SQLite engine: queues — Queue/JobHandle over the writer slot, engine-side backoff curve, extent guard (task sqlite-engine-queues)

queue.rs: SqliteQueueHandle (QueueOpts-carrying, stamp-resolving
enqueue over the seam's shared resolution arithmetic), claim_one/
claim_batch through the writer slot with ADR-023 §2's extent guard
(n <= 0 -> empty Vec at the trait-impl entry), the full JobHandle impl
(one-shot ack/retry/fail as 'static boxed futures, repeatable absolute
reset heartbeat, substrate's uniform validity predicate), and the
engine-owned equal-jitter exponential backoff (std-only RandomState
hash jitter, integerized inclusive [ceil(half), cap], 1-hour cap;
no rand dep - documented).

ack_batch loses its substrate worker filter (register D-31 - ADR-019
§1's worker-less batch form); job_from_json decode + stamps_with_
override moved to their one owners (queue.rs / resolution.rs);
reader-pool helpers lifted from stream.rs into seam.rs. Store::queue
wired; 10 acceptance tests (lifecycle/stamps, extent guard,
exactly-once under concurrency, backoff range + cap + override,
validity predicate + reclaim, dead-letter defaults + get_job
visibility, cancel, ack_batch, sweep both-states + retention,
validation + closed-store). Workspace 25+3+171 green, clippy
-D warnings, fmt clean; sqlite suite 4x green.

alkstore-sqlite/src/store.rs

@@ -166,13 +166,23 @@ impl Store for SqliteStore {
 
     fn queue<'a>(
         &'a self,
-        _name: &str,
-        _opts: alkstore::QueueOpts,
+        name: &str,
+        opts: alkstore::QueueOpts,
     ) -> alkstore::BoxedFuture<'a, alkstore::Result<Box<dyn alkstore::Queue>>> {
-        Box::pin(async {
-            Err(database_error(
-                "queue wiring lands with the mechanism tasks",
-            ))
+        if let Err(e) = alkstore::validate_shared_name(name) {
+            return Box::pin(async move { Err(e) });
+        }
+        if self.closed.load(std::sync::atomic::Ordering::Acquire) {
+            return Box::pin(async { Err(crate::seam::database_error("the store is closed")) });
+        }
+        let name = name.to_string();
+        let writer = self.writer.clone();
+        let readers = self.readers.clone();
+        let closed = self.closed.clone();
+        Box::pin(async move {
+            Ok(Box::new(crate::queue::SqliteQueueHandle::new(
+                name, opts, writer, readers, closed,
+            )) as Box<dyn alkstore::Queue>)
         })
     }
 
@@ -236,6 +246,8 @@ mod notify_tests;
 #[cfg(test)]
 mod open_tests;
 #[cfg(test)]
+mod queue_tests;
+#[cfg(test)]
 mod stream_tests;
 #[cfg(test)]
 mod tx_tests;