fix: Fix diff view not clearing on sidebar tab switch

[flex-yj-kim]

Summary

• Clear diff view state when switching from Versions tab to Contents tab in the sidebar
• Dismiss diff view overlay on Escape key press
• Add dev mock API for version history to support local development

[backnotprop]

Code review

Found 1 issue:

1. isPlanDiffActive is read inside the tab-switch useEffect but missing from its dependency array, creating a stale closure. The Escape key effect directly below correctly includes [isPlanDiffActive] in its deps. This is the same class of bug that was caught in PR feat: Plan Diff marketing dialog, Pi origin, and docs #177.

plannotator/packages/editor/App.tsx

Lines 409 to 414 in 69a6728

	// Clear diff view when switching away from versions tab
	useEffect(() => {
	if (sidebar.activeTab === 'toc' && isPlanDiffActive) {
	setIsPlanDiffActive(false);
	}
	}, [sidebar.activeTab]);

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[backnotprop]

Correction to my earlier review — disregard the previous comment.

After pulling the branch locally and tracing the data flow more carefully, the missing isPlanDiffActive dependency is intentional, not a bug.

The effect's purpose is to clear the diff view when activeTab transitions to toc. The isPlanDiffActive check inside the body is just a guard to skip a redundant state update. If isPlanDiffActive were added to the deps array, it would create a worse bug: activating diff view while already on the TOC tab would immediately get cleared by the effect re-firing.

The closure captures isPlanDiffActive from the render where activeTab changed, which is always fresh at that point. No issue here.

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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