fix: release storage locks on testnet76 migration

Refs #4430.

crates/bin/pd/src/migrate/testnet76.rs

@@ -1,6 +1,6 @@
 //! Contains functions related to the migration script of Testnet74
 
-use anyhow;
+use anyhow::Context;
 use cnidarium::{Snapshot, StateDelta, Storage};
 use futures::TryStreamExt;
 use jmt::RootHash;
@@ -63,11 +63,13 @@ async fn heal_auction_vcb(delta: &mut StateDelta<Snapshot>) -> anyhow::Result<()
     Ok(())
 }
 
+#[instrument(skip_all)]
 async fn write_shielded_pool_params(delta: &mut StateDelta<Snapshot>) -> anyhow::Result<()> {
     delta.put_shielded_pool_params(ShieldedPoolParameters::default());
     Ok(())
 }
 
+#[instrument(skip_all)]
 async fn write_fmd_params(delta: &mut StateDelta<Snapshot>) -> anyhow::Result<()> {
     delta.put_previous_fmd_parameters(FmdParameters::default());
     delta.put_current_fmd_parameters(FmdParameters::default());
@@ -94,6 +96,7 @@ pub async fn migrate(
         .expect("can get block height");
     let post_upgrade_height = pre_upgrade_height.wrapping_add(1);
 
+    tracing::debug!("initializing StateDelta");
     // We initialize a `StateDelta` and start by reaching into the JMT for all entries matching the
     // swap execution prefix. Then, we write each entry to the nv-storage.
     let mut delta = StateDelta::new(export_state);
@@ -110,7 +113,6 @@ pub async fn migrate(
         delta.put_block_height(0u64);
         let post_upgrade_root_hash = storage.commit_in_place(delta).await?;
         tracing::info!(?post_upgrade_root_hash, "post-upgrade root hash");
-
         (
             start_time.elapsed().expect("start time not set"),
             post_upgrade_root_hash,
@@ -119,13 +121,16 @@ pub async fn migrate(
 
     storage.release().await;
     let rocksdb_dir = pd_home.join("rocksdb");
-    let storage = Storage::load(rocksdb_dir, SUBSTORE_PREFIXES.to_vec()).await?;
+    // FAILS HERE. Why?
+    let storage = Storage::load(rocksdb_dir, SUBSTORE_PREFIXES.to_vec()).await
+        .context("failed to reload state after writing")?;
     let migrated_state = storage.latest_snapshot();
     storage.release().await;
 
     // The migration is complete, now we need to generate a genesis file. To do this, we need
     // to lookup a validator view from the chain, and specify the post-upgrade app hash and
     // initial height.
+    tracing::debug!("looking up chain id on new copy of state");
     let chain_id = migrated_state.get_chain_id().await?;
     let app_state = penumbra_app::genesis::Content {
         chain_id,