[P0 / Blocker] Remote compact task fails 100% with "tools.defer_loading requires tools.tool_search" — GPT-5.5 unusable at context limit, no client-side workaround

Severity: Blocker / P0

Codex becomes unusable the moment any non-trivial conversation reaches the auto-compact threshold. 100% reproducible. No viable client-side workaround — rolling back the desktop app does not help because the failing call is constructed server-side.

This bug effectively makes the headline GPT-5.5 launch experience on Codex desktop dead on arrival for anyone running the default plugin set.

Environment

• Codex desktop (macOS, Apple Silicon)
• Reproduced on 26.422.30944 (current)
• Reproduced on 26.422.21459 after manual rollback — identical failure
• Model: GPT-5.5, reasoning effort \xhigh\
• Plugins enabled (default-ish set): \github\, \browser-use\, \documents\, \spreadsheets\, \presentations\, \computer-use\

Error

As soon as the conversation hits the compact threshold:

\\\
Error running remote compact task: {
"error": {
"message": "Invalid Value: 'tools.defer_loading'. Deferred tools require tools.tool_search.",
"type": "invalid_request_error",
"param": "tools.defer_loading",
"code": null
}
}
\\\

The session stalls. Every retry reproduces the same 400. The conversation cannot progress.

Reproduction

1. Install Codex desktop 26.422.x on Apple Silicon.
2. Select GPT-5.5.
3. Keep default plugins enabled so tool descriptions cross the ~10% context threshold that auto-enables \tool_search\ + \defer_loading\.
4. Work normally until the conversation approaches the compact threshold.
5. The remote compact endpoint returns the 400 above — every time, with no recovery path.

Likely root cause

The server-side compact task (\chatgpt.com/backend-api/codex/responses/compact\) rebuilds the Responses API payload with \defer_loading\ on individual tool entries but omits the paired \tool_search\ entry at the top level of the \tools\ array. The Responses API then rejects its own internally-constructed request. This regression coincides with \"tool discovery enabled by default\" in the recent changelog.

In other words: the server is failing its own schema validation against itself.

Why the obvious workarounds do not work

• Rolling back the desktop client (30944 → 21459): identical failure. Compact is remote — client version is irrelevant.
• Starting new threads: resets context, but any substantive session hits the same wall again.
• Switching to GPT-5.4: \defer_loading\ was introduced in 5.4, so it almost certainly exercises the same path.
• Disabling plugins until tool descriptions drop under the ~10% threshold is the only thing that might avoid it — i.e., asking paying users to disable advertised features to get the product to function.

Impact

• GPT-5.5 + Codex desktop is non-functional for any user with the default plugin set as soon as a conversation fills.
• This is the flagship model from last week's launch.
• There is no preserved-functionality workaround.
• The fix does not require a client release — it is a pure server-side correction in the compact-task request builder.

Requested fix

Either:

• (a) Include \tool_search\ in the rebuilt compact request whenever any tool entry carries \defer_loading\, or
• (b) Strip \defer_loading\ from tool entries in the rebuilt compact request when \tool_search\ is intentionally omitted.

Please prioritize. This is a top-of-funnel regression on a paid flagship model.

Related

• #19009 — Compact fails in CLI and VS Code Extension
• #19279 — Experimental feature check disabling app startup
• #19295 — White screen on v26.422.21637 (Pro)
• #19370 — GPT-5.5 not usable in Codex App for remote projects