diagram: Menu cannot be dismissed by clicking its own trigger button

[bpowers]

Problem

The reimplemented Menu component (src/diagram/components/Menu.tsx) cannot be dismissed by clicking its own trigger button while it is open. Clicking the trigger flickers the menu closed and immediately reopens it.

The outside-dismiss effect (Menu.tsx:91-112) registers a document mousedown listener that calls onClose() whenever a press lands outside the menu content (contentRef):

const onMouseDown = (event: MouseEvent): void => {
  const content = contentRef.current;
  if (content && !content.contains(event.target as Node)) {
    onClose();
  }
};

The trigger button is not inside the menu content (e.g. the account IconButton in src/app/Home.tsx:256-274), and the menu's own proxy <span> is pointer-events: none (Menu.tsx:136-146), so it cannot absorb the press either. Clicking the trigger while the menu is open therefore produces:

1. mousedown -> document outside listener -> onClose() (menu closes)
2. click -> trigger's handleMenu -> setAnchorEl(currentTarget) (menu reopens)

Net effect: the toolbar account menu can no longer be toggled shut by clicking its own trigger; it flickers closed and immediately reopens. Escape and clicking elsewhere still dismiss it correctly.

Why it matters

This is a behavioral regression in a shared, reused component. Toggling a menu by clicking its trigger again is a standard, expected interaction (the prior Radix-based implementation handled this). It affects every caller that uses a trigger button outside the menu content, including the account menu in the app toolbar.

Component(s) affected

• src/diagram/components/Menu.tsx (the dismiss effect)
• Callers with an external trigger, e.g. src/app/Home.tsx account menu

Suggested fix

Pass anchorEl into the dismiss effect and skip onClose() when the press lands on the trigger:

if (content && !content.contains(target) && !(anchorEl?.contains(target))) {
  onClose();
}

(Add anchorEl to the effect's dependency array.)

Also add a regression test in src/diagram/tests/menu.test.tsx -- the current tests only cover anchor positioning, not outside-click / trigger-toggle dismissal. Cover: (a) clicking outside closes, (b) clicking the trigger while open does not leave the menu reopened, (c) Escape closes.

How discovered

Identified during review of PR #804 (branch dep-diet-round2), which reimplements the Menu component. This may merge with #804 if not caught.

[bpowers]

Addressed in PR #804 (branch dep-diet-round2): the reimplemented Menu now moves focus to the first item on open, supports Up/Down/Home/End roving, returns focus to the anchor on Escape, dismisses on focus-leave, and excludes the anchor from outside-press dismissal so a trigger press no longer triggers a redundant close->reopen. Covered by new menu.test.tsx cases.