The Codex desktop app's execution service (`codex-code-mode-host.exe`) exits during handshake, so every `exec` tool call fails. The error is intermittent but frequent.bug

codex_bug_report.md

Bug Report: "code-mode host exited during handshake"

Summary

The Codex desktop app's execution service (codex-code-mode-host.exe) exits during handshake, so every exec tool call fails. The error is intermittent but frequent.

Error message

error=code-mode host exited during handshake
target=codex_core::tools::router

Environment

• App: ChatGPT desktop app (Codex) — OpenAI.Codex_26.820.7780.0_x64__2p2nqsd0c76g0
• Bundled CLI: codex-cli 0.150.0-alpha.8 (windows-x86_64)
• OS: Windows 10 (10.0.19045, build 19045.6466), Chinese locale, ANSI code page 936 (GBK)
• Model: gpt-5.6-terra / gpt-5.6-sol

When it started

Immediately after the auto-update on 2026-08-26 (~17:47 local time), which bumped the bundled CLI from 0.149.0-alpha.4.x to 0.150.0-alpha.8. No such errors before the update.

Repro steps

1. Open the Codex desktop app.
2. Start any task that triggers the exec tool (e.g. "run echo hello").
3. The exec tool call fails with code-mode host exited during handshake; the model retries and fails repeatedly.

Key observations

• The error is intermittent: some exec calls succeed, then a cluster of failures follows.
• It reproduces in both ASCII and non-ASCII working directories (so it is not path/encoding specific).
• No crash dump or WER report is generated for codex-code-mode-host.exe — the host exits cleanly, so this is a handshake/protocol failure, not a crash.
• Running codex-code-mode-host.exe manually works; it starts and waits for the client hello.
• Disabling the feature code_mode_host makes exec fail closed (the model cannot run commands at all), so that is not a viable workaround.
• codex doctor reports: search command not verified, and a generic Microsoft Defender advisory (exclusions were added but did not resolve the issue).

Impact

All exec-based work (running commands, Python, spreadsheet/document artifact creation, etc.) is blocked intermittently in the desktop app. The older VS Code extension CLI (0.147.0-alpha.6.5) does NOT have this problem.

Log excerpt

codex_core::tools::router (core\src\tools\router.rs:225)
... dispatch_tool_call_with_code_mode_result{otel.name=exec tool_name=exec ...}:dispatch_tool_call_with_terminal_outcome: error=code-mode host exited during handshake

Start at core/src/tools/router.rs:225 and trace the exec code-mode handshake using the reported error and log excerpt. Reproduce with the bundled codex-cli 0.150.0-alpha.8 on the listed Windows environment, comparing behavior with the older CLI where useful. Done means the code-mode host completes handshakes reliably and exec calls no longer fail intermittently.