JetBrains Codex remote compaction fails with 404 Not Found

What version of the IDE extension are you using?

2025.3.4

What subscription do you have?

codex

Which IDE are you using?

IntelliJ IDEA

What platform is your computer?

x86

What issue are you seeing?

Title:
JetBrains Codex remote compaction fails with 404 Not Found

Environment:

• OS: Windows
• IntelliJ IDEA: 2025.3.4
• Codex ACP adapter: 1.2.0
• @openai/codex: 0.147.0
• Authentication: ChatGPT OAuth
• Date/time: 2026-08-14 around 16:02 UTC+8

Description:
A long-running Codex conversation in JetBrains AI Chat fails when
automatic context compaction is triggered.

The conversation had grown to approximately 230,000 tokens.

Actual error:
Error running remote compact task: unexpected status 404 Not Found:
{"detail":"Not Found"}

URL:
https://chatgpt.com/backend-api/codex/responses/compact

Request ID:
97a2936b-6c4d-409d-9a36-0707821bae42

CF-Ray:
a2a764cc4bf1f514-LAX

Expected behavior:
Codex should compact the long conversation and continue.

Actual behavior:
The compact request returns HTTP 404 and the task cannot continue.

Additional information:
Starting a new conversation avoids triggering compaction immediately.

What steps can reproduce the bug?

Title:
JetBrains Codex remote compaction fails with 404 Not Found

Environment:

• OS: Windows
• IntelliJ IDEA: 2025.3.4
• Codex ACP adapter: 1.2.0
• @openai/codex: 0.147.0
• Authentication: ChatGPT OAuth
• Date/time: 2026-08-14 around 16:02 UTC+8

Description:
A long-running Codex conversation in JetBrains AI Chat fails when
automatic context compaction is triggered.

The conversation had grown to approximately 230,000 tokens.

Actual error:
Error running remote compact task: unexpected status 404 Not Found:
{"detail":"Not Found"}

URL:
https://chatgpt.com/backend-api/codex/responses/compact

Request ID:
97a2936b-6c4d-409d-9a36-0707821bae42

CF-Ray:
a2a764cc4bf1f514-LAX

Expected behavior:
Codex should compact the long conversation and continue.

Actual behavior:
The compact request returns HTTP 404 and the task cannot continue.

Additional information:
Starting a new conversation avoids triggering compaction immediately.

What is the expected behavior?

No response

Additional information

No response

Start by tracing the remote compaction request to https://chatgpt.com/backend-api/codex/responses/compact and inspect how the Codex ACP adapter handles the 404 response. Reproduce the failure with the listed Codex and adapter versions, then verify that a long conversation compacts successfully and continues instead of failing.