File browser: extract useSftpTransfers and useElevation hooks from FileBrowserPanel #825

Goal

Uploads/downloads with progress and conflicts, and the elevated (sudo) browsing mode, each live in one hook, so their state transitions can be read and tested in isolation.

Context

apps/smart-ssh-community/frontend/src/components/FileBrowserPanel.tsx has 3,634 lines. The component function FileBrowserPanel alone spans lines 206–2845 (logic 206–1646, JSX 1646–2845) with 51 useState, 29 useRef and 23 useEffect. Eight sub-components follow in the same file: FileEntryMenu (:2864), FilePropertiesDialog (:2991), ColumnsMenu (:3050), ChmodDialog (:3114), ChownDialog (:3292), RenamePrompt (:3390, with isValidEntryName :3456), DirectoryMenu (:3463), ColumnResizeHandle (:3552), ElevationFailureDialog (:3577); helpers findMenuTrigger/focusMenuTrigger (:2845–2863), formatMb, localDirName, revealLabelKey (:120–140). Tests: FileBrowserPanel.test.tsx (3,371 lines, 144 tests), FileBrowserPanel.android.test.tsx, FileBrowserPanel.startDirectory.test.tsx. Line numbers are from develop before the colour-token migration and may shift slightly.

Responsibilities to extract (state names as on develop):

1. Transfers: transfers, uploadConflict, folderConfirm, folderSummary, dragOver, the onSftpTransfer* event subscriptions, cancel, drop and folder upload.
2. Elevation: elevation, enablingElevation, elevationTargetUser, otherUser*, elevationFailure, elevationWarning, stopPrompt and the calls that enable/disable the elevated channel (about 84 occurrences of "elevat" in the file).

End state of the series: no file over 800 lines, no function component over 400 lines, at most 12 useState per component, sub-components and hooks under src/components/fileBrowser/.

Requirements

• src/components/fileBrowser/useSftpTransfers.ts: useSftpTransfers(sessionId, …) owns the transfer list, conflicts and event subscriptions; it exposes start/cancel/resolve-conflict functions.
• src/components/fileBrowser/useElevation.ts: useElevation(sessionId) owns the elevation state, the enable/disable flow, the failure and warning state and the stop prompt for running elevated operations.
• Event subscriptions keep their exact filter by session id and are cleaned up on unmount; the subscription effect of each hook depends only on the values it really needs.
• Hook unit tests with renderHook: transfer progress event updates the matching transfer only, cancel, conflict resolution; elevation enable success, enable failure shows the failure state, disable with running operations asks first.

Acceptance Criteria

• useSftpTransfers and useElevation exist with unit tests (at least the cases listed above).
• FileBrowserPanel has at most 20 useState calls left.
• Elevated mode still never applies to a different session than the one it was enabled for (existing tests pass unchanged).
• The test count of FileBrowserPanel*.test.tsx is not lower than before; all pass.
• npm run lint, npx vitest run, npm run build and npm run test:e2e pass.

Technical Notes

• Pure refactoring: no change to behaviour, visible text, i18n keys, CSS classes, data-testids, ARIA attributes, keyboard handling, invoked Tauri commands or listened events. Behaviour changes, if you find a bug, go into a separate issue (mention it in the PR).

• Colour classes in these files are being migrated to theme tokens in a separate issue that must be merged first; keep exactly the classes that are on develop when you start.

• Exports that other files or tests import from the original file keep working: either update the importers or re-export from the original path. The extension API (src/extensions/*, src/api.ts, src/components/ui) does not change.

• Tests: count it(/test( in the listed test files before and after; the number must not decrease. Tests may move next to an extracted unit, but their assertions stay the same. Tests drive the user-visible behaviour through FileBrowserPanel/ChatPanel/ServerForm as today.

• New code comments in English; existing German comments may move unchanged.

• No filter, risk, redaction or credential logic is touched (frontend only).

• Gate: npm run lint, npx vitest run, npm run build in apps/smart-ssh-community/frontend, plus npm run test:e2e if a browser test covers the component.

• The elevated channel is enforced in the backend; the frontend only requests it. Do not change which commands are invoked with an elevated user or when.

Spec impact: none

Related Work

• Previous: File browser: move the sub-components out of FileBrowserPanel.tsx into components/fileBrowser/ #819, File browser: extract FileTable, FileToolbar, TransferList and ElevationControls from FileBrowserPanel #821, File browser: extract useRemoteDirectory and useFileColumns hooks from FileBrowserPanel #824; next: File browser: useFileOperations reducer for dialog state; FileBrowserPanel within the size limits #827