diff --git a/.config/nextest.toml b/.config/nextest.toml
index beb0ea8..cfcfcee 100644
--- a/.config/nextest.toml
+++ b/.config/nextest.toml
@@ -72,6 +72,10 @@ test-group = "io-heavy-sim"
 filter = "test(/test_scale_/) | test(/full_backup_and_restore/)"
 slow-timeout = { period = "120s", terminate-after = 4 }
 
+[[profile.default.overrides]]
+filter = "binary(compaction_restart) | binary(mst_refcount_integrity) | binary(gc_compaction_restart)"
+slow-timeout = { period = "120s", terminate-after = 4 }
+
 [[profile.ci.overrides]]
 filter = "test(/import_with_verification/) | test(/plc_migration/)"
 test-group = "serial-env-tests"
diff --git a/Cargo.lock b/Cargo.lock
index 2e9d586..19d4db1 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -7405,7 +7405,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-api"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "anyhow",
  "axum",
@@ -7456,7 +7456,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-auth"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "anyhow",
  "base32",
@@ -7479,7 +7479,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-cache"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "base64 0.22.1",
@@ -7493,7 +7493,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-comms"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "base64 0.22.1",
@@ -7511,7 +7511,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-config"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "confique",
  "serde",
@@ -7519,7 +7519,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-crypto"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "aes-gcm",
  "base64 0.22.1",
@@ -7535,7 +7535,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-db"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "chrono",
@@ -7552,7 +7552,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-db-traits"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "base64 0.22.1",
@@ -7568,7 +7568,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-infra"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "bytes",
@@ -7579,7 +7579,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-lexicon"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "chrono",
  "hickory-resolver",
@@ -7597,7 +7597,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-oauth"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "anyhow",
  "axum",
@@ -7620,7 +7620,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-oauth-server"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "axum",
  "base64 0.22.1",
@@ -7653,7 +7653,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-pds"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "aes-gcm",
  "anyhow",
@@ -7745,7 +7745,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-repo"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "bytes",
  "cid",
@@ -7757,7 +7757,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-ripple"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "backon",
@@ -7782,7 +7782,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-scopes"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "axum",
  "futures",
@@ -7798,7 +7798,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-server"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "axum",
  "clap",
@@ -7819,7 +7819,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-signal"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "chrono",
@@ -7842,7 +7842,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-storage"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "aws-config",
@@ -7859,7 +7859,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-store"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "async-trait",
  "bytes",
@@ -7906,7 +7906,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-sync"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "anyhow",
  "axum",
@@ -7928,7 +7928,7 @@ dependencies = [
 
 [[package]]
 name = "tranquil-types"
-version = "0.5.3"
+version = "0.5.4"
 dependencies = [
  "chrono",
  "cid",
diff --git a/Cargo.toml b/Cargo.toml
index a8995d0..4b00bee 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -26,7 +26,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.5.3"
+version = "0.5.4"
 edition = "2024"
 license = "AGPL-3.0-or-later"
 
diff --git a/crates/tranquil-pds/tests/gc_compaction_restart.rs b/crates/tranquil-pds/tests/gc_compaction_restart.rs
new file mode 100644
index 0000000..aedef91
--- /dev/null
+++ b/crates/tranquil-pds/tests/gc_compaction_restart.rs
@@ -0,0 +1,175 @@
+mod common;
+
+use chrono::Utc;
+use common::*;
+use reqwest::StatusCode;
+use serde_json::{Value, json};
+
+fn run_compaction(store: &tranquil_store::blockstore::TranquilBlockStore) {
+    let liveness = store.compaction_liveness(0).unwrap();
+    liveness
+        .iter()
+        .filter(|(_, info)| info.total_blocks > 0 && info.ratio() < 0.95)
+        .map(|(&fid, _)| fid)
+        .collect::<Vec<_>>()
+        .into_iter()
+        .for_each(|fid| {
+            match store.compact_file(fid, 0) {
+                Ok(_) => {}
+                Err(tranquil_store::blockstore::CompactionError::ActiveFileCannotBeCompacted) => {}
+                Err(e) => eprintln!("compaction: {e}"),
+            }
+        });
+}
+
+#[tokio::test]
+async fn mst_blocks_survive_full_store_reopen() {
+    if !is_store_backend() {
+        eprintln!("skipping: only meaningful with tranquil-store backend");
+        return;
+    }
+
+    let client = client();
+    let base = base_url().await;
+    let block_store = get_test_block_store().await;
+
+    let store = block_store
+        .as_tranquil_store()
+        .expect("expected tranquil-store backend");
+
+    let (jwt, did) = create_account_and_login(&client).await;
+
+    let mut posts = Vec::new();
+    for i in 0..30 {
+        let res = client
+            .post(format!("{base}/xrpc/com.atproto.repo.createRecord"))
+            .bearer_auth(&jwt)
+            .json(&json!({
+                "repo": did,
+                "collection": "app.bsky.feed.post",
+                "record": {
+                    "$type": "app.bsky.feed.post",
+                    "text": format!("compaction test post {i}"),
+                    "createdAt": Utc::now().to_rfc3339()
+                }
+            }))
+            .send()
+            .await
+            .unwrap();
+        assert_eq!(res.status(), StatusCode::OK);
+        let body: Value = res.json().await.unwrap();
+        posts.push((
+            body["uri"].as_str().unwrap().to_string(),
+            body["cid"].as_str().unwrap().to_string(),
+        ));
+    }
+
+    for (uri, cid) in &posts[..20] {
+        let res = client
+            .post(format!("{base}/xrpc/com.atproto.repo.createRecord"))
+            .bearer_auth(&jwt)
+            .json(&json!({
+                "repo": did,
+                "collection": "app.bsky.feed.like",
+                "record": {
+                    "$type": "app.bsky.feed.like",
+                    "subject": { "uri": uri, "cid": cid },
+                    "createdAt": Utc::now().to_rfc3339()
+                }
+            }))
+            .send()
+            .await
+            .unwrap();
+        assert_eq!(res.status(), StatusCode::OK, "like failed for {uri}");
+    }
+
+    let data_dir = store.data_dir().to_path_buf();
+    let index_dir = data_dir
+        .parent()
+        .unwrap()
+        .join("index");
+
+    let store_clone = store.clone();
+    tokio::task::spawn_blocking(move || {
+        (0..40).for_each(|_| run_compaction(&store_clone));
+    })
+    .await
+    .unwrap();
+
+    let repo_root_str: String = get_test_repos()
+        .await
+        .repo
+        .get_repo_root_by_did(&tranquil_types::Did::new(did.clone()).unwrap())
+        .await
+        .expect("db error")
+        .expect("no repo root")
+        .to_string();
+
+    let head_cid = cid::Cid::try_from(repo_root_str.as_str()).expect("invalid cid");
+
+    let car_blocks =
+        tranquil_pds::scheduled::collect_current_repo_blocks(block_store, &head_cid)
+            .await
+            .expect("collect blocks");
+
+    let block_count_before = car_blocks.len();
+
+    let max_file_size = store
+        .list_data_files()
+        .ok()
+        .and_then(|_| Some(4 * 1024 * 1024u64))
+        .unwrap_or(4 * 1024 * 1024);
+
+    let reopened_missing = tokio::task::spawn_blocking(move || {
+        let rt = tokio::runtime::Handle::current();
+        let _guard = rt.enter();
+
+        let config = tranquil_store::blockstore::BlockStoreConfig {
+            data_dir: data_dir.clone(),
+            index_dir,
+            max_file_size,
+            group_commit: tranquil_store::blockstore::GroupCommitConfig::default(),
+            shard_count: 1,
+        };
+        let fresh = tranquil_store::blockstore::TranquilBlockStore::open(config)
+            .expect("reopen failed");
+
+        let missing: Vec<String> = car_blocks
+            .iter()
+            .filter_map(|cid_bytes| {
+                if cid_bytes.len() < 36 {
+                    return None;
+                }
+                let mut arr = [0u8; 36];
+                arr.copy_from_slice(&cid_bytes[..36]);
+                match fresh.get_block_sync(&arr) {
+                    Ok(Some(_)) => None,
+                    Ok(None) => Some(format!(
+                        "missing {}",
+                        cid::Cid::try_from(cid_bytes.as_slice())
+                            .map(|c| c.to_string())
+                            .unwrap_or_else(|_| hex::encode(cid_bytes))
+                    )),
+                    Err(e) => Some(format!("error: {e}")),
+                }
+            })
+            .collect();
+
+        drop(fresh);
+        missing
+    })
+    .await
+    .unwrap();
+
+    assert!(
+        reopened_missing.is_empty(),
+        "{} of {block_count_before} blocks missing after blockstore reopen:\n{}",
+        reopened_missing.len(),
+        reopened_missing
+            .iter()
+            .take(20)
+            .map(|s| s.as_str())
+            .collect::<Vec<_>>()
+            .join("\n"),
+    );
+}
diff --git a/crates/tranquil-store/src/blockstore/hash_index.rs b/crates/tranquil-store/src/blockstore/hash_index.rs
index fece45d..e9668ec 100644
--- a/crates/tranquil-store/src/blockstore/hash_index.rs
+++ b/crates/tranquil-store/src/blockstore/hash_index.rs
@@ -215,6 +215,10 @@ impl HashTable {
         self.get(cid).is_some()
     }
 
+    pub fn contains_live(&self, cid: &[u8; CID_SIZE]) -> bool {
+        self.get(cid).is_some_and(|s| !s.refcount.is_zero())
+    }
+
     pub fn insert(&mut self, new_slot: Slot) -> Result<Option<Slot>, CapacityExhausted> {
         if is_empty(&new_slot.cid) {
             tracing::error!("attempted to insert all-zero CID into hash table");
@@ -1195,7 +1199,7 @@ impl BlockIndex {
     }
 
     pub fn has(&self, cid: &[u8; CID_SIZE]) -> bool {
-        self.table.read().contains(cid)
+        self.table.read().contains_live(cid)
     }
 
     pub fn batch_put(
diff --git a/crates/tranquil-store/tests/common/mod.rs b/crates/tranquil-store/tests/common/mod.rs
index e00af4e..92443b3 100644
--- a/crates/tranquil-store/tests/common/mod.rs
+++ b/crates/tranquil-store/tests/common/mod.rs
@@ -104,6 +104,70 @@ pub fn compact_all_sealed(store: &TranquilBlockStore) {
         });
 }
 
+pub fn tiny_blockstore_config(dir: &std::path::Path) -> BlockStoreConfig {
+    BlockStoreConfig {
+        data_dir: dir.join("data"),
+        index_dir: dir.join("index"),
+        max_file_size: 300,
+        group_commit: GroupCommitConfig {
+            checkpoint_interval_ms: 100,
+            checkpoint_write_threshold: 10,
+            ..GroupCommitConfig::default()
+        },
+        shard_count: 1,
+    }
+}
+
+pub fn compact_by_liveness(store: &TranquilBlockStore) {
+    let liveness = store.compaction_liveness(0).unwrap();
+    liveness
+        .iter()
+        .filter(|(_, info)| info.total_blocks > 0 && info.ratio() < 0.99)
+        .map(|(&fid, _)| fid)
+        .collect::<Vec<_>>()
+        .into_iter()
+        .for_each(|fid| match store.compact_file(fid, 0) {
+            Ok(_) => {}
+            Err(tranquil_store::blockstore::CompactionError::ActiveFileCannotBeCompacted) => {}
+            Err(e) => eprintln!("compaction: {e}"),
+        });
+}
+
+pub fn compact_lowest_liveness(store: &TranquilBlockStore) {
+    let liveness = store.compaction_liveness(0).unwrap();
+    let candidate = liveness
+        .iter()
+        .filter(|(_, info)| info.total_blocks > 0 && info.ratio() < 0.99)
+        .min_by(|(_, a), (_, b)| {
+            a.ratio()
+                .partial_cmp(&b.ratio())
+                .unwrap_or(std::cmp::Ordering::Equal)
+        })
+        .map(|(&fid, _)| fid);
+
+    if let Some(fid) = candidate {
+        match store.compact_file(fid, 0) {
+            Ok(_) => {}
+            Err(tranquil_store::blockstore::CompactionError::ActiveFileCannotBeCompacted) => {}
+            Err(e) => eprintln!("compaction: {e}"),
+        }
+    }
+}
+
+pub fn collect_refcounts(store: &TranquilBlockStore, cids: &[CidBytes]) -> Vec<(u32, u32)> {
+    cids.iter()
+        .map(|cid| {
+            let seed = u32::from_le_bytes([cid[4], cid[5], cid[6], cid[7]]);
+            let rc = store
+                .block_index()
+                .get(cid)
+                .map(|e| e.refcount.raw())
+                .unwrap_or(0);
+            (seed, rc)
+        })
+        .collect()
+}
+
 pub struct TestStores {
     pub blockstore: TranquilBlockStore,
     pub eventlog: Arc<EventLog<RealIO>>,
diff --git a/crates/tranquil-store/tests/compaction_restart.rs b/crates/tranquil-store/tests/compaction_restart.rs
new file mode 100644
index 0000000..08f38b5
--- /dev/null
+++ b/crates/tranquil-store/tests/compaction_restart.rs
@@ -0,0 +1,567 @@
+mod common;
+
+use std::path::Path;
+use std::sync::Arc;
+
+use common::{
+    collect_refcounts, compact_by_liveness, compact_lowest_liveness, test_cid,
+    tiny_blockstore_config, with_runtime,
+};
+use tranquil_store::RealIO;
+use tranquil_store::blockstore::{CidBytes, TranquilBlockStore};
+use tranquil_store::eventlog::{EventLog, EventLogBridge, EventLogConfig};
+use tranquil_store::metastore::handler::HandlerPool;
+use tranquil_store::metastore::partitions::Partition;
+use tranquil_store::metastore::{Metastore, MetastoreConfig};
+
+struct FullStack {
+    blockstore: TranquilBlockStore,
+    _pool: Arc<HandlerPool>,
+    _event_log: Arc<EventLog<RealIO>>,
+}
+
+fn open_full_stack(base_dir: &Path) -> FullStack {
+    let metastore_dir = base_dir.join("metastore");
+    let segments_dir = base_dir.join("eventlog").join("segments");
+    let blockstore_data = base_dir.join("blockstore").join("data");
+    let blockstore_index = base_dir.join("blockstore").join("index");
+
+    [&metastore_dir, &segments_dir, &blockstore_data, &blockstore_index]
+        .iter()
+        .for_each(|d| std::fs::create_dir_all(d).unwrap());
+
+    let metastore = Metastore::open(&metastore_dir, MetastoreConfig::default()).unwrap();
+
+    let blockstore = TranquilBlockStore::open(tranquil_store::blockstore::BlockStoreConfig {
+        data_dir: blockstore_data,
+        index_dir: blockstore_index,
+        max_file_size: 512,
+        group_commit: tranquil_store::blockstore::GroupCommitConfig::default(),
+        shard_count: 1,
+    })
+    .unwrap();
+
+    let event_log = Arc::new(
+        EventLog::open(
+            EventLogConfig {
+                segments_dir,
+                ..EventLogConfig::default()
+            },
+            RealIO::new(),
+        )
+        .unwrap(),
+    );
+
+    let bridge = Arc::new(EventLogBridge::new(Arc::clone(&event_log)));
+
+    let was_clean = tranquil_store::consistency::had_clean_shutdown(base_dir);
+    tranquil_store::consistency::remove_clean_shutdown_marker(base_dir).ok();
+
+    let indexes = metastore.partition(Partition::Indexes).clone();
+    let event_ops = metastore.event_ops(Arc::clone(&bridge));
+    let recovered = event_ops
+        .recover_metastore_mutations(&indexes)
+        .unwrap();
+    if recovered > 0 {
+        eprintln!("replayed {recovered} metastore mutations from eventlog");
+    }
+
+    if !was_clean || recovered > 0 {
+        let report = tranquil_store::consistency::verify_store_consistency(
+            &blockstore,
+            &metastore,
+            &event_log,
+        );
+        report.log_findings();
+        if report.has_repairable_issues() {
+            let repair = tranquil_store::consistency::repair_known_issues(&blockstore, &report);
+            if repair.orphan_files_removed > 0 {
+                eprintln!("removed {} orphan files", repair.orphan_files_removed);
+            }
+        }
+    }
+
+    let pool = Arc::new(HandlerPool::spawn::<RealIO>(
+        metastore,
+        bridge,
+        Some(blockstore.clone()),
+        None,
+    ));
+
+    FullStack {
+        blockstore,
+        _pool: pool,
+        _event_log: event_log,
+    }
+}
+
+fn close_full_stack(stack: FullStack, base_dir: &Path) {
+    let rt = tokio::runtime::Handle::current();
+    rt.block_on(stack._pool.close());
+    if let Err(e) = stack._event_log.shutdown() {
+        eprintln!("eventlog shutdown: {e}");
+    }
+    tranquil_store::consistency::write_clean_shutdown_marker(base_dir).ok();
+    drop(stack.blockstore);
+}
+
+fn verify_blocks_and_refcounts(
+    store: &TranquilBlockStore,
+    live_cids: &[CidBytes],
+    expected_refcounts: Option<&[(u32, u32)]>,
+    label: &str,
+) {
+    let missing: Vec<u32> = live_cids
+        .iter()
+        .filter(|cid| store.get_block_sync(cid).unwrap().is_none())
+        .map(|cid| u32::from_le_bytes([cid[4], cid[5], cid[6], cid[7]]))
+        .collect();
+
+    assert!(
+        missing.is_empty(),
+        "{label}: live blocks missing after reopen: {missing:?}"
+    );
+
+    match expected_refcounts {
+        Some(expected) => {
+            let actual = collect_refcounts(store, live_cids);
+            let mismatches: Vec<_> = expected
+                .iter()
+                .zip(actual.iter())
+                .filter(|((_, exp_rc), (_, act_rc))| exp_rc != act_rc)
+                .map(|((seed, exp), (_, act))| format!("seed {seed}: before={exp} after={act}"))
+                .collect();
+
+            assert!(
+                mismatches.is_empty(),
+                "{label}: refcounts changed across reopen:\n{}",
+                mismatches.join("\n"),
+            );
+        }
+        None => {
+            live_cids.iter().for_each(|cid| {
+                let rc = store
+                    .block_index()
+                    .get(cid)
+                    .map(|e| e.refcount.raw())
+                    .unwrap_or(0);
+                assert!(
+                    rc > 0,
+                    "{label}: refcount dropped to 0 for seed {}",
+                    u32::from_le_bytes([cid[4], cid[5], cid[6], cid[7]])
+                );
+            });
+        }
+    }
+}
+
+#[test]
+fn hundreds_of_compaction_cycles() {
+    with_runtime(|| {
+        let dir = tempfile::TempDir::new().unwrap();
+
+        let live_cids: Vec<CidBytes> = (0..15u32).map(test_cid).collect();
+
+        {
+            let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+
+            live_cids.iter().for_each(|cid| {
+                store
+                    .put_blocks_blocking(vec![(*cid, vec![0xAA; 80])])
+                    .unwrap();
+            });
+
+            (0..500u32).for_each(|round| {
+                let churn = test_cid(2000 + round);
+                store
+                    .put_blocks_blocking(vec![(churn, vec![0xDD; 80])])
+                    .unwrap();
+                store.apply_commit_blocking(vec![], vec![churn]).unwrap();
+
+                if round % 3 == 0 {
+                    compact_lowest_liveness(&store);
+                }
+            });
+
+            (0..200).for_each(|_| compact_by_liveness(&store));
+
+            live_cids.iter().for_each(|cid| {
+                assert!(
+                    store.get_block_sync(cid).unwrap().is_some(),
+                    "sanity: block present before drop"
+                );
+            });
+
+            drop(store);
+        }
+
+        let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+        verify_blocks_and_refcounts(&store, &live_cids, None, "500 churn + 200 compact rounds");
+    });
+}
+
+#[test]
+fn commit_style_decrements() {
+    with_runtime(|| {
+        let dir = tempfile::TempDir::new().unwrap();
+
+        let shared_nodes: Vec<CidBytes> = (0..10u32).map(test_cid).collect();
+
+        let refcounts_before = {
+            let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+
+            shared_nodes.iter().for_each(|cid| {
+                store
+                    .put_blocks_blocking(vec![(*cid, vec![0xAA; 80])])
+                    .unwrap();
+            });
+
+            let mut prev_commit = test_cid(5000);
+            store
+                .put_blocks_blocking(vec![(prev_commit, vec![0xCC; 80])])
+                .unwrap();
+
+            (0..500u32).for_each(|round| {
+                let new_commit = test_cid(5001 + round);
+                let new_mst_node = test_cid(6000 + round);
+                let old_mst_node = test_cid(7000 + round);
+
+                store
+                    .put_blocks_blocking(vec![
+                        (new_commit, vec![0xBB; 80]),
+                        (new_mst_node, vec![0xCC; 60]),
+                        (old_mst_node, vec![0xDD; 60]),
+                    ])
+                    .unwrap();
+
+                store
+                    .apply_commit_blocking(vec![], vec![prev_commit, old_mst_node])
+                    .unwrap();
+
+                if round > 0 {
+                    let prev_mst = test_cid(6000 + round - 1);
+                    store
+                        .apply_commit_blocking(vec![], vec![prev_mst])
+                        .unwrap();
+                }
+
+                prev_commit = new_commit;
+
+                if round % 2 == 0 {
+                    compact_lowest_liveness(&store);
+                }
+            });
+
+            (0..300).for_each(|_| {
+                compact_by_liveness(&store);
+                std::thread::sleep(std::time::Duration::from_millis(1));
+            });
+
+            shared_nodes.iter().for_each(|cid| {
+                assert!(
+                    store.get_block_sync(cid).unwrap().is_some(),
+                    "sanity: shared node present before drop"
+                );
+            });
+
+            let rc = collect_refcounts(&store, &shared_nodes);
+            drop(store);
+            rc
+        };
+
+        let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+        verify_blocks_and_refcounts(
+            &store,
+            &shared_nodes,
+            Some(&refcounts_before),
+            "500 commits + 300 compact rounds",
+        );
+    });
+}
+
+#[test]
+fn extreme_file_churn_with_dedup_hits() {
+    with_runtime(|| {
+        let dir = tempfile::TempDir::new().unwrap();
+
+        let live_cids: Vec<CidBytes> = (0..8u32).map(test_cid).collect();
+        let live_data: Vec<u8> = vec![0xAA; 80];
+
+        let refcounts_before = {
+            let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+
+            live_cids.iter().for_each(|cid| {
+                store
+                    .put_blocks_blocking(vec![(*cid, live_data.clone())])
+                    .unwrap();
+            });
+
+            (0..300u32).for_each(|round| {
+                let churn = test_cid(3000 + round);
+                store
+                    .put_blocks_blocking(vec![(churn, vec![0xEE; 80])])
+                    .unwrap();
+                store.apply_commit_blocking(vec![], vec![churn]).unwrap();
+
+                if round % 50 == 0 {
+                    live_cids.iter().for_each(|cid| {
+                        store
+                            .put_blocks_blocking(vec![(*cid, live_data.clone())])
+                            .unwrap();
+                    });
+                }
+
+                if round % 2 == 0 {
+                    compact_lowest_liveness(&store);
+                }
+            });
+
+            (0..200).for_each(|_| compact_by_liveness(&store));
+
+            let rc = collect_refcounts(&store, &live_cids);
+            drop(store);
+            rc
+        };
+
+        let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+        verify_blocks_and_refcounts(
+            &store,
+            &live_cids,
+            Some(&refcounts_before),
+            "300 churn + dedup re-puts + 200 compacts",
+        );
+    });
+}
+
+#[test]
+fn long_idle_compaction_only_phase() {
+    with_runtime(|| {
+        let dir = tempfile::TempDir::new().unwrap();
+
+        let live_cids: Vec<CidBytes> = (0..20u32).map(test_cid).collect();
+
+        {
+            let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+
+            live_cids.iter().for_each(|cid| {
+                store
+                    .put_blocks_blocking(vec![(*cid, vec![0xAA; 80])])
+                    .unwrap();
+            });
+
+            (0..100u32).for_each(|round| {
+                let churn = test_cid(4000 + round);
+                store
+                    .put_blocks_blocking(vec![(churn, vec![0xFF; 80])])
+                    .unwrap();
+                store.apply_commit_blocking(vec![], vec![churn]).unwrap();
+            });
+
+            (0..500).for_each(|_| {
+                compact_by_liveness(&store);
+                std::thread::sleep(std::time::Duration::from_millis(1));
+            });
+
+            live_cids.iter().for_each(|cid| {
+                assert!(
+                    store.get_block_sync(cid).unwrap().is_some(),
+                    "sanity: block present before drop"
+                );
+            });
+
+            drop(store);
+        }
+
+        let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+        verify_blocks_and_refcounts(
+            &store,
+            &live_cids,
+            None,
+            "idle with 500 compaction-only rounds",
+        );
+    });
+}
+
+#[test]
+fn multiple_restart_cycles_blockstore() {
+    with_runtime(|| {
+        let dir = tempfile::TempDir::new().unwrap();
+
+        let live_cids: Vec<CidBytes> = (0..10u32).map(test_cid).collect();
+
+        {
+            let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+            live_cids.iter().for_each(|cid| {
+                store
+                    .put_blocks_blocking(vec![(*cid, vec![0xAA; 80])])
+                    .unwrap();
+            });
+            (0..50u32).for_each(|round| {
+                let churn = test_cid(8000 + round);
+                store
+                    .put_blocks_blocking(vec![(churn, vec![0xBB; 80])])
+                    .unwrap();
+                store.apply_commit_blocking(vec![], vec![churn]).unwrap();
+            });
+            drop(store);
+        }
+
+        (0..10u32).for_each(|cycle| {
+            {
+                let store =
+                    TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+
+                (0..50u32).for_each(|round| {
+                    let churn = test_cid(9000 + cycle * 100 + round);
+                    store
+                        .put_blocks_blocking(vec![(churn, vec![0xCC; 80])])
+                        .unwrap();
+                    store.apply_commit_blocking(vec![], vec![churn]).unwrap();
+                    compact_lowest_liveness(&store);
+                });
+
+                (0..50).for_each(|_| compact_by_liveness(&store));
+
+                live_cids.iter().for_each(|cid| {
+                    assert!(
+                        store.get_block_sync(cid).unwrap().is_some(),
+                        "cycle {cycle}: block missing before drop"
+                    );
+                });
+
+                drop(store);
+            }
+
+            let store = TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap();
+            verify_blocks_and_refcounts(
+                &store,
+                &live_cids,
+                None,
+                &format!("blockstore restart cycle {cycle}"),
+            );
+        });
+    });
+}
+
+#[test]
+fn full_stack_compaction_restart_preserves_refcounts() {
+    with_runtime(|| {
+        let base = tempfile::TempDir::new().unwrap();
+        let base_dir = base.path().to_path_buf();
+
+        let live_cids: Vec<CidBytes> = (0..15u32).map(test_cid).collect();
+
+        let refcounts_before = {
+            let stack = open_full_stack(&base_dir);
+
+            live_cids.iter().for_each(|cid| {
+                stack
+                    .blockstore
+                    .put_blocks_blocking(vec![(*cid, vec![0xAA; 80])])
+                    .unwrap();
+            });
+
+            (0..500u32).for_each(|round| {
+                let churn = test_cid(2000 + round);
+                stack
+                    .blockstore
+                    .put_blocks_blocking(vec![(churn, vec![0xDD; 80])])
+                    .unwrap();
+                stack
+                    .blockstore
+                    .apply_commit_blocking(vec![], vec![churn])
+                    .unwrap();
+
+                if round % 3 == 0 {
+                    compact_lowest_liveness(&stack.blockstore);
+                }
+            });
+
+            (0..200).for_each(|_| compact_by_liveness(&stack.blockstore));
+
+            let rc = collect_refcounts(&stack.blockstore, &live_cids);
+
+            live_cids.iter().for_each(|cid| {
+                assert!(
+                    stack.blockstore.get_block_sync(cid).unwrap().is_some(),
+                    "sanity: block present before shutdown"
+                );
+            });
+
+            close_full_stack(stack, &base_dir);
+            rc
+        };
+
+        let stack = open_full_stack(&base_dir);
+        verify_blocks_and_refcounts(
+            &stack.blockstore,
+            &live_cids,
+            Some(&refcounts_before),
+            "full stack restart",
+        );
+        close_full_stack(stack, &base_dir);
+    });
+}
+
+#[test]
+fn full_stack_multiple_restart_cycles() {
+    with_runtime(|| {
+        let base = tempfile::TempDir::new().unwrap();
+        let base_dir = base.path().to_path_buf();
+
+        let live_cids: Vec<CidBytes> = (0..10u32).map(test_cid).collect();
+
+        {
+            let stack = open_full_stack(&base_dir);
+            live_cids.iter().for_each(|cid| {
+                stack
+                    .blockstore
+                    .put_blocks_blocking(vec![(*cid, vec![0xAA; 80])])
+                    .unwrap();
+            });
+            close_full_stack(stack, &base_dir);
+        }
+
+        (0..10u32).for_each(|cycle| {
+            let refcounts_before = {
+                let stack = open_full_stack(&base_dir);
+
+                (0..50u32).for_each(|round| {
+                    let churn = test_cid(5000 + cycle * 100 + round);
+                    stack
+                        .blockstore
+                        .put_blocks_blocking(vec![(churn, vec![0xBB; 80])])
+                        .unwrap();
+                    stack
+                        .blockstore
+                        .apply_commit_blocking(vec![], vec![churn])
+                        .unwrap();
+                    compact_lowest_liveness(&stack.blockstore);
+                });
+
+                (0..30).for_each(|_| compact_by_liveness(&stack.blockstore));
+
+                let rc = collect_refcounts(&stack.blockstore, &live_cids);
+
+                live_cids.iter().for_each(|cid| {
+                    assert!(
+                        stack.blockstore.get_block_sync(cid).unwrap().is_some(),
+                        "cycle {cycle}: block missing before shutdown"
+                    );
+                });
+
+                close_full_stack(stack, &base_dir);
+                rc
+            };
+
+            let stack = open_full_stack(&base_dir);
+            verify_blocks_and_refcounts(
+                &stack.blockstore,
+                &live_cids,
+                Some(&refcounts_before),
+                &format!("full stack cycle {cycle}"),
+            );
+            close_full_stack(stack, &base_dir);
+        });
+    });
+}
diff --git a/crates/tranquil-store/tests/mst_integration.rs b/crates/tranquil-store/tests/mst_integration.rs
index 818ade0..fe4c907 100644
--- a/crates/tranquil-store/tests/mst_integration.rs
+++ b/crates/tranquil-store/tests/mst_integration.rs
@@ -268,12 +268,12 @@ async fn mst_create_update_delete_with_refcounts() {
     assert_eq!(&retrieved_a_v2.unwrap()[..], &record_a_v2);
 
     assert!(
-        store.has(&cid_a_v1).await.unwrap(),
-        "cid_a_v1 should still exist, tombstoned but not GC'd"
+        store.get(&cid_a_v1).await.unwrap().is_some(),
+        "cid_a_v1 data should still exist, tombstoned but not GC'd"
     );
     assert!(
-        store.has(&cid_b).await.unwrap(),
-        "cid_b should still exist, tombstoned but not GC'd"
+        store.get(&cid_b).await.unwrap().is_some(),
+        "cid_b data should still exist, tombstoned but not GC'd"
     );
 
     assert!(
@@ -284,8 +284,8 @@ async fn mst_create_update_delete_with_refcounts() {
     assert_eq!(&retrieved_c[..], &record_c);
 
     assert!(
-        store.has(&cid_shared).await.unwrap(),
-        "shared-content block should still exist, tombstoned but not GC'd"
+        store.get(&cid_shared).await.unwrap().is_some(),
+        "shared-content block data should still exist, tombstoned but not GC'd"
     );
 
     let loaded_mst = Mst::load(storage.clone(), mst_root_v2, None);
diff --git a/crates/tranquil-store/tests/mst_refcount_integrity.rs b/crates/tranquil-store/tests/mst_refcount_integrity.rs
new file mode 100644
index 0000000..8421ed7
--- /dev/null
+++ b/crates/tranquil-store/tests/mst_refcount_integrity.rs
@@ -0,0 +1,217 @@
+mod common;
+
+use std::sync::Arc;
+
+use cid::Cid;
+use common::{compact_by_liveness, tiny_blockstore_config};
+use jacquard_repo::mst::Mst;
+use jacquard_repo::storage::BlockStore;
+use tranquil_store::blockstore::TranquilBlockStore;
+
+fn cid_to_fixed(cid: &Cid) -> [u8; 36] {
+    let bytes = cid.to_bytes();
+    let mut arr = [0u8; 36];
+    arr.copy_from_slice(&bytes[..36]);
+    arr
+}
+
+fn make_record_bytes(seed: u32) -> Vec<u8> {
+    serde_ipld_dagcbor::to_vec(&serde_json::json!({
+        "$type": "app.bsky.feed.post",
+        "text": format!("record {seed}"),
+        "createdAt": "2026-01-01T00:00:00Z"
+    }))
+    .unwrap()
+}
+
+fn make_fake_commit_cid(counter: u32) -> Cid {
+    let data = format!("commit-{counter}");
+    let mh = multihash::Multihash::wrap(0x12, &{
+        use sha2::Digest;
+        sha2::Sha256::digest(data.as_bytes())
+    })
+    .unwrap();
+    Cid::new_v1(0x71, mh)
+}
+
+async fn compute_obsolete_from_diff<S: BlockStore + Sync + Send + 'static>(
+    old_mst: &Mst<S>,
+    new_mst: &Mst<S>,
+    old_commit_cid: Cid,
+) -> Vec<Cid> {
+    let diff = old_mst.diff(new_mst).await.unwrap();
+    std::iter::once(old_commit_cid)
+        .chain(diff.removed_mst_blocks.into_iter())
+        .chain(diff.removed_cids.into_iter())
+        .collect()
+}
+
+#[tokio::test]
+async fn mst_shared_subtrees_survive_incremental_writes_compaction_restart() {
+    let dir = tempfile::TempDir::new().unwrap();
+
+    let mut commit_counter = 0u32;
+    let final_node_cids: Vec<Cid>;
+
+    {
+        let store = Arc::new(TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap());
+
+        let mut mst = Mst::new(store.clone());
+        let mut root: Option<Cid> = None;
+        let mut prev_commit = make_fake_commit_cid(commit_counter);
+        commit_counter += 1;
+
+        for i in 0..30u32 {
+            let record_bytes = make_record_bytes(i);
+            let record_cid = store.put(&record_bytes).await.unwrap();
+            let key = format!("app.bsky.feed.post/{i:06}");
+            mst = match root {
+                None => mst.add(&key, record_cid).await.unwrap(),
+                Some(r) => {
+                    let loaded = Mst::load(store.clone(), r, None);
+                    loaded.add(&key, record_cid).await.unwrap()
+                }
+            };
+            let new_root = mst.persist().await.unwrap();
+
+            if let Some(old_root) = root {
+                let old_settled = Mst::load(store.clone(), old_root, None);
+                let new_settled = Mst::load(store.clone(), new_root, None);
+
+                let obsolete =
+                    compute_obsolete_from_diff(&old_settled, &new_settled, prev_commit).await;
+                let obsolete_fixed: Vec<[u8; 36]> =
+                    obsolete.iter().map(|c| cid_to_fixed(c)).collect();
+                let s = store.clone();
+                tokio::task::spawn_blocking(move || {
+                    s.apply_commit_blocking(vec![], obsolete_fixed).unwrap();
+                })
+                .await
+                .unwrap();
+            }
+
+            root = Some(new_root);
+            prev_commit = make_fake_commit_cid(commit_counter);
+            commit_counter += 1;
+
+            if i % 5 == 0 {
+                let s = store.clone();
+                tokio::task::spawn_blocking(move || compact_by_liveness(&s))
+                    .await
+                    .unwrap();
+            }
+        }
+
+        for i in 0..15u32 {
+            let record_bytes = make_record_bytes(1000 + i);
+            let record_cid = store.put(&record_bytes).await.unwrap();
+            let key = format!("app.bsky.feed.like/{i:06}");
+            let loaded = Mst::load(store.clone(), root.unwrap(), None);
+            mst = loaded.add(&key, record_cid).await.unwrap();
+            let new_root = mst.persist().await.unwrap();
+
+            let old_settled = Mst::load(store.clone(), root.unwrap(), None);
+            let new_settled = Mst::load(store.clone(), new_root, None);
+
+            let obsolete =
+                compute_obsolete_from_diff(&old_settled, &new_settled, prev_commit).await;
+            let obsolete_fixed: Vec<[u8; 36]> =
+                obsolete.iter().map(|c| cid_to_fixed(c)).collect();
+            let s = store.clone();
+            tokio::task::spawn_blocking(move || {
+                s.apply_commit_blocking(vec![], obsolete_fixed).unwrap();
+            })
+            .await
+            .unwrap();
+
+            root = Some(new_root);
+            prev_commit = make_fake_commit_cid(commit_counter);
+            commit_counter += 1;
+
+            if i % 3 == 0 {
+                let s = store.clone();
+                tokio::task::spawn_blocking(move || compact_by_liveness(&s))
+                    .await
+                    .unwrap();
+            }
+        }
+
+        let final_settled = Mst::load(store.clone(), root.unwrap(), None);
+        final_node_cids = final_settled.collect_node_cids().await.unwrap();
+
+        final_node_cids.iter().for_each(|cid| {
+            let fixed = cid_to_fixed(cid);
+            let rc = store.block_index().get(&fixed).map(|e| e.refcount.raw());
+            assert!(
+                rc.is_some_and(|r| r > 0),
+                "MST node {cid} has refcount {rc:?} before shutdown"
+            );
+        });
+
+        let s = store.clone();
+        tokio::task::spawn_blocking(move || {
+            (0..100).for_each(|_| compact_by_liveness(&s));
+        })
+        .await
+        .unwrap();
+
+        final_node_cids.iter().for_each(|cid| {
+            let fixed = cid_to_fixed(cid);
+            let block = store.get_block_sync(&fixed).unwrap();
+            assert!(
+                block.is_some(),
+                "MST node {cid} missing after compaction before shutdown"
+            );
+        });
+
+        drop(store);
+    }
+
+    {
+        let store = Arc::new(
+            TranquilBlockStore::open(tiny_blockstore_config(dir.path())).unwrap(),
+        );
+
+        let missing: Vec<String> = final_node_cids
+            .iter()
+            .filter_map(|cid| {
+                let fixed = cid_to_fixed(cid);
+                match store.get_block_sync(&fixed) {
+                    Ok(Some(_)) => None,
+                    Ok(None) => {
+                        let rc = store.block_index().get(&fixed).map(|e| e.refcount.raw());
+                        Some(format!("{cid} missing, index refcount {rc:?}"))
+                    }
+                    Err(e) => Some(format!("{cid} error: {e}")),
+                }
+            })
+            .collect();
+
+        assert!(
+            missing.is_empty(),
+            "{} of {} MST nodes missing after reopen:\n{}",
+            missing.len(),
+            final_node_cids.len(),
+            missing.join("\n"),
+        );
+
+        let refcount_issues: Vec<String> = final_node_cids
+            .iter()
+            .filter_map(|cid| {
+                let fixed = cid_to_fixed(cid);
+                let rc = store.block_index().get(&fixed).map(|e| e.refcount.raw());
+                match rc {
+                    Some(0) => Some(format!("{cid} refcount dropped to 0")),
+                    None => Some(format!("{cid} not in index")),
+                    _ => None,
+                }
+            })
+            .collect();
+
+        assert!(
+            refcount_issues.is_empty(),
+            "MST nodes with bad refcounts after reopen:\n{}",
+            refcount_issues.join("\n"),
+        );
+    }
+}