From 4b841745fd45b7f1859b2465734f621fa62eb0c7 Mon Sep 17 00:00:00 2001
From: npub1qyvc0c5kl4gqv2fd97fsk46tu378sqgy35vc83rvgfwne90sel7s0ed67d
 <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>
Date: Sat, 1 Aug 2026 09:14:40 -0400
Subject: [PATCH] perf(relay): serve relay-membership checks from the read
 replica
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Route Db::is_relay_member through route_read on the bounded arm, the
same proved-reader-session contract as every other routed read: a
replica answer is served only when the session's heartbeat observation
proves an entry within the configured budget
(BUZZ_REPLICA_READ_MAX_AGE_MS, deploy target 1s); anything else —
budget unset, fence closed/stale, proof behind, replica error — fails
closed to the writer.

This replaces the 10s relay-membership cache proposed in #3844: the
bounded-staleness contract is already guaranteed fleet-wide by the
replica fence, is an order of magnitude tighter than a 10s TTL, and
needs no invalidation machinery.

The check runs on every authenticated HTTP request and WS AUTH, so
this moves the relay's hottest auth query off the writer pool wherever
a replica is configured. It is deliberately the one permission read
that routes — not precedent for others.

Co-authored-by: Tyler <109685178+tlongwell-block@users.noreply.github.com>
Signed-off-by: Tyler <109685178+tlongwell-block@users.noreply.github.com>
---
 crates/buzz-db/src/lib.rs           | 99 ++++++++++++++++++++++++++++-
 crates/buzz-db/src/relay_members.rs | 14 +++-
 2 files changed, 111 insertions(+), 2 deletions(-)

diff --git a/crates/buzz-db/src/lib.rs b/crates/buzz-db/src/lib.rs
index 245e49bb2d..b6b0882af4 100644
--- a/crates/buzz-db/src/lib.rs
+++ b/crates/buzz-db/src/lib.rs
@@ -3999,8 +3999,33 @@ impl Db {
     }
 
     /// Returns `true` if `pubkey` (64-char hex) is a member of `community`.
+    ///
+    /// Replica-routed on the bounded arm — the one PERMISSION read routed by
+    /// explicit product decision (bounded-stale membership beats the 10s
+    /// cache it replaced). Admits and revokes may lag by at most the budget
+    /// `B`; everything else fails closed to the writer, exactly like
+    /// [`Db::query_events_routed_bounded`]. Not precedent for routing other
+    /// permission reads.
     pub async fn is_relay_member(&self, community: CommunityId, pubkey: &str) -> Result<bool> {
-        relay_members::is_relay_member(&self.pool, community, pubkey).await
+        let path = "relay_membership";
+        match self.route_read(path, RoutePredicate::Bounded).await {
+            RouteDecision::Replica(mut tx, _entry, reason) => {
+                match relay_members::is_relay_member_on(&mut tx, community, pubkey).await {
+                    Ok(is_member) => {
+                        Self::record_route(path, "replica", reason);
+                        Ok(is_member)
+                    }
+                    Err(e) => {
+                        tracing::warn!(path, "replica read failed; re-running on writer: {e}");
+                        Self::record_route(path, "writer", "replica_error");
+                        relay_members::is_relay_member(&self.pool, community, pubkey).await
+                    }
+                }
+            }
+            RouteDecision::Writer => {
+                relay_members::is_relay_member(&self.pool, community, pubkey).await
+            }
+        }
     }
 
     /// Returns the relay member record for `pubkey` in `community`, or `None` if not found.
@@ -7408,6 +7433,78 @@ mod tests {
         drop_scratch_db(&admin, writer, &wname).await;
     }
 
+    /// Routed relay-membership check: budget unset ⇒ writer; budget set +
+    /// fresh proved entry ⇒ replica (bounded arm); over-budget entry ⇒
+    /// writer. Divergent membership rows prove which pool answered.
+    #[tokio::test]
+    #[ignore = "requires Postgres"]
+    async fn is_relay_member_is_bounded_routed_and_fails_closed() {
+        let admin = PgPool::connect(&admin_url().await)
+            .await
+            .expect("connect admin");
+        let (writer, wname) = create_scratch_db(&admin, "mem_w").await;
+        let (replica, rname) = create_scratch_db(&admin, "mem_r").await;
+
+        let community = Uuid::new_v4();
+        for pool in [&writer, &replica] {
+            sqlx::query("INSERT INTO communities (id, host) VALUES ($1, $2)")
+                .bind(community)
+                .bind(format!("member-routing-{}.example", community.simple()))
+                .execute(pool)
+                .await
+                .expect("insert community");
+        }
+        let cid = CommunityId::from_uuid(community);
+        let writer_only = "aa".repeat(32);
+        let replica_only = "bb".repeat(32);
+        relay_members::add_relay_member(&writer, cid, &writer_only, "member", None)
+            .await
+            .expect("seed writer member");
+        relay_members::add_relay_member(&replica, cid, &replica_only, "member", None)
+            .await
+            .expect("seed replica member");
+
+        let mut db = Db::from_pools(writer.clone(), replica.clone());
+        db.fence().force_open_for_tests(chrono::Utc::now());
+
+        // Budget unset ⇒ bounded arm disabled ⇒ writer.
+        assert!(
+            db.is_relay_member(cid, &writer_only)
+                .await
+                .expect("gate off"),
+            "budget unset must answer from the writer"
+        );
+        assert!(!db.is_relay_member(cid, &replica_only).await.unwrap());
+
+        // Budget set + fresh entry ⇒ replica.
+        db.set_replica_read_max_age_for_tests(Some(std::time::Duration::from_secs(5)));
+        assert!(
+            db.is_relay_member(cid, &replica_only)
+                .await
+                .expect("gate on"),
+            "budget set must answer from the replica"
+        );
+        assert!(!db.is_relay_member(cid, &writer_only).await.unwrap());
+
+        // Entry older than the budget ⇒ fail closed to the writer. Close
+        // first so no prior fresh entry can be the one proved (matches the
+        // count test; today `force_open_for_tests_at` also clears the ring).
+        db.fence().close();
+        db.fence().force_open_for_tests_at(
+            chrono::Utc::now(),
+            std::time::Instant::now() - std::time::Duration::from_secs(10),
+        );
+        assert!(
+            db.is_relay_member(cid, &writer_only)
+                .await
+                .expect("entry too old"),
+            "an over-budget entry must fail closed to the writer"
+        );
+
+        drop_scratch_db(&admin, replica, &rname).await;
+        drop_scratch_db(&admin, writer, &wname).await;
+    }
+
     /// Community separation across every routed seam, verified on
     /// REPLICA-SERVED reads.
     ///
diff --git a/crates/buzz-db/src/relay_members.rs b/crates/buzz-db/src/relay_members.rs
index bfc56f82de..3ce7efaef7 100644
--- a/crates/buzz-db/src/relay_members.rs
+++ b/crates/buzz-db/src/relay_members.rs
@@ -29,10 +29,22 @@ pub struct RelayMember {
 
 /// Returns `true` if `pubkey` (64-char hex) is a member of `community`.
 pub async fn is_relay_member(pool: &PgPool, community: CommunityId, pubkey: &str) -> Result<bool> {
+    let mut conn = pool.acquire().await?;
+    is_relay_member_on(&mut conn, community, pubkey).await
+}
+
+/// [`is_relay_member`] on a specific session — the replica-routing path runs
+/// the lookup on the exact reader connection whose heartbeat observation
+/// proved fence coverage.
+pub(crate) async fn is_relay_member_on(
+    conn: &mut sqlx::PgConnection,
+    community: CommunityId,
+    pubkey: &str,
+) -> Result<bool> {
     let row = sqlx::query("SELECT 1 FROM relay_members WHERE community_id = $1 AND pubkey = $2")
         .bind(community.as_uuid())
         .bind(pubkey)
-        .fetch_optional(pool)
+        .fetch_optional(conn)
         .await?;
     Ok(row.is_some())
 }