H5 browser use needs to keep local desktop WebUI testing open while giving remote phones a usable chat-first surface. This change scopes browser auth by origin and target host, hides non-chat desktop chrome on H5 mobile, compacts the empty-session composer, and unifies mobile selectors behind a full-width bottom sheet with an explicit close action.
Constraint: Local browser development may bypass H5 auth only for loopback or private LAN server hosts; public or remote hosts still require an H5 token.
Constraint: Mobile H5 scope is chat-first; settings and scheduled-task surfaces stay hidden instead of fully redesigned.
Rejected: Reuse desktop popovers on mobile | hover/anchored dropdown behavior leaves key actions hard to dismiss and cramped on narrow screens.
Rejected: Let any localhost origin bypass remote auth | it would let arbitrary local pages access public H5 servers without a token.
Confidence: medium
Scope-risk: moderate
Directive: Keep future H5 selector popups on MobileBottomSheet unless a selector needs a reviewed custom mobile interaction.
Tested: cd desktop && bun run lint
Tested: cd desktop && bun run test -- src/pages/EmptySession.test.tsx src/components/chat/ChatInput.test.tsx src/lib/desktopRuntime.test.ts src/components/shared/RepositoryLaunchControls.test.tsx src/components/controls/PermissionModeSelector.test.tsx src/components/controls/ModelSelector.test.tsx src/components/shared/DirectoryPicker.test.tsx src/__tests__/pages.test.tsx
Tested: bun test src/server/__tests__/h5-access-auth.test.ts src/server/middleware/cors.test.ts
Tested: Chrome mobile viewport smoke for context, model, permission, project, branch, and worktree bottom sheets with no horizontal overflow.
Not-tested: Full bun run verify quality gate.
