Summary

Fixes ELECTRON-3Y — RangeError: Position X is out of range for changeset of length Y in ChangeDesc.mapPos (6 events, last seen 6 hours ago, still active).

Root cause: When the active tab changes in PreviewPanel, CodeMirror editors receive a completely new value prop. Without a key tied to the tab ID, React reuses the same component instance and @uiw/react-codemirror tries to reconcile the old internal state with the new value via ChangeDesc.mapPos(), which throws when stale positions exceed the new document length.

Additionally, InlineAgentEditor's handleJsonChange had overlapping setTimeout calls that could prematurely clear the editing flag, allowing useEffect to overwrite CodeMirror's value mid-edit.

Fix:

• Add key={activeTabId} to all CodeMirror editor instances in PreviewPanel.tsx — forces React to unmount/remount the editor on tab switch, preventing stale position errors entirely
• Fix timer race condition in InlineAgentEditor.tsx — clear previous timer before setting a new one

Test plan

• New unit test previewEditorKeyRemount.test.ts verifies timer cleanup prevents premature flag reset
• Full test suite passes (210/211 — 1 pre-existing failure in previewFileWatch.dom.test.ts)
• bunx tsc --noEmit passes
• bun run lint:fix passes (0 errors)
• bun run format passes