diff --git a/apps/server/package.json b/apps/server/package.json
index cf243b40c1071..25d57720deec4 100644
--- a/apps/server/package.json
+++ b/apps/server/package.json
@@ -69,7 +69,8 @@
     "stream-json": "3.6.0",
     "undici": "catalog:",
     "yaml": "catalog:",
-    "yauzl": "^3.4.0"
+    "yauzl": "^3.4.0",
+    "zod": "^4.6.5"
   },
   "devDependencies": {
     "@effect/graphql-generator": "catalog:",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index dbd9dfa57bb33..61af37debf8e7 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -940,6 +940,9 @@ importers:
       yauzl:
         specifier: ^3.4.0
         version: 3.4.0
+      zod:
+        specifier: ^4.6.5
+        version: 4.6.5
     devDependencies:
       '@effect/graphql-generator':
         specifier: 'catalog:'
diff --git a/scripts/lib/cli-external-packages.test.ts b/scripts/lib/cli-external-packages.test.ts
index b55e3a9c10c18..09803de29e70c 100644
--- a/scripts/lib/cli-external-packages.test.ts
+++ b/scripts/lib/cli-external-packages.test.ts
@@ -12,6 +12,7 @@ import { findEsmImportsOfExternalPackages } from "./cli-executable-imports.ts";
 import {
   isRuntimeExternalCliDependency,
   findInlinedExternalPackages,
+  selectCliRuntimeExternalDependencies,
   shouldBundleCliDependency,
 } from "./cli-external-packages.ts";
 
@@ -20,6 +21,9 @@ const PackageManifest = Schema.Struct({
   dependencies: Schema.optional(Schema.Record(Schema.String, Schema.String)),
   optionalDependencies: Schema.optional(Schema.Record(Schema.String, Schema.String)),
   peerDependencies: Schema.optional(Schema.Record(Schema.String, Schema.String)),
+  peerDependenciesMeta: Schema.optional(
+    Schema.Record(Schema.String, Schema.Struct({ optional: Schema.optional(Schema.Boolean) })),
+  ),
 });
 type PackageManifest = typeof PackageManifest.Type;
 
@@ -120,6 +124,47 @@ it.layer(NodeServices.layer)("external package dependency closure", (it) => {
       );
     }),
   );
+
+  // The stage installs only externals the server lists, so a required peer must be reachable from them.
+  it.effect("stages a provider for every required peer of a staged external", () =>
+    Effect.gen(function* () {
+      const fileSystem = yield* FileSystem.FileSystem;
+      const path = yield* Path.Path;
+      const installed = yield* readInstalledPackages;
+      const server = decodeManifest(
+        yield* fileSystem.readFileString(
+          path.resolve(
+            path.dirname(NodeURL.fileURLToPath(import.meta.url)),
+            "../../apps/server/package.json",
+          ),
+        ),
+      );
+
+      const staged = new Set<string>();
+      const queue = Object.keys(selectCliRuntimeExternalDependencies(server.dependencies ?? {}));
+      for (const name of queue) {
+        if (staged.has(name)) continue;
+        staged.add(name);
+        const manifest = installed.get(name);
+        queue.push(
+          ...Object.keys({ ...manifest?.dependencies, ...manifest?.optionalDependencies }),
+        );
+      }
+
+      const missing = [...staged].flatMap((name) => {
+        const manifest = installed.get(name);
+        return Object.keys(manifest?.peerDependencies ?? {})
+          .filter((peer) => !manifest?.peerDependenciesMeta?.[peer]?.optional && !staged.has(peer))
+          .map((peer) => `${name} -> ${peer}`);
+      });
+
+      assert.deepStrictEqual(
+        missing,
+        [],
+        `these peers of staged external packages are missing from the packaged app; add them to apps/server dependencies: ${missing.join(", ")}`,
+      );
+    }),
+  );
 });
 
 describe("findInlinedExternalPackages", () => {