diff --git a/crates/tranquil-pds/tests/mst_integrity.rs b/crates/tranquil-pds/tests/mst_integrity.rs
new file mode 100644
index 0000000..d4edd7a
--- /dev/null
+++ b/crates/tranquil-pds/tests/mst_integrity.rs
@@ -0,0 +1,334 @@
+mod common;
+mod firehose;
+mod helpers;
+
+use std::collections::BTreeMap;
+use std::io::Cursor;
+use std::sync::Arc;
+use std::time::Duration;
+
+use bytes::Bytes;
+use cid::Cid;
+use common::*;
+use firehose::FirehoseConsumer;
+use helpers::build_car_with_signature;
+use iroh_car::CarReader;
+use jacquard_repo::commit::Commit;
+use jacquard_repo::mst::Mst;
+use jacquard_repo::storage::{BlockStore, MemoryBlockStore};
+use k256::ecdsa::SigningKey;
+use reqwest::StatusCode;
+use serde_json::{Value, json};
+use tranquil_db_traits::{EventBlocks, RepoEventType, SequenceNumber, SequencedEvent};
+use tranquil_scopes::RepoAction;
+use tranquil_types::Did;
+
+async fn car_to_blocks(car_bytes: &[u8]) -> (Vec<Cid>, BTreeMap<Cid, Bytes>) {
+    let mut reader = CarReader::new(Cursor::new(car_bytes))
+        .await
+        .expect("parse CAR");
+    let roots = reader.header().roots().to_vec();
+    let mut blocks = BTreeMap::new();
+    while let Ok(Some((cid, data))) = reader.next_block().await {
+        blocks.insert(cid, Bytes::from(data));
+    }
+    (roots, blocks)
+}
+
+async fn create_post(client: &reqwest::Client, token: &str, did: &str, rkey: &str, text: &str) {
+    let now = chrono::Utc::now().to_rfc3339();
+    let res = client
+        .post(format!(
+            "{}/xrpc/com.atproto.repo.createRecord",
+            base_url().await
+        ))
+        .bearer_auth(token)
+        .json(&json!({
+            "repo": did,
+            "collection": "app.bsky.feed.post",
+            "rkey": rkey,
+            "record": {
+                "$type": "app.bsky.feed.post",
+                "text": text,
+                "createdAt": now,
+            }
+        }))
+        .send()
+        .await
+        .expect("createRecord");
+    assert_eq!(res.status(), StatusCode::OK);
+}
+
+#[tokio::test]
+async fn getrepo_car_roundtrips_mst_structure_and_records() {
+    let client = client();
+    let (token, did) = create_account_and_login(&client).await;
+
+    let expected_records: Vec<(String, String)> = (0..20)
+        .map(|i| {
+            let rkey = format!("3krtp{:08}", i);
+            let text = format!("roundtrip record {i}");
+            (rkey, text)
+        })
+        .collect();
+    for (rkey, text) in &expected_records {
+        create_post(&client, &token, &did, rkey, text).await;
+    }
+
+    let res = client
+        .get(format!(
+            "{}/xrpc/com.atproto.sync.getRepo",
+            base_url().await
+        ))
+        .query(&[("did", did.as_str())])
+        .send()
+        .await
+        .expect("getRepo");
+    assert_eq!(res.status(), StatusCode::OK);
+    let car_bytes = res.bytes().await.unwrap();
+
+    let (roots, block_map) = car_to_blocks(&car_bytes).await;
+    assert_eq!(roots.len(), 1, "CAR must have exactly one root");
+    let commit_cid = roots[0];
+    let storage = Arc::new(MemoryBlockStore::new_from_blocks(block_map));
+
+    let commit_bytes = storage
+        .get(&commit_cid)
+        .await
+        .unwrap()
+        .expect("CAR contains commit block");
+    let commit = Commit::from_cbor(&commit_bytes).expect("parse commit");
+    let data_cid = *commit.data();
+
+    let mst = Mst::load(storage.clone(), data_cid, None);
+    let loaded_root = mst.get_pointer().await.expect("load root");
+    assert_eq!(loaded_root, data_cid, "loaded MST pointer == commit.data()");
+
+    for (rkey, _) in &expected_records {
+        let path = format!("app.bsky.feed.post/{rkey}");
+        let leaf = mst
+            .get(&path)
+            .await
+            .expect("mst.get")
+            .unwrap_or_else(|| panic!("record {path} missing from exported MST"));
+        let leaf_bytes = storage
+            .get(&leaf)
+            .await
+            .unwrap()
+            .unwrap_or_else(|| panic!("record block {leaf} missing from CAR"));
+        assert!(!leaf_bytes.is_empty(), "record bytes empty");
+    }
+}
+
+#[tokio::test]
+async fn concurrent_swap_commit_writes_serialize() {
+    let client = client();
+    let (token, did) = create_account_and_login(&client).await;
+
+    create_post(&client, &token, &did, "3kswap00000001", "anchor").await;
+
+    let latest_res = client
+        .get(format!(
+            "{}/xrpc/com.atproto.sync.getLatestCommit",
+            base_url().await
+        ))
+        .query(&[("did", did.as_str())])
+        .send()
+        .await
+        .expect("getLatestCommit");
+    assert_eq!(latest_res.status(), StatusCode::OK);
+    let latest: Value = latest_res.json().await.unwrap();
+    let swap_cid = latest["cid"].as_str().unwrap().to_string();
+
+    let now = chrono::Utc::now().to_rfc3339();
+    let payload_a = json!({
+        "repo": did,
+        "collection": "app.bsky.feed.post",
+        "rkey": "3kswap00000002",
+        "record": {
+            "$type": "app.bsky.feed.post",
+            "text": "writer A",
+            "createdAt": now,
+        },
+        "swapCommit": swap_cid,
+    });
+    let payload_b = json!({
+        "repo": did,
+        "collection": "app.bsky.feed.post",
+        "rkey": "3kswap00000003",
+        "record": {
+            "$type": "app.bsky.feed.post",
+            "text": "writer B",
+            "createdAt": now,
+        },
+        "swapCommit": swap_cid,
+    });
+
+    let base = base_url().await;
+    let (res_a, res_b) = tokio::join!(
+        client
+            .post(format!("{base}/xrpc/com.atproto.repo.putRecord"))
+            .bearer_auth(&token)
+            .json(&payload_a)
+            .send(),
+        client
+            .post(format!("{base}/xrpc/com.atproto.repo.putRecord"))
+            .bearer_auth(&token)
+            .json(&payload_b)
+            .send(),
+    );
+    let status_a = res_a.expect("A send").status();
+    let status_b = res_b.expect("B send").status();
+
+    let ok_a = status_a == StatusCode::OK;
+    let ok_b = status_b == StatusCode::OK;
+    assert!(
+        ok_a ^ ok_b,
+        "exactly one swap_commit write must succeed: status_a={status_a}, status_b={status_b}"
+    );
+}
+
+#[tokio::test]
+async fn imported_repo_emits_commit_event_with_valid_car() {
+    let client = client();
+    let (token, did) = create_account_and_login(&client).await;
+
+    let signing_key = SigningKey::random(&mut rand::thread_rng());
+    let (car_bytes, _car_root_cid) = build_car_with_signature(&did, &signing_key);
+
+    let import_res = client
+        .post(format!(
+            "{}/xrpc/com.atproto.repo.importRepo",
+            base_url().await
+        ))
+        .bearer_auth(&token)
+        .header("Content-Type", "application/vnd.ipld.car")
+        .body(car_bytes)
+        .send()
+        .await
+        .expect("importRepo");
+    assert_eq!(
+        import_res.status(),
+        StatusCode::OK,
+        "import failed: {:?}",
+        import_res.text().await.unwrap_or_default()
+    );
+
+    let repos = get_test_repos().await;
+    let typed_did = Did::new(did.clone()).unwrap();
+    let events = repos
+        .repo
+        .get_events_since_seq(SequenceNumber::ZERO, None)
+        .await
+        .expect("events");
+    let our: Vec<&SequencedEvent> = events
+        .iter()
+        .filter(|e| e.did == typed_did && e.event_type == RepoEventType::Commit)
+        .collect();
+    let last = our.last().expect("at least one commit event after import");
+
+    let inline = match last.blocks.as_ref().expect("blocks present") {
+        EventBlocks::Inline(v) => v,
+        _ => panic!("expected inline blocks"),
+    };
+    assert!(
+        !inline.is_empty(),
+        "import event inline blocks must not be empty"
+    );
+
+    let have_commit = inline.iter().any(|b| {
+        let cid = Cid::read_bytes(b.cid_bytes.as_slice()).unwrap();
+        last.commit_cid
+            .as_ref()
+            .and_then(|c| c.to_cid())
+            .map(|commit_cid| cid == commit_cid)
+            .unwrap_or(false)
+    });
+    assert!(have_commit, "import event CAR must include commit block");
+}
+
+#[tokio::test]
+async fn firehose_commit_block_bytes_roundtrip_to_same_cid() {
+    let client = client();
+    let (token, did) = create_account_and_login(&client).await;
+
+    let repos = get_test_repos().await;
+    let cursor = repos.repo.get_max_seq().await.unwrap().as_i64();
+    let consumer = FirehoseConsumer::connect_with_cursor(app_port(), cursor).await;
+    tokio::time::sleep(Duration::from_millis(100)).await;
+
+    create_post(&client, &token, &did, "3krt001", "round-trip me").await;
+    let frames = consumer
+        .wait_for_commits(&did, 1, Duration::from_secs(10))
+        .await;
+    let frame = frames.last().expect("frame");
+
+    let (_, block_map) = car_to_blocks(&frame.blocks).await;
+    use sha2::{Digest, Sha256};
+    for (cid, bytes) in &block_map {
+        let mut hasher = Sha256::new();
+        hasher.update(bytes);
+        let hash = hasher.finalize();
+        let mh = multihash::Multihash::wrap(0x12, hash.as_slice()).expect("wrap");
+        let recomputed = Cid::new_v1(cid.codec(), mh);
+        assert_eq!(
+            recomputed, *cid,
+            "CAR block {cid} bytes do not hash back to same CID"
+        );
+    }
+}
+
+#[tokio::test]
+async fn firehose_commit_car_contains_new_record_bytes_for_every_create() {
+    let client = client();
+    let (token, did) = create_account_and_login(&client).await;
+
+    let repos = get_test_repos().await;
+    let cursor = repos.repo.get_max_seq().await.unwrap().as_i64();
+    let consumer = FirehoseConsumer::connect_with_cursor(app_port(), cursor).await;
+    tokio::time::sleep(Duration::from_millis(100)).await;
+
+    let now = chrono::Utc::now().to_rfc3339();
+    let writes: Vec<Value> = (0..8)
+        .map(|i| {
+            json!({
+                "$type": "com.atproto.repo.applyWrites#create",
+                "collection": "app.bsky.feed.post",
+                "rkey": format!("3krec{:08}", i),
+                "value": {
+                    "$type": "app.bsky.feed.post",
+                    "text": format!("rec {i}"),
+                    "createdAt": now,
+                }
+            })
+        })
+        .collect();
+    let res = client
+        .post(format!(
+            "{}/xrpc/com.atproto.repo.applyWrites",
+            base_url().await
+        ))
+        .bearer_auth(&token)
+        .json(&json!({ "repo": did, "writes": writes }))
+        .send()
+        .await
+        .expect("applyWrites");
+    assert_eq!(res.status(), StatusCode::OK);
+
+    let frames = consumer
+        .wait_for_commits(&did, 1, Duration::from_secs(10))
+        .await;
+    let frame = frames.last().expect("frame");
+
+    let (_, block_map) = car_to_blocks(&frame.blocks).await;
+    for op in &frame.ops {
+        if op.action == RepoAction::Create {
+            let cid = op.cid.expect("create cid");
+            assert!(
+                block_map.contains_key(&cid),
+                "record CID {cid} for path {} missing from CAR",
+                op.path
+            );
+        }
+    }
+}
diff --git a/crates/tranquil-pds/tests/mst_property_fuzz.rs b/crates/tranquil-pds/tests/mst_property_fuzz.rs
new file mode 100644
index 0000000..cc80d49
--- /dev/null
+++ b/crates/tranquil-pds/tests/mst_property_fuzz.rs
@@ -0,0 +1,348 @@
+mod common;
+mod mst_verify;
+
+use std::collections::HashMap;
+use std::str::FromStr;
+
+use cid::Cid;
+use common::*;
+use jacquard_common::smol_str::SmolStr;
+use jacquard_repo::commit::Commit;
+use jacquard_repo::mst::{Mst, VerifiedWriteOp};
+use jacquard_repo::storage::BlockStore;
+use mst_verify::{extract_event_blocks, inline_to_store};
+use rand::rngs::StdRng;
+use rand::{Rng, SeedableRng};
+use reqwest::StatusCode;
+use serde_json::{Value, json};
+use tranquil_db_traits::{RepoEventType, SequenceNumber, SequencedEvent};
+use tranquil_types::Did;
+
+const COLLECTIONS: &[&str] = &[
+    "app.bsky.feed.post",
+    "app.bsky.feed.like",
+    "app.bsky.graph.follow",
+    "app.bsky.feed.repost",
+];
+
+#[derive(Copy, Clone, Debug)]
+enum FuzzOp {
+    Create,
+    Update,
+    Delete,
+}
+
+fn pick_op(rng: &mut StdRng, have_keys: bool) -> FuzzOp {
+    match (have_keys, rng.gen_range(0..10)) {
+        (false, _) => FuzzOp::Create,
+        (_, 0..=5) => FuzzOp::Create,
+        (_, 6..=7) => FuzzOp::Update,
+        _ => FuzzOp::Delete,
+    }
+}
+
+fn random_rkey(rng: &mut StdRng) -> String {
+    let tid_char_pool = b"234567abcdefghijklmnopqrstuvwxyz";
+    let mut out = Vec::with_capacity(13);
+    (0..13).for_each(|_| {
+        let c = tid_char_pool[rng.gen_range(0..tid_char_pool.len())];
+        out.push(c);
+    });
+    String::from_utf8(out).unwrap()
+}
+
+fn random_collection(rng: &mut StdRng) -> &'static str {
+    COLLECTIONS[rng.gen_range(0..COLLECTIONS.len())]
+}
+
+fn record_for_collection(col: &str, text: &str, now: &str) -> Value {
+    match col {
+        "app.bsky.feed.post" | "app.bsky.feed.repost" | "app.bsky.feed.like" => json!({
+            "$type": col,
+            "text": text,
+            "createdAt": now,
+        }),
+        _ => json!({
+            "$type": col,
+            "subject": format!("did:plc:synthetic{text}"),
+            "createdAt": now,
+        }),
+    }
+}
+
+async fn verify_commit_forward_and_inverse(event: &SequencedEvent) -> Result<(), String> {
+    let prev_data = event
+        .prev_data_cid
+        .as_ref()
+        .and_then(|c| c.to_cid())
+        .ok_or("no prev_data_cid")?;
+    let commit_cid = event
+        .commit_cid
+        .as_ref()
+        .and_then(|c| c.to_cid())
+        .ok_or("no commit_cid")?;
+    let inline = extract_event_blocks(event)?;
+    let ops = event
+        .ops
+        .as_ref()
+        .and_then(|v| v.as_array())
+        .ok_or("ops not array")?;
+
+    let storage = inline_to_store(inline);
+    let commit_bytes = storage
+        .get(&commit_cid)
+        .await
+        .map_err(|e| format!("get commit: {e:?}"))?
+        .ok_or("missing commit block")?;
+    let commit = Commit::from_cbor(&commit_bytes).map_err(|e| format!("parse commit: {e:?}"))?;
+    let new_data = *commit.data();
+
+    let mut forward = Mst::load(storage.clone(), prev_data, None);
+    for op in ops {
+        let action = op["action"].as_str().ok_or("op.action")?;
+        let path = op["path"].as_str().ok_or("op.path")?;
+        match action {
+            "create" | "update" => {
+                let cid = Cid::from_str(op["cid"].as_str().ok_or("op.cid")?)
+                    .map_err(|e| format!("{e:?}"))?;
+                forward = forward
+                    .add(path, cid)
+                    .await
+                    .map_err(|e| format!("fwd add {path}: {e:?}"))?;
+            }
+            "delete" => {
+                forward = forward
+                    .delete(path)
+                    .await
+                    .map_err(|e| format!("fwd delete {path}: {e:?}"))?;
+            }
+            other => return Err(format!("unknown action {other}")),
+        }
+    }
+    let got = forward
+        .persist()
+        .await
+        .map_err(|e| format!("persist: {e:?}"))?;
+    if got != new_data {
+        return Err(format!("forward root mismatch exp={new_data} got={got}"));
+    }
+
+    let mut inverse = Mst::load(storage, new_data, None);
+    for op in ops {
+        let action = op["action"].as_str().ok_or("op.action")?;
+        let path = op["path"].as_str().ok_or("op.path")?;
+        let key = SmolStr::new(path);
+        let verified = match action {
+            "create" => {
+                let cid = Cid::from_str(op["cid"].as_str().ok_or("op.cid")?)
+                    .map_err(|e| format!("{e:?}"))?;
+                VerifiedWriteOp::Create { key, cid }
+            }
+            "update" => {
+                let cid = Cid::from_str(op["cid"].as_str().ok_or("op.cid")?)
+                    .map_err(|e| format!("{e:?}"))?;
+                let prev = Cid::from_str(op["prev"].as_str().ok_or("op.prev")?)
+                    .map_err(|e| format!("{e:?}"))?;
+                VerifiedWriteOp::Update { key, cid, prev }
+            }
+            "delete" => {
+                let prev = Cid::from_str(op["prev"].as_str().ok_or("op.prev")?)
+                    .map_err(|e| format!("{e:?}"))?;
+                VerifiedWriteOp::Delete { key, prev }
+            }
+            other => return Err(format!("unknown action {other}")),
+        };
+        let inverted = inverse
+            .invert_op(verified.clone())
+            .await
+            .map_err(|e| format!("invert {verified:?}: {e:?}"))?;
+        if !inverted {
+            return Err(format!("op not invertible: {verified:?}"));
+        }
+    }
+    let got_prev = inverse
+        .get_pointer()
+        .await
+        .map_err(|e| format!("get_pointer: {e:?}"))?;
+    if got_prev != prev_data {
+        return Err(format!(
+            "inverse root mismatch exp={prev_data} got={got_prev}"
+        ));
+    }
+    Ok(())
+}
+
+async fn fuzz_run_with_seed(seed: u64, steps: usize) -> Vec<String> {
+    let client = client();
+    let (token, did) = create_account_and_login(&client).await;
+    let mut rng = StdRng::seed_from_u64(seed);
+
+    let mut live_keys: HashMap<String, String> = HashMap::new();
+
+    for step in 0..steps {
+        let now = chrono::Utc::now().to_rfc3339();
+        let op = pick_op(&mut rng, !live_keys.is_empty());
+        match op {
+            FuzzOp::Create => {
+                let col = random_collection(&mut rng);
+                let rkey = random_rkey(&mut rng);
+                let path = format!("{col}/{rkey}");
+                if live_keys.contains_key(&path) {
+                    continue;
+                }
+                let record = record_for_collection(col, &format!("s{seed}-n{step}"), &now);
+                let res = client
+                    .post(format!(
+                        "{}/xrpc/com.atproto.repo.createRecord",
+                        base_url().await
+                    ))
+                    .bearer_auth(&token)
+                    .json(&json!({
+                        "repo": did,
+                        "collection": col,
+                        "rkey": rkey,
+                        "record": record,
+                    }))
+                    .send()
+                    .await
+                    .expect("createRecord");
+                if res.status() == StatusCode::OK {
+                    live_keys.insert(path, col.to_string());
+                }
+            }
+            FuzzOp::Update => {
+                let keys: Vec<&String> = live_keys.keys().collect();
+                if keys.is_empty() {
+                    continue;
+                }
+                let path = keys[rng.gen_range(0..keys.len())].clone();
+                let col = live_keys.get(&path).unwrap().clone();
+                let rkey = path.split('/').nth(1).unwrap().to_string();
+                let record = record_for_collection(&col, &format!("s{seed}-u{step}"), &now);
+                let res = client
+                    .post(format!(
+                        "{}/xrpc/com.atproto.repo.putRecord",
+                        base_url().await
+                    ))
+                    .bearer_auth(&token)
+                    .json(&json!({
+                        "repo": did,
+                        "collection": col,
+                        "rkey": rkey,
+                        "record": record,
+                    }))
+                    .send()
+                    .await
+                    .expect("putRecord");
+                assert_eq!(res.status(), StatusCode::OK, "putRecord failed");
+            }
+            FuzzOp::Delete => {
+                let keys: Vec<String> = live_keys.keys().cloned().collect();
+                if keys.is_empty() {
+                    continue;
+                }
+                let path = keys[rng.gen_range(0..keys.len())].clone();
+                let col = live_keys.get(&path).unwrap().clone();
+                let rkey = path.split('/').nth(1).unwrap().to_string();
+                let res = client
+                    .post(format!(
+                        "{}/xrpc/com.atproto.repo.deleteRecord",
+                        base_url().await
+                    ))
+                    .bearer_auth(&token)
+                    .json(&json!({
+                        "repo": did,
+                        "collection": col,
+                        "rkey": rkey,
+                    }))
+                    .send()
+                    .await
+                    .expect("deleteRecord");
+                if res.status() == StatusCode::OK {
+                    live_keys.remove(&path);
+                }
+            }
+        }
+    }
+
+    let repos = get_test_repos().await;
+    let typed_did = Did::new(did.clone()).unwrap();
+    let events = repos
+        .repo
+        .get_events_since_seq(SequenceNumber::ZERO, None)
+        .await
+        .expect("get_events_since_seq");
+
+    let our: Vec<SequencedEvent> = events
+        .into_iter()
+        .filter(|e| {
+            e.did == typed_did
+                && e.event_type == RepoEventType::Commit
+                && e.prev_data_cid.is_some()
+                && e.ops
+                    .as_ref()
+                    .and_then(|v| v.as_array())
+                    .is_some_and(|a| !a.is_empty())
+        })
+        .collect();
+
+    let mut failures = Vec::new();
+    for event in &our {
+        if let Err(msg) = verify_commit_forward_and_inverse(event).await {
+            failures.push(format!(
+                "seed={seed} seq={} ops={:?}: {msg}",
+                event.seq.as_i64(),
+                event
+                    .ops
+                    .as_ref()
+                    .and_then(|v| v.as_array())
+                    .map(|a| a.len())
+            ));
+        }
+    }
+    failures
+}
+
+#[tokio::test]
+async fn mst_property_fuzz_seed_1() {
+    let failures = fuzz_run_with_seed(1, 150).await;
+    assert!(
+        failures.is_empty(),
+        "fuzz seed=1 found {} invalid commits:\n  - {}",
+        failures.len(),
+        failures.join("\n  - ")
+    );
+}
+
+#[tokio::test]
+async fn mst_property_fuzz_seed_42() {
+    let failures = fuzz_run_with_seed(42, 150).await;
+    assert!(
+        failures.is_empty(),
+        "fuzz seed=42 found {} invalid commits:\n  - {}",
+        failures.len(),
+        failures.join("\n  - ")
+    );
+}
+
+#[tokio::test]
+async fn mst_property_fuzz_seed_9001() {
+    let failures = fuzz_run_with_seed(9001, 150).await;
+    assert!(
+        failures.is_empty(),
+        "fuzz seed=9001 found {} invalid commits:\n  - {}",
+        failures.len(),
+        failures.join("\n  - ")
+    );
+}
+
+#[tokio::test]
+async fn mst_property_fuzz_deep_tree_seed_7() {
+    let failures = fuzz_run_with_seed(7, 400).await;
+    assert!(
+        failures.is_empty(),
+        "fuzz deep seed=7 found {} invalid commits:\n  - {}",
+        failures.len(),
+        failures.join("\n  - ")
+    );
+}