 {
-		delete(ct.perIP, ip)
-	}
-}
-
-func (ct *connTracker) tryCreateRoom(ip string) bool {
-	ct.mu.Lock()
-	defer ct.mu.Unlock()
-	if ct.roomsPerIP[ip] >= maxRoomsPerIP {
-		return false
-	}
-	ct.roomsPerIP[ip]++
-	return true
-}
-
-func (ct *connTracker) releaseRoom(ip string) {
-	ct.mu.Lock()
-	defer ct.mu.Unlock()
-	if ct.roomsPerIP[ip] > 0 {
-		ct.roomsPerIP[ip]--
-	}
-	if ct.roomsPerIP[ip] == 0 {
-		delete(ct.roomsPerIP, ip)
-	}
-}
-
-func (ct *connTracker) cleanup() {
-	ct.mu.Lock()
-	defer ct.mu.Unlock()
-	for ip := range ct.ipRate {
-		if ct.perIP[ip] == 0 {
-			delete(ct.ipRate, ip)
-		}
-	}
-}
-
 // --- Messages ---
 
 type clientMsg struct {
@@ -222,9 +84,10 @@ type serverMsg struct {
 // --- Client (serializes writes to a single goroutine) ---
 
 type Client struct {
-	conn *websocket.Conn
-	send chan []byte
-	done chan struct{}
+	conn      *websocket.Conn
+	send      chan []byte
+	done      chan struct{}
+	closeOnce sync.Once
 }
 
 func newClient(conn *websocket.Conn) *Client {
@@ -270,7 +133,10 @@ func (c *Client) sendJSON(msg serverMsg) {
 }
 
 func (c *Client) close() {
-	close(c.done)
+	c.closeOnce.Do(func() {
+		close(c.done)
+		_ = c.conn.Close()
+	})
 }
 
 // --- Room ---
@@ -312,15 +178,16 @@ func (r *Room) broadcastExcept(senderID string, msg serverMsg) {
 	if err != nil {
 		return
 	}
-	// Copy peers under lock, then send without holding it
-	r.mu.RLock()
+	// Copy peers and record activity under lock, then send without holding it.
+	r.mu.Lock()
 	targets := make([]*Client, 0, len(r.Peers))
+	r.LastActivityAt = time.Now()
 	for id, client := range r.Peers {
 		if id != senderID {
 			targets = append(targets, client)
 		}
 	}
-	r.mu.RUnlock()
+	r.mu.Unlock()
 
 	for _, client := range targets {
 		client.trySend(data)
@@ -332,9 +199,12 @@ func (r *Room) sendTo(targetID string, msg serverMsg) bool {
 	if err != nil {
 		return false
 	}
-	r.mu.RLock()
+	r.mu.Lock()
 	client, ok := r.Peers[targetID]
-	r.mu.RUnlock()
+	if ok {
+		r.LastActivityAt = time.Now()
+	}
+	r.mu.Unlock()
 	if !ok {
 		return false
 	}
@@ -346,14 +216,18 @@ func (r *Room) sendTo(targetID string, msg serverMsg) bool {
 
 type logEntry struct {
 	Size      int
+	CreatedAt time.Time
 	ExpiresAt time.Time
 }
 
+var errLogStoreFull = errors.New("log store full")
+
 type logStore struct {
-	entries   map[string]logEntry
-	rateLimit map[string]time.Time // IP -> last upload time
-	dir       string
-	mu        sync.RWMutex
+	entries    map[string]logEntry
+	rateLimit  map[string]time.Time // IP -> last upload time
+	dir        string
+	generateID func() string
+	mu         sync.RWMutex
 }
 
 func newLogStore(dir string) *logStore {
@@ -361,15 +235,12 @@ func newLogStore(dir string) *logStore {
 		log.Fatalf("failed to create log dir %s: %v", dir, err)
 	}
 	ls := &logStore{
-		entries:   make(map[string]logEntry),
-		rateLimit: make(map[string]time.Time),
-		dir:       dir,
-	}
-	// Clean orphaned files from prior runs
-	files, _ := os.ReadDir(dir)
-	for _, f := range files {
-		os.Remove(filepath.Join(dir, f.Name()))
+		entries:    make(map[string]logEntry),
+		rateLimit:  make(map[string]time.Time),
+		dir:        dir,
+		generateID: generateLogID,
 	}
+	ls.loadExisting(time.Now())
 	return ls
 }
 
@@ -392,21 +263,154 @@ func generateLogID() string {
 	return generateID(logIDLength)
 }
 
+func logIDFromFilename(filename string) (string, bool) {
+	if filepath.Ext(filename) != ".log" {
+		return "", false
+	}
+	id := strings.TrimSuffix(filename, ".log")
+	return id, validID(id, logIDLength)
+}
+
+func (ls *logStore) loadExisting(now time.Time) {
+	ls.mu.Lock()
+	defer ls.mu.Unlock()
+
+	files, err := os.ReadDir(ls.dir)
+	if err != nil {
+		log.Printf("logs: failed to read dir %s: %v", ls.dir, err)
+		return
+	}
+	for _, file := range files {
+		filename := file.Name()
+		path := filepath.Join(ls.dir, filename)
+		if file.IsDir() || strings.HasSuffix(filename, ".tmp") {
+			os.RemoveAll(path)
+			continue
+		}
+		id, ok := logIDFromFilename(filename)
+		if !ok {
+			os.Remove(path)
+			continue
+		}
+		info, err := file.Info()
+		if err != nil || info.Size() <= 0 || info.Size() > maxLogSize {
+			os.Remove(path)
+			continue
+		}
+		createdAt := info.ModTime()
+		expiresAt := createdAt.Add(logMaxAge)
+		if !now.Before(expiresAt) {
+			os.Remove(path)
+			continue
+		}
+		ls.entries[id] = logEntry{
+			Size:      int(info.Size()),
+			CreatedAt: createdAt,
+			ExpiresAt: expiresAt,
+		}
+	}
+	ls.evictOldestLocked(maxLogEntries)
+}
+
+func (ls *logStore) store(data []byte, now time.Time) (string, logEntry, error) {
+	if len(data) == 0 {
+		return "", logEntry{}, errors.New("empty log")
+	}
+	if len(data) > maxLogSize {
+		return "", logEntry{}, errors.New("log too large")
+	}
+
+	ls.mu.Lock()
+	defer ls.mu.Unlock()
+	ls.cleanupExpiredLocked(now)
+	if len(ls.entries) >= maxLogEntries {
+		return "", logEntry{}, errLogStoreFull
+	}
+
+	id := ls.generateID()
+	for {
+		if _, exists := ls.entries[id]; !exists {
+			if _, err := os.Stat(ls.filePath(id)); errors.Is(err, fs.ErrNotExist) {
+				break
+			}
+		}
+		id = ls.generateID()
+	}
+
+	path := ls.filePath(id)
+	tmpPath := path + ".tmp"
+	if err := os.WriteFile(tmpPath, data, 0644); err != nil {
+		os.Remove(tmpPath)
+		return "", logEntry{}, err
+	}
+	if err := os.Rename(tmpPath, path); err != nil {
+		os.Remove(tmpPath)
+		return "", logEntry{}, err
+	}
+	_ = os.Chtimes(path, now, now)
+
+	entry := logEntry{
+		Size:      len(data),
+		CreatedAt: now,
+		ExpiresAt: now.Add(logMaxAge),
+	}
+	ls.entries[id] = entry
+	return id, entry, nil
+}
+
+func (ls *logStore) lookup(id string, now time.Time) (logEntry, bool) {
+	if !validID(id, logIDLength) {
+		return logEntry{}, false
+	}
+	ls.mu.Lock()
+	defer ls.mu.Unlock()
+	entry, ok := ls.entries[id]
+	if !ok {
+		return logEntry{}, false
+	}
+	if !now.Before(entry.ExpiresAt) {
+		ls.deleteEntryLocked(id)
+		return logEntry{}, false
+	}
+	return entry, true
+}
+
+func (ls *logStore) cleanupExpiredLocked(now time.Time) {
+	for id, entry := range ls.entries {
+		if !now.Before(entry.ExpiresAt) {
+			ls.deleteEntryLocked(id)
+		}
+	}
+}
+
+func (ls *logStore) evictOldestLocked(limit int) {
+	for len(ls.entries) > limit {
+		var oldestID string
+		var oldest logEntry
+		for id, entry := range ls.entries {
+			if oldestID == "" || entry.CreatedAt.Before(oldest.CreatedAt) {
+				oldestID = id
+				oldest = entry
+			}
+		}
+		if oldestID == "" {
+			return
+		}
+		ls.deleteEntryLocked(oldestID)
+	}
+}
+
+func (ls *logStore) deleteEntryLocked(id string) {
+	os.Remove(ls.filePath(id))
+	delete(ls.entries, id)
+}
+
 func (ls *logStore) cleanup() {
 	ls.mu.Lock()
 	defer ls.mu.Unlock()
 	now := time.Now()
-	for id, entry := range ls.entries {
-		if now.After(entry.ExpiresAt) {
-			os.Remove(ls.filePath(id))
-			delete(ls.entries, id)
-		}
-	}
-	for ip, lastTime := range ls.rateLimit {
-		if now.Sub(lastTime) > logRateInterval {
-			delete(ls.rateLimit, ip)
-		}
-	}
+	ls.cleanupExpiredLocked(now)
+	cleanupRateWindows(ls.rateLimit, now, logRateInterval)
 }
 
 // --- Poster store ---
@@ -903,7 +907,7 @@ func (s *Server) loadSnapshot(path string) error {
 	loaded, skipped := 0, 0
 	s.mu.Lock()
 	for _, r := range snap.Rooms {
-		if r.SessionID == "" || r.HostPeerID == "" {
+		if !validRelayID(r.SessionID, maxSessionIDLength) || !validRelayID(r.HostPeerID, maxPeerIDLength) {
 			skipped++
 			continue
 		}
@@ -940,33 +944,45 @@ func (s *Server) cleanupLoop() {
 func (s *Server) runCleanupStep(now time.Time) {
 	s.mu.Lock()
 	changed := false
+	var expiredClients []*Client
 	for id, room := range s.rooms {
 		room.mu.RLock()
 		empty := len(room.Peers) == 0
 		age := now.Sub(room.CreatedAt)
 		idle := now.Sub(room.LastActivityAt)
+		expired := age > roomMaxAge
+		if expired && !empty {
+			for _, client := range room.Peers {
+				expiredClients = append(expiredClients, client)
+			}
+		}
 		room.mu.RUnlock()
 
-		if (empty && idle > emptyRoomMaxAge) || age > roomMaxAge {
+		if (empty && idle > emptyRoomMaxAge) || expired {
 			log.Printf("cleanup: removing room %s (empty=%v, idle=%v, age=%v)", id, empty, idle, age)
 			delete(s.rooms, id)
 			changed = true
 		}
 	}
+	roomCount := len(s.rooms)
 	s.mu.Unlock()
+
+	for _, client := range expiredClients {
+		client.close()
+	}
 	if changed {
 		s.snap.schedule()
 	}
 	s.logs.cleanup()
 	s.posters.cleanup(now)
-	s.conns.cleanup()
+	s.conns.cleanup(now)
 	if s.oauth != nil {
 		s.oauth.cleanup()
 	}
 
 	s.conns.mu.Lock()
 	log.Printf("stats: conns=%d ips=%d rooms=%d",
-		s.conns.globalCount, len(s.conns.perIP), len(s.rooms))
+		s.conns.globalCount, len(s.conns.perIP), roomCount)
 	s.conns.mu.Unlock()
 }
 
@@ -1021,29 +1037,18 @@ func (s *Server) handlePostLogs(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	s.logs.mu.Lock()
-	if len(s.logs.entries) >= maxLogEntries {
-		s.logs.mu.Unlock()
-		http.Error(w, "Log store full", http.StatusServiceUnavailable)
-		return
-	}
-	s.logs.mu.Unlock()
-
-	id := generateLogID()
-	if err := os.WriteFile(s.logs.filePath(id), body, 0644); err != nil {
-		log.Printf("logs: failed to write %s: %v", id, err)
+	id, entry, err := s.logs.store(body, time.Now())
+	if err != nil {
+		if errors.Is(err, errLogStoreFull) {
+			http.Error(w, "Log store full", http.StatusServiceUnavailable)
+			return
+		}
+		log.Printf("logs: failed to store from %s: %v", ip, err)
 		http.Error(w, "Failed to store log", http.StatusInternalServerError)
 		return
 	}
 
-	s.logs.mu.Lock()
-	s.logs.entries[id] = logEntry{
-		Size:      len(body),
-		ExpiresAt: time.Now().Add(logMaxAge),
-	}
-	s.logs.mu.Unlock()
-
-	log.Printf("logs: stored %s (%d bytes) from %s", id, len(body), ip)
+	log.Printf("logs: stored %s (%d bytes) from %s", id, entry.Size, ip)
 
 	w.Header().Set("Content-Type", "application/json")
 	json.NewEncoder(w).Encode(map[string]string{"id": id})
@@ -1061,11 +1066,8 @@ func (s *Server) handleGetLogs(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	s.logs.mu.RLock()
-	entry, ok := s.logs.entries[id]
-	s.logs.mu.RUnlock()
-
-	if !ok || time.Now().After(entry.ExpiresAt) {
+	entry, ok := s.logs.lookup(id, time.Now())
+	if !ok {
 		http.Error(w, "Not found", http.StatusNotFound)
 		return
 	}
@@ -1185,6 +1187,17 @@ func (s *Server) handleWS(w http.ResponseWriter, r *http.Request) {
 	var currentRoom *Room
 	var currentPeerID string
 	var isHost bool
+	rejectRoomTransition := func() bool {
+		if currentRoom == nil {
+			return false
+		}
+		client.sendJSON(serverMsg{
+			Type:    relayTypeError,
+			Code:    relayErrorAlreadyInRoom,
+			Message: "Leave the current room before creating or joining another",
+		})
+		return true
+	}
 
 	// Cleanup on disconnect — only if our Client is still the one in the room.
 	// A reconnecting peer reuses the same peerId, so the map entry may have
@@ -1200,7 +1213,7 @@ func (s *Server) handleWS(w http.ResponseWriter, r *http.Request) {
 			currentRoom.mu.Unlock()
 			if !stale {
 				currentRoom.broadcastExcept(currentPeerID, serverMsg{
-					Type:   "peerLeft",
+					Type:   relayTypePeerLeft,
 					PeerID: currentPeerID,
 				})
 				s.snap.schedule()
@@ -1222,24 +1235,27 @@ func (s *Server) handleWS(w http.ResponseWriter, r *http.Request) {
 		}
 
 		if !rl.allow() {
-			client.sendJSON(serverMsg{Type: "error", Code: "rate_limited", Message: "Too many messages"})
+			client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorRateLimited, Message: "Too many messages"})
 			continue
 		}
 
 		var msg clientMsg
 		if err := json.Unmarshal(raw, &msg); err != nil {
-			client.sendJSON(serverMsg{Type: "error", Code: "invalid_message", Message: "Invalid JSON"})
+			client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorInvalidMessage, Message: "Invalid JSON"})
 			continue
 		}
 
 		switch msg.Type {
-		case "create":
-			if msg.SessionID == "" || msg.PeerID == "" {
-				client.sendJSON(serverMsg{Type: "error", Code: "invalid_message", Message: "sessionId and peerId required"})
+		case relayTypeCreate:
+			if !validRelayID(msg.SessionID, maxSessionIDLength) || !validRelayID(msg.PeerID, maxPeerIDLength) {
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorInvalidMessage, Message: "Invalid sessionId or peerId"})
+				continue
+			}
+			if rejectRoomTransition() {
 				continue
 			}
 			if !s.conns.tryCreateRoom(ip) {
-				client.sendJSON(serverMsg{Type: "error", Code: "rate_limited", Message: "Too many rooms created"})
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorRateLimited, Message: "Too many rooms created"})
 				continue
 			}
 			s.mu.Lock()
@@ -1250,7 +1266,7 @@ func (s *Server) handleWS(w http.ResponseWriter, r *http.Request) {
 				if !empty {
 					s.mu.Unlock()
 					s.conns.releaseRoom(ip)
-					client.sendJSON(serverMsg{Type: "error", Code: "room_exists", Message: "Room already exists"})
+					client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorRoomExists, Message: "Room already exists"})
 					continue
 				}
 				// Empty stale room — reclaim the ID
@@ -1270,25 +1286,28 @@ func (s *Server) handleWS(w http.ResponseWriter, r *http.Request) {
 			currentPeerID = msg.PeerID
 			isHost = true
 			log.Printf("room %s created by %s", msg.SessionID, msg.PeerID)
-			client.sendJSON(serverMsg{Type: "created", SessionID: msg.SessionID})
+			client.sendJSON(serverMsg{Type: relayTypeCreated, SessionID: msg.SessionID})
 			s.snap.schedule()
 
-		case "join":
-			if msg.SessionID == "" || msg.PeerID == "" {
-				client.sendJSON(serverMsg{Type: "error", Code: "invalid_message", Message: "sessionId and peerId required"})
+		case relayTypeJoin:
+			if !validRelayID(msg.SessionID, maxSessionIDLength) || !validRelayID(msg.PeerID, maxPeerIDLength) {
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorInvalidMessage, Message: "Invalid sessionId or peerId"})
+				continue
+			}
+			if rejectRoomTransition() {
 				continue
 			}
 			s.mu.RLock()
 			room, exists := s.rooms[msg.SessionID]
 			s.mu.RUnlock()
 			if !exists {
-				client.sendJSON(serverMsg{Type: "error", Code: "room_not_found", Message: "Room does not exist"})
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorRoomNotFound, Message: "Room does not exist"})
 				continue
 			}
 			room.mu.Lock()
 			if len(room.Peers) >= maxRoomSize {
 				room.mu.Unlock()
-				client.sendJSON(serverMsg{Type: "error", Code: "room_full", Message: "Room is full"})
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorRoomFull, Message: "Room is full"})
 				continue
 			}
 			room.Peers[msg.PeerID] = client
@@ -1306,43 +1325,43 @@ func (s *Server) handleWS(w http.ResponseWriter, r *http.Request) {
 					existingPeers = append(existingPeers, p)
 				}
 			}
-			client.sendJSON(serverMsg{Type: "joined", SessionID: msg.SessionID, Peers: existingPeers})
-			room.broadcastExcept(msg.PeerID, serverMsg{Type: "peerJoined", PeerID: msg.PeerID})
+			client.sendJSON(serverMsg{Type: relayTypeJoined, SessionID: msg.SessionID, Peers: existingPeers})
+			room.broadcastExcept(msg.PeerID, serverMsg{Type: relayTypePeerJoined, PeerID: msg.PeerID})
 			s.snap.schedule()
 
-		case "broadcast":
+		case relayTypeBroadcast:
 			if currentRoom == nil {
-				client.sendJSON(serverMsg{Type: "error", Code: "not_in_room", Message: "Not in a room"})
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorNotInRoom, Message: "Not in a room"})
 				continue
 			}
 			currentRoom.broadcastExcept(currentPeerID, serverMsg{
-				Type:    "message",
+				Type:    relayTypeMessage,
 				From:    currentPeerID,
 				Payload: msg.Payload,
 			})
 
-		case "sendTo":
+		case relayTypeSendTo:
 			if currentRoom == nil {
-				client.sendJSON(serverMsg{Type: "error", Code: "not_in_room", Message: "Not in a room"})
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorNotInRoom, Message: "Not in a room"})
 				continue
 			}
-			if msg.To == "" {
-				client.sendJSON(serverMsg{Type: "error", Code: "invalid_message", Message: "to field required"})
+			if !validRelayID(msg.To, maxPeerIDLength) {
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorInvalidMessage, Message: "Invalid to field"})
 				continue
 			}
 			if !currentRoom.sendTo(msg.To, serverMsg{
-				Type:    "message",
+				Type:    relayTypeMessage,
 				From:    currentPeerID,
 				Payload: msg.Payload,
 			}) {
-				client.sendJSON(serverMsg{Type: "error", Code: "not_in_room", Message: "Target peer not found"})
+				client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorNotInRoom, Message: "Target peer not found"})
 			}
 
-		case "ping":
-			client.sendJSON(serverMsg{Type: "pong"})
+		case relayTypePing:
+			client.sendJSON(serverMsg{Type: relayTypePong})
 
 		default:
-			client.sendJSON(serverMsg{Type: "error", Code: "invalid_message", Message: "Unknown message type"})
+			client.sendJSON(serverMsg{Type: relayTypeError, Code: relayErrorInvalidMessage, Message: "Unknown message type"})
 		}
 	}
 }
diff --git a/server/main_test.go b/server/main_test.go
index cb14ad97..c0b195fa 100644
--- a/server/main_test.go
+++ b/server/main_test.go
@@ -392,6 +392,21 @@ func (h *relayHarness) waitRoomPeers(t *testing.T, sessionID string, want int) {
 	t.Fatalf("room %s never reached %d peers within 2s", sessionID, want)
 }
 
+func (h *relayHarness) waitIPConnections(t *testing.T, ip string, want int) {
+	t.Helper()
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		h.srv.conns.mu.Lock()
+		got := h.srv.conns.perIP[ip]
+		h.srv.conns.mu.Unlock()
+		if got == want {
+			return
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+	t.Fatalf("IP %s never reached %d connections within 2s", ip, want)
+}
+
 type testConn struct {
 	t    *testing.T
 	conn *websocket.Conn
@@ -521,6 +536,40 @@ func TestRateLimiterAllowRace(t *testing.T) {
 	}
 }
 
+func TestRateLimiterReclaimableOnlyAfterFullRefill(t *testing.T) {
+	now := time.Now()
+	limiter := &rateLimiter{
+		tokens:     0,
+		maxTokens:  5,
+		refillRate: 1,
+		lastTime:   now,
+	}
+
+	if limiter.reclaimable(now.Add(4 * time.Second)) {
+		t.Fatal("partially refilled limiter must retain its effective state")
+	}
+	if !limiter.reclaimable(now.Add(5 * time.Second)) {
+		t.Fatal("fully refilled limiter should be reclaimable")
+	}
+}
+
+func TestCleanupRateWindowsUsesWindowBoundary(t *testing.T) {
+	now := time.Now()
+	windows := map[string]time.Time{
+		"active":  now.Add(-logRateInterval + time.Nanosecond),
+		"expired": now.Add(-logRateInterval),
+	}
+
+	cleanupRateWindows(windows, now, logRateInterval)
+
+	if _, ok := windows["active"]; !ok {
+		t.Fatal("active fixed-window limiter was removed early")
+	}
+	if _, ok := windows["expired"]; ok {
+		t.Fatal("expired fixed-window limiter was retained")
+	}
+}
+
 // ======================================================================
 // connTracker unit tests
 // ======================================================================
@@ -588,25 +637,34 @@ func TestConnTrackerRoomQuota(t *testing.T) {
 	}
 }
 
-func TestConnTrackerCleanupPrunesStaleRateLimiters(t *testing.T) {
+func TestConnTrackerCleanupPreservesEffectiveRateLimits(t *testing.T) {
 	ct := newConnTracker()
-	for i := 0; i < 50; i++ {
-		ip := fmt.Sprintf("10.0.1.%d", i)
-		ct.tryConnect(ip)
+	ip := "10.0.1.1"
+	for i := range connRateBurst {
+		if !ct.tryConnect(ip) {
+			t.Fatalf("tryConnect %d: expected true", i)
+		}
+	}
+	for range connRateBurst {
 		ct.disconnect(ip)
 	}
-	ct.mu.Lock()
-	sizeBefore := len(ct.ipRate)
-	ct.mu.Unlock()
-	if sizeBefore == 0 {
-		t.Fatal("expected some rate limiter entries before cleanup")
+
+	ct.cleanup(time.Now())
+	if ct.tryConnect(ip) {
+		t.Fatal("cleanup reset a connection rate limit that was still effective")
 	}
-	ct.cleanup()
+
+	ct.cleanup(time.Now().Add(10 * time.Second))
+	if !ct.tryConnect(ip) {
+		t.Fatal("fully refilled limiter should be reclaimable")
+	}
+
+	ct.cleanup(time.Now().Add(10 * time.Second))
 	ct.mu.Lock()
-	sizeAfter := len(ct.ipRate)
+	_, retainedWhileConnected := ct.ipRate[ip]
 	ct.mu.Unlock()
-	if sizeAfter != 0 {
-		t.Errorf("cleanup should prune all stale rate limiters, got %d", sizeAfter)
+	if !retainedWhileConnected {
+		t.Fatal("cleanup removed a limiter with an active connection")
 	}
 }
 
@@ -771,6 +829,39 @@ func TestCreateHitsRoomsPerIPLimit(t *testing.T) {
 	c.expectError("rate_limited")
 }
 
+func TestConnectionCannotRetainMultipleRoomMemberships(t *testing.T) {
+	h := newRelayHarness(t)
+	ip := "1.1.1.8"
+	client := h.dial(t, ip)
+	client.send(clientMsg{Type: "create", SessionID: "PRIMARY", PeerID: "host"})
+	client.expect("created")
+
+	otherHost := h.dial(t, "1.1.1.9")
+	otherHost.send(clientMsg{Type: "create", SessionID: "OTHER", PeerID: "other-host"})
+	otherHost.expect("created")
+
+	client.send(clientMsg{Type: "join", SessionID: "OTHER", PeerID: "ghost"})
+	client.expectError("already_in_room")
+	client.send(clientMsg{Type: "create", SessionID: "EXTRA", PeerID: "extra-host"})
+	client.expectError("already_in_room")
+
+	h.waitRoomPeers(t, "PRIMARY", 1)
+	h.waitRoomPeers(t, "OTHER", 1)
+	h.srv.mu.RLock()
+	_, extraExists := h.srv.rooms["EXTRA"]
+	h.srv.mu.RUnlock()
+	if extraExists {
+		t.Fatal("rejected create retained an extra room")
+	}
+
+	h.srv.conns.mu.Lock()
+	roomsForIP := h.srv.conns.roomsPerIP[ip]
+	h.srv.conns.mu.Unlock()
+	if roomsForIP != 1 {
+		t.Fatalf("roomsPerIP[%q]=%d, want 1", ip, roomsForIP)
+	}
+}
+
 // ======================================================================
 // handleWS — join case
 // ======================================================================
@@ -805,6 +896,22 @@ func TestJoinMissingFieldsRejected(t *testing.T) {
 	c.expectError("invalid_message")
 }
 
+func TestRelayIdentifiersRejectUnsafeOrOversizedValues(t *testing.T) {
+	h := newRelayHarness(t)
+	c := h.dial(t, "2.0.0.30")
+
+	invalid := []string{"has space", "has/slash", strings.Repeat("x", maxSessionIDLength+1)}
+	for _, sessionID := range invalid {
+		c.send(clientMsg{Type: "create", SessionID: sessionID, PeerID: "H"})
+		c.expectError("invalid_message")
+	}
+
+	c.send(clientMsg{Type: "create", SessionID: "SAFE_ID-1", PeerID: "H"})
+	c.expect("created")
+	c.send(clientMsg{Type: "sendTo", To: "bad target", Payload: json.RawMessage(`{}`)})
+	c.expectError("invalid_message")
+}
+
 func TestJoinUnknownRoomFails(t *testing.T) {
 	h := newRelayHarness(t)
 	c := h.dial(t, "2.0.0.4")
@@ -907,6 +1014,47 @@ func TestSendToDeliversToTargetOnly(t *testing.T) {
 	g2.recvNothing(200 * time.Millisecond)
 }
 
+func TestRelayMessagesRefreshRoomActivity(t *testing.T) {
+	h := newRelayHarness(t)
+	host := h.dial(t, "4.0.0.7")
+	host.send(clientMsg{Type: "create", SessionID: "ACTIVE", PeerID: "H"})
+	host.expect("created")
+
+	guest := h.dial(t, "4.0.0.8")
+	guest.send(clientMsg{Type: "join", SessionID: "ACTIVE", PeerID: "G"})
+	guest.expect("joined")
+	host.expect("peerJoined")
+
+	h.srv.mu.RLock()
+	room := h.srv.rooms["ACTIVE"]
+	h.srv.mu.RUnlock()
+	old := time.Now().Add(-time.Hour)
+
+	room.mu.Lock()
+	room.LastActivityAt = old
+	room.mu.Unlock()
+	host.send(clientMsg{Type: "broadcast", Payload: json.RawMessage(`{"broadcast":true}`)})
+	guest.expect("message")
+	room.mu.RLock()
+	broadcastActivity := room.LastActivityAt
+	room.mu.RUnlock()
+	if !broadcastActivity.After(old) {
+		t.Fatalf("broadcast activity=%v, want after %v", broadcastActivity, old)
+	}
+
+	room.mu.Lock()
+	room.LastActivityAt = old
+	room.mu.Unlock()
+	host.send(clientMsg{Type: "sendTo", To: "G", Payload: json.RawMessage(`{"direct":true}`)})
+	guest.expect("message")
+	room.mu.RLock()
+	directActivity := room.LastActivityAt
+	room.mu.RUnlock()
+	if !directActivity.After(old) {
+		t.Fatalf("sendTo activity=%v, want after %v", directActivity, old)
+	}
+}
+
 func TestSendToUnknownTargetRejected(t *testing.T) {
 	h := newRelayHarness(t)
 	host := h.dial(t, "4.0.0.4")
@@ -1027,6 +1175,103 @@ func TestStalePeerSkipsCleanupBroadcast(t *testing.T) {
 	host.recvNothing(300 * time.Millisecond)
 }
 
+func TestHostReconnectReplacesStaleConnectionWithoutLeaving(t *testing.T) {
+	h := newRelayHarness(t)
+	oldHostIP := "6.1.1.1"
+	oldHost := h.dial(t, oldHostIP)
+	oldHost.send(clientMsg{Type: "create", SessionID: "REJOIN", PeerID: "H"})
+	oldHost.expect("created")
+
+	guest := h.dial(t, "6.1.1.2")
+	guest.send(clientMsg{Type: "join", SessionID: "REJOIN", PeerID: "G"})
+	guest.expect("joined")
+	oldHost.expect("peerJoined")
+
+	newHost := h.dial(t, "6.1.1.3")
+	newHost.send(clientMsg{Type: "join", SessionID: "REJOIN", PeerID: "H"})
+	joined := newHost.expect("joined")
+	if len(joined.Peers) != 1 || joined.Peers[0] != "G" {
+		t.Fatalf("reconnected host peers=%v, want [G]", joined.Peers)
+	}
+	guest.expect("peerJoined")
+
+	oldHost.conn.Close()
+	h.waitIPConnections(t, oldHostIP, 0)
+
+	newHost.send(clientMsg{Type: "broadcast", Payload: json.RawMessage(`{"state":"ready"}`)})
+	message := guest.expect("message")
+	if message.From != "H" {
+		t.Fatalf("message sender=%q, want H", message.From)
+	}
+}
+
+func TestEmptyRoomSupportsJoinThenExpiresForReconnectFallback(t *testing.T) {
+	h := newRelayHarness(t)
+	host := h.dial(t, "6.1.2.1")
+	host.send(clientMsg{Type: "create", SessionID: "EMPTY", PeerID: "H"})
+	host.expect("created")
+	host.conn.Close()
+	h.waitRoomPeers(t, "EMPTY", 0)
+
+	reconnected := h.dial(t, "6.1.2.2")
+	reconnected.send(clientMsg{Type: "join", SessionID: "EMPTY", PeerID: "H"})
+	joined := reconnected.expect("joined")
+	if len(joined.Peers) != 0 {
+		t.Fatalf("empty-room reconnect peers=%v, want none", joined.Peers)
+	}
+	reconnected.conn.Close()
+	h.waitRoomPeers(t, "EMPTY", 0)
+
+	now := time.Now()
+	h.srv.mu.RLock()
+	room := h.srv.rooms["EMPTY"]
+	h.srv.mu.RUnlock()
+	room.mu.Lock()
+	room.LastActivityAt = now.Add(-emptyRoomMaxAge - time.Second)
+	room.mu.Unlock()
+	h.srv.runCleanupStep(now)
+
+	fallback := h.dial(t, "6.1.2.3")
+	fallback.send(clientMsg{Type: "join", SessionID: "EMPTY", PeerID: "H"})
+	fallback.expectError("room_not_found")
+}
+
+func TestCleanupDisconnectsPeersBeforeRemovingExpiredOccupiedRoom(t *testing.T) {
+	h := newRelayHarness(t)
+	host := h.dial(t, "6.2.0.1")
+	host.send(clientMsg{Type: "create", SessionID: "EXPIRED", PeerID: "H"})
+	host.expect("created")
+
+	guest := h.dial(t, "6.2.0.2")
+	guest.send(clientMsg{Type: "join", SessionID: "EXPIRED", PeerID: "G"})
+	guest.expect("joined")
+	host.expect("peerJoined")
+
+	now := time.Now()
+	h.srv.mu.RLock()
+	room := h.srv.rooms["EXPIRED"]
+	h.srv.mu.RUnlock()
+	room.mu.Lock()
+	room.CreatedAt = now.Add(-roomMaxAge - time.Second)
+	room.mu.Unlock()
+
+	h.srv.runCleanupStep(now)
+
+	h.srv.mu.RLock()
+	_, exists := h.srv.rooms["EXPIRED"]
+	h.srv.mu.RUnlock()
+	if exists {
+		t.Fatal("expired room still exists after cleanup")
+	}
+
+	for name, connection := range map[string]*testConn{"host": host, "guest": guest} {
+		connection.conn.SetReadDeadline(time.Now().Add(2 * time.Second))
+		if _, _, err := connection.conn.ReadMessage(); err == nil {
+			t.Errorf("%s remained connected after occupied room removal", name)
+		}
+	}
+}
+
 // ======================================================================
 // Logs endpoints
 // ======================================================================
@@ -1132,6 +1377,44 @@ func TestLogsRoundTrip(t *testing.T) {
 	}
 }
 
+func TestLogStorePersistsAcrossRestartAndAvoidsIDCollisions(t *testing.T) {
+	dir := t.TempDir()
+	now := time.Now().Add(-time.Second)
+	first := newLogStore(dir)
+	first.generateID = func() string { return "aaaaa" }
+	firstID, _, err := first.store([]byte("original"), now)
+	if err != nil {
+		t.Fatalf("store original: %v", err)
+	}
+
+	restarted := newLogStore(dir)
+	if _, ok := restarted.lookup(firstID, time.Now()); !ok {
+		t.Fatal("stored log was not restored after restart")
+	}
+
+	ids := []string{firstID, "bbbbb"}
+	restarted.generateID = func() string {
+		id := ids[0]
+		ids = ids[1:]
+		return id
+	}
+	secondID, _, err := restarted.store([]byte("second"), time.Now())
+	if err != nil {
+		t.Fatalf("store after restart: %v", err)
+	}
+	if secondID != "bbbbb" {
+		t.Fatalf("collision generated id %q, want bbbbb", secondID)
+	}
+
+	original, err := os.ReadFile(restarted.filePath(firstID))
+	if err != nil {
+		t.Fatalf("read original: %v", err)
+	}
+	if string(original) != "original" {
+		t.Fatalf("colliding store overwrote original: %q", original)
+	}
+}
+
 func TestLogsUploadRateLimitedPerIP(t *testing.T) {
 	h := newRelayHarness(t)
 	r1 := postLog(t, h.baseURL, "7.0.0.2", []byte("first"))
diff --git a/server/oauth.go b/server/oauth.go
index 970b84cd..58408cc5 100644
--- a/server/oauth.go
+++ b/server/oauth.go
@@ -25,14 +25,14 @@ import (
 )
 
 const (
-	oauthSessionTTL        = 10 * time.Minute
-	oauthResultWait        = 50 * time.Second
-	oauthMaxSessions       = 5000
-	oauthStartBurst        = 3
+	oauthSessionTTL         = 10 * time.Minute
+	oauthResultWait         = 50 * time.Second
+	oauthMaxSessions        = 5000
+	oauthStartBurst         = 3
 	oauthStartRateSustained = 1
-	oauthSessionIDBytes    = 18 // 144 bits → 24 base64url chars
-	oauthPKCEVerifierLen   = 64
-	oauthUpstreamTimeout   = 15 * time.Second
+	oauthSessionIDBytes     = 18 // 144 bits → 24 base64url chars
+	oauthPKCEVerifierLen    = 64
+	oauthUpstreamTimeout    = 15 * time.Second
 )
 
 // oauthServiceConfig describes a single upstream OAuth provider. Populated from
@@ -422,11 +422,7 @@ func (p *oauthProxy) cleanup() {
 	p.mu.Unlock()
 
 	p.ipMu.Lock()
-	for ip, rl := range p.ipRate {
-		if rl.stale(now) {
-			delete(p.ipRate, ip)
-		}
-	}
+	cleanupRateLimiters(p.ipRate, now, nil)
 	p.ipMu.Unlock()
 }
 
diff --git a/server/rate_limit.go b/server/rate_limit.go
new file mode 100644
index 00000000..195573df
--- /dev/null
+++ b/server/rate_limit.go
@@ -0,0 +1,157 @@
+package main
+
+import (
+	"sync"
+	"time"
+)
+
+// --- Rate limiter (token bucket) ---
+
+type rateLimiter struct {
+	tokens     float64
+	maxTokens  float64
+	refillRate float64
+	lastTime   time.Time
+	mu         sync.Mutex
+}
+
+func newRateLimiter(burst, sustained int) *rateLimiter {
+	return &rateLimiter{
+		tokens:     float64(burst),
+		maxTokens:  float64(burst),
+		refillRate: float64(sustained),
+		lastTime:   time.Now(),
+	}
+}
+
+func (rl *rateLimiter) allow() bool {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+
+	now := time.Now()
+	elapsed := now.Sub(rl.lastTime).Seconds()
+	rl.lastTime = now
+
+	rl.tokens += elapsed * rl.refillRate
+	if rl.tokens > rl.maxTokens {
+		rl.tokens = rl.maxTokens
+	}
+
+	if rl.tokens < 1 {
+		return false
+	}
+	rl.tokens--
+	return true
+}
+
+// reclaimable reports whether discarding this limiter would preserve its
+// behavior: enough idle time has passed for the bucket to be full again.
+func (rl *rateLimiter) reclaimable(now time.Time) bool {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+	missingTokens := rl.maxTokens - rl.tokens
+	return missingTokens <= 0 || now.Sub(rl.lastTime).Seconds()*rl.refillRate >= missingTokens
+}
+
+func cleanupRateLimiters(limiters map[string]*rateLimiter, now time.Time, inUse func(string) bool) {
+	for ip, limiter := range limiters {
+		if (inUse == nil || !inUse(ip)) && limiter.reclaimable(now) {
+			delete(limiters, ip)
+		}
+	}
+}
+
+func cleanupRateWindows(windows map[string]time.Time, now time.Time, duration time.Duration) {
+	for ip, startedAt := range windows {
+		if now.Sub(startedAt) >= duration {
+			delete(windows, ip)
+		}
+	}
+}
+
+// --- Connection tracker (per-IP limits) ---
+
+type connTracker struct {
+	mu          sync.Mutex
+	perIP       map[string]int
+	ipRate      map[string]*rateLimiter
+	roomsPerIP  map[string]int
+	globalCount int
+}
+
+func newConnTracker() *connTracker {
+	return &connTracker{
+		perIP:      make(map[string]int),
+		ipRate:     make(map[string]*rateLimiter),
+		roomsPerIP: make(map[string]int),
+	}
+}
+
+func (ct *connTracker) tryConnect(ip string) bool {
+	ct.mu.Lock()
+	defer ct.mu.Unlock()
+
+	if ct.globalCount >= maxGlobalConns {
+		return false
+	}
+	if ct.perIP[ip] >= maxConnsPerIP {
+		return false
+	}
+
+	rl, ok := ct.ipRate[ip]
+	if !ok {
+		rl = newRateLimiter(connRateBurst, connRateSustained)
+		ct.ipRate[ip] = rl
+	}
+	// Unlock ct.mu before calling rl.allow() would be cleaner,
+	// but since rl has its own mutex this is safe (no deadlock).
+	if !rl.allow() {
+		return false
+	}
+
+	ct.perIP[ip]++
+	ct.globalCount++
+	return true
+}
+
+func (ct *connTracker) disconnect(ip string) {
+	ct.mu.Lock()
+	defer ct.mu.Unlock()
+
+	if ct.perIP[ip] > 0 {
+		ct.perIP[ip]--
+		ct.globalCount--
+	}
+	if ct.perIP[ip] == 0 {
+		delete(ct.perIP, ip)
+	}
+}
+
+func (ct *connTracker) tryCreateRoom(ip string) bool {
+	ct.mu.Lock()
+	defer ct.mu.Unlock()
+	if ct.roomsPerIP[ip] >= maxRoomsPerIP {
+		return false
+	}
+	ct.roomsPerIP[ip]++
+	return true
+}
+
+func (ct *connTracker) releaseRoom(ip string) {
+	ct.mu.Lock()
+	defer ct.mu.Unlock()
+	if ct.roomsPerIP[ip] > 0 {
+		ct.roomsPerIP[ip]--
+	}
+	if ct.roomsPerIP[ip] == 0 {
+		delete(ct.roomsPerIP, ip)
+	}
+}
+
+func (ct *connTracker) cleanup(now time.Time) {
+	ct.mu.Lock()
+	defer ct.mu.Unlock()
+	cleanupRateLimiters(ct.ipRate, now, func(ip string) bool {
+		return ct.perIP[ip] > 0
+	})
+}
diff --git a/server/relay_protocol_gen.go b/server/relay_protocol_gen.go
new file mode 100644
index 00000000..2a23b003
--- /dev/null
+++ b/server/relay_protocol_gen.go
@@ -0,0 +1,43 @@
+// Code generated by scripts/generate_relay_protocol.py. DO NOT EDIT.
+
+package main
+
+const (
+	relayTypeCreate          = "create"
+	relayTypeJoin            = "join"
+	relayTypeBroadcast       = "broadcast"
+	relayTypeSendTo          = "sendTo"
+	relayTypePing            = "ping"
+	relayTypeCreated         = "created"
+	relayTypeJoined          = "joined"
+	relayTypePeerJoined      = "peerJoined"
+	relayTypePeerLeft        = "peerLeft"
+	relayTypeMessage         = "message"
+	relayTypeError           = "error"
+	relayTypePong            = "pong"
+	relayErrorRateLimited    = "rate_limited"
+	relayErrorInvalidMessage = "invalid_message"
+	relayErrorRoomExists     = "room_exists"
+	relayErrorRoomNotFound   = "room_not_found"
+	relayErrorRoomFull       = "room_full"
+	relayErrorNotInRoom      = "not_in_room"
+	relayErrorAlreadyInRoom  = "already_in_room"
+
+	maxRoomSize        = 8
+	maxMessageSize     = 65536
+	maxSessionIDLength = 64
+	maxPeerIDLength    = 128
+)
+
+func validRelayID(value string, maxLength int) bool {
+	if len(value) == 0 || len(value) > maxLength {
+		return false
+	}
+	for _, ch := range value {
+		if (ch < 'a' || ch > 'z') && (ch < 'A' || ch > 'Z') &&
+			(ch < '0' || ch > '9') && ch != '_' && ch != '-' {
+			return false
+		}
+	}
+	return true
+}
diff --git a/test/screens/settings/logs_screen_test.dart b/test/screens/settings/logs_screen_test.dart
new file mode 100644
index 00000000..1f6e15a3
--- /dev/null
+++ b/test/screens/settings/logs_screen_test.dart
@@ -0,0 +1,25 @@
+import 'dart:convert';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:plezy/screens/settings/logs_screen.dart';
+
+void main() {
+  test('log upload payload preserves the header and newest complete lines', () {
+    const header = 'Plezy test device\n---\n';
+    const logs = 'oldest line that should be removed\nmiddle line that should be removed\nnewest 🚀 line';
+
+    final payload = constrainLogUploadPayload(header: header, logs: logs, maxBytes: 52);
+
+    expect(utf8.encode(payload).length, lessThanOrEqualTo(52));
+    expect(payload, startsWith(header));
+    expect(payload, endsWith('newest 🚀 line'));
+    expect(payload, isNot(contains('oldest line')));
+  });
+
+  test('log upload payload remains unchanged below the server limit', () {
+    const header = 'device\n---\n';
+    const logs = 'one\ntwo';
+
+    expect(constrainLogUploadPayload(header: header, logs: logs, maxBytes: 128), '$header$logs');
+  });
+}
diff --git a/test/services/discord_rpc_service_test.dart b/test/services/discord_rpc_service_test.dart
new file mode 100644
index 00000000..088689a9
--- /dev/null
+++ b/test/services/discord_rpc_service_test.dart
@@ -0,0 +1,27 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:plezy/services/discord_rpc_service.dart';
+
+void main() {
+  group('posterCacheExpiryFromResponse', () {
+    final receivedAt = DateTime.utc(2026, 7, 12, 12);
+
+    test('honors the relay-provided expiry', () {
+      expect(
+        posterCacheExpiryFromResponse({'expiresIn': 90}, receivedAt: receivedAt),
+        receivedAt.add(const Duration(seconds: 90)),
+      );
+    });
+
+    test('treats a non-positive relay expiry as immediately expired', () {
+      expect(posterCacheExpiryFromResponse({'expiresIn': 0}, receivedAt: receivedAt), receivedAt);
+    });
+
+    test('retains the legacy fallback for older or invalid relays', () {
+      final fallback = receivedAt.add(const Duration(hours: 3));
+
+      expect(posterCacheExpiryFromResponse({'url': '/posters/a.png'}, receivedAt: receivedAt), fallback);
+      expect(posterCacheExpiryFromResponse({'expiresIn': '90'}, receivedAt: receivedAt), fallback);
+      expect(posterCacheExpiryFromResponse({'expiresIn': 1 << 62}, receivedAt: receivedAt), fallback);
+    });
+  });
+}
diff --git a/test/watch_together/watch_together_peer_service_test.dart b/test/watch_together/watch_together_peer_service_test.dart
index d53d29d9..314e1371 100644
--- a/test/watch_together/watch_together_peer_service_test.dart
+++ b/test/watch_together/watch_together_peer_service_test.dart
@@ -4,6 +4,7 @@ import 'dart:io';
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:plezy/watch_together/services/watch_together_peer_service.dart';
+import 'package:plezy/watch_together/models/sync_message.dart';
 
 typedef _MessageHandler = FutureOr<void> Function(int connection, WebSocket socket, Map<String, dynamic> message);
 
@@ -72,6 +73,18 @@ void main() {
     relays.clear();
   });
 
+  test('invalid relay identifiers fail before network access', () async {
+    final service = WatchTogetherPeerService();
+    services.add(service);
+
+    await expectLater(service.createSession(sessionId: 'bad room'), throwsArgumentError);
+    await expectLater(service.joinSession('bad/room'), throwsArgumentError);
+    expect(
+      () => service.sendTo('bad peer', const SyncMessage(type: SyncMessageType.requestState, timestamp: 0)),
+      throwsArgumentError,
+    );
+  });
+
   test('host connects, listens, and announces create with the existing wire format', () async {
     late final _RelayServer relay;
     relay = await relayWith((_, socket, message) {