Web Shell split-pane header actions

Goal

Let a host embedding @qwen-code/web-shell contribute per-session actions to each split-view pane header, next to the built-in close control, and collapse those actions into a … overflow menu when the pane is too narrow to show them inline without crushing the title.

Problem

Split view mounts one DaemonSessionProvider per pane. Host actions such as environment, artifacts, context usage, and share are per session, so a toolbar above the whole split is ambiguous. Today ChatPane has no header render slot, and renderChatHeader-style slots (if any) sit above the transcript, not in the pane title bar. Hosts either drop those actions while split is open or inject into hashed CSS-module DOM.

Design

API

• ChatPaneProps.renderHeaderActions?: (info) => ReactNode where info = { sessionId: string; workspaceCwd?: string }.
• SplitViewProps.renderPaneHeaderActions and WebShellProps.renderPaneHeaderActions passthrough the same callback into each pane. Hosts that drive split via splitSessionIds / onSplitSessionIdsChange do not need to render SplitView themselves.

Layout

Header row: optional workspace tag | truncating title | host actions | maximize | close. Host actions render before the built-in maximize/close controls, which always stay visible outside the overflow menu.

Overflow

Web-shell owns measurement. Host actions render once into a single host slot; a ResizeObserver on the header compares that slot's natural width against the remaining space after a minimum title width (reserving room for the workspace tag and the built-in trailing controls). When the actions no longer fit, the host slot is hidden in place (visibility: hidden, absolutely positioned) so stateful actions stay mounted across collapse, and the actions are listed in a … dropdown (Radix DropdownMenu via the shared UI wrapper / portal root) that proxies a click to the interactive element inside each hidden slot. The built-in maximize/close controls stay visible outside the menu so panes remain dismissible without opening the overflow.

Scope

• In: prop surface, ChatPane header UI, overflow collapsing, unit tests, i18n for the overflow trigger.
• Out: maximize/restore pane chrome, changing host action content, single- session (non-split) toolbars.

Files

Area	Files
Pane header	ChatPane.tsx, ChatPane.module.css, optional small header-actions helper
Passthrough	SplitView.tsx, App.tsx (WebShellProps)
i18n	i18n.tsx
Tests	ChatPane.test.tsx, SplitView.test.tsx, optionally App.test.tsx