diff --git a/src/verification.test.ts b/src/verification.test.ts
index 54cda99..4d1ba94 100644
--- a/src/verification.test.ts
+++ b/src/verification.test.ts
@@ -10,6 +10,7 @@ import {
   isVerificationProfile,
   runVerificationRequest,
 } from './verification.js';
+import { hasInstalledNodeModules } from './workspace-package-manager.js';
 
 describe('verification helpers', () => {
   it('recognizes only fixed verification profiles', () => {
@@ -82,16 +83,18 @@ describe('verification helpers', () => {
     expect(third).not.toBe(first);
   });
 
-  it('fails verification when node_modules contains only cache noise', async () => {
+  it('backfills legacy node_modules state before verification', async () => {
     const repoDir = fs.mkdtempSync(
-      path.join(os.tmpdir(), 'ejclaw-verification-noise-'),
+      path.join(os.tmpdir(), 'ejclaw-verification-legacy-'),
     );
-    fs.mkdirSync(path.join(repoDir, 'node_modules', '.vite'), {
+    fs.mkdirSync(path.join(repoDir, 'node_modules', '.bin'), {
       recursive: true,
     });
     fs.writeFileSync(
       path.join(repoDir, 'package.json'),
       JSON.stringify({
+        name: 'verification-legacy',
+        packageManager: 'bun@1.3.11',
         scripts: {
           test: 'vitest run',
           typecheck: 'tsc --noEmit',
@@ -99,16 +102,22 @@ describe('verification helpers', () => {
         },
       }),
     );
+    fs.writeFileSync(path.join(repoDir, 'bun.lock'), '');
+    fs.writeFileSync(path.join(repoDir, 'node_modules', '.bin', 'tsc'), '');
+
+    expect(hasInstalledNodeModules(repoDir)).toBe(false);
 
     const result = await runVerificationRequest(
       {
-        requestId: 'req-noise',
+        requestId: 'req-legacy-node-modules',
         profile: 'typecheck',
+        expectedSnapshotId: 'fs:mismatch',
       },
       { repoDir },
     );
 
+    expect(hasInstalledNodeModules(repoDir)).toBe(true);
     expect(result.ok).toBe(false);
-    expect(result.error).toContain('installed node_modules tree');
+    expect(result.error).toContain('Snapshot mismatch before verification');
   });
 });
diff --git a/src/verification.ts b/src/verification.ts
index af2efa0..51a37ad 100644
--- a/src/verification.ts
+++ b/src/verification.ts
@@ -15,6 +15,7 @@ import { resolveGroupIpcPath } from './group-folder.js';
 import {
   buildWorkspaceScriptCommand,
   detectPnpmStorePath,
+  ensureWorkspaceDependenciesInstalled,
   hasInstalledNodeModules,
 } from './workspace-package-manager.js';
 import {
@@ -271,6 +272,27 @@ export async function runVerificationRequest(
     };
   }
 
+  if (!hasInstalledNodeModules(repoDir)) {
+    try {
+      ensureWorkspaceDependenciesInstalled(repoDir);
+    } catch (error) {
+      return {
+        ok: false,
+        profile: request.profile,
+        command: command.commandText,
+        stdout: '',
+        stderr: '',
+        exitCode: 1,
+        snapshotId: 'unknown',
+        runtimeVersion,
+        error:
+          error instanceof Error
+            ? error.message
+            : String(error),
+      };
+    }
+  }
+
   if (!hasInstalledNodeModules(repoDir)) {
     return {
       ok: false,
diff --git a/src/workspace-package-manager.test.ts b/src/workspace-package-manager.test.ts
index 406b606..70e3dd4 100644
--- a/src/workspace-package-manager.test.ts
+++ b/src/workspace-package-manager.test.ts
@@ -181,4 +181,32 @@ describe('workspace package manager helpers', () => {
     );
     expect(hasInstalledNodeModules(repoDir)).toBe(false);
   });
+
+  it('backfills install state for a legacy runnable node_modules tree', () => {
+    const repoDir = path.join(tempRoot, 'legacy');
+    fs.mkdirSync(path.join(repoDir, 'node_modules', '.bin'), {
+      recursive: true,
+    });
+    fs.writeFileSync(
+      path.join(repoDir, 'package.json'),
+      JSON.stringify({
+        name: 'legacy',
+        packageManager: 'bun@1.3.11',
+        scripts: { test: 'vitest run' },
+      }),
+    );
+    fs.writeFileSync(path.join(repoDir, 'bun.lock'), '');
+    fs.writeFileSync(path.join(repoDir, 'node_modules', '.bin', 'vitest'), '');
+
+    expect(hasInstalledNodeModules(repoDir)).toBe(false);
+
+    const result = ensureWorkspaceDependenciesInstalled(repoDir);
+
+    expect(result).toMatchObject({
+      installed: false,
+      packageManager: 'bun',
+    });
+    expect(hasInstalledNodeModules(repoDir)).toBe(true);
+    expect(execFileSyncMock).not.toHaveBeenCalled();
+  });
 });
diff --git a/src/workspace-package-manager.ts b/src/workspace-package-manager.ts
index 208ae44..0a55ba7 100644
--- a/src/workspace-package-manager.ts
+++ b/src/workspace-package-manager.ts
@@ -194,6 +194,27 @@ function hasRunnableNodeModulesTree(repoDir: string): boolean {
   }
 }
 
+function backfillInstallFingerprintIfPossible(
+  repoDir: string,
+  packageManager: WorkspacePackageManager,
+): boolean {
+  if (!hasRunnableNodeModulesTree(repoDir)) {
+    return false;
+  }
+
+  if (readInstallFingerprint(repoDir)) {
+    return false;
+  }
+
+  const expectedFingerprint = computeInstallFingerprint(repoDir);
+  if (!expectedFingerprint) {
+    return false;
+  }
+
+  writeInstallFingerprint(repoDir, packageManager, expectedFingerprint);
+  return true;
+}
+
 export function detectWorkspacePackageManager(
   repoDir: string,
 ): WorkspacePackageManager | null {
@@ -326,6 +347,10 @@ export function ensureWorkspaceDependenciesInstalled(
     return { installed: false, packageManager };
   }
 
+  if (backfillInstallFingerprintIfPossible(repoDir, packageManager)) {
+    return { installed: false, packageManager };
+  }
+
   const command = resolveWorkspaceInstallCommand(repoDir);
   if (!command) {
     return { installed: false, packageManager };