Host: `safe.rs` is a flag in this process's memory, never written to disk, so the next normal start is back to the owner's setup. While it is on a site tab gets the tab bridge and nothing of the app's page layers: its document-start scripts are `SiteHooks::safe_init_scripts` (default: the bridge alone) instead of `init_scripts`; `site_page_loaded`, `tab_placed` and `tab_background` are not called; `page_scripts` is empty; `eval_in_site_tabs` does nothing. So no page runtime, plugins, theme, custom CSS, feature flags, fixes, hotfix data or words reach a page: the site runs as in a browser, and only the shell is the app's. It starts from the launch argument `--safe-mode` (for when the interface itself is broken), from Shift held while the app starts (Windows), or from the shell: `safe_mode_get` / `safe_mode_set {on}` (shell-only), where a switch rebuilds every tab webview (profiles marked stale, `tabs-rebuild` asks the shell for its layout) so document-start scripts change too. Tests: the argument, the flag, and that app.rs and host.rs gate every layer.
Frame: the app menu's "Restart in safe mode…" says what it does before anything reloads; while on, the titlebar shows an amber "Safe mode | Leave" chip (one click leaves) and the row reads "Leave safe mode"; the chrome drops its theme (and pane themes) and takes it back on leaving, without touching the first-frame cache. `features.safeMode` (on by default).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
