fix(discord): use channel_id instead of sender for replies (fixes #483)

fix(misc): complete parking_lot::Mutex migration (fixes #505)

- DiscordChannel: store actual channel_id in ChannelMessage.channel
  instead of hardcoded "discord" string
- channels/mod.rs: use msg.channel instead of msg.sender for replies
- Migrate all std::sync::Mutex to parking_lot::Mutex:
  * src/security/audit.rs
  * src/memory/sqlite.rs
  * src/memory/response_cache.rs
  * src/memory/lucid.rs
  * src/channels/email_channel.rs
  * src/gateway/mod.rs
  * src/observability/traits.rs
  * src/providers/reliable.rs
  * src/providers/router.rs
  * src/agent/agent.rs
- Remove all .lock().unwrap() and .map_err(PoisonError) patterns
  since parking_lot::Mutex never poisons

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

src/channels/discord.rs

@@ -344,7 +344,7 @@ impl Channel for DiscordChannel {
                     }
 
                     let message_id = d.get("id").and_then(|i| i.as_str()).unwrap_or("");
-                    let _channel_id = d.get("channel_id").and_then(|c| c.as_str()).unwrap_or("").to_string();
+                    let channel_id = d.get("channel_id").and_then(|c| c.as_str()).unwrap_or("").to_string();
 
                     let channel_msg = ChannelMessage {
                         id: if message_id.is_empty() {
@@ -354,7 +354,7 @@ impl Channel for DiscordChannel {
                         },
                         sender: author_id.to_string(),
                         content: content.to_string(),
-                        channel: "discord".to_string(),
+                        channel: channel_id,
                         timestamp: std::time::SystemTime::now()
                             .duration_since(std::time::UNIX_EPOCH)
                             .unwrap_or_default()

src/channels/email_channel.rs

@@ -17,7 +17,7 @@ use serde::{Deserialize, Serialize};
 use std::collections::HashSet;
 use std::io::Write as IoWrite;
 use std::net::TcpStream;
-use std::sync::Mutex;
+use parking_lot::Mutex;
 use std::time::{Duration, SystemTime, UNIX_EPOCH};
 use tokio::sync::mpsc;
 use tokio::time::{interval, sleep};
@@ -415,7 +415,7 @@ impl Channel for EmailChannel {
                             let mut seen = self
                                 .seen_messages
                                 .lock()
-                                .expect("seen_messages mutex should not be poisoned");
+                ;
                             if seen.contains(&id) {
                                 continue;
                             }

src/channels/mod.rs

@@ -213,7 +213,7 @@ async fn process_channel_message(ctx: Arc<ChannelRuntimeContext>, msg: traits::C
                 truncate_with_ellipsis(&response, 80)
             );
             if let Some(channel) = target_channel.as_ref() {
-                if let Err(e) = channel.send(&response, &msg.sender).await {
+                if let Err(e) = channel.send(&response, &msg.channel).await {
                     eprintln!("  ❌ Failed to reply on {}: {e}", channel.name());
                 }
             }