fix(app): add hosts without leaving the current screen (#8512)

* fix(app): add hosts without leaving the current screen

A retained Settings route replayed its addHost query after appearance remounts. Own the connection flow outside screen lifetimes and let each consumer choose its completion navigation.

* fix(app): release the project dialog before adding a host

* fix(app): size the QR scanner viewport on wide layouts

* test(app): align creation and desktop setup with in-place host flow

docs/design.md

@@ -35,7 +35,7 @@ The authored interface ramp uses a 14px base. New native installs default to 15p
 Weight has three tiers, applied by role:
 
 - **Screen titles** — the title in app chrome — use `<ScreenTitle>` (`packages/app/src/components/headers/screen-title.tsx`), which renders `fontSize.base` at weight `400` on compact and `300` on desktop. The New workspace hero is the only larger product title; it uses `fontSize["2xl"]` (`packages/app/src/screens/new-workspace-screen.tsx`).
-- **Structural labels** use `fontWeight.medium`. This applies to section labels above a stack of rows (`packages/app/src/components/agent-list.tsx:519-523`, `packages/app/src/components/keyboard-shortcuts-dialog.tsx:63-67`), form field labels above an input inside a modal (`packages/app/src/components/add-host-modal.tsx:19-23`, `packages/app/src/components/pair-link-modal.tsx:24-28`), the title at the top of a modal/sheet/dialog (`packages/app/src/components/adaptive-modal-sheet.tsx:90-94`, `packages/app/src/components/ui/combobox.tsx:1607-1611`, `packages/app/src/components/welcome-screen.tsx:48-53`), action button labels in tight components such as the sidebar callout actions (`packages/app/src/components/sidebar-callout.tsx:218-221`), and inline data emphasis on dense metadata rows (`packages/app/src/components/git-diff-pane.tsx:2322-2327`, `packages/app/src/components/file-explorer-pane.tsx:1115-1122`).
+- **Structural labels** use `fontWeight.medium`. This applies to section labels above a stack of rows (`packages/app/src/components/agent-list.tsx:519-523`, `packages/app/src/components/keyboard-shortcuts-dialog.tsx:63-67`), form field labels above an input inside a modal (`packages/app/src/hosts/add-host/internal/add-host-modal.tsx:19-23`, `packages/app/src/hosts/add-host/internal/pair-link-modal.tsx:24-28`), the title at the top of a modal/sheet/dialog (`packages/app/src/components/adaptive-modal-sheet.tsx:90-94`, `packages/app/src/components/ui/combobox.tsx:1607-1611`, `packages/app/src/components/welcome-screen.tsx:48-53`), action button labels in tight components such as the sidebar callout actions (`packages/app/src/components/sidebar-callout.tsx:218-221`), and inline data emphasis on dense metadata rows (`packages/app/src/components/git-diff-pane.tsx:2322-2327`, `packages/app/src/components/file-explorer-pane.tsx:1115-1122`).
 - **Content** uses `fontWeight.normal`. This applies to settings rows (`packages/app/src/styles/settings.ts`), sidebar primary list-item titles (`packages/app/src/components/sidebar-workspace-list.tsx:2680-2686`, `packages/app/src/components/agent-list.tsx:572-578`), `<Button>` text (`packages/app/src/components/ui/button.tsx:80-84`), `<StatusBadge>` text (`packages/app/src/components/ui/status-badge.tsx:56-60`), and `<SidebarCallout>` titles (`packages/app/src/components/sidebar-callout.tsx:175-180`).
 
 The rule, condensed: text that _names_ a surface or a group is `medium`. Text that lives _inside_ a surface or a group is `normal`. Top-of-screen titles are `<ScreenTitle>`, which is lighter still.
@@ -102,7 +102,7 @@ Five primitives. The pick is determined by option count, the need to search, and
 
 `<ContextMenu>` is for right-click and long-press on a target. The row is the trigger; there is no visible affordance. Used for incidental actions on workspace rows in the sidebar (`packages/app/src/components/sidebar-workspace-list.tsx`).
 
-`<AdaptiveModalSheet>` is for a focused task. Multi-field forms (`packages/app/src/components/add-host-modal.tsx`, `packages/app/src/components/pair-link-modal.tsx`, `packages/app/src/components/project-picker-modal.tsx`), confirmations with detail, anything that earns a backdrop. Bottom sheet on compact, centered card on desktop. Raw `Modal` is wrong for any of these.
+`<AdaptiveModalSheet>` is for a focused task. Multi-field forms (`packages/app/src/hosts/add-host/internal/add-host-modal.tsx`, `packages/app/src/hosts/add-host/internal/pair-link-modal.tsx`, `packages/app/src/components/project-picker-modal.tsx`), confirmations with detail, anything that earns a backdrop. Bottom sheet on compact, centered card on desktop. Raw `Modal` is wrong for any of these.
 
 `<AdaptiveModalSheet>` owns the presentation. Its content inset — the gutter that puts sheet content on the same rails as the sheet header — and compact bottom safe-area padding are the sheet's, not the caller's. A caller declares layout intent through `contentStyle` and never branches on form factor to add its own margins. If a sheet's first snap point is shorter than its header, content, and safe-area clearance, raise that snap point rather than moving the sheet container.
 
@@ -114,7 +114,7 @@ Three themes is `DropdownMenu`. Thirty hosts is `Combobox`. A label and a value
 
 ## 7. Density and rhythm
 
-Settings detail pages, the projects detail page, and any list+detail content sit inside a centered, max-width 720 column (`packages/app/src/screens/settings-screen.tsx`, `packages/app/src/screens/projects-screen.tsx`). Lines stay readable, the eye does not have to track wide horizontal distances. Form modals carry their own narrower content frame (`packages/app/src/components/add-host-modal.tsx`).
+Settings detail pages, the projects detail page, and any list+detail content sit inside a centered, max-width 720 column (`packages/app/src/screens/settings-screen.tsx`, `packages/app/src/screens/projects-screen.tsx`). Lines stay readable, the eye does not have to track wide horizontal distances. Form modals carry their own narrower content frame (`packages/app/src/hosts/add-host/internal/add-host-modal.tsx`).
 
 Workspace and chat surfaces use the full width — these are working surfaces, not reading surfaces. The composer carries `MAX_CONTENT_WIDTH` from `packages/app/src/constants/layout.ts` to keep lines readable while letting the workspace pane fill the rest.
 
@@ -278,7 +278,7 @@ New status pills use `<StatusBadge>`. Identity, shortcut, and interactive link b
 | List+detail (compact stack, desktop sidebar+pane)   | `packages/app/src/screens/settings-screen.tsx`, `packages/app/src/screens/projects-screen.tsx`                                                                                                                                                                                                           |
 | Detail card+row                                     | `packages/app/src/screens/settings/host-page.tsx`, `packages/app/src/screens/settings/providers-section.tsx`                                                                                                                                                                                             |
 | Section grouping inside a card list                 | `packages/app/src/screens/settings/settings-section.tsx`                                                                                                                                                                                                                                                 |
-| Form modal (label + input fields, primary + cancel) | `packages/app/src/components/add-host-modal.tsx`, `packages/app/src/components/pair-link-modal.tsx`, `packages/app/src/components/project-picker-modal.tsx`                                                                                                                                              |
+| Form modal (label + input fields, primary + cancel) | `packages/app/src/hosts/add-host/internal/add-host-modal.tsx`, `packages/app/src/hosts/add-host/internal/pair-link-modal.tsx`, `packages/app/src/components/project-picker-modal.tsx`                                                                                                                    |
 | Destructive confirmation                            | `confirmDialog` invoked from `packages/app/src/screens/settings/host-page.tsx:541-547`                                                                                                                                                                                                                   |
 | Centered hero / first-run                           | `packages/app/src/components/welcome-screen.tsx`                                                                                                                                                                                                                                                         |
 | Sidebar list (workspaces, hosts)                    | `packages/app/src/components/sidebar-workspace-list.tsx`, `packages/app/src/components/left-sidebar.tsx`                                                                                                                                                                                                 |

docs/expo-router.md

@@ -58,6 +58,12 @@ restore the same workspace and could repeat the crash.
 
 ## App-Wide Route Hops
 
+Keep Add host in `hosts/add-host`, opened through `useAddHost()`. It is an in-place
+flow; callers choose what happens after success. Settings opts into the new host’s
+Overview. Do not send callers to Settings with an `addHost` query parameter: a
+retained route replays that request when appearance changes remount its content.
+The flow provider and sheet host stay outside appearance keys so open drafts survive.
+
 When app-wide routes such as `/new`, `/settings`, or `/sessions` navigate back
 into a host workspace, use `navigateToWorkspace()`. Do not make the caller
 branch on its current route.