compute: carry the rebase of the layers below into the stash transition

The abort-handle test follows `promote`'s signature here, where a walk
takes its stash target rather than the trace bundle. The guard the
offloaded driver mirrored from the inline one goes with the diversion it
guarded: this layer keeps one scan across the stash boundary, so there is
no second ok-trace-only walk to divert into and no way to reach the stash
with the error trace half-read.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: antiguru

src/compute/src/compute_state/peek_offload.rs

@@ -32,7 +32,6 @@ use mz_compute_types::dyncfgs::{
 use mz_dyncfg::{ConfigSet, ConfigValHandle};
 use mz_expr::ColumnOrder;
 use mz_ore::cast::CastFrom;
-use mz_ore::soft_panic_or_log;
 use mz_ore::task::AbortOnDropHandle;
 use timely::scheduling::SyncActivator;
 use tokio::sync::{OwnedSemaphorePermit, Semaphore, oneshot};

src/compute/src/compute_state/peek_offload/tests.rs

@@ -686,8 +686,8 @@ async fn dropping_a_promoted_peek_aborts_its_walk() {
 
     let mut promoted = OffloadedPeek::promote(
         peek.clone(),
-        bundle,
         scan,
+        None,
         &permits,
         offload_config(1),
         PeekWalkMetrics::new(&metrics),

src/compute/src/compute_state/peek_scan.rs

@@ -308,11 +308,6 @@ where
         Some(self.take_results())
     }
 
-    /// The collection this scan reads.
-    pub(super) fn target_id(&self) -> GlobalId {
-        self.target_id
-    }
-
     /// The number of cursor positions the ok walk has evaluated.
     pub(super) fn rows_processed(&self) -> usize {
         self.oks.rows_processed()