Add Gboard-style progressive text selection mode (extend/shrink selection with cursor keys)

[raxelbyte]

HeliBoard currently offers only coarse text selection via the toolbar: Select Word or Select All (long-press toggles between them). After selecting a word, pressing any arrow / navigation key immediately collapses the selection and only moves the cursor. It is therefore impossible to select an arbitrary custom range of text (partial word, multiple words, part of a sentence, etc.) purely from the keyboard.

This forces users to fall back to Android’s on-screen selection handles, which is slow and imprecise on long text, notes, code, or messages.

Describe the solution you'd like

Implement a proper selection mode similar to Gboard’s Text Editing mode:

1. Add a toggleable Select action (toolbar key or dedicated button in a D-pad / editing layout).
2. When selection mode is active:
   • Arrow keys (and word/line/page navigation keys) extend or shrink the selection from the original anchor point instead of collapsing it.
   • The Select button itself should stay highlighted / in an active state so the user knows the mode is on.
3. Tapping Select again (or performing Cut/Copy/Paste/Delete) exits the mode.
4. Ideally the mode can also be assigned to the existing toolbar or a functional-key layout so power users can keep it always reachable.

Gboard behaviour (for reference)

In Gboard:

• Open the text-editing panel (I-with-arrows icon).
• Move the cursor with the directional pad.
• Tap the central Select button → it becomes active/highlighted.
• Subsequent arrow presses now grow or shrink the selection character-by-character (or by word on long-press).
• You can therefore select any desired length of text without leaving the keyboard.
• Cut / Copy / Paste / Delete buttons remain available on the same panel.

This is exactly the workflow that is missing in HeliBoard.

Use case

Frequent editing of notes, messages, code snippets, or long-form text. Users who prefer a fully offline, privacy-respecting keyboard currently have to switch to Gboard/Samsung/SwiftKey just for precise selection, or struggle with the system handles.

Alternatives considered

• Using Select Word then manually dragging the selection handles → slow and inaccurate.
• Temporarily switching keyboards → defeats the purpose of staying on HeliBoard.
• Existing issues such as Add a text selection mode for cursor keys #2590, Improved Text Selection Options #1932, Shift text selection / highlight. #1033, Text selector as a new shortcuts for toolbar #1616 and discussion Selectoin mode #2299 already request similar functionality; this request specifically emphasises the “selection stays alive while using arrows” behaviour that Gboard provides.

Additional context

HeliBoard already has excellent cursor navigation keys and a highly customisable toolbar. Adding a sticky selection mode would complete the editing experience and bring it to parity with the major commercial keyboards while remaining 100 % offline and FOSS.

Thank you for the fantastic keyboard! @Helium314