feat(db): add community host lookup seam

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

@@ -47,7 +47,7 @@ use sqlx::{PgPool, QueryBuilder, Row};
 use std::time::Duration;
 use uuid::Uuid;
 
-use buzz_core::StoredEvent;
+use buzz_core::{CommunityId, StoredEvent};
 
 /// Extract p-tag mentions from an event and insert into the `event_mentions` table.
 ///
@@ -162,6 +162,15 @@ impl Default for DbConfig {
     }
 }
 
+/// Community host-map row returned by [`Db::lookup_community_by_host`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CommunityRecord {
+    /// Stable server-resolved community id.
+    pub id: CommunityId,
+    /// Normalized host that maps to this community.
+    pub host: String,
+}
+
 /// Token summary returned by [`Db::list_active_tokens`].
 #[derive(Debug, Clone)]
 pub struct TokenSummary {
@@ -216,6 +225,67 @@ impl Db {
         self.pool.begin().await.map_err(Into::into)
     }
 
+    /// Returns the community mapped to a normalized request host, if one exists.
+    ///
+    /// The caller owns host normalization and turns `None` into the fail-closed
+    /// request/connection error. buzz-db only reads the durable host map.
+    pub async fn lookup_community_by_host(
+        &self,
+        normalized_host: &str,
+    ) -> Result<Option<CommunityRecord>> {
+        let row = sqlx::query(
+            r#"
+            SELECT id, host
+            FROM communities
+            WHERE host = $1
+            "#,
+        )
+        .bind(normalized_host)
+        .fetch_optional(&self.pool)
+        .await?;
+
+        row.map(|row| {
+            let id: Uuid = row.try_get("id")?;
+            let host: String = row.try_get("host")?;
+
+            Ok(CommunityRecord {
+                id: CommunityId::from_uuid(id),
+                host,
+            })
+        })
+        .transpose()
+    }
+
+    /// Ensure a configured community host exists and return its row.
+    ///
+    /// This is the startup/config seeding path for N=1 deployments. Migrations
+    /// create the schema only; deployment-specific hosts are not hardcoded into
+    /// schema history.
+    pub async fn ensure_configured_community(
+        &self,
+        normalized_host: &str,
+    ) -> Result<CommunityRecord> {
+        let row = sqlx::query(
+            r#"
+            INSERT INTO communities (host)
+            VALUES ($1)
+            ON CONFLICT (host) DO UPDATE SET host = EXCLUDED.host
+            RETURNING id, host
+            "#,
+        )
+        .bind(normalized_host)
+        .fetch_one(&self.pool)
+        .await?;
+
+        let id: Uuid = row.try_get("id")?;
+        let host: String = row.try_get("host")?;
+
+        Ok(CommunityRecord {
+            id: CommunityId::from_uuid(id),
+            host,
+        })
+    }
+
     /// Inserts an event. Returns `(StoredEvent, was_inserted)` — `false` on duplicate.
     pub async fn insert_event(
         &self,

crates/buzz-db/src/migration.rs

@@ -131,6 +131,13 @@ mod tests {
         assert_eq!(migrations.len(), 3);
         assert_eq!(migrations[0].version, 1);
         assert_eq!(&*migrations[0].description, "initial schema");
+        assert!(
+            migrations[0]
+                .sql
+                .as_str()
+                .contains("CREATE TABLE communities"),
+            "initial schema migration should include tenant host map"
+        );
         assert!(
             migrations[0].sql.as_str().contains("CREATE TABLE channels"),
             "initial schema migration should include Buzz core tables"

migrations/0001_initial_schema.sql

@@ -17,6 +17,17 @@ CREATE TYPE subscription_status AS ENUM ('active', 'paused', 'deleted');
 CREATE TYPE pause_reason AS ENUM ('user', 'system', 'rate_limit');
 CREATE TYPE channel_add_policy AS ENUM ('anyone', 'owner_only', 'nobody');
 
+-- ── Communities ───────────────────────────────────────────────────────────────
+
+CREATE TABLE communities (
+    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    host            VARCHAR(255) NOT NULL UNIQUE,
+    signing_key     BYTEA,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    CONSTRAINT chk_communities_host_not_empty CHECK (LENGTH(TRIM(host)) > 0),
+    CONSTRAINT chk_communities_host_normalized CHECK (host = LOWER(host))
+);
+
 -- ── Channels ──────────────────────────────────────────────────────────────────
 
 CREATE TABLE channels (

schema/schema.sql

@@ -18,6 +18,17 @@ CREATE TYPE subscription_status AS ENUM ('active', 'paused', 'deleted');
 CREATE TYPE pause_reason AS ENUM ('user', 'system', 'rate_limit');
 CREATE TYPE channel_add_policy AS ENUM ('anyone', 'owner_only', 'nobody');
 
+-- ── Communities ───────────────────────────────────────────────────────────────
+
+CREATE TABLE communities (
+    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    host            VARCHAR(255) NOT NULL UNIQUE,
+    signing_key     BYTEA,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    CONSTRAINT chk_communities_host_not_empty CHECK (LENGTH(TRIM(host)) > 0),
+    CONSTRAINT chk_communities_host_normalized CHECK (host = LOWER(host))
+);
+
 -- ── Channels ──────────────────────────────────────────────────────────────────
 
 CREATE TABLE channels (