fix(telegram): treat "message is not modified" as success in finalize_draft

Telegram returns 400 with "message is not modified" when editMessageText
is called with content identical to the current message. This happens
when streaming deltas have already updated the draft to the final text.
Previously this triggered a fallback to sendMessage, producing a
duplicate message.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/channels/telegram.rs

@@ -1607,6 +1607,16 @@ impl Channel for TelegramChannel {
             return Ok(());
         }
 
+        // Check if edit failed because content is identical (Telegram returns 400
+        // with "message is not modified" when the draft already has the final text).
+        let status = resp.status();
+        let resp_body = resp.text().await.unwrap_or_default();
+        if status == reqwest::StatusCode::BAD_REQUEST
+            && resp_body.contains("message is not modified")
+        {
+            return Ok(());
+        }
+
         // Markdown failed — retry without parse_mode
         let plain_body = serde_json::json!({
             "chat_id": chat_id,
@@ -1625,6 +1635,15 @@ impl Channel for TelegramChannel {
             return Ok(());
         }
 
+        // Also check plain-text edit for "not modified"
+        let status = resp.status();
+        let resp_body = resp.text().await.unwrap_or_default();
+        if status == reqwest::StatusCode::BAD_REQUEST
+            && resp_body.contains("message is not modified")
+        {
+            return Ok(());
+        }
+
         // Edit failed entirely — fall back to new message
         tracing::warn!("Telegram finalize_draft edit failed; falling back to sendMessage");
         self.send_text_chunks(text, &chat_id, thread_id.as_deref())