diff --git a/tests/infrastructure/test_chat_store.py b/tests/infrastructure/test_chat_store.py
new file mode 100644
index 00000000..0846af9c
--- /dev/null
+++ b/tests/infrastructure/test_chat_store.py
@@ -0,0 +1,247 @@
+"""Unit tests for src/infrastructure/chat_store.py."""
+
+import sqlite3
+import threading
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+from src.infrastructure.chat_store import MAX_MESSAGES, Message, MessageLog, _get_conn
+
+pytestmark = pytest.mark.unit
+
+
+@pytest.fixture()
+def tmp_db(tmp_path: Path) -> Path:
+    """Return a temporary database path."""
+    return tmp_path / "test_chat.db"
+
+
+@pytest.fixture()
+def log(tmp_db: Path) -> MessageLog:
+    """Return a MessageLog backed by a temp database."""
+    ml = MessageLog(db_path=tmp_db)
+    yield ml
+    ml.close()
+
+
+# ── Message dataclass ──────────────────────────────────────────────────
+
+
+class TestMessage:
+    def test_default_source(self):
+        m = Message(role="user", content="hi", timestamp="2026-01-01T00:00:00")
+        assert m.source == "browser"
+
+    def test_custom_source(self):
+        m = Message(role="agent", content="ok", timestamp="t1", source="telegram")
+        assert m.source == "telegram"
+
+    def test_fields(self):
+        m = Message(role="error", content="boom", timestamp="t2", source="api")
+        assert m.role == "error"
+        assert m.content == "boom"
+        assert m.timestamp == "t2"
+
+
+# ── _get_conn context manager ──────────────────────────────────────────
+
+
+class TestGetConn:
+    def test_creates_db_and_table(self, tmp_db: Path):
+        with _get_conn(tmp_db) as conn:
+            tables = conn.execute(
+                "SELECT name FROM sqlite_master WHERE type='table'"
+            ).fetchall()
+            names = [t["name"] for t in tables]
+            assert "chat_messages" in names
+
+    def test_creates_parent_dirs(self, tmp_path: Path):
+        deep = tmp_path / "a" / "b" / "c" / "chat.db"
+        with _get_conn(deep) as conn:
+            assert deep.parent.exists()
+
+    def test_connection_closed_after_context(self, tmp_db: Path):
+        with _get_conn(tmp_db) as conn:
+            conn.execute("SELECT 1")
+        # Connection should be closed — operations should fail
+        with pytest.raises(Exception):
+            conn.execute("SELECT 1")
+
+
+# ── MessageLog core operations ─────────────────────────────────────────
+
+
+class TestMessageLogAppendAndAll:
+    def test_append_and_all(self, log: MessageLog):
+        log.append("user", "hello", "t1")
+        log.append("agent", "hi back", "t2", source="api")
+        msgs = log.all()
+        assert len(msgs) == 2
+        assert msgs[0].role == "user"
+        assert msgs[0].content == "hello"
+        assert msgs[0].source == "browser"
+        assert msgs[1].role == "agent"
+        assert msgs[1].source == "api"
+
+    def test_all_returns_ordered_by_id(self, log: MessageLog):
+        for i in range(5):
+            log.append("user", f"msg{i}", f"t{i}")
+        msgs = log.all()
+        assert [m.content for m in msgs] == [f"msg{i}" for i in range(5)]
+
+    def test_all_empty_store(self, log: MessageLog):
+        assert log.all() == []
+
+
+class TestMessageLogRecent:
+    def test_recent_returns_newest(self, log: MessageLog):
+        for i in range(10):
+            log.append("user", f"msg{i}", f"t{i}")
+        recent = log.recent(limit=3)
+        assert len(recent) == 3
+        assert recent[0].content == "msg7"
+        assert recent[2].content == "msg9"
+
+    def test_recent_oldest_first(self, log: MessageLog):
+        for i in range(5):
+            log.append("user", f"msg{i}", f"t{i}")
+        recent = log.recent(limit=3)
+        # Should be oldest-first within the window
+        assert recent[0].content == "msg2"
+        assert recent[1].content == "msg3"
+        assert recent[2].content == "msg4"
+
+    def test_recent_more_than_exists(self, log: MessageLog):
+        log.append("user", "only", "t0")
+        recent = log.recent(limit=100)
+        assert len(recent) == 1
+
+    def test_recent_empty_store(self, log: MessageLog):
+        assert log.recent() == []
+
+
+class TestMessageLogClear:
+    def test_clear_removes_all(self, log: MessageLog):
+        for i in range(5):
+            log.append("user", f"msg{i}", f"t{i}")
+        assert len(log) == 5
+        log.clear()
+        assert len(log) == 0
+        assert log.all() == []
+
+    def test_clear_empty_store(self, log: MessageLog):
+        log.clear()  # Should not raise
+        assert len(log) == 0
+
+
+class TestMessageLogLen:
+    def test_len_empty(self, log: MessageLog):
+        assert len(log) == 0
+
+    def test_len_after_appends(self, log: MessageLog):
+        for i in range(7):
+            log.append("user", f"msg{i}", f"t{i}")
+        assert len(log) == 7
+
+
+class TestMessageLogClose:
+    def test_close_sets_conn_none(self, tmp_db: Path):
+        ml = MessageLog(db_path=tmp_db)
+        ml.append("user", "x", "t0")
+        ml.close()
+        assert ml._conn is None
+
+    def test_close_idempotent(self, tmp_db: Path):
+        ml = MessageLog(db_path=tmp_db)
+        ml.close()
+        ml.close()  # Should not raise
+
+    def test_reopen_after_close(self, tmp_db: Path):
+        ml = MessageLog(db_path=tmp_db)
+        ml.append("user", "before", "t0")
+        ml.close()
+        # Should reconnect on next use
+        ml.append("user", "after", "t1")
+        assert len(ml) == 2
+        ml.close()
+
+
+# ── Pruning ────────────────────────────────────────────────────────────
+
+
+class TestPrune:
+    def test_prune_keeps_max_messages(self, tmp_db: Path):
+        with patch("src.infrastructure.chat_store.MAX_MESSAGES", 5):
+            ml = MessageLog(db_path=tmp_db)
+            for i in range(10):
+                ml.append("user", f"msg{i}", f"t{i}")
+            # Should have pruned to 5
+            assert len(ml) == 5
+            msgs = ml.all()
+            # Oldest should be pruned, newest kept
+            assert msgs[0].content == "msg5"
+            assert msgs[-1].content == "msg9"
+            ml.close()
+
+    def test_no_prune_under_limit(self, tmp_db: Path):
+        with patch("src.infrastructure.chat_store.MAX_MESSAGES", 100):
+            ml = MessageLog(db_path=tmp_db)
+            for i in range(10):
+                ml.append("user", f"msg{i}", f"t{i}")
+            assert len(ml) == 10
+            ml.close()
+
+
+# ── Thread safety ──────────────────────────────────────────────────────
+
+
+class TestThreadSafety:
+    def test_concurrent_appends(self, tmp_db: Path):
+        ml = MessageLog(db_path=tmp_db)
+        errors = []
+
+        def writer(start: int):
+            try:
+                for i in range(20):
+                    ml.append("user", f"msg{start + i}", f"t{start + i}")
+            except Exception as e:
+                errors.append(e)
+
+        threads = [threading.Thread(target=writer, args=(i * 20,)) for i in range(5)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
+        assert not errors, f"Thread errors: {errors}"
+        assert len(ml) == 100
+        ml.close()
+
+
+# ── Edge cases ─────────────────────────────────────────────────────────
+
+
+class TestEdgeCases:
+    def test_empty_content(self, log: MessageLog):
+        log.append("user", "", "t0")
+        msgs = log.all()
+        assert len(msgs) == 1
+        assert msgs[0].content == ""
+
+    def test_unicode_content(self, log: MessageLog):
+        log.append("user", "こんにちは 🎉 مرحبا", "t0")
+        msgs = log.all()
+        assert msgs[0].content == "こんにちは 🎉 مرحبا"
+
+    def test_multiline_content(self, log: MessageLog):
+        content = "line1\nline2\nline3"
+        log.append("user", content, "t0")
+        assert log.all()[0].content == content
+
+    def test_special_sql_characters(self, log: MessageLog):
+        log.append("user", "Robert'; DROP TABLE chat_messages;--", "t0")
+        msgs = log.all()
+        assert len(msgs) == 1
+        assert "DROP TABLE" in msgs[0].content