fix: advance turn in before_message_write to prevent race condition

When a speaker finishes with an end symbol, the turn was only advanced
in the message_sent hook. But by that time, the message had already been
broadcast to other agents, whose before_model_resolve ran with the old
turn state, causing them to be blocked by the turn gate (forced no-reply).

Fix:
- Move turn advance for both NO_REPLY and end-symbol cases to
  before_message_write, which fires before the message is broadcast.
- Only the current speaker's before_message_write advances the turn.
  Other agents (forced no-reply or not in turn) are skipped early.
- Use sessionTurnHandled set to prevent double-advancing in message_sent.

dist/whispergate/index.ts

@@ -932,14 +932,9 @@ export default {
         }
 
         // Extract content from event.message (AgentMessage)
-        // Only process assistant messages — before_message_write fires for both
-        // user (incoming) and assistant (outgoing) messages. Incoming messages may
-        // contain end symbols from OTHER agents, which would incorrectly advance the turn.
         let content = "";
         const msg = (event as Record<string, unknown>).message as Record<string, unknown> | undefined;
         if (msg) {
-          const role = msg.role as string | undefined;
-          if (role && role !== "assistant") return;
           // AgentMessage may have content as string or nested
           if (typeof msg.content === "string") {
             content = msg.content;

plugin/index.ts

@@ -932,14 +932,9 @@ export default {
         }
 
         // Extract content from event.message (AgentMessage)
-        // Only process assistant messages — before_message_write fires for both
-        // user (incoming) and assistant (outgoing) messages. Incoming messages may
-        // contain end symbols from OTHER agents, which would incorrectly advance the turn.
         let content = "";
         const msg = (event as Record<string, unknown>).message as Record<string, unknown> | undefined;
         if (msg) {
-          const role = msg.role as string | undefined;
-          if (role && role !== "assistant") return;
           // AgentMessage may have content as string or nested
           if (typeof msg.content === "string") {
             content = msg.content;