diff --git a/scripts/lib/state-store/file-lock.js b/scripts/lib/state-store/file-lock.js
index 200622299..02a18c533 100644
--- a/scripts/lib/state-store/file-lock.js
+++ b/scripts/lib/state-store/file-lock.js
@@ -73,7 +73,10 @@ function acquireLock(dbPath, timeoutMs) {
     try {
       descriptor = fs.openSync(lockPath, 'wx', 0o600);
     } catch (error) {
-      if (!hasCode(error, 'EEXIST')) throw error;
+      // Windows may report EPERM while the previous owner's unlinked file is
+      // pending deletion. Retry exclusive creation within the same deadline.
+      const pendingDelete = process.platform === 'win32' && hasCode(error, 'EPERM');
+      if (!hasCode(error, 'EEXIST') && !pendingDelete) throw error;
       const remaining = deadline - performance.now();
       if (remaining <= 0) {
         const busy = new Error(`State store is busy: ${dbPath}. Retry after the other ECC operation finishes. `
diff --git a/tests/lib/helpers/state-store-worker.js b/tests/lib/helpers/state-store-worker.js
index ccb6294f3..184921a9e 100644
--- a/tests/lib/helpers/state-store-worker.js
+++ b/tests/lib/helpers/state-store-worker.js
@@ -30,11 +30,12 @@ function startOwnedChild(script, args = [], dependencies = {}) {
   let child;
   try {
     fs.mkdirSync(home); fs.mkdirSync(tmp);
-    const dependencyRoot = path.resolve(path.dirname(require.resolve('sql.js/package.json')), '..');
+    // Absolute fixture paths resolve dependencies from the checkout, even with
+    // an isolated cwd. No package-private metadata or NODE_PATH is needed.
     child = forkChild(script, args, {
       execPath: process.execPath, execArgv: [], shell: false, detached: platform !== 'win32',
       cwd: root, stdio: ['ignore', 'pipe', 'pipe', 'ipc'],
-      env: { PATH: path.dirname(process.execPath), NODE_PATH: dependencyRoot,
+      env: { PATH: path.dirname(process.execPath),
         HOME: home, USERPROFILE: home, APPDATA: home, LOCALAPPDATA: home,
         TMPDIR: tmp, TMP: tmp, TEMP: tmp, NODE_USE_ENV_PROXY: '0' },
     });
@@ -47,6 +48,8 @@ function startOwnedChild(script, args = [], dependencies = {}) {
   const closeWaiters = new Set();
   let ownedPid = null;
   let closed = false;
+  let ipcClosed = false;
+  const closedStreams = new Set();
   let reaped = false;
   let exitCode = null;
   let exitSignal = null;
@@ -59,17 +62,25 @@ function startOwnedChild(script, args = [], dependencies = {}) {
     if (!failed) { failed = true; failure = error; }
     for (const waiter of [...waiters]) waiter.reject(error);
   };
+  const markClosed = () => {
+    closed = true;
+    for (const done of [...closeWaiters]) done(true);
+  };
+  // Some Node versions omit the aggregate close event after a parent-initiated
+  // IPC disconnect. Require public confirmation of every owned resource instead.
+  const checkClosed = () => {
+    if (reaped && ipcClosed && closedStreams.size === 2) markClosed();
+  };
+  child.once('disconnect', () => { ipcClosed = true; checkClosed(); });
   child.once('spawn', () => { if (Number.isInteger(child.pid) && child.pid > 0) ownedPid = child.pid; });
   child.on('error', fail);
   child.once('exit', (code, signal) => {
     reaped = true; exitCode = code; exitSignal = signal;
     const error = new Error(`Fixture exited (${code}, ${signal || 'no signal'}): ${stderr}`);
     for (const waiter of [...waiters]) waiter.reject(error);
+    checkClosed();
   });
-  child.once('close', () => {
-    closed = true;
-    for (const done of [...closeWaiters]) done(true);
-  });
+  child.once('close', markClosed);
   child.on('message', message => {
     for (const observer of [...observers]) {
       try { observer(message); } catch (error) { fail(error); }
@@ -77,6 +88,7 @@ function startOwnedChild(script, args = [], dependencies = {}) {
     for (const waiter of [...waiters]) waiter.check(message);
   });
   for (const stream of [child.stdout, child.stderr]) {
+    stream.once('close', () => { closedStreams.add(stream); checkClosed(); });
     stream.on('data', data => {
       captured += data.length;
       if (captured > 128 * 1024) { fail(new Error('Fixture output exceeded 128 KiB')); return; }
diff --git a/tests/lib/state-store-concurrency.test.js b/tests/lib/state-store-concurrency.test.js
index d9dfbb082..c96a27196 100644
--- a/tests/lib/state-store-concurrency.test.js
+++ b/tests/lib/state-store-concurrency.test.js
@@ -4,6 +4,7 @@ const assert = require('assert');
 const fs = require('fs');
 const os = require('os');
 const path = require('path');
+const { EventEmitter } = require('events');
 const { startOwnedChild, withOwnedChildren, withCleanup } = require('./helpers/state-store-worker');
 const { createStateStore } = require('../../scripts/lib/state-store');
 
@@ -61,6 +62,37 @@ async function run() {
 
   console.log('\n=== Testing state-store concurrency ===\n');
 
+  await test('owned fixtures wait for exit, both pipes, and IPC when aggregate close is absent', async () => {
+    const events = ['exit', 'stdout', 'stderr', 'disconnect'];
+    for (const last of events) {
+      const child = new EventEmitter();
+      child.stdout = new EventEmitter();
+      child.stderr = new EventEmitter();
+      child.stdout.destroy = () => child.stdout.emit('close');
+      child.stderr.destroy = () => child.stderr.emit('close');
+      child.connected = true;
+      child.pid = 12345;
+      child.disconnect = () => { child.connected = false; };
+      const signals = [];
+      const client = startOwnedChild(WORKER, [], {
+        fork: () => child, platform: 'linux', kill: (...args) => signals.push(args)
+      });
+      child.emit('spawn');
+      const stopping = client.stop();
+      const emit = event => {
+        if (event === 'exit') child.emit('exit', 0, null);
+        else if (event === 'disconnect') child.emit('disconnect');
+        else child[event].emit('close');
+      };
+      for (const event of events.filter(event => event !== last)) emit(event);
+      assert.strictEqual(client.diagnostics.closed, false, `Must wait for ${last}`);
+      emit(last);
+      await stopping;
+      assert.strictEqual(client.diagnostics.closed, true);
+      assert.deepStrictEqual(signals, [], 'Fully closed fixtures need no forced termination');
+    }
+  });
+
   await test('closing an old reader preserves a task saved by the real CLI', async dbPath => {
     const reader = await createStateStore({ dbPath });
     await withCleanup(async () => {
diff --git a/tests/lib/state-store-persistence.test.js b/tests/lib/state-store-persistence.test.js
index 2a8077f66..a6d5609da 100644
--- a/tests/lib/state-store-persistence.test.js
+++ b/tests/lib/state-store-persistence.test.js
@@ -48,10 +48,47 @@ function lockFixture(overrides = {}, platform = 'linux') {
   }
   const lock = loadPrivate(LOCK, { fs: facade, os: { hostname: () => 'fixture' } }, undefined,
     { platform, pid: 7 });
-  return { ...state, calls, run: callback => lock.withStateStoreLock('synthetic.db', callback, { timeoutMs: 0 }) };
+  return { ...state, calls, run: (callback, timeoutMs = 0) => lock.withStateStoreLock('synthetic.db', callback, { timeoutMs }) };
 }
 
 async function runSynthetic(test) {
+  await test('Windows pending-delete EPERM retries until exclusive creation succeeds', () => {
+    const denied = Object.assign(new Error('pending deletion'), { code: 'EPERM' });
+    let attempts = 0;
+    let callbacks = 0;
+    const fixture = lockFixture({ openSync(state, open, file, flags, mode) {
+      assert.strictEqual(file, 'synthetic.db.ecc-state.lock');
+      assert.strictEqual(flags, 'wx');
+      assert.strictEqual(mode, 0o600);
+      attempts += 1;
+      if (attempts === 1) { state.calls.push('open'); throw denied; }
+      return open();
+    } }, 'win32');
+    assert.strictEqual(fixture.run(() => { callbacks += 1; return 'done'; }, 1000), 'done');
+    assert.strictEqual(attempts, 2);
+    assert.strictEqual(callbacks, 1);
+    assert.deepStrictEqual(fixture.calls, ['open', 'open', 'fstat', 'write', 'lstat', 'unlink', 'close']);
+  });
+  await test('sustained Windows open EPERM times out as busy without touching the lock', () => {
+    const denied = Object.assign(new Error('pending deletion'), { code: 'EPERM' });
+    const fixture = lockFixture({ openSync(state) { state.calls.push('open'); throw denied; } }, 'win32');
+    const result = thrownBy(() => fixture.run(() => assert.fail('callback must not run'), 20));
+    assert.ok(result.failed);
+    assert.strictEqual(result.error.code, 'STATE_STORE_BUSY');
+    assert.match(result.error.message, /synthetic\.db\.ecc-state\.lock/);
+    assert.ok(fixture.calls.length > 0);
+    assert.ok(fixture.calls.every(call => call === 'open'));
+  });
+  for (const [platform, code] of [['linux', 'EPERM'], ['darwin', 'EPERM'], ['win32', 'EACCES'], ['win32', 'EIO']]) {
+    await test(`unrelated lock-open errors propagate immediately (${platform}, ${code})`, () => {
+      const denied = Object.assign(new Error('open denied'), { code });
+      const fixture = lockFixture({ openSync(state) { state.calls.push('open'); throw denied; } }, platform);
+      const result = thrownBy(() => fixture.run(() => assert.fail('callback must not run'), 1000));
+      assert.ok(result.failed);
+      assert.strictEqual(result.error, denied);
+      assert.deepStrictEqual(fixture.calls, ['open']);
+    });
+  }
   await test('owned lock unlinks before its only close', () => {
     const fixture = lockFixture();
     assert.strictEqual(fixture.run(() => 'done'), 'done');