vector: Lease::forget hands the tag name off without releasing (#12174)

* vector: Lease::forget hands the tag name off without releasing

A distributed planner pins the planned version and forwards the tag
name to the executor — the guard must not release on drop.

* vector: forget untracks the lease so an abandoned handoff expires

The tag left LIVE_TAGS but the drop-time release was disabled — an
abandoned handoff survived forever locally. Untrack it so the lease
TTL still reaps it.

seaweed-vector/crates/core/src/maintenance.rs

@@ -45,6 +45,16 @@ impl Lease {
         untrack(&tag);
         release(&self.dataset, &tag).await
     }
+
+    /// Hand the tag name off and skip the drop-time release — a distributed
+    /// planner keeps the version pinned until an executor takes over. The
+    /// tag leaves LIVE_TAGS so an abandoned handoff still expires at the
+    /// lease TTL instead of surviving forever locally.
+    pub fn forget(mut self) -> String {
+        let tag = std::mem::take(&mut self.tag);
+        untrack(&tag);
+        tag
+    }
 }
 
 impl Drop for Lease {