diff --git a/bun.lock b/bun.lock
index 568f1260d..861a623b2 100644
--- a/bun.lock
+++ b/bun.lock
@@ -63,8 +63,12 @@
       "peerDependencies": {
         "@earendil-works/pi-coding-agent": "*",
         "@earendil-works/pi-tui": "*",
+        "@ff-labs/fff-bun": "*",
         "@sinclair/typebox": "*",
       },
+      "optionalPeers": [
+        "@ff-labs/fff-bun",
+      ],
     },
   },
   "packages": {
diff --git a/packages/pi-fff/package.json b/packages/pi-fff/package.json
index 04a250cb7..bf40c6928 100644
--- a/packages/pi-fff/package.json
+++ b/packages/pi-fff/package.json
@@ -45,8 +45,14 @@
   "peerDependencies": {
     "@earendil-works/pi-coding-agent": "*",
     "@earendil-works/pi-tui": "*",
+    "@ff-labs/fff-bun": "*",
     "@sinclair/typebox": "*"
   },
+  "peerDependenciesMeta": {
+    "@ff-labs/fff-bun": {
+      "optional": true
+    }
+  },
   "devDependencies": {
     "@types/node": "^22.0.0",
     "typescript": "^5.0.0"
diff --git a/packages/pi-fff/src/index.ts b/packages/pi-fff/src/index.ts
index 86eff2329..6d8ea80ca 100644
--- a/packages/pi-fff/src/index.ts
+++ b/packages/pi-fff/src/index.ts
@@ -12,16 +12,49 @@ import {
   Text,
 } from "@earendil-works/pi-tui";
 import type {
+  FileFinderApi,
   GrepCursor,
   GrepMode,
   GrepResult,
+  InitOptions,
   MixedItem,
+  Result,
   SearchResult,
 } from "@ff-labs/fff-node";
-import { FileFinder } from "@ff-labs/fff-node";
 import { Type } from "@sinclair/typebox";
 import { buildQuery } from "./query";
 
+// Isomorphic SDK loading. pi hosts run under either bun (omp / oh-my-pi) or
+// node; the two SDKs implement the same FileFinderApi. Static imports of
+// @ff-labs/fff-node pull ffi-rs + optional native binaries into the module
+// graph, which trips oh-my-pi's static extension validator (issue #668). We
+// defeat static resolution with a variable-name dynamic import.
+type FileFinderStatic = {
+  create(options: InitOptions): Result<FileFinderApi>;
+};
+
+let sdkPromise: Promise<{ FileFinder: FileFinderStatic }> | null = null;
+
+function detectRuntime(): "bun" | "node" {
+  if (typeof (globalThis as { Bun?: unknown }).Bun !== "undefined") return "bun";
+  if (
+    typeof process !== "undefined" &&
+    (process as { versions?: { bun?: string } }).versions?.bun
+  )
+    return "bun";
+  return "node";
+}
+
+function loadSdk(): Promise<{ FileFinder: FileFinderStatic }> {
+  if (sdkPromise) return sdkPromise;
+  // Fail loud on wrong-runtime SDK rather than falling back — a fallback would
+  // re-introduce the ffi-rs cost on bun (the whole point of the bun SDK is to
+  // avoid it) and mask packaging bugs where the correct SDK wasn't installed.
+  const pkg = detectRuntime() === "bun" ? "@ff-labs/fff-bun" : "@ff-labs/fff-node";
+  sdkPromise = import(pkg) as Promise<{ FileFinder: FileFinderStatic }>;
+  return sdkPromise;
+}
+
 // ---------------------------------------------------------------------------
 // Constants
 // ---------------------------------------------------------------------------
@@ -277,13 +310,13 @@ function createFffMentionProvider(
 // ---------------------------------------------------------------------------
 
 export default function fffExtension(pi: ExtensionAPI) {
-  let finder: FileFinder | null = null;
+  let finder: FileFinderApi | null = null;
   let finderCwd: string | null = null;
   // Concurrent ensureFinder() callers share the same in-flight promise so
   // FileFinder.create() (which takes native DB locks) runs at most once per
   // base path at a time — otherwise parallel tool calls would race and
   // deadlock at the native layer (issue #403).
-  let finderPromise: Promise<FileFinder> | null = null;
+  let finderPromise: Promise<FileFinderApi> | null = null;
   let activeCwd = process.cwd();
 
   // Mode resolution: flag > env > default
@@ -331,7 +364,7 @@ export default function fffExtension(pi: ExtensionAPI) {
     return currentMode !== "tools-only";
   }
 
-  function ensureFinder(cwd: string): Promise<FileFinder> {
+  function ensureFinder(cwd: string): Promise<FileFinderApi> {
     if (finder && !finder.isDestroyed && finderCwd === cwd)
       return Promise.resolve(finder);
     if (finderPromise) return finderPromise;
@@ -343,6 +376,7 @@ export default function fffExtension(pi: ExtensionAPI) {
         finderCwd = null;
       }
 
+      const { FileFinder } = await loadSdk();
       const result = FileFinder.create({
         basePath: cwd,
         frecencyDbPath,
diff --git a/packages/pi-fff/test/extension.test.ts b/packages/pi-fff/test/extension.test.ts
index 3695a84e0..c0d351c6e 100644
--- a/packages/pi-fff/test/extension.test.ts
+++ b/packages/pi-fff/test/extension.test.ts
@@ -34,7 +34,7 @@ function createMockFinder(): MockFinder {
   };
 }
 
-mock.module("@ff-labs/fff-node", () => ({
+const finderModule = {
   FileFinder: {
     create: mock((options: unknown) => {
       createCalls.push(options);
@@ -43,7 +43,10 @@ mock.module("@ff-labs/fff-node", () => ({
       return { ok: true, value: finder };
     }),
   },
-}));
+};
+
+mock.module("@ff-labs/fff-node", () => finderModule);
+mock.module("@ff-labs/fff-bun", () => finderModule);
 
 mock.module("@earendil-works/pi-tui", () => ({
   Text: class Text {