replace tokio::broadcast event bus with SQLite-backed event queue (ADR-0003)

- DomainEvent: add Serialize/Deserialize
- EventConsumer port: poll_next/ack/nack replacing recv()
- EventEnvelope: wraps event with id/retry_count/created_at
- SqliteEventPublisher/SqliteEventConsumer: INSERT/poll/DLQ
- migration: event_queue + dead_letter_queue tables
- InMemoryEventBus: combined publisher+consumer test double
- NoopEventConsumer: test stub
- webhook_consumer: polls EventConsumer instead of broadcast::Receiver
- presentation+mcp wiring: create from SqlitePool

crates/adapters/event-publisher/Cargo.toml

@@ -8,3 +8,7 @@ domain = { workspace = true }
 async-trait = { workspace = true }
 tokio = { workspace = true }
 tracing = { workspace = true }
+sqlx = { workspace = true, features = ["sqlite"] }
+serde = { workspace = true }
+serde_json = { workspace = true }
+chrono = { workspace = true }

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

@@ -1,42 +1,170 @@
 use async_trait::async_trait;
 use domain::errors::{DomainError, DomainResult};
-use domain::events::DomainEvent;
+use domain::events::{DomainEvent, EventEnvelope};
 use domain::ports::events::{EventConsumer, EventPublisher};
-use tokio::sync::broadcast;
+use sqlx::SqlitePool;
 
-pub struct ChannelEventBus {
-    tx: broadcast::Sender<DomainEvent>,
+fn event_type_label(event: &DomainEvent) -> &'static str {
+    match event {
+        DomainEvent::BroadcastTransition { .. } => "broadcast_transition",
+        DomainEvent::NoSignal { .. } => "no_signal",
+        DomainEvent::ScheduleGenerated { .. } => "schedule_generated",
+        DomainEvent::ChannelCreated { .. } => "channel_created",
+        DomainEvent::ChannelUpdated { .. } => "channel_updated",
+        DomainEvent::ChannelDeleted { .. } => "channel_deleted",
+        DomainEvent::UserRegistered { .. } => "user_registered",
+        _ => "unknown",
+    }
 }
 
-impl ChannelEventBus {
-    pub fn new(capacity: usize) -> Self {
-        let (tx, _) = broadcast::channel(capacity);
-        Self { tx }
-    }
+pub struct SqliteEventPublisher {
+    pool: SqlitePool,
+}
 
-    pub fn subscriber(&self) -> broadcast::Receiver<DomainEvent> {
-        self.tx.subscribe()
-    }
-
-    pub fn sender(&self) -> broadcast::Sender<DomainEvent> {
-        self.tx.clone()
+impl SqliteEventPublisher {
+    pub fn new(pool: SqlitePool) -> Self {
+        Self { pool }
     }
 }
 
 #[async_trait]
-impl EventPublisher for ChannelEventBus {
+impl EventPublisher for SqliteEventPublisher {
     async fn publish(&self, event: DomainEvent) -> DomainResult<()> {
-        let _ = self.tx.send(event);
+        let event_type = event_type_label(&event);
+        let payload = serde_json::to_string(&event)
+            .map_err(|e| DomainError::InfrastructureError(format!("event serialize: {e}")))?;
+
+        sqlx::query(
+            "INSERT INTO event_queue (event_type, payload, status) VALUES (?, ?, 'pending')",
+        )
+        .bind(event_type)
+        .bind(&payload)
+        .execute(&self.pool)
+        .await
+        .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+
         Ok(())
     }
 }
 
-#[async_trait]
-impl EventConsumer for ChannelEventBus {
-    async fn recv(&self) -> DomainResult<DomainEvent> {
-        let mut rx = self.tx.subscribe();
-        rx.recv()
-            .await
-            .map_err(|e| DomainError::InfrastructureError(e.to_string()))
+pub struct SqliteEventConsumer {
+    pool: SqlitePool,
+}
+
+impl SqliteEventConsumer {
+    pub fn new(pool: SqlitePool) -> Self {
+        Self { pool }
     }
 }
+
+#[derive(sqlx::FromRow)]
+struct EventRow {
+    id: i64,
+    payload: String,
+    retry_count: i32,
+    created_at: String,
+    max_retries: i32,
+    event_type: String,
+}
+
+#[async_trait]
+impl EventConsumer for SqliteEventConsumer {
+    async fn poll_next(&self) -> DomainResult<Option<EventEnvelope>> {
+        let row: Option<EventRow> = sqlx::query_as(
+            "SELECT id, event_type, payload, retry_count, created_at, max_retries \
+             FROM event_queue WHERE status = 'pending' ORDER BY id ASC LIMIT 1",
+        )
+        .fetch_optional(&self.pool)
+        .await
+        .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+
+        let row = match row {
+            Some(r) => r,
+            None => return Ok(None),
+        };
+
+        sqlx::query("UPDATE event_queue SET status = 'processing', updated_at = datetime('now') WHERE id = ?")
+            .bind(row.id)
+            .execute(&self.pool)
+            .await
+            .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+
+        match serde_json::from_str::<DomainEvent>(&row.payload) {
+            Ok(event) => Ok(Some(EventEnvelope::from_persistence(
+                row.id,
+                event,
+                row.retry_count as u32,
+                row.created_at,
+            ))),
+            Err(e) => {
+                move_to_dlq(&self.pool, &row, &e.to_string()).await?;
+                Ok(None)
+            }
+        }
+    }
+
+    async fn ack(&self, event_id: i64) -> DomainResult<()> {
+        sqlx::query("DELETE FROM event_queue WHERE id = ?")
+            .bind(event_id)
+            .execute(&self.pool)
+            .await
+            .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+        Ok(())
+    }
+
+    async fn nack(&self, event_id: i64, error: &str) -> DomainResult<()> {
+        let row: Option<EventRow> = sqlx::query_as(
+            "SELECT id, event_type, payload, retry_count, created_at, max_retries FROM event_queue WHERE id = ?",
+        )
+        .bind(event_id)
+        .fetch_optional(&self.pool)
+        .await
+        .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+
+        let row = match row {
+            Some(r) => r,
+            None => return Ok(()),
+        };
+
+        let new_retry = row.retry_count + 1;
+        if new_retry >= row.max_retries {
+            move_to_dlq(&self.pool, &row, error).await?;
+        } else {
+            sqlx::query(
+                "UPDATE event_queue SET status = 'pending', retry_count = ?, error_message = ?, updated_at = datetime('now') WHERE id = ?",
+            )
+            .bind(new_retry)
+            .bind(error)
+            .bind(event_id)
+            .execute(&self.pool)
+            .await
+            .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+        }
+
+        Ok(())
+    }
+}
+
+async fn move_to_dlq(pool: &SqlitePool, row: &EventRow, error: &str) -> DomainResult<()> {
+    sqlx::query(
+        "INSERT INTO dead_letter_queue (original_event_id, event_type, payload, error_message, retry_count, original_created_at) \
+         VALUES (?, ?, ?, ?, ?, ?)",
+    )
+    .bind(row.id)
+    .bind(&row.event_type)
+    .bind(&row.payload)
+    .bind(error)
+    .bind(row.retry_count)
+    .bind(&row.created_at)
+    .execute(pool)
+    .await
+    .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+
+    sqlx::query("DELETE FROM event_queue WHERE id = ?")
+        .bind(row.id)
+        .execute(pool)
+        .await
+        .map_err(|e| DomainError::InfrastructureError(e.to_string()))?;
+
+    Ok(())
+}