feat(db): expose channel community lookup

Co-authored-by: npub1jh9wn95s0472h86ahapupaf7m6kx4v9sx2n0atj2hltcfer8k06s5n3pyf <95cae996907d7cab9f5dbf43c0f53edeac6ab0b032a6feae4abfd784e467b3f5@sprout-oss.stage.blox.sqprod.co>
Signed-off-by: npub1jh9wn95s0472h86ahapupaf7m6kx4v9sx2n0atj2hltcfer8k06s5n3pyf <95cae996907d7cab9f5dbf43c0f53edeac6ab0b032a6feae4abfd784e467b3f5@sprout-oss.stage.blox.sqprod.co>

crates/buzz-db/src/lib.rs

@@ -286,6 +286,30 @@ impl Db {
         })
     }
 
+    /// Returns the community that owns a channel, if the channel exists.
+    ///
+    /// Internal relay producers use this to derive tenant context from the row
+    /// they are acting on, rather than falling back to an implicit default.
+    pub async fn community_of_channel(&self, channel_id: Uuid) -> Result<Option<CommunityId>> {
+        let row = sqlx::query(
+            r#"
+            SELECT community_id
+            FROM channels
+            WHERE id = $1
+              AND deleted_at IS NULL
+            "#,
+        )
+        .bind(channel_id)
+        .fetch_optional(&self.pool)
+        .await?;
+
+        row.map(|row| {
+            let id: Uuid = row.try_get("community_id")?;
+            Ok(CommunityId::from_uuid(id))
+        })
+        .transpose()
+    }
+
     /// Inserts an event. Returns `(StoredEvent, was_inserted)` — `false` on duplicate.
     pub async fn insert_event(
         &self,

migrations/0001_initial_schema.sql

@@ -32,6 +32,7 @@ CREATE TABLE communities (
 
 CREATE TABLE channels (
     id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    community_id    UUID NOT NULL REFERENCES communities(id),
     name            VARCHAR(255) NOT NULL,
     channel_type    channel_type NOT NULL DEFAULT 'stream',
     visibility      channel_visibility NOT NULL DEFAULT 'open',

schema/schema.sql

@@ -33,6 +33,7 @@ CREATE TABLE communities (
 
 CREATE TABLE channels (
     id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    community_id    UUID NOT NULL REFERENCES communities(id),
     name            VARCHAR(255) NOT NULL,
     channel_type    channel_type NOT NULL DEFAULT 'stream',
     visibility      channel_visibility NOT NULL DEFAULT 'open',