feat(event-payload): serializable NATS event payload types

Cargo.toml

@@ -33,6 +33,8 @@ axum = { version = "0.8", features = ["macros"] }
 tower-http = { version = "0.6", features = ["cors", "trace"] }
 futures = "0.3"
 dotenvy = "0.15"
+async-nats = "0.38"
+async-stream = "0.3"
 
 domain           = { path = "crates/domain" }
 application      = { path = "crates/application" }

crates/adapters/event-payload/Cargo.toml

@@ -2,3 +2,7 @@
 name = "event-payload"
 version = "0.1.0"
 edition = "2021"
+
+[dependencies]
+serde      = { workspace = true }
+serde_json = { workspace = true }

crates/adapters/event-payload/src/lib.rs

@@ -0,0 +1,118 @@
+use serde::{Deserialize, Serialize};
+
+/// Serializable mirror of domain::events::DomainEvent.
+/// All IDs are Strings (UUID hex) — no domain type dependencies.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type", content = "data")]
+pub enum EventPayload {
+    ThoughtCreated {
+        thought_id: String,
+        user_id: String,
+        in_reply_to_id: Option<String>,
+    },
+    ThoughtDeleted {
+        thought_id: String,
+        user_id: String,
+    },
+    ThoughtUpdated {
+        thought_id: String,
+        user_id: String,
+    },
+    LikeAdded {
+        like_id: String,
+        user_id: String,
+        thought_id: String,
+    },
+    LikeRemoved {
+        user_id: String,
+        thought_id: String,
+    },
+    BoostAdded {
+        boost_id: String,
+        user_id: String,
+        thought_id: String,
+    },
+    BoostRemoved {
+        user_id: String,
+        thought_id: String,
+    },
+    FollowRequested {
+        follower_id: String,
+        following_id: String,
+    },
+    FollowAccepted {
+        follower_id: String,
+        following_id: String,
+    },
+    FollowRejected {
+        follower_id: String,
+        following_id: String,
+    },
+    Unfollowed {
+        follower_id: String,
+        following_id: String,
+    },
+    UserBlocked {
+        blocker_id: String,
+        blocked_id: String,
+    },
+}
+
+impl EventPayload {
+    /// Returns the NATS subject for this event.
+    pub fn subject(&self) -> &'static str {
+        match self {
+            Self::ThoughtCreated { .. }  => "thoughts.created",
+            Self::ThoughtDeleted { .. }  => "thoughts.deleted",
+            Self::ThoughtUpdated { .. }  => "thoughts.updated",
+            Self::LikeAdded { .. }       => "likes.added",
+            Self::LikeRemoved { .. }     => "likes.removed",
+            Self::BoostAdded { .. }      => "boosts.added",
+            Self::BoostRemoved { .. }    => "boosts.removed",
+            Self::FollowRequested { .. } => "follows.requested",
+            Self::FollowAccepted { .. }  => "follows.accepted",
+            Self::FollowRejected { .. }  => "follows.rejected",
+            Self::Unfollowed { .. }      => "follows.removed",
+            Self::UserBlocked { .. }     => "users.blocked",
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn thought_created_roundtrip() {
+        let p = EventPayload::ThoughtCreated {
+            thought_id: "abc".into(),
+            user_id: "def".into(),
+            in_reply_to_id: None,
+        };
+        let json = serde_json::to_string(&p).unwrap();
+        let back: EventPayload = serde_json::from_str(&json).unwrap();
+        assert_eq!(back.subject(), "thoughts.created");
+    }
+
+    #[test]
+    fn all_subjects_are_unique() {
+        let samples: &[EventPayload] = &[
+            EventPayload::ThoughtCreated { thought_id: "a".into(), user_id: "b".into(), in_reply_to_id: None },
+            EventPayload::ThoughtDeleted { thought_id: "a".into(), user_id: "b".into() },
+            EventPayload::ThoughtUpdated { thought_id: "a".into(), user_id: "b".into() },
+            EventPayload::LikeAdded { like_id: "a".into(), user_id: "b".into(), thought_id: "c".into() },
+            EventPayload::LikeRemoved { user_id: "b".into(), thought_id: "c".into() },
+            EventPayload::BoostAdded { boost_id: "a".into(), user_id: "b".into(), thought_id: "c".into() },
+            EventPayload::BoostRemoved { user_id: "b".into(), thought_id: "c".into() },
+            EventPayload::FollowRequested { follower_id: "a".into(), following_id: "b".into() },
+            EventPayload::FollowAccepted { follower_id: "a".into(), following_id: "b".into() },
+            EventPayload::FollowRejected { follower_id: "a".into(), following_id: "b".into() },
+            EventPayload::Unfollowed { follower_id: "a".into(), following_id: "b".into() },
+            EventPayload::UserBlocked { blocker_id: "a".into(), blocked_id: "b".into() },
+        ];
+        let mut subjects: Vec<&str> = samples.iter().map(|p| p.subject()).collect();
+        subjects.sort();
+        subjects.dedup();
+        assert_eq!(subjects.len(), samples.len(), "each event must have a unique subject");
+    }
+}