GPT 5.2 Codex - Compaction happens way too early and context limit is wrong

[Simplereally]

Description

GPT 5.2 Codex via Copilot is compacting at 100k tokens when the model's context is 272k.

Plugins

None

OpenCode version

latest

Steps to reproduce

1. Use gpt-5.2-codex via github copilot
2. Context in top right indicates max 100k when it is actually 272k
3. Reach ~90k+ tokens in session and compaction happens

Screenshot and/or share link

Operating System

Windows 10 latest

Terminal

Windows Terminal

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Default Codex context length not matching Pro plan #7705: Default Codex context length not matching Pro plan - Reports that GPT 5.2 Codex shows 400k but Pro plan actually has 250-260k, causing early compaction
• GitHub Copilot GPT-5 throwing "invalid_request_body" on requests after compaction #10650: GitHub Copilot GPT-5 throwing "invalid_request_body" on requests after compaction - Reports context compaction failures with GitHub Copilot GPT-5
• github copilot: 2x token (counts total=total+cached) compacts at 64k, instead of 128k #3314: github copilot: 2x token (counts total=total+cached) compacts at 64k, instead of 128k - Reports incorrect token counting and premature compaction with GitHub Copilot models
• Compaction overflow check doesn't account for large tool outputs until the next step, causing context overflow #10634: Compaction overflow check doesn't account for large tool outputs until the next step, causing context overflow - Reports compaction being triggered too early due to incomplete overflow checks

Feel free to ignore if none of these address your specific case.