diff --git a/muxplex/main.py b/muxplex/main.py
index bacbb30..345f636 100644
--- a/muxplex/main.py
+++ b/muxplex/main.py
@@ -17,6 +17,7 @@ import logging
 import os
 import pathlib
 import pwd
+import re
 import socket
 import ssl
 import shutil
@@ -527,6 +528,15 @@ _FRONTEND_DIR = pathlib.Path(__file__).parent / "frontend"
 # which machine each muxplex instance is running on.
 _HOSTNAME = socket.gethostname().split(".")[0]
 
+# Canonical version string — sourced from package metadata (same as `app.version`
+# and the `doctor` command).  Used to append `?v=<version>` to every static-asset
+# URL so browsers immediately pick up new code on each release.
+_UI_VERSION: str = importlib.metadata.version("muxplex")
+
+# Matches src="/<path>" and href="/<path>" in served HTML, excluding /api/ URLs.
+# Used by index_page() to inject cache-busting version query parameters.
+_ASSET_URL_RE = re.compile(r'((?:src|href)=")((?!/api/)/[^"?#]*)')
+
 
 # ---------------------------------------------------------------------------
 # Routes
@@ -1204,12 +1214,22 @@ async def federation_terminal_ws_proxy(websocket: WebSocket, device_id: str) ->
 @app.get("/", response_class=HTMLResponse)
 @app.get("/index.html", response_class=HTMLResponse)
 async def index_page():
-    """Serve index.html with hostname injected into the page title."""
+    """Serve index.html with hostname injected into the page title.
+
+    Also appends ``?v=<version>`` to every static-asset URL (script src, link
+    href) so browsers immediately pick up new code on each release rather than
+    serving stale JS/CSS from the HTTP cache.  API URLs (/api/...) are
+    excluded — they are not HTTP-cached by browsers.
+    """
     html = (_FRONTEND_DIR / "index.html").read_text()
     html = html.replace(
         "<title>muxplex</title>",
         f"<title>{_HOSTNAME} \u2014 muxplex</title>",
     )
+    html = _ASSET_URL_RE.sub(
+        lambda m: f"{m.group(1)}{m.group(2)}?v={_UI_VERSION}",
+        html,
+    )
     return HTMLResponse(html)
 
 
diff --git a/muxplex/tests/test_main.py b/muxplex/tests/test_main.py
new file mode 100644
index 0000000..d4b1171
--- /dev/null
+++ b/muxplex/tests/test_main.py
@@ -0,0 +1,177 @@
+"""
+Tests for the cache-busting version suffix on static asset URLs served by index_page().
+
+Verifies that GET / (the main dashboard) injects ?v=<version> on every
+<script src="…"> and <link href="…"> URL so browsers pick up new code
+immediately after each release, rather than serving stale JS/CSS from
+the HTTP cache.
+"""
+
+import importlib.metadata
+
+import pytest
+from bs4 import BeautifulSoup
+from fastapi.testclient import TestClient
+
+from muxplex.main import app
+
+
+# ---------------------------------------------------------------------------
+# Shared fixtures (mirror test_api.py setup so tests run cleanly in isolation)
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture(autouse=True)
+def patch_startup_and_state(tmp_path, monkeypatch):
+    """Redirect state/PID files to tmp_path and stub out long-running startup tasks."""
+    tmp_state_dir = tmp_path / "state"
+    tmp_state_path = tmp_state_dir / "state.json"
+    monkeypatch.setattr("muxplex.state.STATE_DIR", tmp_state_dir)
+    monkeypatch.setattr("muxplex.state.STATE_PATH", tmp_state_path)
+
+    tmp_pid_dir = tmp_path / "ttyd"
+    tmp_pid_path = tmp_pid_dir / "ttyd.pid"
+    monkeypatch.setattr("muxplex.ttyd.TTYD_PID_DIR", tmp_pid_dir)
+    monkeypatch.setattr("muxplex.ttyd.TTYD_PID_PATH", tmp_pid_path)
+
+    async def _mock_kill_orphan():
+        return False
+
+    monkeypatch.setattr("muxplex.main.kill_orphan_ttyd", _mock_kill_orphan)
+
+    async def noop_poll_loop() -> None:
+        pass
+
+    monkeypatch.setattr("muxplex.main._poll_loop", noop_poll_loop)
+
+
+@pytest.fixture(autouse=True)
+def reset_federation_cache():
+    """Clear _federation_cache before and after each test."""
+    import muxplex.main as main_mod
+
+    main_mod._federation_cache.clear()
+    yield
+    main_mod._federation_cache.clear()
+
+
+@pytest.fixture
+def client(monkeypatch):
+    """Authenticated TestClient with the app lifespan active."""
+    monkeypatch.setenv("MUXPLEX_PASSWORD", "test-password")
+    with TestClient(app) as c:
+        from muxplex.auth import create_session_cookie
+        from muxplex.main import _auth_secret, _auth_ttl
+
+        cookie = create_session_cookie(_auth_secret, _auth_ttl)
+        c.cookies.set("muxplex_session", cookie)
+        yield c
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _get_index_soup(client) -> BeautifulSoup:
+    response = client.get("/")
+    assert response.status_code == 200, f"GET / returned {response.status_code}"
+    return BeautifulSoup(response.text, "html.parser")
+
+
+# ---------------------------------------------------------------------------
+# Test 1 — every script src and link href carries the version suffix
+# ---------------------------------------------------------------------------
+
+
+def test_index_all_asset_urls_have_version_suffix(client):
+    """GET / must inject ?v=<version> on every <script src> and <link href> asset URL.
+
+    Regression guard for the "is the user seeing stale JS?" investigation:
+    verifies that the standard HTTP cache is busted on every release by
+    appending a version query parameter to each static asset reference.
+    """
+    version = importlib.metadata.version("muxplex")
+    soup = _get_index_soup(client)
+
+    # All <script src="…"> tags
+    script_tags = soup.find_all("script", src=True)
+    assert len(script_tags) >= 7, (
+        f"Expected at least 7 <script src> tags, found {len(script_tags)}"
+    )
+    for tag in script_tags:
+        src = tag["src"]
+        assert f"?v={version}" in src, (
+            f"<script src> missing ?v={version} suffix: {src!r}"
+        )
+
+    # All <link href="…"> tags
+    link_tags = soup.find_all("link", href=True)
+    assert len(link_tags) >= 1, "Expected at least one <link href> tag"
+    for tag in link_tags:
+        href = tag["href"]
+        assert f"?v={version}" in href, (
+            f"<link href> missing ?v={version} suffix: {href!r}"
+        )
+
+
+# ---------------------------------------------------------------------------
+# Test 2 — vendor scripts are individually versioned (not just app.js)
+# ---------------------------------------------------------------------------
+
+
+def test_index_vendor_scripts_each_versioned(client):
+    """All five vendor JS bundles must carry the version suffix, not just app.js.
+
+    The browser-tester on spark-1 observed bare vendor URLs.  This test
+    ensures that xterm.js and its addons are cache-busted alongside the
+    first-party scripts.
+    """
+    version = importlib.metadata.version("muxplex")
+    soup = _get_index_soup(client)
+
+    script_srcs = [tag["src"] for tag in soup.find_all("script", src=True)]
+
+    expected_versioned = [
+        f"/vendor/xterm.js?v={version}",
+        f"/vendor/xterm-addon-fit.js?v={version}",
+        f"/vendor/xterm-addon-web-links.js?v={version}",
+        f"/vendor/xterm-addon-search.js?v={version}",
+        f"/vendor/addon-image.js?v={version}",
+        f"/app.js?v={version}",
+        f"/terminal.js?v={version}",
+    ]
+    for expected in expected_versioned:
+        assert expected in script_srcs, (
+            f"Expected versioned script {expected!r}; found srcs: {script_srcs}"
+        )
+
+
+# ---------------------------------------------------------------------------
+# Test 3 — versioned asset URLs still resolve to the actual static files
+# ---------------------------------------------------------------------------
+
+
+def test_versioned_asset_url_resolves_to_static_file(client):
+    """GET /app.js?v=<version> must return HTTP 200 (static handler ignores query string).
+
+    Sanity check: adding the version suffix must not break asset loading.
+    Starlette's StaticFiles handler ignores query parameters when looking up
+    files on disk, so the versioned URL must serve identically to the bare URL.
+    """
+    version = importlib.metadata.version("muxplex")
+
+    # First-party assets
+    for path in ("/app.js", "/terminal.js", "/style.css"):
+        url = f"{path}?v={version}"
+        resp = client.get(url)
+        assert resp.status_code == 200, (
+            f"Versioned URL {url!r} returned {resp.status_code}, expected 200"
+        )
+
+    # Vendor asset
+    vendor_url = f"/vendor/xterm.js?v={version}"
+    resp = client.get(vendor_url)
+    assert resp.status_code == 200, (
+        f"Versioned vendor URL {vendor_url!r} returned {resp.status_code}, expected 200"
+    )