fix: harden loop-status snapshot writes

scripts/loop-status.js

@@ -614,12 +614,20 @@ function hashString(value) {
   return crypto.createHash('sha256').update(String(value)).digest('hex');
 }
 
+function isWindowsReservedBasename(value) {
+  const basename = String(value).split('.')[0];
+  return /^(con|prn|aux|nul|com[1-9]|lpt[1-9])$/i.test(basename);
+}
+
 function sanitizeSnapshotName(value, fallback = 'session') {
   const raw = String(value || '').trim() || fallback;
   const sanitized = raw.replace(/[^a-zA-Z0-9._-]/g, '_').replace(/^_+|_+$/g, '');
-  if (sanitized && sanitized.length <= 96) {
+  if (sanitized && sanitized.length <= 96 && !isWindowsReservedBasename(sanitized)) {
     return sanitized;
   }
+  if (sanitized && isWindowsReservedBasename(sanitized)) {
+    return `${sanitized}-${hashString(raw).slice(0, 8)}`;
+  }
 
   const prefix = sanitized ? sanitized.slice(0, 48).replace(/[._-]+$/g, '') : fallback;
   return `${prefix || fallback}-${hashString(raw).slice(0, 12)}`;
@@ -629,7 +637,18 @@ function atomicWriteJson(filePath, payload) {
   const data = JSON.stringify(payload, null, 2) + '\n';
   const tempPath = `${filePath}.${process.pid}.${Date.now()}.${Math.random().toString(16).slice(2)}.tmp`;
   fs.writeFileSync(tempPath, data, 'utf8');
+  try {
     fs.renameSync(tempPath, filePath);
+  } catch (error) {
+    try {
+      fs.unlinkSync(tempPath);
+    } catch (cleanupError) {
+      if (cleanupError.code !== 'ENOENT') {
+        console.error(`[loop-status] WARNING: could not remove temporary snapshot file ${tempPath}: ${cleanupError.message}`);
+      }
+    }
+    throw error;
+  }
 }
 
 function getSnapshotPath(outputDir, session, usedNames) {

tests/scripts/loop-status.test.js

@@ -6,10 +6,16 @@ const assert = require('assert');
 const fs = require('fs');
 const os = require('os');
 const path = require('path');
-const { execFileSync } = require('child_process');
+const { spawnSync } = require('child_process');
 
 const SCRIPT = path.join(__dirname, '..', '..', 'scripts', 'loop-status.js');
-const { analyzeTranscript, buildStatus, getStatusExitCode, parseArgs } = require('../../scripts/loop-status');
+const {
+  analyzeTranscript,
+  buildStatus,
+  getStatusExitCode,
+  parseArgs,
+  writeStatusSnapshots,
+} = require('../../scripts/loop-status');
 const NOW = '2026-04-30T10:00:00.000Z';
 
 function run(args = [], options = {}) {
@@ -25,8 +31,7 @@ function run(args = [], options = {}) {
     envOverrides.HOME = envOverrides.USERPROFILE;
   }
 
-  try {
+  const result = spawnSync('node', [SCRIPT, ...args], {
-    const stdout = execFileSync('node', [SCRIPT, ...args], {
     encoding: 'utf8',
     stdio: ['pipe', 'pipe', 'pipe'],
     timeout: 10000,
@@ -36,15 +41,13 @@ function run(args = [], options = {}) {
       ...envOverrides,
     },
   });
-    return { code: 0, stdout, stderr: '' };
+
-  } catch (error) {
   return {
-      code: error.status || 1,
+    code: result.status || (result.signal ? 1 : 0),
-      stdout: error.stdout || '',
+    stdout: result.stdout || '',
-      stderr: error.stderr || '',
+    stderr: result.stderr || '',
   };
 }
-}
 
 function createTempHome() {
   return fs.mkdtempSync(path.join(os.tmpdir(), 'ecc-loop-status-home-'));
@@ -631,6 +634,77 @@ function runTests() {
     }
   })) passed++; else failed++;
 
+  if (test('avoids Windows reserved basenames for session snapshots', () => {
+    const homeDir = createTempHome();
+    const snapshotDir = fs.mkdtempSync(path.join(os.tmpdir(), 'ecc-loop-status-windows-name-'));
+
+    try {
+      writeTranscript(homeDir, '-Users-affoon-project-windows-name', 'con.jsonl', [
+        assistantMessage('2026-04-30T09:55:00.000Z', 'con', 'Loop checkpoint.'),
+      ]);
+
+      const result = run([
+        '--home',
+        homeDir,
+        '--now',
+        NOW,
+        '--json',
+        '--write-dir',
+        snapshotDir,
+      ]);
+
+      assert.strictEqual(result.code, 0, result.stderr);
+
+      const indexPath = path.join(snapshotDir, 'index.json');
+      const indexPayload = JSON.parse(fs.readFileSync(indexPath, 'utf8'));
+      const snapshotName = path.basename(indexPayload.sessions[0].snapshotPath);
+      assert.strictEqual(indexPayload.sessions[0].sessionId, 'con');
+      assert.notStrictEqual(snapshotName.toLowerCase(), 'con.json');
+
+      const snapshotPayload = JSON.parse(fs.readFileSync(indexPayload.sessions[0].snapshotPath, 'utf8'));
+      assert.strictEqual(snapshotPayload.schemaVersion, 'ecc.loop-status.session.v1');
+      assert.strictEqual(snapshotPayload.session.sessionId, 'con');
+    } finally {
+      fs.rmSync(homeDir, { recursive: true, force: true });
+      fs.rmSync(snapshotDir, { recursive: true, force: true });
+    }
+  })) passed++; else failed++;
+
+  if (test('cleans temporary snapshot files when atomic rename fails', () => {
+    const snapshotDir = fs.mkdtempSync(path.join(os.tmpdir(), 'ecc-loop-status-rename-failure-'));
+    const originalRenameSync = fs.renameSync;
+
+    try {
+      fs.renameSync = () => {
+        throw new Error('simulated rename failure');
+      };
+
+      assert.throws(() => writeStatusSnapshots({
+        errors: [],
+        generatedAt: NOW,
+        sessions: [
+          {
+            eventCount: 1,
+            lastEventAt: NOW,
+            pendingTools: [],
+            recommendedAction: 'No action needed.',
+            sessionId: 'rename-failure',
+            signals: [],
+            state: 'ok',
+            transcriptPath: path.join(snapshotDir, 'rename-failure.jsonl'),
+          },
+        ],
+        source: {},
+      }, snapshotDir), /simulated rename failure/);
+
+      const tempFiles = fs.readdirSync(snapshotDir).filter(fileName => fileName.endsWith('.tmp'));
+      assert.deepStrictEqual(tempFiles, []);
+    } finally {
+      fs.renameSync = originalRenameSync;
+      fs.rmSync(snapshotDir, { recursive: true, force: true });
+    }
+  })) passed++; else failed++;
+
   if (test('write-dir failures do not suppress normal stdout', () => {
     const homeDir = createTempHome();
 
@@ -655,6 +729,7 @@ function runTests() {
       const payload = parsePayload(result.stdout);
       assert.strictEqual(payload.schemaVersion, 'ecc.loop-status.v1');
       assert.strictEqual(payload.sessions[0].sessionId, 'session-write-error');
+      assert.match(result.stderr, /\[loop-status\] WARNING: could not write status snapshots:/);
     } finally {
       fs.rmSync(homeDir, { recursive: true, force: true });
     }