diff --git a/api/src/api/v2-files.test.ts b/api/src/api/v2-files.test.ts
index 540b529b..6a142ee9 100644
--- a/api/src/api/v2-files.test.ts
+++ b/api/src/api/v2-files.test.ts
@@ -1,7 +1,8 @@
 import { describe, expect, test } from 'bun:test';
 import { config } from '../config';
+import { collectExecuteRequestInputFiles } from '../execution-manifest-request';
 import type { TFile } from '../job';
-import { validateExecuteArguments, validateExecuteFiles } from './v2';
+import { validateExecuteArguments, validateExecuteFiles, deduplicateFilesByDestination } from './v2';
 
 function messageOf(fn: () => void): string {
   try {
@@ -85,4 +86,74 @@ describe('execute file validation', () => {
     ];
     expect(() => validateExecuteFiles(files)).not.toThrow();
   });
+
+  test('deduplicateFilesByDestination keeps the latest occurrence in surviving order', () => {
+    const files: TFile[] = [
+      { name: 'data.csv', content: 'first' },
+      { name: 'data.csv', content: 'second' },
+      { name: 'other.csv', content: 'unique' },
+      { name: 'data.csv', content: 'third' },
+    ];
+    const result = deduplicateFilesByDestination(files);
+    expect(result).toHaveLength(2);
+    expect(result[0].name).toBe('other.csv');
+    expect(result[1].name).toBe('data.csv');
+    expect(result[1].content).toBe('third');
+  });
+
+  test('deduplicateFilesByDestination returns the same array when there are no duplicates', () => {
+    const files: TFile[] = [
+      { name: 'a.csv', content: 'a' },
+      { name: 'b.csv', content: 'b' },
+    ];
+    const result = deduplicateFilesByDestination(files);
+    expect(result).toEqual(files);
+  });
+
+  test('preserves the original destination of an unnamed file reference after deduplication', () => {
+    const files: TFile[] = [
+      { name: 'main.py', content: 'print(1)' },
+      { name: 'data.csv', content: 'old' },
+      { name: 'data.csv', content: 'new' },
+      { id: 'file-ref', storage_session_id: 'storage-session' } as TFile,
+    ];
+    const deduped = deduplicateFilesByDestination(files);
+    expect(deduped.map(file => file.name)).toEqual(['main.py', 'data.csv', 'file3.code']);
+    expect(deduped[1].content).toBe('new');
+    expect(collectExecuteRequestInputFiles({ files: deduped })).toEqual(
+      collectExecuteRequestInputFiles({ files }),
+    );
+    expect(() => validateExecuteFiles(deduped)).not.toThrow();
+  });
+
+  test('rejects malformed files even if another entry owns their destination', () => {
+    expect(messageOf(() => deduplicateFilesByDestination([
+      { name: 'file1.code', content: 'source' },
+      null as unknown as TFile,
+    ]))).toContain('files[1] must be an object');
+    expect(messageOf(() => deduplicateFilesByDestination([
+      { name: 'data.csv', content: 'old', encoding: 'invalid' as TFile['encoding'] },
+      { name: 'data.csv', content: 'new' },
+    ]))).toContain('files[0].encoding');
+    expect(messageOf(() => deduplicateFilesByDestination([
+      { name: 'data.csv', content: 'old' },
+      { name: 'data.csv', id: 'file-ref' },
+    ]))).toContain('files[1].storage_session_id');
+  });
+
+  test('caps raw input count before dropping duplicates', () => {
+    const files = Array.from({ length: config.max_input_files + 1 }, () => ({
+      name: 'data.csv', content: 'duplicate',
+    }));
+    expect(messageOf(() => deduplicateFilesByDestination(files))).toContain('cannot contain more than');
+  });
+
+  test('deduplicateFilesByDestination allows validateExecuteFiles to accept previously-duplicate input', () => {
+    const files: TFile[] = [
+      { name: 'data.csv', content: 'first' },
+      { name: 'data.csv', content: 'second' },
+    ];
+    const deduped = deduplicateFilesByDestination(files);
+    expect(() => validateExecuteFiles(deduped)).not.toThrow();
+  });
 });
diff --git a/api/src/api/v2-session-binding.test.ts b/api/src/api/v2-session-binding.test.ts
index 32a245f6..709b3b28 100644
--- a/api/src/api/v2-session-binding.test.ts
+++ b/api/src/api/v2-session-binding.test.ts
@@ -281,6 +281,52 @@ describe('per-request session binding', () => {
     }
   });
 
+  test('uses the latest upload without renumbering later unnamed files', async () => {
+    config.session_workspace_enabled = false;
+    config.require_execution_manifest = false;
+
+    const originalPrime = Job.prototype.prime;
+    const originalExecute = Job.prototype.execute;
+    const originalCleanup = Job.prototype.cleanup;
+
+    let primedFiles: Array<{ name: string; content?: string }> = [];
+    Job.prototype.prime = async function captureFiles(): Promise<void> {
+      primedFiles = this.files.map(({ name, content }) => ({ name, content }));
+    };
+    Job.prototype.execute = async function executeWithoutSandbox() {
+      return {} as Awaited<ReturnType<Job['execute']>>;
+    };
+    Job.prototype.cleanup = async function cleanupWithoutFilesystem(): Promise<void> {};
+
+    try {
+      const response = await fetch(`${baseUrl}/api/v2/execute`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          language: testLanguage,
+          version: testVersion,
+          files: [
+            { name: 'main.txt', content: 'source' },
+            { name: 'data.csv', content: 'old upload' },
+            { name: 'data.csv', content: 'new upload' },
+            { content: 'unnamed source' },
+          ],
+        }),
+      });
+
+      expect(response.status).toBe(200);
+      expect(primedFiles).toEqual([
+        { name: 'main.txt', content: 'source' },
+        { name: 'data.csv', content: 'new upload' },
+        { name: 'file3.code', content: 'unnamed source' },
+      ]);
+    } finally {
+      Job.prototype.prime = originalPrime;
+      Job.prototype.execute = originalExecute;
+      Job.prototype.cleanup = originalCleanup;
+    }
+  });
+
   test('a post-prime failure still reports the workspace as dirty', async () => {
     config.session_workspace_enabled = true;
     config.require_execution_manifest = false;
diff --git a/api/src/api/v2.ts b/api/src/api/v2.ts
index e2f252ce..fe1567bf 100644
--- a/api/src/api/v2.ts
+++ b/api/src/api/v2.ts
@@ -46,72 +46,109 @@ import {
 const router = express.Router();
 const SYNTHETIC_PRINCIPAL_SOURCE = 'synthetic_test';
 
+/**
+ * Deduplicate files by destination name. Some callers (e.g. LibreChat)
+ * send the same file more than once per request when a user re-uploads a
+ * file in the same conversation. The sandbox rejects duplicate destinations,
+ * which surfaces to the end user as a confusing "sandbox is down" error.
+ * Keeps the latest occurrence, preserving the order of surviving files.
+ */
+export function deduplicateFilesByDestination(files: TFile[]): TFile[] {
+  if (files.length > config.max_input_files) {
+    throw { message: `files cannot contain more than ${config.max_input_files} destinations` };
+  }
+  const seen = new Set<string>();
+  const deduped: TFile[] = [];
+  for (let i = files.length - 1; i >= 0; i--) {
+    const file = files[i];
+    // Validate even entries that would otherwise be dropped as duplicates.
+    const destination = validateExecuteFile(file, i);
+    if (seen.has(destination)) continue;
+    seen.add(destination);
+    // Manifest claims use original indices; Job would otherwise renumber this file.
+    deduped.push(file.name ? file : { ...file, name: destination });
+  }
+  deduped.reverse();
+  if (deduped.length < files.length) {
+    logger.warn(
+      { original: files.length, deduped: deduped.length },
+      'Deduplicated file list before validation',
+    );
+  }
+  return deduped;
+}
+
 function existingDestinationConflictMessage(existing: string, destination: string): string {
   return existing === destination
     ? `files contains duplicate destination "${destination}"`
     : `files contains conflicting destinations "${existing}" and "${destination}"`;
 }
 
+function validateExecuteFile(value: TFile, i: number): string {
+  if (value == null || typeof value !== 'object' || Array.isArray(value)) {
+    throw { message: `files[${i}] must be an object` };
+  }
+  const file = value as TFile;
+  const inline = typeof file.content === 'string';
+  const byRef = typeof file.id === 'string' && file.id.length > 0;
+  if (inline === byRef) {
+    throw {
+      message: `files[${i}] must contain exactly one of non-empty id or string content`,
+    };
+  }
+  if (file.id !== undefined && !byRef) {
+    throw { message: `files[${i}].id must be a non-empty string if provided` };
+  }
+  if (byRef) {
+    if (typeof file.storage_session_id !== 'string' || file.storage_session_id.length === 0) {
+      throw { message: `files[${i}].storage_session_id is required as a non-empty string for file refs` };
+    }
+  } else if (file.storage_session_id !== undefined || file.input_cache_key !== undefined) {
+    throw {
+      message: `files[${i}] inline content cannot include storage_session_id or input_cache_key`,
+    };
+  }
+  if (file.name !== undefined && typeof file.name !== 'string') {
+    throw { message: `files[${i}].name must be a string if provided` };
+  }
+  if (
+    file.encoding !== undefined
+    && !(['base64', 'hex', 'utf8'] as const).includes(file.encoding)
+  ) {
+    throw { message: `files[${i}].encoding must be base64, hex, or utf8 if provided` };
+  }
+  if (file.entity_id !== undefined && typeof file.entity_id !== 'string') {
+    throw { message: `files[${i}].entity_id must be a string if provided` };
+  }
+  if (
+    file.input_cache_key !== undefined &&
+    (
+      typeof file.input_cache_key !== 'string' ||
+      !/^[0-9a-f]{64}$/.test(file.input_cache_key)
+    )
+  ) {
+    throw { message: `files[${i}].input_cache_key must be a 64-character lowercase hex digest` };
+  }
+  const destination = file.name || `file${i}.code`;
+  try {
+    validateFilePath(destination, '/tmp/codeapi-request-validation');
+  } catch (error) {
+    throw {
+      message: error instanceof Error
+        ? `files[${i}].name is invalid: ${error.message}`
+        : `files[${i}].name is invalid`,
+    };
+  }
+  return destination;
+}
+
 export function validateExecuteFiles(files: TFile[]): void {
   if (files.length > config.max_input_files) {
     throw { message: `files cannot contain more than ${config.max_input_files} destinations` };
   }
   const destinations = new Set<string>();
   for (const [i, value] of files.entries()) {
-    if (value == null || typeof value !== 'object' || Array.isArray(value)) {
-      throw { message: `files[${i}] must be an object` };
-    }
-    const file = value as TFile;
-    const inline = typeof file.content === 'string';
-    const byRef = typeof file.id === 'string' && file.id.length > 0;
-    if (inline === byRef) {
-      throw {
-        message: `files[${i}] must contain exactly one of non-empty id or string content`,
-      };
-    }
-    if (file.id !== undefined && !byRef) {
-      throw { message: `files[${i}].id must be a non-empty string if provided` };
-    }
-    if (byRef) {
-      if (typeof file.storage_session_id !== 'string' || file.storage_session_id.length === 0) {
-        throw { message: `files[${i}].storage_session_id is required as a non-empty string for file refs` };
-      }
-    } else if (file.storage_session_id !== undefined || file.input_cache_key !== undefined) {
-      throw {
-        message: `files[${i}] inline content cannot include storage_session_id or input_cache_key`,
-      };
-    }
-    if (file.name !== undefined && typeof file.name !== 'string') {
-      throw { message: `files[${i}].name must be a string if provided` };
-    }
-    if (
-      file.encoding !== undefined
-      && !(['base64', 'hex', 'utf8'] as const).includes(file.encoding)
-    ) {
-      throw { message: `files[${i}].encoding must be base64, hex, or utf8 if provided` };
-    }
-    if (file.entity_id !== undefined && typeof file.entity_id !== 'string') {
-      throw { message: `files[${i}].entity_id must be a string if provided` };
-    }
-    if (
-      file.input_cache_key !== undefined &&
-      (
-        typeof file.input_cache_key !== 'string' ||
-        !/^[0-9a-f]{64}$/.test(file.input_cache_key)
-      )
-    ) {
-      throw { message: `files[${i}].input_cache_key must be a 64-character lowercase hex digest` };
-    }
-    const destination = file.name || `file${i}.code`;
-    try {
-      validateFilePath(destination, '/tmp/codeapi-request-validation');
-    } catch (error) {
-      throw {
-        message: error instanceof Error
-          ? `files[${i}].name is invalid: ${error.message}`
-          : `files[${i}].name is invalid`,
-      };
-    }
+    const destination = validateExecuteFile(value, i);
     const conflict = [...destinations].find(
       existing =>
         existing === destination ||
@@ -251,12 +288,13 @@ function getJob(
   runtimeSessionHeader?: string | string[],
 ): Job {
   const {
-    session_id, language, version, args, stdin, files,
+    session_id, language, version, args, stdin, files: rawFiles,
     compile_memory_limit, run_memory_limit,
     compile_timeout,
     run_cpu_time, compile_cpu_time,
     env_vars,
   } = body;
+  let files = rawFiles;
 
   if (!language || typeof language !== 'string') {
     throw { message: 'language is required as a string' };
@@ -271,6 +309,7 @@ function getJob(
     throw { message: 'tool_call_socket must be a boolean if specified' };
   }
   validateExecuteArguments(args, stdin);
+  files = deduplicateFilesByDestination(files);
   validateExecuteFiles(files);
 
   const rt = getLatestRuntimeMatchingLanguageVersion(language, version);