fix: reject invalid history parents on Windows and give questions exclusive composer

scripts/protocol-bridge-regression.ts

@@ -1,5 +1,7 @@
 import assert from 'node:assert/strict'
-import { mkdtemp, readFile, stat, writeFile, rm } from 'node:fs/promises'
+import fs, { mkdir, mkdtemp, readFile, realpath, stat, symlink, writeFile, rm } from 'node:fs/promises'
+import { syncBuiltinESMExports } from 'node:module'
+import { mock } from 'node:test'
 import { join } from 'node:path'
 import { tmpdir } from 'node:os'
 import { createConversionContext } from '../src/main/model-bridge/history'
@@ -158,7 +160,7 @@ try {
     } finally { await Promise.all([lease.close(), lease.close()]) }
     await assert.rejects(fetch(lease.baseUrl)); checks++
   }
-  const dir = await mkdtemp(join(tmpdir(), 'ycode-bridge-'))
+  const dir = await mkdtemp(join(await realpath(tmpdir()), 'ycode-bridge-'))
   try {
     for (const reasoningMode of ['hidden', 'reasoning']) {
       const file = join(dir, reasoningMode + '.json')
@@ -207,6 +209,61 @@ try {
     await writeFile(join(dir, 'blocked'), 'not a directory')
     const blocked = await createConversionContext(join(dir, 'blocked', 'history.json')).catch(() => null)
     check(blocked === null, 'Invalid history path fails closed')
+    await assert.rejects(createConversionContext(join(dir, 'blocked', 'missing', 'history.json')), /history/); checks++
+    await assert.rejects(createConversionContext(dir), /history/); checks++
+    const missingFile = join(dir, 'new', 'nested', 'history.json')
+    const fresh = await createConversionContext(missingFile)
+    check(fresh.responsesHistory.size === 0, 'Genuinely missing parents allow a new history')
+    await fresh.persist!()
+    check((await createConversionContext(missingFile)).responsesHistory.size === 0, 'New nested history persists and reloads')
+
+    // Simulate Windows' leaf ENOENT below a regular-file parent on every platform.
+    const blockedFile = join(dir, 'blocked', 'history.json'), originalLstat = fs.lstat
+    mock.method(fs, 'lstat', async (...args: Parameters<typeof fs.lstat>) => {
+      if (String(args[0]) === blockedFile) throw Object.assign(new Error('missing'), { code: 'ENOENT' })
+      return originalLstat(...args)
+    })
+    syncBuiltinESMExports()
+    try { await assert.rejects(createConversionContext(blockedFile), /history/); checks++ }
+    finally { mock.restoreAll(); syncBuiltinESMExports() }
+
+    // Missing during read is not a new conversation; permission errors are never absence.
+    for (const [method, code, target] of [['readFile', 'ENOENT', snapshotFile], ['lstat', 'EACCES', snapshotFile], ['lstat', 'EACCES', dir]] as const) {
+      const original = fs[method]
+      mock.method(fs, method, async (...args: any[]) => {
+        if (String(args[0]) === target) throw Object.assign(new Error('unavailable'), { code })
+        return (original as Function)(...args)
+      })
+      syncBuiltinESMExports()
+      try { await assert.rejects(createConversionContext(snapshotFile), /history/); checks++ }
+      finally { mock.restoreAll(); syncBuiltinESMExports() }
+    }
+
+    const linkedDir = join(dir, 'linked'), targetDir = join(dir, 'target')
+    await mkdir(targetDir)
+    await symlink(targetDir, linkedDir, process.platform === 'win32' ? 'junction' : 'dir')
+    const linked = await createConversionContext(join(linkedDir, 'history.json'))
+    await linked.persist!()
+    check((await createConversionContext(join(targetDir, 'history.json'))).responsesHistory.size === 0, 'Trusted parent directory links remain supported')
+    const changedFile = join(dir, 'changed', 'history.json'), changed = await createConversionContext(changedFile)
+    await writeFile(join(dir, 'changed'), 'not a directory')
+    await assert.rejects(changed.persist!(), /history/); checks++
+    const danglingDir = join(dir, 'dangling')
+    await symlink(join(dir, 'absent-target'), danglingDir, process.platform === 'win32' ? 'junction' : 'dir')
+    await assert.rejects(createConversionContext(join(danglingDir, 'history.json')), /history/); checks++
+    if (process.platform !== 'win32') {
+      const linkedFile = join(dir, 'linked.json')
+      await symlink(snapshotFile, linkedFile)
+      await assert.rejects(createConversionContext(linkedFile), /history/); checks++
+    }
+
+    const concurrentFile = join(dir, 'concurrent.json')
+    const [left, right] = await Promise.all([createConversionContext(concurrentFile), createConversionContext(concurrentFile)])
+    left.responsesHistory.set(`${'a'.repeat(64)}:${'b'.repeat(64)}`, [])
+    right.responsesHistory.set(`${'c'.repeat(64)}:${'d'.repeat(64)}`, [])
+    await Promise.all([left.persist!(), right.persist!()])
+    check((await createConversionContext(concurrentFile)).responsesHistory.size === 2, 'Concurrent atomic history saves preserve both snapshots')
+    check(!(await fs.readdir(dir)).some(name => name.endsWith('.tmp')), 'Atomic history saves leave no temporary files')
   } finally { await rm(dir, { recursive: true, force: true }) }
 } finally { upstream.closeAllConnections(); await new Promise<void>(resolve => upstream.close(() => resolve())) }
 console.log(`Protocol bridge offline regression: ${checks} checks passed (no SDK/CLI or external API used)`)