diff --git a/src/codex-cache.ts b/src/codex-cache.ts
index 967af2154..9120f77b6 100644
--- a/src/codex-cache.ts
+++ b/src/codex-cache.ts
@@ -1,4 +1,4 @@
-import { readFile, mkdir, stat, open, rename, unlink } from 'fs/promises'
+import { readFile, readdir, mkdir, stat, open, rename, unlink } from 'fs/promises'
 import { existsSync } from 'fs'
 import { randomBytes } from 'crypto'
 import { join, resolve } from 'path'
@@ -137,6 +137,47 @@ function isCurrentCache(cache: ResultCache): boolean {
   return cache.version === CODEX_CACHE_VERSION && !!cache.files && typeof cache.files === 'object'
 }
 
+// Legacy temporary files have no owner information. Give recent writes a full day
+// before reclaiming them; new temporary files also identify their live writer.
+const ORPHAN_AGE_MS = 24 * 60 * 60 * 1000
+
+function errorMessage(error: unknown): string {
+  return error instanceof Error ? error.message : String(error)
+}
+
+async function cleanOrphanedTemps(dir: string): Promise<void> {
+  try {
+    const names = await readdir(dir)
+    for (const name of names) {
+      const match = /^codex-(?:results(?:\.v\d+)?|projects\.v\d+)\.json\.[a-f0-9]{16}(?:\.(\d+))?\.tmp$/.exec(name)
+      if (!match) continue
+      if (match[1]) {
+        try {
+          process.kill(Number(match[1]), 0)
+          continue // Never unlink a live writer's file, even if it is old.
+        } catch (error) {
+          if ((error as NodeJS.ErrnoException).code !== 'ESRCH') continue
+        }
+      }
+      const path = join(dir, name)
+      try {
+        const info = await stat(path)
+        if (!info.isFile()) continue
+        console.warn(`[codeburn] Found unfinished Codex cache write: ${path} (${info.size} bytes). The disk cache may be stale; source fingerprints will be checked.`)
+        if (match[1] || Date.now() - info.mtimeMs >= ORPHAN_AGE_MS) await unlink(path)
+      } catch (error) {
+        if ((error as NodeJS.ErrnoException).code !== 'ENOENT') {
+          console.warn(`[codeburn] Could not clean Codex cache temporary file ${path}: ${errorMessage(error)}`)
+        }
+      }
+    }
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code !== 'ENOENT') {
+      console.warn(`[codeburn] Could not inspect unfinished Codex cache writes in ${dir}: ${errorMessage(error)}`)
+    }
+  }
+}
+
 // Embedded consumers can change CODEBURN_CACHE_DIR without reloading this
 // module. Keep each directory's in-memory state separate so a warm cache (or an
 // unflushed update) from A can never be read from or written into B.
@@ -180,23 +221,34 @@ async function writeProjectIndex(cacheDir: string, cache: ResultCache): Promise<
   }
   try {
     await writeFileAtomic(join(cacheDir, codexProjectsFileName()), JSON.stringify({ version: CODEX_CACHE_VERSION, files }))
-  } catch {}
+  } catch (error) {
+    console.warn(`[codeburn] Failed to update Codex project index ${join(cacheDir, codexProjectsFileName())}; the disk cache may be stale: ${errorMessage(error)}`)
+  }
 }
 
 async function writeFileAtomic(finalPath: string, payload: string): Promise<void> {
-  const tempPath = `${finalPath}.${randomBytes(8).toString('hex')}.tmp`
-  const handle = await open(tempPath, 'w', 0o600)
-  try {
-    await handle.writeFile(payload, { encoding: 'utf-8' })
-    await handle.sync()
-  } finally {
-    await handle.close()
-  }
+  const tempPath = `${finalPath}.${randomBytes(8).toString('hex')}.${process.pid}.tmp`
+  let ownsTemp = false
   try {
+    const handle = await open(tempPath, 'wx', 0o600)
+    ownsTemp = true
+    try {
+      await handle.writeFile(payload, { encoding: 'utf-8' })
+      await handle.sync()
+    } finally {
+      await handle.close()
+    }
     await rename(tempPath, finalPath)
-  } catch (err) {
-    try { await unlink(tempPath) } catch {}
-    throw err
+  } finally {
+    // Cover write, fsync, close, and rename failures. Never remove a file we
+    // did not create (for example, after an exclusive-open collision).
+    if (ownsTemp) {
+      try { await unlink(tempPath) } catch (error) {
+        if ((error as NodeJS.ErrnoException).code !== 'ENOENT') {
+          console.warn(`[codeburn] Could not remove Codex cache temporary file ${tempPath}: ${errorMessage(error)}`)
+        }
+      }
+    }
   }
 }
 
@@ -216,6 +268,7 @@ function loadCache(cacheDir: string): Promise<ResultCache> {
 }
 
 async function loadCacheFromDisk(cacheDir: string): Promise<ResultCache> {
+  await cleanOrphanedTemps(cacheDir)
   const empty = { version: CODEX_CACHE_VERSION, files: {} }
   const versioned = await readExistingTextFile(getCachePath(cacheDir))
   if (versioned.status === 'ok') {
@@ -387,6 +440,7 @@ export async function flushCodexCache(): Promise<void> {
   const memCache = memCaches.get(cacheDir)
   if (!memCache) return
   try {
+    await cleanOrphanedTemps(cacheDir)
     // Evict entries for files that no longer exist on disk
     const paths = Object.keys(memCache.files)
     for (const p of paths) {
@@ -406,5 +460,8 @@ export async function flushCodexCache(): Promise<void> {
     await writeFileAtomic(getCachePath(cacheDir), JSON.stringify(memCache))
     await writeProjectIndex(cacheDir, memCache)
     projectIndexes.delete(cacheDir)
-  } catch {}
+  } catch (error) {
+    // Persistence is optional; reports can still use the parsed results.
+    console.warn(`[codeburn] Failed to update Codex cache ${getCachePath(cacheDir)}; the disk cache may be stale: ${errorMessage(error)}`)
+  }
 }
diff --git a/tests/codex-cache-write.test.ts b/tests/codex-cache-write.test.ts
new file mode 100644
index 000000000..e68bc8b5c
--- /dev/null
+++ b/tests/codex-cache-write.test.ts
@@ -0,0 +1,170 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { mkdir, mkdtemp, readFile, readdir, rm, stat, utimes, writeFile } from 'fs/promises'
+import { join, resolve } from 'path'
+import type { ParsedProviderCall } from '../src/providers/types.js'
+
+const faults = vi.hoisted(() => ({ stage: '', bytes: 0, target: 'codex-results.' }))
+vi.mock('fs/promises', async (importOriginal) => {
+  const fs = await importOriginal<typeof import('fs/promises')>()
+  return {
+    ...fs,
+    open: async (...args: Parameters<typeof fs.open>) => {
+      const handle = await fs.open(...args)
+      const inject = String(args[0]).includes(faults.target)
+      return {
+        writeFile: async (payload: string, options: { encoding: BufferEncoding }) => {
+          if (inject && faults.stage === 'write') {
+            await handle.writeFile(payload.slice(0, faults.bytes), options)
+            throw new Error('injected write EIO')
+          }
+          await handle.writeFile(payload, options)
+        },
+        sync: async () => {
+          if (inject && faults.stage === 'sync') throw new Error('injected sync EIO')
+          await handle.sync()
+        },
+        close: async () => {
+          await handle.close()
+          if (inject && faults.stage === 'close') throw new Error('injected close EIO')
+        },
+      }
+    },
+    rename: async (...args: Parameters<typeof fs.rename>) => {
+      if (String(args[0]).includes(faults.target) && faults.stage === 'rename') throw new Error('injected rename EACCES')
+      return fs.rename(...args)
+    },
+  }
+})
+
+let dir: string
+let session: string
+let finalPath: string
+let previous: string
+let mod: typeof import('../src/codex-cache.js')
+let warning: ReturnType<typeof vi.spyOn>
+const calls = (costUSD: number) => [{ costUSD }] as ParsedProviderCall[]
+
+beforeEach(async () => {
+  vi.resetModules()
+  faults.stage = ''
+  faults.bytes = 0
+  faults.target = 'codex-results.'
+  await mkdir(resolve('.cache'), { recursive: true })
+  dir = await mkdtemp(resolve('.cache/codex-write-'))
+  vi.stubEnv('CODEBURN_CACHE_DIR', dir)
+  warning = vi.spyOn(console, 'warn').mockImplementation(() => {})
+  session = join(dir, 'session.jsonl')
+  await writeFile(session, '{}\n')
+  mod = await import('../src/codex-cache.js')
+  finalPath = join(dir, mod.codexCacheFileName())
+  const fp = (await mod.fingerprintFile(session))!
+  await mod.writeCachedCodexResults(session, 'project', calls(1), fp)
+  await mod.flushCodexCache()
+  previous = await readFile(finalPath, 'utf8')
+  await mod.writeCachedCodexResults(session, 'project', calls(2), fp)
+})
+
+afterEach(async () => {
+  vi.restoreAllMocks()
+  vi.unstubAllEnvs()
+  await rm(dir, { recursive: true, force: true })
+})
+
+describe('Codex cache write failures', () => {
+  it.each([
+    ['write', 0],
+    ['write', 64],
+    ['sync', 0],
+    ['close', 0],
+    ['rename', 0],
+  ])('reports %s failure after %i bytes and preserves the complete cache', async (stage, bytes) => {
+    faults.stage = stage
+    faults.bytes = bytes
+    await mod.flushCodexCache()
+    expect(warning.mock.calls.flat().join(' ')).toContain(`injected ${stage}`)
+    expect(warning.mock.calls.flat().join(' ')).toContain('stale')
+    expect(warning.mock.calls.flat().join(' ')).toContain(finalPath)
+    expect(await readFile(finalPath, 'utf8')).toBe(previous)
+    expect((await readdir(dir)).filter(name => name.endsWith('.tmp'))).toEqual([])
+    faults.stage = ''
+    await mod.flushCodexCache()
+    expect(JSON.parse(await readFile(finalPath, 'utf8')).files[session].calls[0].costUSD).toBe(2)
+  })
+
+  it.each(['write', 'sync', 'close', 'rename'])('reports project-index %s failures and cleans up', async (stage) => {
+    const indexPath = join(dir, mod.codexProjectsFileName())
+    const previousIndex = await readFile(indexPath, 'utf8')
+    faults.target = 'codex-projects.'
+    faults.stage = stage
+    await mod.flushCodexCache()
+    expect(warning.mock.calls.flat().join(' ')).toContain(`injected ${stage}`)
+    expect(warning.mock.calls.flat().join(' ')).toContain(indexPath)
+    expect(await readFile(indexPath, 'utf8')).toBe(previousIndex)
+    expect(JSON.parse(await readFile(finalPath, 'utf8')).files[session].calls[0].costUSD).toBe(2)
+    expect((await readdir(dir)).filter(name => name.endsWith('.tmp'))).toEqual([])
+    faults.stage = ''
+    await mod.flushCodexCache()
+    expect(warning.mock.calls.flat().join(' ')).toContain('stale')
+  })
+
+  it('reports and removes old empty and partial orphans on a cache read', async () => {
+    const empty = join(dir, 'codex-results.json.0123456789abcdef.tmp')
+    const partial = join(dir, 'codex-results.json.fedcba9876543210.tmp')
+    const recent = join(dir, 'codex-results.json.1111111111111111.tmp')
+    const unrelated = join(dir, 'other.tmp')
+    for (const [path, content] of [[empty, ''], [partial, '{"version":'], [recent, 'in progress'], [unrelated, 'keep']]) {
+      await writeFile(path, content)
+    }
+    const old = new Date(Date.now() - 48 * 60 * 60 * 1000)
+    await utimes(empty, old, old)
+    await utimes(partial, old, old)
+    vi.resetModules()
+    mod = await import('../src/codex-cache.js')
+    expect(await mod.readCachedCodexResults(session)).toEqual({ kind: 'exact', calls: calls(1) })
+    expect(warning.mock.calls.flat().join(' ')).toContain('unfinished')
+    expect(await readdir(dir)).not.toContain(empty.split('/').at(-1))
+    expect(await readdir(dir)).not.toContain(partial.split('/').at(-1))
+    expect(await readFile(recent, 'utf8')).toBe('in progress')
+    expect(await readFile(unrelated, 'utf8')).toBe('keep')
+    expect(await readFile(finalPath, 'utf8')).toBe(previous)
+  })
+
+  it('reclaims a dead writer immediately but leaves a live writer alone', async () => {
+    const dead = join(dir, `${mod.codexProjectsFileName()}.2222222222222222.2147483647.tmp`)
+    const live = join(dir, `${mod.codexCacheFileName()}.3333333333333333.${process.pid}.tmp`)
+    await writeFile(dead, 'partial')
+    await writeFile(live, 'active')
+    const old = new Date(Date.now() - 48 * 60 * 60 * 1000)
+    await utimes(live, old, old)
+    vi.resetModules()
+    mod = await import('../src/codex-cache.js')
+    await mod.readCachedCodexResults(session)
+    expect(await readdir(dir)).not.toContain(dead.split('/').at(-1))
+    expect(await readFile(live, 'utf8')).toBe('active')
+    expect(warning.mock.calls.flat().join(' ')).toContain('unfinished')
+  })
+
+  it('does not serve the old entry when a session changes after a failed flush', async () => {
+    faults.stage = 'write'
+    faults.bytes = 64
+    await mod.flushCodexCache()
+    await writeFile(session, '{"new":"session data"}\n')
+    vi.resetModules()
+    mod = await import('../src/codex-cache.js')
+    expect(await mod.readCachedCodexResults(session)).toBeNull()
+    expect(await mod.getCachedCodexProject(session)).toBeNull()
+    expect((await stat(finalPath)).size).toBe(Buffer.byteLength(previous))
+  })
+
+  it('writes a cache larger than 60 MB completely', async () => {
+    await mod.writeCachedCodexResults(session, 'project', [
+      { costUSD: 3, userMessage: 'x'.repeat(60_543_405) } as ParsedProviderCall,
+    ], (await mod.fingerprintFile(session))!)
+    await mod.flushCodexCache()
+    const raw = await readFile(finalPath, 'utf8')
+    expect(raw.length).toBeGreaterThan(60_543_405)
+    expect(JSON.parse(raw).files[session].calls[0].userMessage.length).toBe(60_543_405)
+    expect((await readdir(dir)).filter(name => name.endsWith('.tmp'))).toEqual([])
+    expect(warning).not.toHaveBeenCalled()
+  })
+})