Every existing plugin slot renders wherever it's placed in the page (a
toolbar row, an attachment's hover-action bar, etc.) and is constrained
by that spot's own CSS - fine for small controls, but there's no way
for a plugin to show a large custom UI (a graphical file browser, a
multi-step wizard) since even a position:fixed overlay rendered from
inside such a slot is clipped to the surrounding row's own layout, not
the real page (confirmed live building the webdav-storage plugin: a
folder browser rendered but was squeezed into an unusable sliver).
Adds:
- host-dialog.ts: new 'custom' DialogKind + awaitCustomDialog(), reusing
the existing confirm/alert/prompt queue plumbing.
- host-api.ts: 'ui.openDialog' API method.
- runtime.tsx: sandbox-side api.ui.openDialog(opts) proxy.
- plugin-types.ts: new 'plugin-dialog' SlotName - a plugin implements
this slot with its actual custom UI.
- plugin-dialog-host.tsx: renders the requested slot via the existing
PluginIframeSlot INSIDE the dialog's real app-root fixed overlay
(position: fixed; inset: 0, above everything) instead of the
confirm/prompt form, for kind: 'custom'. Resolves via a generic
onResult callback in extraProps (marshalled the same way
composer-attachment-source's onAttach already is - no new plumbing
needed there).
A plugin calls api.ui.openDialog({ slot: 'plugin-dialog', extraProps,
title, width }) and awaits the Promise, which resolves to whatever its
own slot component passes to props.onResult(), or null if the user
closes the dialog without doing so.
The plugin runtime received the active locale (init payload + 'locale-change')
and plugins could declare a `locales` map, but none of it was usable: the
locales never reached the runtime, and buildPluginApi exposed no i18n. So
plugin code calling pluginApi.i18n.t(...) (as the External Link Warning plugin
does) always got undefined and fell back to English.
Thread plugin locales end to end and surface an i18n API:
- ServerPlugin gains `locales`; the upload route persists manifest.locales
(alongside configSchema/settingsSchema), and /api/plugins surfaces it to the
client so it flows registry -> client -> sandbox host-bridge -> runtime.
- runtime sets __PLUGIN_LOCALE__ at init (not only on later 'locale-change')
and buildPluginApi exposes `i18n.locale` + `i18n.t(key, vars)` resolving
against the plugin's declared locales (manifest.locales) with English/key
fallback and {placeholder} interpolation.
Lets any sandboxed plugin localize its strings from its manifest.