protocol: read the watch's refusals instead of dropping them

Endpoint 0 is the meta endpoint: the watch answers there when it will not
answer on the endpoint that was addressed, with an error code and the id
of the request it is about. Nothing decoded it, so PacketRegistry threw,
the inbound loop swallowed the exception (its warning is commented out),
and the refusal reached nobody.

Whoever was waiting for the real answer therefore waited for a reply that
was never coming. sendPing has no deadline of its own — unlike
getFirmwareUpdateStatus, which does — so a ping to a watch in its recovery
firmware never returned. That firmware refuses nearly every endpoint, and
answers endpoint 0 with `DC 07 D1`: "endpoint 2001 is not handled here".

MetaMessage now decodes it, and SystemService fails a pending ping when
the watch says it will not answer one, the way WatchFactoryDataError
already fails a pending watch-model request.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: zunda-pixel

libpebble3/src/commonMain/kotlin/io/rebble/libpebblecommon/packets/Meta.kt

@@ -0,0 +1,55 @@
+package io.rebble.libpebblecommon.packets
+
+import io.rebble.libpebblecommon.protocolhelpers.PacketRegistry
+import io.rebble.libpebblecommon.protocolhelpers.PebblePacket
+import io.rebble.libpebblecommon.protocolhelpers.ProtocolEndpoint
+import io.rebble.libpebblecommon.structmapper.SOptional
+import io.rebble.libpebblecommon.structmapper.SUByte
+import io.rebble.libpebblecommon.structmapper.SUShort
+import io.rebble.libpebblecommon.structmapper.StructMapper
+import io.rebble.libpebblecommon.util.Endian
+
+/**
+ * Meta endpoint (0x00, spelled [ProtocolEndpoint.RECOVERY]). The watch answers here when it will
+ * not answer on the endpoint that was addressed: an [error] saying why, and the [rejectedEndpoint]
+ * the refused request was for. A recovery firmware refuses nearly every endpoint, so there this is
+ * the only reply most requests get.
+ */
+class MetaMessage : PebblePacket(endpoint) {
+    /**
+     * Why the request was refused. See [Error].
+     */
+    val error = SUByte(m)
+
+    /**
+     * The endpoint the refused request was addressed to. Absent for [Error.CorruptedMessage],
+     * which the watch cannot attribute to an endpoint.
+     */
+    val rejectedEndpoint =
+        SOptional(m, SUShort(StructMapper(), endianness = Endian.Big), present = true)
+
+    enum class Error(val value: UByte) {
+        NoError(0x00u),
+        CorruptedMessage(0xd0u),
+        Unhandled(0xdcu),
+        Disallowed(0xddu),
+        ;
+
+        companion object {
+            fun fromValue(value: UByte): Error? = entries.firstOrNull { it.value == value }
+        }
+    }
+
+    override fun toString(): String {
+        val name = Error.fromValue(error.get())?.name ?: "0x${error.get().toInt().toString(16)}"
+        return "MetaMessage(error=$name, rejectedEndpoint=${rejectedEndpoint.get()})"
+    }
+
+    companion object {
+        val endpoint = ProtocolEndpoint.RECOVERY
+    }
+}
+
+fun metaPacketsRegister() {
+    PacketRegistry.register(MetaMessage.endpoint) { MetaMessage() }
+}

libpebble3/src/commonMain/kotlin/io/rebble/libpebblecommon/protocolhelpers/PacketRegistry.kt

@@ -15,6 +15,7 @@ import io.rebble.libpebblecommon.packets.dataLoggingPacketsRegister
 import io.rebble.libpebblecommon.packets.getBytesIncomingPacketsRegister
 import io.rebble.libpebblecommon.packets.healthSyncPacketsRegister
 import io.rebble.libpebblecommon.packets.logDumpPacketsRegister
+import io.rebble.libpebblecommon.packets.metaPacketsRegister
 import io.rebble.libpebblecommon.packets.musicPacketsRegister
 import io.rebble.libpebblecommon.packets.phoneControlPacketsRegister
 import io.rebble.libpebblecommon.packets.putBytesIncomingPacketsRegister
@@ -34,6 +35,7 @@ object PacketRegistry {
         mutableMapOf()
 
     init {
+        metaPacketsRegister()
         systemPacketsRegister()
         timePacketsRegister()
         timelinePacketsRegister()

libpebble3/src/commonMain/kotlin/io/rebble/libpebblecommon/services/SystemService.kt

@@ -14,13 +14,15 @@ import io.rebble.libpebblecommon.metadata.WatchColor.TimeRoundBlackSilverPolish2
 import io.rebble.libpebblecommon.metadata.WatchHardwarePlatform
 import io.rebble.libpebblecommon.metadata.WatchType.CHALK
 import io.rebble.libpebblecommon.packets.FirmwareProperty
+import io.rebble.libpebblecommon.packets.MetaMessage
 import io.rebble.libpebblecommon.packets.PhoneAppVersion
 import io.rebble.libpebblecommon.packets.PingPong
 import io.rebble.libpebblecommon.packets.ProtocolCapsFlag
 import io.rebble.libpebblecommon.packets.ResetMessage
 import io.rebble.libpebblecommon.packets.SystemMessage
 import io.rebble.libpebblecommon.packets.TimeMessage
 import io.rebble.libpebblecommon.packets.WatchFactoryData
+import io.rebble.libpebblecommon.protocolhelpers.ProtocolEndpoint
 import io.rebble.libpebblecommon.packets.WatchFirmwareVersion
 import io.rebble.libpebblecommon.packets.WatchVersion
 import io.rebble.libpebblecommon.packets.WatchVersion.WatchVersionResponse
@@ -213,6 +215,15 @@ class SystemService(
                         pongCallback = null
                     }
 
+                    is MetaMessage -> {
+                        if (packet.rejectedEndpoint.get() == ProtocolEndpoint.PING.value) {
+                            pongCallback?.completeExceptionally(
+                                Exception("Watch will not answer a ping: $packet")
+                            )
+                            pongCallback = null
+                        }
+                    }
+
                     is TimeMessage.GetTimeUtcRequest-> {
                         updateTime()
                     }