codex - 💡(How to fix) Fix VS Code extension cannot reopen some local sessions that CLI can resume [4 comments, 3 participants]

Summary

Some local Codex sessions become permanently unopenable in the VS Code Codex extension, while the same sessions can still be resumed successfully with the Codex CLI (/resume).

This is not a temporary WebView glitch: reloading VS Code, restarting VS Code Remote, reinstalling the extension, and updating extension versions do not make the affected sessions open again. Once a session hits this state, clicking it in the Codex sidebar leaves the page blank with no loading indicator.

Observed behavior

• Affected sessions are visible/clickable in the VS Code Codex sidebar.
• Clicking an affected session opens a blank page.
• There is no visible loading state or error in the sidebar.
• The model indicator in the lower-right UI falls back to custom or 5.4.
• The same session was actually created and used with gpt-5.5 and medium reasoning.
• Smaller sessions often still open normally in the extension and keep showing gpt-5.5 medium.
• The affected sessions remain readable/resumable in the Codex CLI via /resume.

Why this looks like an extension/session hydration issue

The local JSONL session file is present and parseable. One concrete affected session:

thread_id: 019dd6e6-44ba-7772-abab-cc47e88f36de
thread_name: 添加查询模式附加组件
session file: ~/.codex/sessions/2026/04/29/rollout-2026-04-29T01-41-48-019dd6e6-44ba-7772-abab-cc47e88f36de.jsonl
size: 719858 bytes
jsonl lines: 401
originator: codex_vscode
source: vscode
session cli_version: 0.126.0-alpha.8
model in turn_context: gpt-5.5
effort in turn_context: medium

Validation:

All 401 JSONL lines parse successfully with JSON.parse.
Codex CLI can resume the session.
VS Code extension cannot open/render the session.

This has happened with multiple sessions over time. Large session size may be a trigger, but may not be the only trigger.

Local environment

VS Code Codex extension id: openai.chatgpt
Installed extension versions observed:
  openai.chatgpt-26.422.62136-linux-x64
  openai.chatgpt-26.422.71525-linux-x64

Bundled extension CLI:
  codex-cli 0.126.0-alpha.8

User/system CLI:
  codex-cli 0.125.0

Host:
  VS Code Remote on Linux

Relevant logs

~/.vscode-server/data/logs/20260429T003025/exthost3/remoteexthost.log:

2026-04-29 02:12:19.807 [error] PendingMigrationError: navigator is now a global in nodejs, please see https://aka.ms/vscode-extensions/navigator for additional info on this error.
    at /home/.../.vscode-server/extensions/openai.chatgpt-26.422.71525-linux-x64/out/extension.js:...

~/.vscode-server/data/logs/20260429T003025/exthost2/openai.chatgpt/Codex.log around the affected session creation/open period:

[warning] [IpcClient] Received broadcast but no handler is configured method=thread-stream-state-changed
[warning] [IpcClient] Received broadcast but no handler is configured method=thread-read-state-changed
[error] [desktop-notifications][global-error] ResizeObserver loop completed with undelivered notifications.

Steps to reproduce

1. Use the VS Code Codex extension for a longer/local session until the session grows large or otherwise reaches the problematic state.
2. Close/reopen the Codex sidebar, reload VS Code, or restart VS Code Remote.
3. Click the affected session in the Codex sidebar.
4. Observe a blank page with no loading indicator.
5. Resume the same session with Codex CLI /resume.

Expected behavior

The VS Code extension should either:

• open/render any local session that the CLI can resume, or
• show a clear recoverable error if a session is too large or unsupported, or
• safely summarize/page/trim the UI rendering without making the thread permanently inaccessible from the extension.

It should not silently show a blank page or show a misleading fallback model (custom / 5.4) when the persisted turn context says gpt-5.5 medium.

Related issues

This appears related to earlier VS Code extension/session restore issues:

• #5902: VS Code extension crashes after a single conversation exceeds the session size limit.
• #14812: VS Code extension loses thread history after restart even though session files still exist.
• #15368: session list cap / local thread hydration issues under heavy usage.
• #3834: session files exist under .codex/sessions but the extension does not read them after a format change.