diff --git a/src/gui/app.py b/src/gui/app.py
index 2ace7bf..53693be 100644
--- a/src/gui/app.py
+++ b/src/gui/app.py
@@ -24,6 +24,7 @@ if str(_project_root) not in sys.path:
 from src.gui.components import (
     findings_count_for_tool,
     hide_streamlit_chrome,
+    quit_button,
     upload_and_analyze_section,
 )
 
@@ -87,7 +88,11 @@ for row_start in range(0, len(TOOLS), 3):
 # ---------------------------------------------------------------------------
 
 st.divider()
-st.caption(
-    "Runs locally. Your data never leaves this computer. "
-    "| DataTools v3.0"
-)
+footer_left, footer_right = st.columns([4, 1])
+with footer_left:
+    st.caption(
+        "Runs locally. Your data never leaves this computer. "
+        "| DataTools v3.0"
+    )
+with footer_right:
+    quit_button()
diff --git a/src/gui/components/__init__.py b/src/gui/components/__init__.py
index 0b7c26a..ede0990 100644
--- a/src/gui/components/__init__.py
+++ b/src/gui/components/__init__.py
@@ -41,6 +41,7 @@ from . import _legacy as _legacy  # noqa: F401  (keep for direct access)
 __all__ = [
     # Shared chrome / pickup / gate
     "hide_streamlit_chrome",
+    "quit_button",
     "pickup_or_upload",
     "require_normalization_gate",
     # Dedup widgets
diff --git a/src/gui/components/_legacy.py b/src/gui/components/_legacy.py
index 6892077..b38de87 100644
--- a/src/gui/components/_legacy.py
+++ b/src/gui/components/_legacy.py
@@ -3,6 +3,8 @@
 from __future__ import annotations
 
 import io
+import os
+import signal
 from typing import Optional
 
 import pandas as pd
@@ -30,25 +32,31 @@ from src.core.normalizers import NormalizerType
 
 _HIDE_CHROME_CSS = """
 <style>
-/* Hide Streamlit header bar */
+/* Make the Streamlit header transparent and out of the way, but DO NOT
+   `display: none` it — the sidebar's collapsed-state expand button is
+   anchored in the header region, and removing the header makes a
+   collapsed sidebar impossible to reopen. */
 header[data-testid="stHeader"] {
+    background: transparent !important;
+    height: 0 !important;
+}
+/* Hide main hamburger menu and deploy button explicitly (don't rely on
+   hiding the whole header). */
+#MainMenu,
+[data-testid="stMainMenu"],
+[data-testid="stAppDeployButton"] {
     display: none !important;
 }
-/* Hide hamburger menu */
-button[kind="header"] {
-    display: none !important;
-}
-#MainMenu {
-    display: none !important;
+/* Keep the sidebar expand control visible and clickable above page content. */
+[data-testid="stSidebarCollapsedControl"] {
+    display: flex !important;
+    visibility: visible !important;
+    z-index: 999 !important;
 }
 /* Hide footer */
 footer {
     display: none !important;
 }
-/* Hide deploy button */
-[data-testid="stAppDeployButton"] {
-    display: none !important;
-}
 /* Reclaim top padding lost from hidden header */
 .stAppViewBlockContainer,
 [data-testid="stAppViewBlockContainer"] {
@@ -67,6 +75,31 @@ def hide_streamlit_chrome() -> None:
     st.markdown(_HIDE_CHROME_CSS, unsafe_allow_html=True)
 
 
+# ---------------------------------------------------------------------------
+# Clean shutdown
+# ---------------------------------------------------------------------------
+
+def quit_button(label: str = "Quit app", *, key: str = "quit_app_button") -> None:
+    """Render a Quit button that terminates the Streamlit server.
+
+    Streamlit has no first-class shutdown hook, so closing the browser tab
+    leaves the server (and the python process running it) alive — the user
+    has to Ctrl+C in the shell. This helper signals the Streamlit process
+    so the shell returns cleanly. SIGTERM lets Streamlit run its own
+    shutdown handlers; if that's unavailable on the platform, fall back to
+    SIGINT (the same signal Ctrl+C delivers).
+    """
+    if st.session_state.get("_app_shutting_down"):
+        st.success("App shut down. You can close this browser tab.")
+        st.stop()
+
+    if st.button(label, key=key, type="secondary"):
+        st.session_state["_app_shutting_down"] = True
+        sig = getattr(signal, "SIGTERM", signal.SIGINT)
+        os.kill(os.getpid(), sig)
+        st.rerun()
+
+
 # ---------------------------------------------------------------------------
 # Config panel (advanced options)
 # ---------------------------------------------------------------------------