fix(core): stop emitting spurious blur for non-focused widgets on unregister

[atul-upadhyay-7]

Summary

Fixes a bug where FocusManager.unregister() emitted a blur event for non-focused widgets, causing downstream handlers to crash when looking up the removed widget by ID.

Closes #1660

Root Cause

In the unregister() method, when a widget that precedes the focused widget was removed (idx < this._currentIndex), the code emitted both blur and focus events:

} else if (idx < this._currentIndex) {
    this._currentIndex--;
    this._events.emit('blur', { targetId: id, ... }); // BUG: id is already removed
    this._events.emit('focus', { targetId: this._focusables[this._currentIndex].id, ... });
}

The blur event targeted the removed widget (id) which was never focused. Handlers that looked up this widget by ID got undefined and crashed.

Fix

• Non-focused widgets: When unregistering a widget that isn't currently focused, silently adjust _currentIndex if needed. No blur/focus events because the focused widget hasn't changed.
• Focused widget: When unregistering the currently focused widget, emit blur for it (valid transition), then move focus to the next available widget.

Tests added

Test	What it verifies
does not emit blur when unregistering a non-focused widget	The original bug scenario
emits blur when unregistering the focused widget	Correct blur on focused removal
moves focus to next widget when focused widget is unregistered	Focus transitions correctly
sets currentId to null when last widget is unregistered	Edge case: empty list
adjusts index correctly when non-focused widget before focused is removed	Index bookkeeping
unregistering a non-focused widget after focused one does not affect focus	No spurious focus change
does not emit any events when unregistering a non-focused widget	Zero side effects

Verification

• All 444 core tests pass (including 7 new tests)
• Typecheck passes across all packages
• No breaking changes to public API

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 0ee113c1-6043-467e-ac68-99df6ba873ed

📥 Commits

Reviewing files that changed from the base of the PR and between 4b874c0 and 8d7eec3.

📒 Files selected for processing (2)

• packages/core/src/events/FocusManager.test.ts
• packages/core/src/events/FocusManager.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[github-actions]

Hi @atul-upadhyay-7 👋

⭐ Star this repo before your PR merges.

Why? GSSoC 2026 contributors who star get priority review and points credit. After you star, push any commit (or re-run this check). The needs-star label lifts automatically.

Thanks for your contribution to TermUI.