feat: add cross-plugin secret references gated by the provider's RBAC permission

plugins/ai/backend/index.mjs

@@ -54,6 +54,28 @@ export async function activate(ctx) {
   routesModule = await loadRelative("routes");
   routesModule.startAiService();
 
+  // Offered by reference, not copied: this hands over a resolver, so the key
+  // stays ours. Rotating or deleting the provider takes effect on the next
+  // read by any borrower, and deactivate() below withdraws the offer entirely.
+  // The resolve is per-user because the keys are stored per-user and encrypted
+  // under that user's data key, so a borrowed read returns the acting user's
+  // own default key, never someone else's.
+  ctx.secrets.offer("api-key", async (userId) => {
+    const { createCurrentAiRepository } = await loadRelative(
+      "../../../backend/backend/database/repositories/factory",
+    );
+    const repository = createCurrentAiRepository();
+    const providers = await repository.listProviders(userId);
+    const preferred = providers.find((provider) => provider.apiKeyPrefix);
+    if (!preferred) return null;
+
+    const withSecret = await repository.findProviderWithSecret(
+      preferred.id,
+      userId,
+    );
+    return withSecret?.apiKey ?? null;
+  });
+
   ctx.log.info("AI assistant router registered at /ai");
 }