feat(db): add append-only audit repository (record, history_for)

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

crates/db/src/audit.rs

@@ -0,0 +1,92 @@
+//! Append-only audit log access.
+
+use domain::{AuditActor, AuditEntry, FieldChange, NewAuditEvent};
+use sqlx::Row;
+use uuid::Uuid;
+
+/// Append an audit event. Accepts any executor, so callers can record the event
+/// inside the same transaction as the change it describes.
+pub async fn record<'e, E>(executor: E, event: &NewAuditEvent) -> Result<(), sqlx::Error>
+where
+    E: sqlx::PgExecutor<'e>,
+{
+    let (actor_kind, actor_id) = match event.actor {
+        AuditActor::User(id) => ("user", Some(id)),
+        AuditActor::System => ("system", None),
+    };
+
+    sqlx::query(
+        "INSERT INTO audit_log \
+         (actor_kind, actor_id, action, entity_type, entity_id, changes) \
+         VALUES ($1, $2, $3, $4, $5, $6)",
+    )
+    .bind(actor_kind)
+    .bind(actor_id)
+    .bind(event.action.as_str())
+    .bind(&event.entity_type)
+    .bind(event.entity_id)
+    .bind(sqlx::types::Json(&event.changes))
+    .execute(executor)
+    .await?;
+
+    Ok(())
+}
+
+/// Read the full history for one entity, oldest first.
+pub async fn history_for<'e, E>(
+    executor: E,
+    entity_type: &str,
+    entity_id: Uuid,
+) -> Result<Vec<AuditEntry>, sqlx::Error>
+where
+    E: sqlx::PgExecutor<'e>,
+{
+    let rows = sqlx::query(
+        "SELECT seq, at, actor_kind, actor_id, action, entity_type, entity_id, changes \
+         FROM audit_log \
+         WHERE entity_type = $1 AND entity_id = $2 \
+         ORDER BY seq",
+    )
+    .bind(entity_type)
+    .bind(entity_id)
+    .fetch_all(executor)
+    .await?;
+
+    rows.into_iter().map(map_row).collect()
+}
+
+fn map_row(row: sqlx::postgres::PgRow) -> Result<AuditEntry, sqlx::Error> {
+    let seq: i64 = row.try_get("seq")?;
+    let at: time::OffsetDateTime = row.try_get("at")?;
+    let actor_kind: String = row.try_get("actor_kind")?;
+    let actor_id: Option<Uuid> = row.try_get("actor_id")?;
+    let action: String = row.try_get("action")?;
+    let entity_type: String = row.try_get("entity_type")?;
+    let entity_id: Uuid = row.try_get("entity_id")?;
+    let changes: sqlx::types::Json<Vec<FieldChange>> = row.try_get("changes")?;
+
+    let actor = match actor_kind.as_str() {
+        "user" => AuditActor::User(
+            actor_id.ok_or_else(|| sqlx::Error::Decode("user actor missing actor_id".into()))?,
+        ),
+        "system" => AuditActor::System,
+        other => {
+            return Err(sqlx::Error::Decode(
+                format!("unknown actor_kind: {other}").into(),
+            ));
+        }
+    };
+
+    let action = domain::AuditAction::from_db(&action)
+        .ok_or_else(|| sqlx::Error::Decode(format!("unknown action: {action}").into()))?;
+
+    Ok(AuditEntry {
+        seq,
+        at,
+        actor,
+        action,
+        entity_type,
+        entity_id,
+        changes: changes.0,
+    })
+}