feat(suggestion-menu): add the keymap and dismissal

[kianbazza]

Summary

SuggestionMenu handles the keyboard from the host input, and closes when the user leaves it.

Key while open	Result
↑/↓, Ctrl+N/P, Home/End	Move the highlight
Enter	Choose the highlighted row
Escape	Close, without reaching an enclosing dialog
Tab, ←/→, typing, ⌘/Alt/Shift combinations, IME composition	Stay with the host

The host passes key presses to handle.handleKeyDown(event), which returns true when the menu used the key. That matches how ProseMirror, CodeMirror and Lexical order their keymaps.

Dismissal:

• The menu closes when focus leaves the host, but not when focus moves into the menu, when the window loses focus, or when the host gets focus back straight away. This also works in iframes and shadow roots.
• Pressing inside the menu keeps focus in the host. Form fields inside the popup keep their own focus.
• Choosing a row reports item-press even when the row's onSelect edits the text and the editor closes the menu from there. A close requested during Enter, or during a click on a row, waits until the menu's own close.

Evidence

suggestion-menu.keymap.test.tsx (22 tests):

• One test for each row of the key table.
• Escape stops before a document listener, with keys forwarded from a native listener.
• Choosing by Enter and by click reports item-press once from a contenteditable host. A row that keeps the menu open still applies its own close().
• Shadow-root hosts, a host attached before it's in the page, and a Root that unmounts right after focus leaves.

Checked in Chromium with ProseMirror:

• Enter doesn't split the paragraph.
• A real mouse click reports item-press once. Browsers run microtasks between event listeners, which jsdom doesn't reproduce, so this needed a real browser.
• Escape reports escape-key, and clicking elsewhere reports outside-press.

Merge Danger

Door: two-way

Blast Radius: SuggestionMenu only

Closes UI-561

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Project	Deployment	Actions	Updated
ui-canary	Ready	Preview	Sep 29, 2026 2:31pm UTC

[linear-code]

UI-561