SQL pools time out; task locks are a renewed five-minute lease

A 3-node rehearsal (PostgreSQL + NATS + Garage) found two ways a crash
leaves work stuck:

Pool hangs. The PostgreSQL pool (deadpool) was built with no timeouts,
so a request waited for a free connection, and for one to be opened or
recycled, for as long as it took: forever when the server stopped
answering. MySQL's pool (mysql_async) has no wait timeout at all.

- PostgreSQL: wait 30 s (or the store's timeout if longer), create the
  store's timeout or 15 s (it bounds the whole handshake, where
  tokio-postgres's connect_timeout covers only the TCP connect), recycle
  10 s. The pool config is now always set, not only with
  poolMaxConnections.
- MySQL: every connection is taken through MysqlStore::conn(), which
  gives up after 30 s.
- Both: TCP keepalive after 60 s idle, so a server that vanished
  without closing the connection is noticed in minutes rather than the
  two-hour system default.

The DataStore schema has no pool timeout settings, so these are fixed
defaults; the store's own timeout bounds connecting on PostgreSQL.

Task locks. A task lock lasted an hour, so after a hard crash the dead
node's tasks waited up to an hour and five minutes. The lock is now a
five-minute lease: while this node runs a task, the task manager renews
its lock every third of the lifetime (InMemoryStore::renew_lock, a
compare-and-set on the store backends and SET XX EX on Redis, which
leaves a lock that already expired alone). A killed node's tasks run
elsewhere within about five minutes plus the claim recheck. A task this
node holds isn't handed to a worker again by the scan.

store::pool_timeout (new): a local listener that accepts connections
and never answers plays a hung server; a PostgreSQL store with a 2 s
timeout returns an error in about 4 s, and a MySQL store in 30 s.
Without the timeouts both wait for good. store::task_locks gains a
task held for 1.5 lock lifetimes: its lease is still held, and released
when the task ends.

crates/store/src/dispatch/lookup.rs

@@ -401,6 +401,57 @@ impl InMemoryStore {
         }
     }
 
+    /// inbuxa: extends a lock this node holds to `duration` seconds from now.
+    /// Returns false when the lock is gone or has expired: it may have been
+    /// taken by someone else since, so it is left alone.
+    pub async fn renew_lock(&self, prefix: u8, key: &[u8], duration: u64) -> trc::Result<bool> {
+        match self {
+            InMemoryStore::Store(store) => {
+                let key = KeyValue::<()>::build_key(prefix, key);
+                let key = ValueClass::InMemory(InMemoryClass::Key(key));
+                let Some(lock_expiry) = store
+                    .get_value::<u64>(ValueKey::from(key.clone()))
+                    .await
+                    .caused_by(trc::location!())?
+                else {
+                    return Ok(false);
+                };
+                let now = now();
+                if lock_expiry <= now {
+                    return Ok(false);
+                }
+
+                let mut batch = BatchBuilder::new();
+                batch.assert_value(key.clone(), AssertValue::U64(lock_expiry));
+                batch.set(key, (now + duration).serialize());
+                match store.write(batch.build_all()).await {
+                    Ok(_) => Ok(true),
+                    Err(err) if err.is_assertion_failure() => Ok(false),
+                    Err(err) => Err(err
+                        .details("Failed to renew lock.")
+                        .caused_by(trc::location!())),
+                }
+            }
+            InMemoryStore::Sharded(store) => {
+                Box::pin(
+                    store
+                        .member(&KeyValue::<()>::build_key(prefix, key))
+                        .renew_lock(prefix, key, duration),
+                )
+                .await
+            }
+            #[cfg(feature = "redis")]
+            InMemoryStore::Redis(store) => {
+                store
+                    .renew_lock(&KeyValue::<()>::build_key(prefix, key), duration)
+                    .await
+            }
+            InMemoryStore::Static(_) | InMemoryStore::Http(_) => {
+                Err(trc::StoreEvent::NotSupported.into_err())
+            }
+        }
+    }
+
     pub async fn remove_lock(&self, prefix: u8, key: &[u8]) -> trc::Result<()> {
         self.key_delete(KeyValue::<()>::build_key(prefix, key))
             .await