feat: add a permission-gated UI action registry and action slots for plugins

Moves the terminal toolbar's hardwired AI button into a slot the ssh-terminal
plugin offers and the ai plugin fills, gated on ai.services.use.

plugins/ai/frontend/index.mjs

@@ -13,26 +13,56 @@
  * tabUtils.tsx (railView === "ai", case "ai"), the same way the terminal's
  * tab is baked into Terminal.tsx rather than going through the generic tab
  * registry. What gates it is isTabTypeAvailable("ai") in
- * src/ui/shell/pluginLoader.ts's BUILT_IN_TABS_BY_PLUGIN map, which is
- * consulted directly by AppShell.tsx, CommandPalette.tsx and HostItem.tsx --
- * the same live mechanism ssh-terminal's "terminal" entry already uses.
+ * src/ui/shell/pluginLoader.ts's BUILT_IN_TABS_BY_PLUGIN map.
  *
- * register()/unregister() exist for parity with the other first-party
- * plugins' frontend halves. Nothing invokes them yet: there is no frontend
- * plugin loader (see src/ui/tests/sidebar/plugin-extension-seam.test.tsx),
- * and the "ai" surface does not need registerRailItem/registerTabComponent
- * in the first place, since it is gated through BUILT_IN_TABS_BY_PLUGIN
- * instead.
+ * What this file DOES contribute is the terminal toolbar's AI button, through
+ * the action registry: ai.openWithContext, declared in manifest.json and
+ * gated on ai.services.use. The button used to be hardwired into
+ * TerminalToolbar.tsx behind a showAiAssistant prop.
+ *
+ * There is still no frontend plugin loader, so nothing imports this file yet
+ * (see src/ui/tests/sidebar/plugin-extension-seam.test.tsx). Until one exists,
+ * pluginLoader.ts performs the same registration itself when the ai plugin is
+ * enabled. This file is the version that runs once a loader lands, and the two
+ * must be kept in step.
  */
 
 export const id = "ai";
 export const tabId = "ai";
+export const actionId = "ai.openWithContext";
 
-export async function register() {
-  // Nothing to register: "ai" is a built-in rail-view/tab gated through
-  // isTabTypeAvailable, not a runtime-registered surface. See the header.
+/** Asks the focused terminal to open its AI panel seeded with `context`. */
+export function openWithContext(context) {
+  window.dispatchEvent(
+    new CustomEvent("termix:ai:openWithContext", {
+      detail: { context: typeof context === "string" ? context : "" },
+    }),
+  );
 }
 
-export async function unregister() {
-  // Nothing to unregister; see register().
+export async function register({
+  registerAction,
+  registerSlotContribution,
+  icons,
+}) {
+  registerAction(actionId, openWithContext, {
+    permission: "ai.services.use",
+    pluginId: id,
+  });
+
+  registerSlotContribution("terminal.toolbar", {
+    actionId,
+    titleKey: "ai.assistant",
+    icon: icons.Bot,
+    kind: "button",
+    pluginId: id,
+  });
+}
+
+export async function unregister({
+  unregisterAction,
+  unregisterSlotContribution,
+}) {
+  unregisterSlotContribution("terminal.toolbar", actionId);
+  unregisterAction(actionId);
 }

plugins/ai/manifest.json

@@ -36,7 +36,18 @@
       "defaultForRole": {
         "admin": ["ai.services.use"]
       }
-    }
+    },
+    "actions": [
+      {
+        "id": "ai.openWithContext",
+        "titleKey": "ai.assistant",
+        "handler": "openWithContext",
+        "icon": "Bot",
+        "permission": "ai.services.use",
+        "slot": "terminal.toolbar",
+        "kind": "button"
+      }
+    ]
   },
   "sidecars": []
 }

plugins/ssh-terminal/frontend/index.mjs

@@ -12,10 +12,12 @@
 
 export const id = "ssh-terminal";
 export const tabId = "terminal";
+export const toolbarSlotId = "terminal.toolbar";
 
 export async function register({
   registerRailItem,
   registerTabComponent,
+  declareActionSlot,
   icons,
 }) {
   registerTabComponent(tabId, () =>
@@ -30,12 +32,18 @@ export async function register({
     labelKey: "nav.terminal",
     kind: "tab",
   });
+
+  // Offers other plugins a place in the terminal toolbar. The terminal does
+  // not know or care who fills it.
+  declareActionSlot({ id: toolbarSlotId, accepts: ["button"] });
 }
 
 export async function unregister({
   unregisterRailItem,
   unregisterTabComponent,
+  undeclareActionSlot,
 }) {
   unregisterRailItem(tabId);
   unregisterTabComponent(tabId);
+  undeclareActionSlot(toolbarSlotId);
 }

plugins/ssh-terminal/manifest.json

@@ -24,6 +24,12 @@
         "icon": "SquareTerminal",
         "openFrom": ["rail", "host-context-menu", "palette"]
       }
+    ],
+    "actionSlots": [
+      {
+        "id": "terminal.toolbar",
+        "accepts": ["button"]
+      }
     ]
   },
   "sidecars": []