diff --git a/dsh-plugin-desktop/src/crash-evidence.ts b/dsh-plugin-desktop/src/crash-evidence.ts
index 62a85940a4..4c97693f26 100644
--- a/dsh-plugin-desktop/src/crash-evidence.ts
+++ b/dsh-plugin-desktop/src/crash-evidence.ts
@@ -1,5 +1,21 @@
-import { existsSync, mkdirSync, readFileSync, unlinkSync, writeFileSync } from 'node:fs'
-import { dirname } from 'node:path'
+import { randomUUID } from 'node:crypto'
+import {
+  chmodSync,
+  closeSync,
+  constants,
+  fstatSync,
+  lstatSync,
+  mkdirSync,
+  openSync,
+  readFileSync,
+  renameSync,
+  unlinkSync,
+  writeFileSync,
+} from 'node:fs'
+import { basename, dirname, join } from 'node:path'
+
+const PRIVATE_DIRECTORY_MODE = 0o700
+const PRIVATE_FILE_MODE = 0o600
 
 /** Minimal Electron crash reporter surface used before the app is ready. */
 export interface DesktopCrashReporter {
@@ -51,34 +67,111 @@ export interface DesktopRun {
   markClean(): void
 }
 
-function readPreviousRun(statePath: string): DesktopRunRecord | UnreadableDesktopRun | undefined {
-  if (!existsSync(statePath)) return undefined
+interface StoredDesktopRun extends DesktopRunRecord {
+  readonly ownerId?: string
+}
+
+function lstatOptional(filename: string): ReturnType<typeof lstatSync> | undefined {
   try {
-    const value: unknown = JSON.parse(readFileSync(statePath, 'utf8'))
+    return lstatSync(filename)
+  } catch (cause) {
+    if ((cause as NodeJS.ErrnoException).code === 'ENOENT') return undefined
+    throw cause
+  }
+}
+
+function assertOwnedMarker(stats: NonNullable<ReturnType<typeof lstatSync>>): void {
+  if (stats.isSymbolicLink() || !stats.isFile() || stats.nlink > 1) {
+    throw new Error('dsh-plugin-desktop: active run marker is invalid')
+  }
+}
+
+function readStoredRun(statePath: string): StoredDesktopRun | UnreadableDesktopRun | undefined {
+  const pathStats = lstatOptional(statePath)
+  if (pathStats === undefined) return undefined
+  assertOwnedMarker(pathStats)
+  const descriptor = openSync(statePath, constants.O_RDONLY | noFollowFlag())
+  try {
+    assertOwnedMarker(fstatSync(descriptor))
+    const value: unknown = JSON.parse(readFileSync(descriptor, 'utf8'))
     if (typeof value !== 'object' || value === null) return { unreadable: true }
-    const record = value as Partial<DesktopRunRecord>
+    const record = value as Partial<StoredDesktopRun>
     if (typeof record.startedAt !== 'string'
       || typeof record.pid !== 'number'
       || typeof record.version !== 'string') return { unreadable: true }
-    return { startedAt: record.startedAt, pid: record.pid, version: record.version }
+    return {
+      startedAt: record.startedAt,
+      pid: record.pid,
+      version: record.version,
+      ...(typeof record.ownerId === 'string' ? { ownerId: record.ownerId } : {}),
+    }
   } catch (cause) {
     if (cause instanceof SyntaxError) return { unreadable: true }
     throw cause
+  } finally {
+    closeSync(descriptor)
+  }
+}
+
+function unlinkTemporary(filename: string): void {
+  try {
+    unlinkSync(filename)
+  } catch (cause) {
+    if ((cause as NodeJS.ErrnoException).code !== 'ENOENT') throw cause
+  }
+}
+
+function writeCurrentRun(statePath: string, currentRun: StoredDesktopRun): void {
+  const directory = dirname(statePath)
+  mkdirSync(directory, { recursive: true, mode: PRIVATE_DIRECTORY_MODE })
+  const directoryStats = lstatSync(directory)
+  if (directoryStats.isSymbolicLink() || !directoryStats.isDirectory()) {
+    throw new Error('dsh-plugin-desktop: active run directory is invalid')
+  }
+  try { chmodSync(directory, PRIVATE_DIRECTORY_MODE) } catch {}
+
+  const temporary = join(directory, `.${basename(statePath)}.${process.pid}.${randomUUID()}.tmp`)
+  try {
+    writeFileSync(temporary, `${JSON.stringify(currentRun)}\n`, {
+      encoding: 'utf8',
+      flag: 'wx',
+      mode: PRIVATE_FILE_MODE,
+    })
+    try { chmodSync(temporary, PRIVATE_FILE_MODE) } catch {}
+    renameSync(temporary, statePath)
+  } finally {
+    unlinkTemporary(temporary)
   }
 }
 
 /** Persist this launch and return a marker left behind by an unclean exit. */
 export function beginDesktopRun(statePath: string, currentRun: DesktopRunRecord): DesktopRun {
-  const previousRun = readPreviousRun(statePath)
-  mkdirSync(dirname(statePath), { recursive: true })
-  writeFileSync(statePath, `${JSON.stringify(currentRun)}\n`, 'utf8')
+  const storedPreviousRun = readStoredRun(statePath)
+  const previousRun = storedPreviousRun === undefined || 'unreadable' in storedPreviousRun
+    ? storedPreviousRun
+    : {
+        startedAt: storedPreviousRun.startedAt,
+        pid: storedPreviousRun.pid,
+        version: storedPreviousRun.version,
+      }
+  const ownerId = randomUUID()
+  writeCurrentRun(statePath, { ...currentRun, ownerId })
   let clean = false
   return {
     previousRun,
     markClean() {
       if (clean) return
-      clean = true
+      const storedRun = readStoredRun(statePath)
+      if (storedRun === undefined || 'unreadable' in storedRun || storedRun.ownerId !== ownerId) {
+        clean = true
+        return
+      }
       unlinkSync(statePath)
+      clean = true
     },
   }
 }
+
+function noFollowFlag(): number {
+  return process.platform === 'win32' ? 0 : constants.O_NOFOLLOW
+}
diff --git a/dsh-plugin-desktop/tests/crash-evidence.spec.ts b/dsh-plugin-desktop/tests/crash-evidence.spec.ts
index 9996ef0c3c..74555087ae 100644
--- a/dsh-plugin-desktop/tests/crash-evidence.spec.ts
+++ b/dsh-plugin-desktop/tests/crash-evidence.spec.ts
@@ -1,4 +1,4 @@
-import { mkdtempSync, writeFileSync } from 'node:fs'
+import { existsSync, linkSync, mkdtempSync, readFileSync, writeFileSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 import { describe, expect, it, vi } from 'vitest'
@@ -81,4 +81,39 @@ describe('desktop crash evidence', () => {
     expect(run.previousRun).toEqual({ unreadable: true })
     expect(() => run.markClean()).not.toThrow()
   })
+
+  it('only clears the marker owned by the current run', () => {
+    const statePath = join(mkdtempSync(join(tmpdir(), 'dsh-run-')), 'active-run.json')
+    const first = beginDesktopRun(statePath, {
+      startedAt: '2026-08-18T00:00:00.000Z',
+      pid: 41,
+      version: '2.0.1',
+    })
+    const second = beginDesktopRun(statePath, {
+      startedAt: '2026-08-18T00:01:00.000Z',
+      pid: 42,
+      version: '2.0.1',
+    })
+
+    first.markClean()
+
+    expect(JSON.parse(readFileSync(statePath, 'utf8'))).toMatchObject({ pid: 42 })
+    expect(() => second.markClean()).not.toThrow()
+    expect(existsSync(statePath)).toBe(false)
+  })
+
+  it('does not read or overwrite a linked marker', () => {
+    const directory = mkdtempSync(join(tmpdir(), 'dsh-run-'))
+    const target = join(directory, 'outside.json')
+    const statePath = join(directory, 'active-run.json')
+    writeFileSync(target, '{"outside":true}\n', 'utf8')
+    linkSync(target, statePath)
+
+    expect(() => beginDesktopRun(statePath, {
+      startedAt: '2026-08-18T00:01:00.000Z',
+      pid: 42,
+      version: '2.0.1',
+    })).toThrow('active run marker is invalid')
+    expect(readFileSync(target, 'utf8')).toBe('{"outside":true}\n')
+  })
 })