diff --git a/tests/unit/test_notebook_sync.py b/tests/unit/test_notebook_sync.py
index 1ecfc049..aaa29ce8 100644
--- a/tests/unit/test_notebook_sync.py
+++ b/tests/unit/test_notebook_sync.py
@@ -61,18 +61,26 @@ def test_sync_performs_delete_then_add(mock_nlm_path):
                     # Check list call
                     args, kwargs = mock_run.call_args_list[0]
                     assert "list" in args[0]
+                    assert "--json" in args[0]
+                    assert "--" in args[0]
                     assert notebook_id in args[0]
                     
                     # Check delete call
                     args, kwargs = mock_run.call_args_list[1]
                     assert "delete" in args[0]
+                    assert "-y" in args[0]
+                    assert "--" in args[0]
+                    assert notebook_id in args[0]
                     assert source_id in args[0]
                     
                     # Check add call
                     args, kwargs = mock_run.call_args_list[2]
                     assert "add" in args[0]
-                    assert "--text" in args[0]
-                    assert content in args[0]
+                    assert "--file" in args[0]
+                    assert str(digest_path) in args[0]
+                    assert "--wait" in args[0]
+                    assert "--" in args[0]
+                    assert notebook_id in args[0]
 
 def test_sync_adds_directly_when_none_exists(mock_nlm_path):
     """Should add new source directly if no existing one is found."""
diff --git a/tests/unit/test_security_notebook_sync.py b/tests/unit/test_security_notebook_sync.py
new file mode 100644
index 00000000..5403ac21
--- /dev/null
+++ b/tests/unit/test_security_notebook_sync.py
@@ -0,0 +1,107 @@
+import json
+import os
+import subprocess
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+import pytest
+from tradingagents.notebook_sync import sync_to_notebooklm
+
+@pytest.fixture
+def mock_nlm_path(tmp_path):
+    nlm = tmp_path / "nlm"
+    nlm.touch(mode=0o755)
+    return str(nlm)
+
+def test_security_argument_injection(mock_nlm_path, tmp_path):
+    """
+    Test that positional arguments starting with a hyphen are handled safely
+    and that content is passed via file to avoid ARG_MAX issues and injection.
+    """
+    # Malicious notebook_id that looks like a flag
+    notebook_id = "--some-flag"
+    digest_path = tmp_path / "malicious.md"
+    digest_path.write_text("Some content")
+    date = "2026-03-19"
+
+    with patch.dict(os.environ, {"NOTEBOOKLM_ID": notebook_id}):
+        with patch("shutil.which", return_value=mock_nlm_path):
+            with patch("subprocess.run") as mock_run:
+                # Mock 'source list'
+                list_result = MagicMock()
+                list_result.returncode = 0
+                list_result.stdout = "[]"
+
+                # Mock 'source add'
+                add_result = MagicMock()
+                add_result.returncode = 0
+
+                mock_run.side_effect = [list_result, add_result]
+
+                sync_to_notebooklm(digest_path, date)
+
+                # 1. Check 'source list' call
+                # Expected: [nlm, "source", "list", "--json", "--", notebook_id]
+                list_args = mock_run.call_args_list[0][0][0]
+                assert list_args[0] == mock_nlm_path
+                assert list_args[1:3] == ["source", "list"]
+                assert "--json" in list_args
+                assert "--" in list_args
+                # "--" should be before the notebook_id
+                dash_idx = list_args.index("--")
+                id_idx = list_args.index(notebook_id)
+                assert dash_idx < id_idx
+
+                # 2. Check 'source add' call
+                # Expected: [nlm, "source", "add", "--title", title, "--file", str(digest_path), "--wait", "--", notebook_id]
+                add_args = mock_run.call_args_list[1][0][0]
+                assert add_args[0] == mock_nlm_path
+                assert add_args[1:3] == ["source", "add"]
+                assert "--title" in add_args
+                assert "--file" in add_args
+                assert str(digest_path) in add_args
+                assert "--text" not in add_args  # Vulnerable --text should be gone
+                assert "--wait" in add_args
+                assert "--" in add_args
+
+                dash_idx = add_args.index("--")
+                id_idx = add_args.index(notebook_id)
+                assert dash_idx < id_idx
+
+def test_security_delete_injection(mock_nlm_path):
+    """Test that source_id in delete is also handled safely with --."""
+    notebook_id = "normal-id"
+    source_id = "--delete-everything"
+
+    with patch.dict(os.environ, {"NOTEBOOKLM_ID": notebook_id}):
+        with patch("shutil.which", return_value=mock_nlm_path):
+            with patch("subprocess.run") as mock_run:
+                # Mock 'source list' finding the malicious source_id
+                list_result = MagicMock()
+                list_result.returncode = 0
+                list_result.stdout = json.dumps([{"id": source_id, "title": "Daily Trading Digest (2026-03-19)"}])
+
+                # Mock 'source delete'
+                delete_result = MagicMock()
+                delete_result.returncode = 0
+
+                # Mock 'source add'
+                add_result = MagicMock()
+                add_result.returncode = 0
+
+                mock_run.side_effect = [list_result, delete_result, add_result]
+
+                sync_to_notebooklm(Path("test.md"), "2026-03-19")
+
+                # Check 'source delete' call
+                # Expected: [nlm, "source", "delete", "-y", "--", notebook_id, source_id]
+                delete_args = mock_run.call_args_list[1][0][0]
+                assert delete_args[1:3] == ["source", "delete"]
+                assert "-y" in delete_args
+                assert "--" in delete_args
+
+                dash_idx = delete_args.index("--")
+                id_idx = delete_args.index(notebook_id)
+                sid_idx = delete_args.index(source_id)
+                assert dash_idx < id_idx
+                assert dash_idx < sid_idx
diff --git a/tradingagents/notebook_sync.py b/tradingagents/notebook_sync.py
index 7610d5af..77674c19 100644
--- a/tradingagents/notebook_sync.py
+++ b/tradingagents/notebook_sync.py
@@ -51,7 +51,6 @@ def sync_to_notebooklm(digest_path: Path, date: str, notebook_id: str | None = N
         console.print("[yellow]Warning: nlm CLI not found — skipping NotebookLM sync[/yellow]")
         return
 
-    content = digest_path.read_text()
     title = f"Daily Trading Digest ({date})"
 
     # Find and delete existing source with the same title
@@ -60,14 +59,15 @@ def sync_to_notebooklm(digest_path: Path, date: str, notebook_id: str | None = N
         _delete_source(nlm, notebook_id, existing_source_id)
 
     # Add as a new source
-    _add_source(nlm, notebook_id, content, title)
+    _add_source(nlm, notebook_id, digest_path, title)
 
 
 def _find_source(nlm: str, notebook_id: str, title: str) -> str | None:
     """Return the source ID for the daily digest, or None if not found."""
     try:
+        # Use -- to separate options from positional arguments
         result = subprocess.run(
-            [nlm, "source", "list", notebook_id, "--json"],
+            [nlm, "source", "list", "--json", "--", notebook_id],
             capture_output=True,
             text=True,
         )
@@ -85,8 +85,9 @@ def _find_source(nlm: str, notebook_id: str, title: str) -> str | None:
 def _delete_source(nlm: str, notebook_id: str, source_id: str) -> None:
     """Delete an existing source."""
     try:
+        # Use -- to separate options from positional arguments
         subprocess.run(
-            [nlm, "source", "delete", notebook_id, source_id, "-y"],
+            [nlm, "source", "delete", "-y", "--", notebook_id, source_id],
             capture_output=True,
             text=True,
             check=False,  # Ignore non-zero exit since nlm sometimes fails even on success
@@ -95,11 +96,13 @@ def _delete_source(nlm: str, notebook_id: str, source_id: str) -> None:
         pass
 
 
-def _add_source(nlm: str, notebook_id: str, content: str, title: str) -> None:
+def _add_source(nlm: str, notebook_id: str, digest_path: Path, title: str) -> None:
     """Add content as a new source."""
     try:
+        # Use --file instead of --text to avoid ARG_MAX issues and shell injection.
+        # Use -- to separate options from positional arguments.
         result = subprocess.run(
-            [nlm, "source", "add", notebook_id, "--title", title, "--text", content, "--wait"],
+            [nlm, "source", "add", "--title", title, "--file", str(digest_path), "--wait", "--", notebook_id],
             capture_output=True,
             text=True,
         )