diff --git a/pyproject.toml b/pyproject.toml
index ccf8c44..d2ccc82 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,7 +24,9 @@ dependencies = [
 anthropic = ["anthropic"]
 openai = ["openai"]
 agent = ["anthropic"]  # convenience alias: the default provider
-# L2: durable per-user analysts as objects on S3-compatible storage
+# L2: durable per-user analysts as objects on S3-compatible storage.
+# The DAO primitive ships as chdb.durable (subpackage of the main chdb package);
+# chdb[durable] pulls its S3 backend deps.
 durable = ["chdb[durable]"]
 # L3: analytical agent-memory layer on top of the durable object
 memory = ["chdb-memory"]
diff --git a/src/chdb_serverless/durable.py b/src/chdb_serverless/durable.py
new file mode 100644
index 0000000..5838840
--- /dev/null
+++ b/src/chdb_serverless/durable.py
@@ -0,0 +1,84 @@
+"""L2 store: a Durable Analytical Object as the engine.
+
+The whole difference between the stateless L1 recipe and a durable per-user
+analyst is this file being chosen by the store seam. The same app, image, and
+deploy scripts run unchanged; `CHDB_STORE=durable:<url>?id=<who>` points the
+engine at a `chdb.durable` object on object storage you own, so the analyst's
+tables and history survive the instance and are portable across clouds.
+
+Spec (the part after `durable:`):
+    durable:s3://bucket/prefix?id=user-123
+    durable:local:/var/data?id=user-123
+Object id also readable from CHDB_DURABLE_ID; writer identity from
+CHDB_DURABLE_OWNER (defaults to the hostname); database from CHDB_DURABLE_DB.
+
+Reads go straight to the object; writes are logged to its WAL and flushed
+immediately, so a committed write survives an instance dying mid-session.
+chDB is single-writer per process, so this store IS the process's one engine.
+"""
+from __future__ import annotations
+
+import os
+import socket
+import threading
+import re
+from urllib.parse import parse_qs
+
+from .store import Store
+
+_WRITE_KEYWORDS = {
+    "INSERT", "CREATE", "ALTER", "DROP", "RENAME", "TRUNCATE",
+    "DELETE", "UPDATE", "OPTIMIZE", "ATTACH", "DETACH", "BACKUP", "RESTORE",
+}
+
+# Leading SQL comment — a `-- line` comment or a `/* block */` comment. Stripped
+# before reading the first keyword so `/* migration */ CREATE TABLE ...` and
+# `-- note\nINSERT ...` are still classified as writes (and routed to the WAL),
+# not misread as reads because the comment was the "first token".
+_LEADING_COMMENT = re.compile(r"^\s*(?:--[^\n]*(?:\n|$)|/\*.*?\*/)", re.DOTALL)
+
+
+def _is_write(sql: str) -> bool:
+    s = sql.strip()
+    while True:
+        m = _LEADING_COMMENT.match(s)
+        if not m:
+            break
+        s = s[m.end():].lstrip()
+    if not s:
+        return False
+    return s.split(None, 1)[0].upper() in _WRITE_KEYWORDS
+
+
+class DurableStore(Store):
+    def __init__(self, target: str) -> None:
+        from chdb import durable as cd
+
+        url, _, query = target.partition("?")
+        params = parse_qs(query)
+        oid = params.get("id", [os.getenv("CHDB_DURABLE_ID", "default")])[0]
+        owner = os.getenv("CHDB_DURABLE_OWNER") or socket.gethostname()
+        db = os.getenv("CHDB_DURABLE_DB", "mem")
+
+        self._ns = cd.Namespace(url, owner=owner, db=db)
+        self._obj = self._ns.open(oid)
+        self._lock = threading.Lock()
+        self.db = db
+        self.oid = oid
+
+    def query(self, sql: str, fmt: str = "JSONCompact") -> str:
+        with self._lock:
+            if _is_write(sql):
+                self._obj.execute(sql)
+                self._obj.flush()  # RPO≈0: a committed write is durable at return
+                return ""
+            return self._obj.query(sql, fmt).data()
+
+    def checkpoint(self) -> None:
+        """Fold the WAL into a fresh base (call periodically / before shutdown)."""
+        with self._lock:
+            self._obj.checkpoint()
+
+    def close(self) -> None:
+        with self._lock:
+            self._obj.close()