refactor(tests): reformat code and update dependency management

- Reorganized import statements in adapter tests for better readability
- Replaced or_insert_with(Vec::new) with or_default() in test closures
- Updated Cargo.lock with new dependency versions and checksums
- Added TLS features to tonic dependency configuration
- Included sqlx, chrono, and uuid dependencies with specific features
- Added jsonwebtoken and arc-swap as project dependencies
- Reformatted assertion statements to comply with line length limits
- Adjusted base64 import order in engine codec module
- Updated protobuf include statement formatting

models/message_thread_participant.rs

@@ -0,0 +1,71 @@
+//! Thread participant membership — maps to `message_thread_participant` table.
+//!
+//! Tracks which users are part of a thread. A user becomes a participant when
+//! they reply in a thread, get @mentioned, or are explicitly added.
+//! Without this table, `message_thread.participants_count` is un-verifiable.
+
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use uuid::Uuid;
+
+/// A user participating in a thread.
+///
+/// Maps to the `message_thread_participant` table. Users become participants
+/// when they reply, get @mentioned, or are explicitly added.
+#[derive(Debug, Clone, Serialize, Deserialize, sqlx::FromRow)]
+pub struct MessageThreadParticipant {
+    pub id: Uuid,
+    pub thread_id: Uuid,
+    pub user_id: Uuid,
+    /// How the user joined the thread.
+    pub joined_reason: Option<String>,
+    pub last_read_message_id: Option<Uuid>,
+    pub last_read_at: Option<DateTime<Utc>>,
+    pub joined_at: DateTime<Utc>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum JoinReason {
+    /// User sent a reply in the thread.
+    #[default]
+    Reply,
+    /// User was @mentioned in a thread message.
+    Mentioned,
+    /// User was explicitly added by another participant.
+    Added,
+    /// User joined the thread themselves.
+    Joined,
+}
+
+impl JoinReason {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            Self::Reply => "reply",
+            Self::Mentioned => "mentioned",
+            Self::Added => "added",
+            Self::Joined => "joined",
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_participant_serialize() {
+        let p = MessageThreadParticipant {
+            id: Uuid::now_v7(),
+            thread_id: Uuid::now_v7(),
+            user_id: Uuid::now_v7(),
+            joined_reason: Some(JoinReason::Reply.as_str().into()),
+            last_read_message_id: None,
+            last_read_at: None,
+            joined_at: Utc::now(),
+        };
+
+        let json = serde_json::to_value(&p).unwrap();
+        assert_eq!(json["joined_reason"], "reply");
+    }
+}