**Problem:** When a language was selected in a code block's language
dropdown, there was no way to reset it back to "Plain Text" (no syntax
highlighting). The dropdown only contained shiki languages, and the null
value representing Plain Text had no corresponding selectable option.
**Solution:** Added a "Plain Text" entry as the first item in the
language selector dropdown. This entry:
- Maps to language: null when selected
- Shows a checkmark when Plain Text is active
- Persists in localStorage alongside recently used languages
- Is searchable via aliases ("plain", "text", "none")
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## Summary by CodeRabbit
* **New Features**
* Added Plain Text as a selectable code block language.
* Plain Text is available in newly generated and previously saved
language lists.
* Code blocks correctly show Plain Text when no language is selected.
* Recognizes common names including “plain,” “text,” “plaintext,” “txt,”
and “none.”
* **Tests**
* Added coverage for switching between Rust and Plain Text.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **New Features**
* Typst code block preview with interactive rendering controls (zoom,
pan, reset) and user-friendly error messages
* **Style**
* Centered Mermaid diagram rendering for improved layout
* **Tests**
* Added end-to-end preview validation tests for Typst and Mermaid
* **Chores**
* Added WebAssembly type declarations and updated frontend packages;
removed a build debug configuration entry
<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
#### PR Dependency Tree
* **PR #12848** 👈
This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
- **New Features**
- Introduced a feature flag to enable or disable web container
functionality for code block previews.
- **Improvements**
- Code block HTML previews now support an alternative rendering method
based on the new feature flag, enhancing flexibility.
- **Chores**
- Updated feature flag settings by removing an obsolete flag and adding
the new web container flag.
- **Tests**
- Simplified code block preview tests for faster and more direct
validation of HTML preview content.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **New Features**
- Introduced a preview mode for code blocks, allowing users to toggle between code and rendered previews (e.g., HTML output) directly within the editor.
- Added a preview toggle button to the code block toolbar for supported languages.
- Enabled dynamic rendering of code block previews using a shared WebContainer, allowing live HTML previews in an embedded iframe.
- Added HTML preview support with loading and error states for enhanced user feedback.
- Integrated the preview feature as a view extension provider for seamless framework support.
- **Bug Fixes**
- Improved toolbar layout and button alignment for a cleaner user interface.
- **Tests**
- Added end-to-end tests to verify the new code block preview functionality and language switching behavior.
- **Chores**
- Updated development server configuration to include enhanced security headers.
- Added a new runtime dependency for WebContainer support.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Jessy Latmi