The Electron shell boots by fetching / and extracting
window.__HERMES_SESSION_TOKEN__ to authenticate /api/ws
(dashboard-token.ts adoptServedDashboardToken). Headless serve 404'd
every path, so when the renderer's spawn token drifted from the
backend's live token — e.g. hermes update replaced the backend and the
env pin no longer matched — the renderer had no way to adopt the served
token, the WebSocket handshake failed, and the primary window
white-screened (#95575).
Serve a minimal token-only HTML page at the exact root path in
mount_spa()'s headless branch, matching the renderer's extraction regex.
Gate it on app.state.auth_required read at request time: a gated
(non-loopback / remote public_url) serve keeps returning the 404 JSON so
the session token never leaks past the loopback boundary. Every other
path stays 404 JSON — the SPA remains unserved.
Regression tests: TestHeadlessServeTokenPage (3 cases) — verified to
fail against the pre-fix headless branch.
Teknium
39a5aa91ed