diff --git a/src/server/workspace-upload-store.ts b/src/server/workspace-upload-store.ts
index c185b084..2b7806d5 100644
--- a/src/server/workspace-upload-store.ts
+++ b/src/server/workspace-upload-store.ts
@@ -1,6 +1,6 @@
 import { randomUUID } from 'node:crypto'
 import { readdirSync, renameSync, rmdirSync, unlinkSync } from 'node:fs'
-import { mkdir, readFile, writeFile } from 'node:fs/promises'
+import { mkdir, open, readFile } from 'node:fs/promises'
 import { basename, dirname, extname, join, resolve, sep } from 'node:path'
 import { HttpError } from './http-errors.js'
 import type { Database } from './sqlite.js'
@@ -283,14 +283,22 @@ export const createWorkspaceUploadStore = (db: Database, uploadsDir: string) =>
         created_at: now,
       }
 
+      let ownsFile = false
       try {
         await mkdir(dirname(storagePath), { recursive: true })
         // Async IO keeps a 100MB write from stalling every PTY/WebSocket on
         // the event loop; `wx` keeps the no-clobber guarantee. The INSERT's
         // WHERE EXISTS guard plus the removeFile cleanup below still cover a
         // workspace deleted while the write was in flight.
-        await writeFile(storagePath, input.data, { flag: 'wx' })
+        const file = await open(storagePath, 'wx')
+        ownsFile = true
+        try {
+          await file.writeFile(input.data)
+        } finally {
+          await file.close()
+        }
       } catch {
+        if (ownsFile) removeFile(storagePath)
         throw new HttpError(500, 'Upload could not be saved')
       }
 
diff --git a/tests/helpers/upload-partial-write.ts b/tests/helpers/upload-partial-write.ts
new file mode 100644
index 00000000..e328301f
--- /dev/null
+++ b/tests/helpers/upload-partial-write.ts
@@ -0,0 +1,62 @@
+import assert from 'node:assert/strict'
+import { readdirSync, readFileSync, statSync } from 'node:fs'
+import { writeFile } from 'node:fs/promises'
+import { join } from 'node:path'
+import { openRuntimeDatabase } from '../../src/server/runtime-database.js'
+import { createWorkspaceUploadStore } from '../../src/server/workspace-upload-store.js'
+
+process.on('SIGXFSZ', () => {})
+const root = process.argv[2]
+assert(root)
+const limit = readFileSync('/proc/self/limits', 'utf8')
+  .split('\n')
+  .find((line) => line.startsWith('Max file size'))
+assert.match(limit ?? '', /65536\s+65536/)
+const db = openRuntimeDatabase()
+db.prepare('INSERT INTO workspaces(id,name,path,created_at) VALUES(?,?,?,?)').run(
+  'fixture',
+  'Fixture',
+  root,
+  0
+)
+const store = createWorkspaceUploadStore(db, join(root, 'uploads'))
+try {
+  const small = await store.saveUpload({
+    workspaceId: 'fixture',
+    originalName: 'small.bin',
+    data: Buffer.from('success'),
+  })
+  const dir = join(root, 'uploads', 'fixture')
+  const before = readdirSync(dir)
+  await assert.rejects(
+    writeFile(join(root, 'native.bin'), Buffer.alloc(1024 * 1024), { flag: 'wx' }),
+    { code: 'EFBIG' }
+  )
+  assert.equal(statSync(join(root, 'native.bin')).size, 65536)
+  await assert.rejects(
+    store.saveUpload({
+      workspaceId: 'fixture',
+      originalName: 'large.bin',
+      data: Buffer.alloc(1024 * 1024),
+    }),
+    { statusCode: 500, message: 'Upload could not be saved' }
+  )
+  assert.equal(store.listUploads('fixture').length, 1)
+  assert.equal((await store.readUpload('fixture', small.id))?.data.toString(), 'success')
+  db.close()
+  const after = readdirSync(dir)
+  console.log(
+    JSON.stringify({
+      nativeError: 'EFBIG',
+      nativePartialBytes: 65536,
+      mappedStoreStatus: 500,
+      rows: 1,
+      before,
+      after,
+      databaseClosed: !db.isOpen,
+    })
+  )
+  assert.deepEqual(after, before, 'failed upload must leave no unrecorded file after close')
+} finally {
+  if (db.isOpen) db.close()
+}
diff --git a/tests/unit/workspace-upload-write.test.ts b/tests/unit/workspace-upload-write.test.ts
new file mode 100644
index 00000000..c08c34e4
--- /dev/null
+++ b/tests/unit/workspace-upload-write.test.ts
@@ -0,0 +1,86 @@
+import { spawnSync } from 'node:child_process'
+import { mkdirSync, mkdtempSync, readdirSync, readFileSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, expect, test, vi } from 'vitest'
+import { openRuntimeDatabase } from '../../src/server/runtime-database.js'
+import { createWorkspaceUploadStore } from '../../src/server/workspace-upload-store.js'
+import { removeTestPath } from '../helpers/fs-cleanup.js'
+
+// Deterministic ID injection only for collision coverage; native child imports are unmocked.
+vi.mock('node:crypto', async (original) => ({
+  ...(await original<typeof import('node:crypto')>()),
+  randomUUID: () => '11111111-1111-4111-8111-111111111111',
+}))
+const dirs: string[] = []
+const fixture = () => {
+  const dir = mkdtempSync(join(tmpdir(), 'hive-upload-write-'))
+  dirs.push(dir)
+  return dir
+}
+afterEach(() => {
+  for (const dir of dirs.splice(0)) removeTestPath(dir)
+})
+
+test.skipIf(process.platform !== 'linux')(
+  'native partial write removes only its created upload',
+  (ctx) => {
+    const available = spawnSync('prlimit', ['--version'], { timeout: 5_000 })
+    if ((available.error as NodeJS.ErrnoException | undefined)?.code === 'ENOENT') {
+      ctx.skip()
+      return
+    }
+    expect(available.error).toBeUndefined()
+    expect(available.status).toBe(0)
+    const result = spawnSync(
+      'prlimit',
+      [
+        '--fsize=65536:65536',
+        '--',
+        process.execPath,
+        '--import',
+        'tsx',
+        'tests/helpers/upload-partial-write.ts',
+        fixture(),
+      ],
+      {
+        timeout: 15_000,
+        env: { ...process.env, TSX_DISABLE_CACHE: '1' },
+        encoding: 'utf8',
+      }
+    )
+    expect(result.error).toBeUndefined()
+    expect(result.status, result.stdout + result.stderr).toBe(0)
+  },
+  20_000
+)
+
+test('injected ID collision preserves existing file and inserts no metadata', async () => {
+  const root = fixture()
+  const db = openRuntimeDatabase()
+  try {
+    db.prepare('INSERT INTO workspaces(id,name,path,created_at) VALUES(?,?,?,?)').run(
+      'fixture',
+      'Fixture',
+      root,
+      0
+    )
+    const store = createWorkspaceUploadStore(db, root)
+    const dir = join(root, 'fixture')
+    mkdirSync(dir)
+    const path = join(dir, '11111111-1111-4111-8111-111111111111.bin')
+    writeFileSync(path, 'existing bytes')
+    await expect(
+      store.saveUpload({
+        workspaceId: 'fixture',
+        originalName: 'collision.bin',
+        data: Buffer.from('replacement'),
+      })
+    ).rejects.toMatchObject({ statusCode: 500, message: 'Upload could not be saved' })
+    expect(readFileSync(path, 'utf8')).toBe('existing bytes')
+    expect(readdirSync(dir)).toEqual(['11111111-1111-4111-8111-111111111111.bin'])
+    expect(store.listUploads('fixture')).toEqual([])
+  } finally {
+    db.close()
+  }
+})