Phase 4: receive waypoint shares and render JourneyMap/Xaero chat links

DefaultBackendConnection handles the new waypoint_share message and
dispatches it through a WaypointShareListener. WaypointChatFormatter
builds the actual chat text for both formats from publicly documented
wire formats (see THIRD_PARTY_NOTICES.md for sources/attribution) —
neither needs a click-event component, since both client mods
auto-detect the right plain-text shape. Forge1122ChatBridge wires this
into a real broadcast; MCMapperMod registers the listener.

Built test-first per the project's TDD workflow; verified live against
the real backend, including a byte-exact JourneyMap-format chat
message produced from a real WS payload.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015tKdPZt78zbPUZMXWzKEKt

forge-1_12_2/src/main/java/com/octoturge/mcmapper/forge1122/Forge1122ChatBridge.java

@@ -1,6 +1,7 @@
 package com.octoturge.mcmapper.forge1122;
 
 import com.octoturge.mcmapper.common.ChatBridge;
+import com.octoturge.mcmapper.common.protocol.WaypointChatFormatter;
 import com.octoturge.mcmapper.common.protocol.WaypointShare;
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.util.text.TextComponentString;
@@ -22,8 +23,10 @@ public class Forge1122ChatBridge implements ChatBridge {
 
     @Override
     public void injectWaypointShare(WaypointShare waypoint) {
-        // Marker sharing lands in Phase 4 (needs the JourneyMap/Xaero wire-format research spike
-        // the plan calls for) — nothing calls this yet.
-        logger.warn("injectWaypointShare called before Phase 4's waypoint sharing is implemented — ignoring");
+        // Neither JourneyMap's nor Xaero's chat-waypoint syntax needs a click-event component —
+        // both client mods auto-detect the right plain-text shape in a normal chat message (see
+        // WaypointChatFormatter's javadoc for sources), so a broadcast TextComponentString is
+        // enough, same as injectWebChatMessage above.
+        server.getPlayerList().sendMessage(new TextComponentString(WaypointChatFormatter.format(waypoint)));
     }
 }

forge-1_12_2/src/main/java/com/octoturge/mcmapper/forge1122/MCMapperMod.java

@@ -92,6 +92,7 @@ public class MCMapperMod {
 
         Forge1122ChatBridge chatBridge = new Forge1122ChatBridge(event.getServer(), LOGGER);
         connection.setChatListener(chatBridge::injectWebChatMessage);
+        connection.setWaypointShareListener(chatBridge::injectWaypointShare);
         event.registerServerCommand(new LinkCommand(connection));
 
         MinecraftForge.EVENT_BUS.register(this);