#20111 cmux NEXT: the pane toolbar's "…" menu opens on press (polish: press-drag-release)

Summary

POLISH sweep, pane toolbar. The "…" button at the trailing end of a pane's tab bar opened its menu only after the mouse came up, so press, drag to a row, release could not pick anything. POLISH.md asks every menu button for press-drag-release, and a plain click must still open the menu and leave it open.

• TitlebarBandButton.pressMenu opens a menu on mouse-down, the way a pop-up button does. "…" uses it.
• The button's action still opens the menu for a keyboard or VoiceOver press.
• "…" stays highlighted while its menu is open.
• Menus now show through presentMenu, so the test can observe the press. The long-press Back/Forward lists use it too, with no change in behavior.

Visible change: pressing "…" in a pane's toolbar opens its menu at once, and you can drag to a row and release to run it.

Verification

Test: PaneToolbarTests.moreOpensItsMenuOnPress. Both runs are fleet cmux-ci run --class light --script scripts/ci/run-swift-testing-suites.sh --arg Packages/macOS/CmuxNext (Xcode 26.6).

• Red on the test commit: (presented → []) == [["Search Agent Chats", "Toggle Pane Zoom"]]. The suite's other 4 tests passed.
• Green on the head: see the comment below.
• Not live-verified: the test proves the menu opens on press. The press-drag-release and click-stays-open behavior after that comes from AppKit (NSMenu.popUp called during mouse-down, the same way NSPopUpButton works), and I did not check it by hand in a running build.

check-concurrency, check-system-blue and check-no-godfiles pass; the godfile notes are all for files already over budget on base.

Changelog

Fixed: The pane toolbar's "…" menu opens when you press it, so you can drag to an item and release to pick it.

🤖 Generated with Claude Code

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Summary by cubic

The pane toolbar's "…" menu now opens on mouse-down, so you can press, drag to a row, and release to run it. Previously the menu waited for the mouse-up, so a single drag couldn't pick anything.

• Adds a pressMenu hook to TitlebarBandButton that opens the menu on press like a pop-up button; a plain click leaves the menu open.
• The button stays visually pressed while its menu is open.
• The button's action still opens the menu for keyboard or VoiceOver presses.
• Routes menu presentation through presentMenu so tests can observe the press; the long-press Back/Forward lists use it too with no behavior change.
• Adds PaneToolbarTests.moreOpensItsMenuOnPress to cover the press path.