diff --git a/browse/src/terminal-agent-control.ts b/browse/src/terminal-agent-control.ts
index bda034539..bb96310e0 100644
--- a/browse/src/terminal-agent-control.ts
+++ b/browse/src/terminal-agent-control.ts
@@ -24,9 +24,10 @@ import { atomicWriteSync } from '../../lib/fs-atomic';
 import { readPidCmdline, readPidStartTime } from './xvfb';
 import { emptyBunConfig, findWindowsBunExe, type BunExeLookup } from './bun-child-config';
 
-function agentProcessInfo(pid: number): { startTime: string; commandLine: string } {
-  if (!Number.isSafeInteger(pid) || pid <= 0) return { startTime: '', commandLine: '' };
-  if (process.platform !== 'win32') return { startTime: readPidStartTime(pid), commandLine: readPidCmdline(pid) };
+const FILETIME_UNIX_EPOCH_MS = 11_644_473_600_000n;
+let win32Kernel: any;
+
+function windowsProcessQuery(pid: number): { startTime: string; commandLine: string } {
   const script = `(Get-CimInstance Win32_Process -Filter 'ProcessId = ${pid}' | Select-Object CreationDate,CommandLine | ConvertTo-Json -Compress)`;
   try {
     const result = spawnSync('powershell.exe', ['-NoProfile', '-NonInteractive', '-Command', script], { encoding: 'utf8', windowsHide: true, timeout: 2000 });
@@ -36,8 +37,40 @@ function agentProcessInfo(pid: number): { startTime: string; commandLine: string
   } catch { return { startTime: '', commandLine: '' }; }
 }
 
+export const win32CreationTimeSource = {
+  read(pid: number): string | undefined {
+    if (!process.versions.bun) return;
+    try {
+      const { dlopen, FFIType, ptr } = require('bun:ffi');
+      win32Kernel ??= dlopen('kernel32.dll', {
+        OpenProcess: { args: [FFIType.u32, FFIType.i32, FFIType.u32], returns: FFIType.u64 },
+        GetProcessTimes: { args: [FFIType.u64, FFIType.ptr, FFIType.ptr, FFIType.ptr, FFIType.ptr], returns: FFIType.i32 },
+        CloseHandle: { args: [FFIType.u64], returns: FFIType.i32 },
+      }).symbols;
+      const handle = win32Kernel.OpenProcess(0x1000, 0, pid);
+      if (!handle) return;
+      try {
+        const times = new BigUint64Array(4);
+        if (!win32Kernel.GetProcessTimes(handle, ptr(times, 0), ptr(times, 8), ptr(times, 16), ptr(times, 24)) || times[0] === 0n) return;
+        return `/Date(${times[0] / 10_000n - FILETIME_UNIX_EPOCH_MS})/`;
+      } finally {
+        win32Kernel.CloseHandle(handle);
+      }
+    } catch { return; }
+  },
+};
+
+function agentProcessInfo(pid: number): { startTime: string; commandLine: string } {
+  if (!Number.isSafeInteger(pid) || pid <= 0) return { startTime: '', commandLine: '' };
+  if (process.platform !== 'win32') return { startTime: readPidStartTime(pid), commandLine: readPidCmdline(pid) };
+  const query = windowsProcessQuery(pid);
+  return { startTime: win32CreationTimeSource.read(pid) ?? query.startTime, commandLine: query.commandLine };
+}
+
 export function readAgentStartTime(pid: number): string {
-  return agentProcessInfo(pid).startTime;
+  if (!Number.isSafeInteger(pid) || pid <= 0) return '';
+  if (process.platform !== 'win32') return readPidStartTime(pid);
+  return win32CreationTimeSource.read(pid) ?? windowsProcessQuery(pid).startTime;
 }
 
 const pendingAgentExits = new Set<any>();
diff --git a/browse/test/cookie-import-native-job.test.ts b/browse/test/cookie-import-native-job.test.ts
index 6b0431008..44b068d52 100644
--- a/browse/test/cookie-import-native-job.test.ts
+++ b/browse/test/cookie-import-native-job.test.ts
@@ -999,9 +999,9 @@ function safeNativeEnvelope(output: string): object {
 
 function assertOwnerReceipt(receipt: { available: boolean; owners: { pid: number; creationMatched: boolean; isTestHost: boolean }[] }, pid: number) {
   const before = JSON.stringify(receipt);
-  expect(receipt.available).toBe(true);
-  expect(Array.isArray(receipt.owners)).toBe(true);
-  expect(receipt.owners.some(owner => owner.pid === pid && owner.creationMatched && owner.isTestHost)).toBe(true);
+  expect(receipt.available, before).toBe(true);
+  expect(Array.isArray(receipt.owners), before).toBe(true);
+  expect(receipt.owners.some(owner => owner.pid === pid && owner.creationMatched && owner.isTestHost), before).toBe(true);
   expect(JSON.stringify(receipt)).toBe(before);
 }
 
diff --git a/browse/test/path-security-realpath.test.ts b/browse/test/path-security-realpath.test.ts
index aa3b03267..cc7518dd8 100644
--- a/browse/test/path-security-realpath.test.ts
+++ b/browse/test/path-security-realpath.test.ts
@@ -11,6 +11,7 @@ import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
 import * as fs from 'node:fs';
 import * as os from 'node:os';
 import * as path from 'node:path';
+import { dlopen, FFIType, ptr } from 'bun:ffi';
 
 const VALIDATOR = path.resolve(import.meta.dir, '../src/path-security.ts');
 const WIN = process.platform === 'win32';
@@ -43,11 +44,16 @@ function validate(tempDir: string, checks: Array<['output' | 'read', string]>):
 }
 
 function shortPath(dir: string): string {
-  const result = Bun.spawnSync(['powershell', '-NoProfile', '-NonInteractive', '-Command',
-    `(New-Object -ComObject Scripting.FileSystemObject).GetFolder($env:GSTACK_LONG_DIR).ShortPath`], {
-    env: { ...process.env, GSTACK_LONG_DIR: dir }, stdout: 'pipe', stderr: 'pipe', timeout: 30_000,
-  });
-  return result.stdout.toString().trim();
+  const kernel = dlopen('kernel32.dll', { GetShortPathNameW: { args: [FFIType.ptr, FFIType.ptr, FFIType.u32], returns: FFIType.u32 } });
+  try {
+    const input = Buffer.from(dir + '\0', 'utf16le');
+    const output = Buffer.alloc(65536);
+    const length = kernel.symbols.GetShortPathNameW(ptr(input), ptr(output), 32768);
+    if (length === 0 || length >= 32768) throw new Error(`GetShortPathNameW failed for ${dir} (returned ${length})`);
+    return output.subarray(0, length * 2).toString('utf16le');
+  } finally {
+    kernel.close();
+  }
 }
 
 describe('#3104 one realpath for safe dirs and targets', () => {
diff --git a/browse/test/process-liveness-windows.test.ts b/browse/test/process-liveness-windows.test.ts
index b2f5f7e93..fff426b3e 100644
--- a/browse/test/process-liveness-windows.test.ts
+++ b/browse/test/process-liveness-windows.test.ts
@@ -4,7 +4,10 @@ import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
 import { isProcessAlive } from '../src/error-handling';
-import { spawnTerminalAgent } from '../src/terminal-agent-control';
+import {
+  isAgentRecordGone, isOurAgent, readAgentStartTime, spawnTerminalAgent, stopAgentByRecord, win32CreationTimeSource, writeAgentRecord,
+  type AgentRecord,
+} from '../src/terminal-agent-control';
 
 // REGRESSION TEST for the Windows terminal-agent leak.
 //
@@ -117,8 +120,10 @@ describe('process liveness probe (Windows terminal-agent leak)', () => {
       }
       return originalProbe(command, options);
     }) as typeof Bun.spawnSync);
+    const powershellCalls: string[] = [];
     const windowsProbe = spyOn(childProcess, 'spawnSync').mockImplementation(((command: string, args: string[], options: any) => {
       if (command === 'powershell.exe') {
+        powershellCalls.push(args.join(' '));
         const owner = args.join(' ').includes(`ProcessId = ${process.pid}'`);
         return { status: 0, stdout: JSON.stringify(owner ? { CreationDate: 'fixture-owner-start', CommandLine: 'test-owner' } : null), stderr: '' };
       }
@@ -143,7 +148,13 @@ describe('process liveness probe (Windows terminal-agent leak)', () => {
       // Owner-PID lifetime tie (#2019): the agent polls this and exits when
       // its owning browse server dies, so it can't be adopted by PID 1.
       expect(captured.env.BROWSE_OWNER_PID).toBe(String(process.pid));
-      expect(captured.env.BROWSE_OWNER_START_TIME).toBe('fixture-owner-start');
+      if (process.platform === 'win32') {
+        expect(captured.env.BROWSE_OWNER_START_TIME).toMatch(/^\/Date\(\d+\)\/$/);
+        expect(captured.env.BROWSE_OWNER_START_TIME).toBe(readAgentStartTime(process.pid));
+        expect(powershellCalls).toEqual([]);
+      } else {
+        expect(captured.env.BROWSE_OWNER_START_TIME).toBe('fixture-owner-start');
+      }
       // Detached background daemon — must not inherit a terminal either.
       expect(captured.stdio).toEqual(['ignore', 'ignore', 'ignore']);
       await exited;
@@ -174,3 +185,130 @@ describe('process liveness probe (Windows terminal-agent leak)', () => {
     expect(windowMs).toBeGreaterThanOrEqual(tick * guardMax);
   });
 });
+
+describe('win32 terminal-agent identity (GSTA-139)', () => {
+  const pid = 2147483645;
+  const gen = 'win32-identity-generation';
+  const birth = '/Date(1761600000123)/';
+  const ownedCommand = `"C:\\bun\\bun.exe" run terminal-agent.ts --agent-gen=${gen}`;
+  const record = (startTime = birth): AgentRecord => ({ pid, gen, startTime, startedAt: 0, ownerPid: pid, ownerStartTime: birth });
+  type PowerShell = { status: number | null; creationDate?: string; commandLine?: string };
+
+  function onWin32(scenario: { ffi: string | undefined; powershell: PowerShell }, run: (calls: { powershell: number; signals: unknown[] }) => void): void {
+    const platform = Object.getOwnPropertyDescriptor(process, 'platform')!;
+    const calls = { powershell: 0, signals: [] as unknown[] };
+    let live = true;
+    const kill = spyOn(process, 'kill').mockImplementation(((target: number, signal: unknown) => {
+      expect(target).toBe(pid);
+      if (!live) throw Object.assign(new Error('gone'), { code: 'ESRCH' });
+      if (signal !== 0) { calls.signals.push(signal); live = false; }
+      return true;
+    }) as typeof process.kill);
+    const read = spyOn(win32CreationTimeSource, 'read').mockImplementation((target: number) => (target === pid && live ? scenario.ffi : undefined));
+    const probe = spyOn(childProcess, 'spawnSync').mockImplementation(((command: string) => {
+      expect(command).toBe('powershell.exe');
+      calls.powershell++;
+      const { status, creationDate, commandLine } = scenario.powershell;
+      return status === 0
+        ? { status, stdout: JSON.stringify({ CreationDate: creationDate, CommandLine: commandLine }), stderr: '' }
+        : { status, stdout: '', stderr: '', error: Object.assign(new Error('spawnSync powershell.exe ETIMEDOUT'), { code: 'ETIMEDOUT' }) };
+    }) as typeof childProcess.spawnSync);
+    Object.defineProperty(process, 'platform', { ...platform, value: 'win32' });
+    try {
+      run(calls);
+    } finally {
+      Object.defineProperty(process, 'platform', platform);
+      probe.mockRestore();
+      read.mockRestore();
+      kill.mockRestore();
+    }
+  }
+
+  test('the start time is read in-process, so a PowerShell launch killed at its timeout cannot empty it', () => {
+    onWin32({ ffi: birth, powershell: { status: null } }, calls => {
+      expect(readAgentStartTime(pid)).toBe(birth);
+      expect(calls.powershell).toBe(0);
+    });
+  });
+
+  test('without the in-process reader (Node daemon) the start time falls back to the PowerShell CreationDate', () => {
+    onWin32({ ffi: undefined, powershell: { status: 0, creationDate: birth, commandLine: ownedCommand } }, calls => {
+      expect(readAgentStartTime(pid)).toBe(birth);
+      expect(calls.powershell).toBe(1);
+    });
+  });
+
+  test('kill-time ownership still requires the generation in the PowerShell command line', () => {
+    onWin32({ ffi: birth, powershell: { status: 0, creationDate: birth, commandLine: ownedCommand } }, calls => {
+      expect(isOurAgent(record())).toBe(true);
+      expect(stopAgentByRecord(record(), 0)).toBe(true);
+      expect(calls.signals).toEqual(['SIGTERM']);
+    });
+    for (const powershell of [{ status: 0, creationDate: birth, commandLine: 'bun run unrelated.ts' }, { status: null }]) {
+      onWin32({ ffi: birth, powershell }, calls => {
+        expect(isOurAgent(record())).toBe(false);
+        expect(isAgentRecordGone(record())).toBe(false);
+        expect(stopAgentByRecord(record(), 0)).toBe(false);
+        expect(calls.signals).toEqual([]);
+      });
+    }
+    onWin32({ ffi: '/Date(1761600000124)/', powershell: { status: 0, creationDate: birth, commandLine: ownedCommand } }, calls => {
+      expect(isAgentRecordGone(record())).toBe(true);
+      expect(calls.signals).toEqual([]);
+    });
+  });
+
+  test('an unreadable start time is unknown: never signalled and never treated as gone', () => {
+    onWin32({ ffi: undefined, powershell: { status: null } }, calls => {
+      expect(readAgentStartTime(pid)).toBe('');
+      expect(isOurAgent(record())).toBe(false);
+      expect(isAgentRecordGone(record())).toBe(false);
+      expect(stopAgentByRecord(record(), 0)).toBe(false);
+      expect(calls.signals).toEqual([]);
+    });
+  });
+
+  test.skipIf(process.platform !== 'win32')('the in-process start time equals the CreationDate earlier releases recorded', () => {
+    const child = Bun.spawn([process.execPath, '-e', 'setInterval(() => {}, 1000)'], { stdio: ['ignore', 'ignore', 'ignore'] });
+    try {
+      for (const target of [process.pid, child.pid]) {
+        const script = `(Get-CimInstance Win32_Process -Filter 'ProcessId = ${target}' | Select-Object CreationDate | ConvertTo-Json -Compress)`;
+        const legacy = childProcess.spawnSync('powershell.exe', ['-NoProfile', '-NonInteractive', '-Command', script], { encoding: 'utf8', windowsHide: true, timeout: 60_000 });
+        expect(legacy.status).toBe(0);
+        const recorded = JSON.parse(legacy.stdout).CreationDate;
+        expect(recorded).toMatch(/^\/Date\(\d+\)\/$/);
+        expect(win32CreationTimeSource.read(target)).toBe(recorded);
+        expect(readAgentStartTime(target)).toBe(recorded);
+      }
+    } finally {
+      child.kill();
+    }
+  }, 150_000);
+
+  test.skipIf(process.platform !== 'win32')('a live agent whose identity cannot be read blocks a second agent', () => {
+    const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-unknown-'));
+    const script = path.join(tmpDir, 'fake-agent.ts');
+    fs.writeFileSync(script, '// no-op\n');
+    const live = Bun.spawn([process.execPath, '-e', 'setInterval(() => {}, 1000)'], { stdio: ['ignore', 'ignore', 'ignore'] });
+    writeAgentRecord(tmpDir, { pid: live.pid, gen, startTime: birth, startedAt: 0, ownerPid: process.pid, ownerStartTime: birth });
+    const original = childProcess.spawnSync;
+    const probe = spyOn(childProcess, 'spawnSync').mockImplementation(((command: string, args: string[], options: any) => (
+      command === 'powershell.exe' ? { status: null, stdout: '', stderr: '' } : original(command, args, options)
+    )) as typeof childProcess.spawnSync);
+    const read = spyOn(win32CreationTimeSource, 'read').mockImplementation(() => undefined);
+    const origSpawn = (Bun as any).spawn;
+    let spawned = 0;
+    (Bun as any).spawn = () => { spawned++; throw new Error('a second agent must not start'); };
+    try {
+      expect(spawnTerminalAgent({ stateFile: path.join(tmpDir, 'state.json'), serverPort: 12345, ownerPid: process.pid, cwd: tmpDir, scriptPath: script })).toBeNull();
+      expect(spawned).toBe(0);
+      expect(isProcessAlive(live.pid)).toBe(true);
+    } finally {
+      (Bun as any).spawn = origSpawn;
+      read.mockRestore();
+      probe.mockRestore();
+      live.kill();
+      fs.rmSync(tmpDir, { recursive: true, force: true, maxRetries: 5 });
+    }
+  });
+});