fix(pdo): align PDO recovery + UndecryptableMessage dispatch with WA Web

src/cache_config.rs

@@ -169,6 +169,10 @@ pub struct CacheConfig {
     pub recent_messages: CacheEntryConfig,
     /// Message retry counts (time_to_live). Default: 5m TTL, 1000 entries.
     pub message_retry_counts: CacheEntryConfig,
+    /// Dedup key for `UndecryptableMessage` dispatch so a server resend of
+    /// the same id does not surface a second notification. Default: 5m TTL,
+    /// 1000 entries.
+    pub undecryptable_dispatched: CacheEntryConfig,
     /// PDO pending requests (time_to_live). Default: 30s TTL, 500 entries.
     pub pdo_pending_requests: CacheEntryConfig,
     /// Sender key device tracking cache (time_to_idle). Default: 1h TTI, 500 entries.
@@ -208,6 +212,7 @@ impl std::fmt::Debug for CacheConfig {
             .field("lid_pn_cache", &self.lid_pn_cache)
             .field("recent_messages", &self.recent_messages)
             .field("message_retry_counts", &self.message_retry_counts)
+            .field("undecryptable_dispatched", &self.undecryptable_dispatched)
             .field("pdo_pending_requests", &self.pdo_pending_requests)
             .field("sender_key_devices_cache", &self.sender_key_devices_cache)
             .field("session_locks_capacity", &self.session_locks_capacity)
@@ -240,6 +245,7 @@ impl Default for CacheConfig {
             lid_pn_cache: CacheEntryConfig::new(one_hour, 10_000),
             recent_messages: CacheEntryConfig::new(five_min, 0),
             message_retry_counts: CacheEntryConfig::new(five_min, 1_000),
+            undecryptable_dispatched: CacheEntryConfig::new(five_min, 1_000),
             pdo_pending_requests: CacheEntryConfig::new(Some(Duration::from_secs(30)), 500),
             sender_key_devices_cache: CacheEntryConfig::new(one_hour, 500),
             // Coordination caches hold live mutexes/senders; capacity eviction

src/client.rs

@@ -174,6 +174,7 @@ pub struct MemoryDiagnostics {
     pub recent_messages: u64,
     pub sender_key_device_cache: u64,
     pub message_retry_counts: u64,
+    pub undecryptable_dispatched: u64,
     pub pdo_pending_requests: u64,
     // -- Moka caches (capacity-only, no TTL) --
     pub session_locks: u64,
@@ -213,6 +214,11 @@ impl std::fmt::Display for MemoryDiagnostics {
             self.sender_key_device_cache
         )?;
         writeln!(f, "  message_retry_counts:   {}", self.message_retry_counts)?;
+        writeln!(
+            f,
+            "  undec_dispatched:       {}",
+            self.undecryptable_dispatched
+        )?;
         writeln!(f, "  pdo_pending_requests:   {}", self.pdo_pending_requests)?;
         writeln!(f, "--- Moka caches (capacity-only) ---")?;
         writeln!(f, "  session_locks:          {}", self.session_locks)?;
@@ -402,6 +408,12 @@ pub struct Client {
     /// Matches WhatsApp Web's MAX_RETRY = 5 behavior.
     pub(crate) message_retry_counts: Cache<String, u8>,
 
+    /// Dispatch-once gate for `UndecryptableMessage`: a server resend of a
+    /// failed id re-enters the failure path and would otherwise fire a
+    /// duplicate event. Mirrors WA Web's DB-level placeholder uniqueness
+    /// in `WAWebMessageProcessPlaceholder`.
+    pub(crate) undecryptable_dispatched: Cache<ChatMessageId, ()>,
+
     pub enable_auto_reconnect: Arc<AtomicBool>,
     pub auto_reconnect_errors: Arc<AtomicU32>,
 
@@ -740,6 +752,8 @@ impl Client {
 
             message_retry_counts: cache_config.message_retry_counts.build_with_ttl(),
 
+            undecryptable_dispatched: cache_config.undecryptable_dispatched.build_with_ttl(),
+
             offline_sync_metrics: Arc::new(OfflineSyncMetrics {
                 active: AtomicBool::new(false),
                 total_messages: AtomicUsize::new(0),
@@ -1416,6 +1430,7 @@ impl Client {
             recent_messages: self.recent_messages.entry_count(),
             sender_key_device_cache: self.sender_key_device_cache.entry_count(),
             message_retry_counts: self.message_retry_counts.entry_count(),
+            undecryptable_dispatched: self.undecryptable_dispatched.entry_count(),
             pdo_pending_requests: self.pdo_pending_requests.entry_count(),
             session_locks: self.session_locks.entry_count(),
             chat_lanes: self.chat_lanes.entry_count(),