Add Ctrl+Alt+Pause keyboard capture toggle and status feedback - #16173

Keyboard-only users have no direct shortcut to return input to the local computer once a remote session captures the keyboard. On Windows, the workaround is to open the local security screen with Ctrl+Alt+Delete and dismiss it with Esc.

This change adds Ctrl+Alt+Pause/Break to release keyboard capture through the existing session enter/leave path. On Windows and macOS, pressing it again reacquires capture. The remote view stays visible and the window keeps its position and focus. The existing toolbar keyboard icon and tooltip indicate Keyboard: local or Keyboard: remote; Windows also raises a UIA notification when the state changes, without adding a visible element or a live region.

The shortcut is inspired by Microsoft RDP's Ctrl+Alt+Pause/Break shortcut. RDP uses it to switch between full-screen and windowed mode; this implementation changes keyboard capture directly.

Fixes #16174. Related: #1098.

Scope and regression surface

• src/keyboard.rs: handle the shortcut in the existing desktop native-input callbacks and publish capture changes to the corresponding session. Existing grab/release operations are reused, including releasing held remote keys. Acquiring capture requires a normal remote-control session with keyboard permission and view-only mode disabled; releasing capture remains available after permission changes. This shortcut does not require relative-mouse support. Windows Pause/Break key codes and macOS's F15 mapping are handled. On Linux/X11 the shortcut releases capture only, because the grab callback stops receiving keys after ungrab.
• flutter/lib/models/model.dart: receive capture state for the icon and Windows notification, suppress duplicate notifications, refresh the indication when the input source changes, and reset capture status when clearing the model so a reused session starts with local status. Unsupported input paths retain the existing toolbar presentation.
• flutter/lib/desktop/widgets/remote_toolbar.dart: reuse the existing icon, colors, tooltip and menu; its layout and actions are retained.
• flutter/windows/runner/flutter_window.cpp and CMakeLists.txt: register the notification channel for secondary windows, reuse Flutter's accessibility provider and call UiaRaiseNotificationEvent. The notification API is resolved dynamically for older Windows versions.
• src/lang/*.rs: add the two status labels according to the repository's localization rules. Each of the 53 affected language tables adds exactly two entries; untranslated entries remain empty. The 61 changed files consist of these 53 tables, five functional/build files, two test files, and one CI workflow.
• .github/workflows/ci.yml: run the native keyboard regression in the existing build job after Rust toolchain setup and before the build. This adds one test step and changes no application runtime path.
• tests/test_keyboard_grab.py and flutter/test/keyboard_grab_status_test.dart: regression tests for shortcut eligibility, release/reacquire, repeated keys, platform-specific Pause mappings and model clearing. The native test compiles the actual shortcut function with session/OS doubles; the Flutter test uses the real FfiModel. Adding these tests changes no production runtime path.

No third-party dependency is added. The remote page, src/platform/windows.rs, generated bridges and legacy Sciter UI are unchanged.

Validation

• Windows Rust compilation check with the release configuration: cargo check --locked --features flutter --lib --release.
• Repository native regression: python3 -m unittest discover -s tests -p test_keyboard_grab.py -v from the repository root (requires rustc on PATH), now configured to run in the existing CI workflow. The workflow parses successfully and its test command passes locally with the local Python interpreter. Windows, macOS and Linux conditional branches pass in the isolated harness. Running the same test against the pre-fix source fails on the missing session eligibility check. Additional isolated negative checks confirm that the new cases fail if Windows VK_CANCEL, macOS F15 or non-Windows Cancel support is removed.
• Repository Flutter regression: flutter test --no-pub test/keyboard_grab_status_test.dart from flutter/.
• Dart analysis of the affected UI files: no errors or warnings.
• Local extracted-source checks (outside the repository) cover shortcut release/reacquire, repeated key events, local Alt+Tab/Win+M pass-through, session-specific state events, notification deduplication, and unchanged toolbar layout/menu behavior. The review regressions were reproduced before the fixes: ineligible sessions acquiring capture and model reuse retaining stale status. The updated checks confirm capture acquisition is rejected for non-control, keyboard-disabled and view-only sessions, release remains available after permission changes, and model clearing resets the status without suppressing the next session's capture notification.
• A native harness using the bundled Flutter engine and a real Windows UIA event subscriber received both localized status notifications while the test window remained hidden and foreground focus was unchanged.

Full Windows Rust/Flutter release builds and verification of all 91 portable-bundle files were completed before the review fixes. The latest source was validated with the checks above and has not been repackaged.

macOS/Linux behavior was checked with local source harnesses, not on physical machines. Actual screen-reader speech output has not been verified; Windows UIA event delivery has been verified.

Summary by CodeRabbit

• New Features

  • Added a Ctrl+Alt plus Pause/Cancel shortcut to switch between local and remote keyboard control.
  • The keyboard control menu now displays the current status and uses inactive styling when control is unavailable.
  • Keyboard status changes are communicated to supported Windows accessibility features.
  • Added local and remote keyboard labels, including Chinese and Traditional Chinese translations.

• Bug Fixes

  • Keyboard status now refreshes after changing the input source and resets correctly between sessions.

Confidence Score: 5/5

The PR appears safe to merge; both previous findings are resolved and no actionable new defect remains.

Findings

1.  Regression test skipped by CI ▶

### Issue 1
tests/test_keyboard_grab.py:140-141
This test is only documented for manual execution, while the repository workflow runs `cargo test` and does not execute these Python tests. As a result, regressions in shortcut eligibility or platform-specific capture toggling can merge without this test detecting them. Please wire it into CI so it provides automated regression protection.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A[Ctrl+Alt+Pause/Break] --> B{Capture state}
  B -->|Remote| C[Release keyboard grab]
  B -->|Local and eligible| D[Acquire keyboard grab]
  C --> E[Publish keyboard_grab event]
  D --> E
  E --> F[Update FfiModel]
  F --> G[Refresh toolbar status]
  F --> H[Raise Windows UIA notification]

_{Reviews (5) · Last reviewed commit: "test: cover platform Pause key mappings"}