fix: honor message tool channel for tool dedupe (#1053)

- Treat message tool `channel` as provider hint for dedupe/suppression.
- Prefer NO_REPLY after message tool sends to avoid duplicate replies.

Co-authored-by: Sash Catanzarite <1166151+thesash@users.noreply.github.com>

src/agents/system-prompt.ts

@@ -95,6 +95,7 @@ function buildMessagingSection(params: {
           "- Use `message` for proactive sends + channel actions (polls, reactions, etc.).",
           "- For `action=send`, include `to` and `message`.",
           `- If multiple channels are configured, pass \`channel\` (${params.messageChannelOptions}).`,
+          `- If you use \`message\` (\`action=send\`) to deliver your user-visible reply, respond with ONLY: ${SILENT_REPLY_TOKEN} (avoid duplicate replies).`,
           params.inlineButtonsEnabled
             ? "- Inline buttons supported. Use `action=send` with `buttons=[[{text,callback_data}]]` (callback_data routes back as a user message)."
             : params.runtimeChannel