diff --git a/scripts/plan-canvas.js b/scripts/plan-canvas.js
index f55ddf511..82aa7a4f6 100755
--- a/scripts/plan-canvas.js
+++ b/scripts/plan-canvas.js
@@ -182,7 +182,17 @@ function processIsAlive(pid) {
   }
 }
 
+let currentProcessIdentity = null;
+
 function readProcessIdentity(pid) {
+  // Only our own PID is safe to cache: other processes can exit and reuse a PID.
+  if (pid === process.pid && currentProcessIdentity !== null) return currentProcessIdentity;
+  const identity = queryProcessIdentity(pid);
+  if (pid === process.pid && identity !== null) currentProcessIdentity = identity;
+  return identity;
+}
+
+function queryProcessIdentity(pid) {
   if (!Number.isInteger(pid) || pid <= 0) return null;
   try {
     if (process.platform === 'linux') {
@@ -198,7 +208,8 @@ function readProcessIdentity(pid) {
       const startTicks = execFileSync(
         'powershell.exe',
         ['-NoProfile', '-NonInteractive', '-Command', command],
-        { encoding: 'utf8', stdio: ['ignore', 'pipe', 'ignore'], timeout: 3000, windowsHide: true }
+        // Cold PowerShell startup on loaded Windows runners can exceed three seconds.
+        { encoding: 'utf8', stdio: ['ignore', 'pipe', 'ignore'], timeout: 10000, windowsHide: true }
       ).trim();
       return startTicks ? `win32:${startTicks}` : null;
     }
diff --git a/tests/integration/plan-canvas-e2e.test.js b/tests/integration/plan-canvas-e2e.test.js
index 75667ac15..d62d446bd 100644
--- a/tests/integration/plan-canvas-e2e.test.js
+++ b/tests/integration/plan-canvas-e2e.test.js
@@ -22,6 +22,8 @@ const fs = require('fs');
 const http = require('http');
 const os = require('os');
 const path = require('path');
+const vm = require('vm');
+const { createRequire } = require('module');
 const { spawn, spawnSync } = require('child_process');
 
 const CLI = path.join(__dirname, '..', '..', 'scripts', 'plan-canvas.js');
@@ -144,6 +146,41 @@ async function main() {
   let key = null;
 
   try {
+    await test('Windows startup identity tolerates slow PowerShell and reuses the current process identity', async () => {
+      const module = { exports: {} };
+      const cliRequire = createRequire(CLI);
+      let lookups = 0;
+      vm.runInNewContext(fs.readFileSync(CLI, 'utf8'), {
+        module,
+        require: name => name === 'child_process' ? {
+          execFileSync: (command, args, options) => {
+            assert.strictEqual(command, 'powershell.exe');
+            lookups += 1;
+            // Model a cold PowerShell launch exceeding the old three-second budget.
+            if (options.timeout < 5000) throw Object.assign(new Error('timed out'), { code: 'ETIMEDOUT' });
+            return '638920000000000000\r\n';
+          }
+        } : cliRequire(name),
+        process: { pid: process.pid, platform: 'win32', kill: process.kill.bind(process) },
+        setTimeout,
+        URL,
+        Buffer
+      }, { filename: CLI });
+      const lockDir = path.join(tmp, 'windows-startup-locks');
+      let active = 0;
+      let maximumActive = 0;
+      const runLocked = () => module.exports.withServerStartLock(port + 7, async () => {
+        active += 1;
+        maximumActive = Math.max(maximumActive, active);
+        await new Promise(resolve => setTimeout(resolve, 40));
+        active -= 1;
+      }, { lockDir, timeoutMs: 2000 });
+      await Promise.all([runLocked(), runLocked()]);
+      assert.strictEqual(maximumActive, 1);
+      assert.strictEqual(lookups, 1, 'same-process tickets must reuse the successful identity lookup');
+      assert.deepStrictEqual(fs.readdirSync(lockDir), []);
+    });
+
     await test('port-scoped startup lock serializes server replacement callers', async () => {
       const lockDir = path.join(tmp, 'startup-locks');
       let active = 0;