fix(desktop): skip cold process probes for dead backend-ownership PIDs

Windows Get-Process and macOS ps exit 1 on a missing PID, so reapOrphans
kept stale records and the next launch paid another 2-8s spawn each.
Throw ESRCH from the existing isPidAlive helper before any shell-out.

Closes #92875

Co-authored-by: Jackal991 <139240222+Jackal991@users.noreply.github.com>
Co-authored-by: jonotonfoto <126111813+jonotonfoto@users.noreply.github.com>
Co-authored-by: foras910521-lab <268267187+foras910521-lab@users.noreply.github.com>

apps/desktop/electron/backend-claim.test.ts

@@ -66,9 +66,15 @@ test('processStartMarker resolves a real marker for the current process', async
   assert.match(marker, /^(linux|win|winms|ps):.+/)
 })
 
-test('processStartMarker rejects for a PID that does not exist', async () => {
+test('a missing PID is classified as ESRCH so reapOrphans can drop the record', async () => {
   // Largest PIDs are bounded well below this on every supported platform.
-  await assert.rejects(processStartMarker(2 ** 30 + 12345))
+  // Windows Get-Process / macOS `ps -p` used to surface exit code 1, which
+  // the identity matchers treated as "unknown" and kept forever. The native
+  // gate throws ESRCH — the errno those catch blocks already map to gone.
+  await assert.rejects(
+    processStartMarker(2 ** 30 + 12345),
+    (error: NodeJS.ErrnoException) => error?.code === 'ESRCH'
+  )
 })
 
 // --- PID-only marker helpers --------------------------------------------------

apps/desktop/electron/backend-claim.ts

@@ -21,6 +21,7 @@ import { execFile } from 'node:child_process'
 import fs from 'node:fs'
 
 import { electronProcessStartMarker } from './parent-process-identity'
+import { isPidAlive } from './update-marker'
 import { hiddenWindowsChildOptions } from './windows-child-options'
 
 export function execText(command: string, args: string[], { timeout = 3000 } = {}): Promise<string> {
@@ -42,6 +43,15 @@ export function execText(command: string, args: string[], { timeout = 3000 } = {
  * `claimDecision` / `probeStartMarker`).
  */
 export async function processStartMarker(pid: number): Promise<string> {
+  // Cheap native dead-PID gate. Windows Get-Process / macOS `ps -p` exit 1
+  // on a missing PID (not ESRCH), so the identity matchers used to keep the
+  // orphan and re-probe it every launch (#92875). ESRCH is the code those
+  // catch blocks already map to "gone". Alive or uninspectable (EPERM) PIDs
+  // still fall through to the platform probe.
+  if (!isPidAlive(pid)) {
+    throw Object.assign(new Error(`PID ${pid} no longer exists`), { code: 'ESRCH' })
+  }
+
   if (process.platform === 'linux') {
     const stat = await fs.promises.readFile(`/proc/${pid}/stat`, 'utf8')