fix(channels): check response status in send() for Telegram, Slack, and Discord

Reliability fix: check HTTP response status in channel send methods

src/channels/discord.rs

@@ -87,13 +87,23 @@ impl Channel for DiscordChannel {
         let url = format!("https://discord.com/api/v10/channels/{channel_id}/messages");
         let body = json!({ "content": message });
 
-        self.client
+        let resp = self
+            .client
             .post(&url)
             .header("Authorization", format!("Bot {}", self.bot_token))
             .json(&body)
             .send()
             .await?;
 
+        if !resp.status().is_success() {
+            let status = resp.status();
+            let err = resp
+                .text()
+                .await
+                .unwrap_or_else(|e| format!("<failed to read response body: {e}>"));
+            anyhow::bail!("Discord send message failed ({status}): {err}");
+        }
+
         Ok(())
     }
 

src/channels/slack.rs

@@ -58,13 +58,34 @@ impl Channel for SlackChannel {
             "text": message
         });
 
-        self.client
+        let resp = self
+            .client
             .post("https://slack.com/api/chat.postMessage")
             .bearer_auth(&self.bot_token)
             .json(&body)
             .send()
             .await?;
 
+        let status = resp.status();
+        let body = resp
+            .text()
+            .await
+            .unwrap_or_else(|e| format!("<failed to read response body: {e}>"));
+
+        if !status.is_success() {
+            anyhow::bail!("Slack chat.postMessage failed ({status}): {body}");
+        }
+
+        // Slack returns 200 for most app-level errors; check JSON "ok" field
+        let parsed: serde_json::Value = serde_json::from_str(&body).unwrap_or_default();
+        if parsed.get("ok") == Some(&serde_json::Value::Bool(false)) {
+            let err = parsed
+                .get("error")
+                .and_then(|e| e.as_str())
+                .unwrap_or("unknown");
+            anyhow::bail!("Slack chat.postMessage failed: {err}");
+        }
+
         Ok(())
     }
 

src/channels/telegram.rs

@@ -376,12 +376,22 @@ impl Channel for TelegramChannel {
             "parse_mode": "Markdown"
         });
 
-        self.client
+        let resp = self
+            .client
             .post(self.api_url("sendMessage"))
             .json(&body)
             .send()
             .await?;
 
+        if !resp.status().is_success() {
+            let status = resp.status();
+            let err = resp
+                .text()
+                .await
+                .unwrap_or_else(|e| format!("<failed to read response body: {e}>"));
+            anyhow::bail!("Telegram sendMessage failed ({status}): {err}");
+        }
+
         Ok(())
     }