ADR-0115: The SDK code editor uses CodeMirror's YAML and JSON language packages

• Status: accepted
• Date: 2026-09-27
• Deciders: Mahdi Amirabdollahi
• Change: openspec/changes/plugin-mcp-tool-access

Context

Plugins increasingly let an operator edit a document (a definition, a request body), and the SDK offered no editor, so each plugin would bundle and style its own. Studio already ships CodeMirror 6 for the SQL console (features/sql/QueryEditor.tsx), coloured from theme.css.

Decision

We add @codemirror/lang-yaml and @codemirror/lang-json, and depend directly on @codemirror/lint, which was already installed. With them we export CodeEditor from the SDK: a YAML or JSON editor with line numbers, a lint gutter, diagnostics passed in by line and column (the server is the validator), a live-region summary of those diagnostics, and a read-only mode. The colours move into ui/codeMirrorTheme.ts, shared with the SQL editor.

Consequences

• Plugins get the console's editor without bundling CodeMirror: the SDK component resolves to the host's copy at runtime.
• Two small official CodeMirror packages join the bundle, and they follow the CodeMirror release line Studio already tracks.
• The editor does no validation or completion of its own. A plugin that wants schema completion would need more, and that is a separate decision.

Alternatives considered

• Monaco. Heavier, a second editor stack, and harder to theme from theme.css. Rejected.
• A plain Textarea. It has no line numbers or located diagnostics, and those are the point of editing a document. Rejected.