diff --git a/scripts/build/colocateOptionals.mjs b/scripts/build/colocateOptionals.mjs
index 91548954b0..367a95c112 100644
--- a/scripts/build/colocateOptionals.mjs
+++ b/scripts/build/colocateOptionals.mjs
@@ -47,7 +47,8 @@
  */
 
 import { cpSync, existsSync, mkdirSync, readFileSync } from "node:fs";
-import { dirname, join } from "node:path";
+import { createRequire } from "node:module";
+import { dirname, join, sep } from "node:path";
 
 /**
  * Entry packages of the SLM optional stack (the closure roots). `@huggingface/transformers` is
@@ -96,6 +97,33 @@ export function computeDependencyClosure(nodeModulesDir, seeds = SEED_PACKAGES)
   return closure;
 }
 
+/**
+ * A package in the target tree counts as PRESENT only when its entrypoint
+ * resolves from inside that tree — the same contract the Dockerfile's
+ * post-build guard enforces. Next's file tracing can materialize a package
+ * PARTIALLY (the package.json lands, the files its `main` points at do not),
+ * and a directory-level `existsSync` check then skips the package forever
+ * while the runtime dies with "Cannot find module <pkg>/dist/index.js".
+ *
+ * @param {string} targetNodeModulesDir
+ * @param {string} name
+ * @returns {boolean}
+ */
+function isPackageIntact(targetNodeModulesDir, name) {
+  if (!existsSync(join(targetNodeModulesDir, name))) return false;
+  try {
+    const probe = createRequire(
+      join(targetNodeModulesDir, "__colocate_probe__.js")
+    );
+    const resolved = probe.resolve(name);
+    // A resolution that walked past the target into an ancestor tree does not
+    // prove the target copy is usable.
+    return resolved.startsWith(targetNodeModulesDir + sep);
+  } catch {
+    return false;
+  }
+}
+
 /**
  * Co-locate the SLM optional dependency closure from `<rootDir>/node_modules`
  * into a standalone bundle's `node_modules`.
@@ -142,11 +170,12 @@ export function colocateLlmlinguaOptionals({
 
   const closure = computeDependencyClosure(rootNm, seeds);
 
-  // Check the complete closure rather than only the entry package. A partially
-  // populated bundle must still receive any missing transitive dependencies.
+  // Check the complete closure rather than only the entry package, and judge
+  // presence by entrypoint integrity — a partially traced directory (see
+  // isPackageIntact) must still receive its missing files.
   if (
     closure.length > 0 &&
-    closure.every((name) => existsSync(join(targetNm, name)))
+    closure.every((name) => isPackageIntact(targetNm, name))
   ) {
     return { skipped: true, reason: "already co-located" };
   }
@@ -155,11 +184,18 @@ export function colocateLlmlinguaOptionals({
 
   for (const name of closure) {
     const dest = join(targetNm, name);
-    if (existsSync(dest)) continue;
+    if (isPackageIntact(targetNm, name)) continue;
 
     try {
       mkdirSync(dirname(dest), { recursive: true });
-      cpSync(join(rootNm, name), dest, { recursive: true });
+      // force:false merges into a partially traced directory: files the trace
+      // already materialized are kept, missing ones (the package payload) are
+      // filled in from the root tree.
+      cpSync(join(rootNm, name), dest, {
+        recursive: true,
+        force: false,
+        errorOnExist: false,
+      });
       copied++;
     } catch (err) {
       log(
diff --git a/tests/unit/docker-llmlingua-optionals-9166.test.ts b/tests/unit/docker-llmlingua-optionals-9166.test.ts
index ba1f245743..da994ed5c4 100644
--- a/tests/unit/docker-llmlingua-optionals-9166.test.ts
+++ b/tests/unit/docker-llmlingua-optionals-9166.test.ts
@@ -55,6 +55,7 @@ function buildLlmlinguaRoot(
     rootNm,
     "@atjsh/llmlingua-2",
     {
+      main: "dist/index.js",
       dependencies: {
         "es-toolkit": "^1.38.0",
       },
@@ -227,6 +228,103 @@ test("#9166 standalone assembly never overwrites an already pinned transformers
   }
 });
 
+test("#9166 co-location completes a partially traced package (package.json without its main)", () => {
+  const root = mkdtempSync(
+    join(tmpdir(), "omniroute-docker-llmlingua-partial-9166-")
+  );
+
+  try {
+    buildLlmlinguaRoot(root);
+    const { distDir, standaloneDir } = createStandalone(root);
+
+    // Next's file tracing materializes @atjsh/llmlingua-2 PARTIALLY in the
+    // standalone: the package.json lands (its "main" points at dist/index.js)
+    // but the dist/ payload does not — the exact state the Docker guard hits
+    // ("Cannot find module .../dist/index.js"). A directory-level no-clobber
+    // sees the dir and skips the package forever.
+    mkPkg(join(standaloneDir, "node_modules"), "@atjsh/llmlingua-2", {
+      main: "dist/index.js",
+    });
+
+    assembleStandalone({
+      distDir,
+      outDir: standaloneDir,
+      projectRoot: root,
+      copyNatives: true,
+    });
+
+    assert.ok(
+      existsSync(
+        join(
+          standaloneDir,
+          "node_modules",
+          "@atjsh",
+          "llmlingua-2",
+          "dist",
+          "index.js"
+        )
+      ),
+      "a partially traced package must be completed, not skipped as already present"
+    );
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
+
+test("#9166 co-location is not skipped when every closure dir exists but one is partial", () => {
+  const root = mkdtempSync(
+    join(tmpdir(), "omniroute-docker-llmlingua-partial-all-9166-")
+  );
+
+  try {
+    buildLlmlinguaRoot(root);
+    const { distDir, standaloneDir } = createStandalone(root);
+    const standaloneNm = join(standaloneDir, "node_modules");
+
+    // Every closure package already has a directory in the standalone (so a
+    // directory-level "already co-located" early-exit would fire), but the
+    // llmlingua-2 one is the partial NFT-trace shell without its main.
+    for (const packageName of [
+      "es-toolkit",
+      "@tensorflow/tfjs",
+      "@tensorflow/tfjs-core",
+      "long",
+      "js-tiktoken",
+      "base64-js",
+      "@huggingface/transformers",
+      "onnxruntime-node",
+    ]) {
+      mkPkg(standaloneNm, packageName, { main: "index.js" }, {
+        "index.js": "export {};\n",
+      });
+    }
+    mkPkg(standaloneNm, "@atjsh/llmlingua-2", { main: "dist/index.js" });
+
+    assembleStandalone({
+      distDir,
+      outDir: standaloneDir,
+      projectRoot: root,
+      copyNatives: true,
+    });
+
+    assert.ok(
+      existsSync(
+        join(
+          standaloneDir,
+          "node_modules",
+          "@atjsh",
+          "llmlingua-2",
+          "dist",
+          "index.js"
+        )
+      ),
+      "the closure-wide early-exit must not fire while any member is partial"
+    );
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});
+
 test("#9166 Docker explicitly installs and validates LLMLingua optionals", () => {
   const dockerfile = readFileSync(
     new URL("../../Dockerfile", import.meta.url),