Add xhigh thinking level for OpenAI codex-max models

- Add 'xhigh' to ThinkingLevel type in ai and agent packages
- Map xhigh to reasoning_effort: 'max' for OpenAI providers
- Add thinkingXhigh color token to theme schema and built-in themes
- Show xhigh option only when using codex-max models
- Update CHANGELOG for both ai and coding-agent packages

closes #143

packages/coding-agent/CHANGELOG.md

@@ -2,10 +2,18 @@
 
 ## [Unreleased]
 
+### Breaking Changes
+
+- **Custom themes require new color tokens**: Themes must now include `thinkingXhigh` and `bashMode` color tokens. The theme loader provides helpful error messages listing missing tokens. See built-in themes (dark.json, light.json) for reference values.
+
 ### Added
 
 - **OpenAI compatibility overrides in models.json**: Custom models using `openai-completions` API can now specify a `compat` object to override provider quirks (`supportsStore`, `supportsDeveloperRole`, `supportsReasoningEffort`, `maxTokensField`). Useful for LiteLLM, custom proxies, and other non-standard endpoints. ([#133](https://github.com/badlogic/pi-mono/issues/133), thanks @fink-andreas for the initial idea and PR)
 
+- **xhigh thinking level**: Added `xhigh` thinking level for OpenAI codex-max models. Cycle through thinking levels with Shift+Tab; `xhigh` appears only when using a codex-max model. ([#143](https://github.com/badlogic/pi-mono/issues/143))
+
+- **Collapse changelog setting**: Add `"collapseChangelog": true` to `~/.pi/agent/settings.json` to show a condensed "Updated to vX.Y.Z" message instead of the full changelog after updates. Use `/changelog` to view the full changelog. ([#148](https://github.com/badlogic/pi-mono/issues/148))
+
 ## [0.13.2] - 2025-12-07
 
 ### Changed