SelectionArea + go_router Dead Zone Bug

Minimal reproduction for a bug where SelectionArea text selection breaks after navigating between routes in a go_router ShellRoute.

Live Demo

https://davidmigloz.github.io/flutter_selection_bug/

The Bug

When a SelectionArea wraps the child of a ShellRoute, navigating from a parent route to a child route creates invisible "dead zones" where drag-to-select silently fails. The dead zones correspond to the bounding boxes of selectable text from the previous (now offstage) page.

• No crash, no assertion error, no console warnings
• The I-beam cursor still appears in the dead zone
• Only drag-to-select initiation fails; dragging INTO the zone from outside works
• The dead zone shifts when scrolling

Reproduction Steps

flutter run -d chrome            # debug (DDC)  — reproduces
flutter run -d chrome --wasm     # debug (WASM) — reproduces

1. Open the entities list screen (/entities)
2. Verify text is selectable in the table (emails, names, phones)
3. Click "View" on any entity to navigate to /entities/:entityId
4. Try to select "First Name: John" by clicking and dragging -- fails
5. Scroll down slightly -- the dead zone shifts, making different rows unselectable
6. Hard-reload /entities/entity-1 directly (without navigating from list) -- works

Build Mode Behavior

Command	Compiler	Bug reproduces?
flutter run -d chrome	DDC (debug)	Yes
flutter run -d chrome --wasm	dart2wasm (debug)	Yes
flutter run -d chrome --release --wasm	dart2wasm (release)	Yes
flutter run -d chrome --release	dart2js (release)	No

Root Cause

When navigating to /entities/entity-1, go_router's route matching produces two RouteMatch objects for the shell's Navigator: /entities (parent) and :entityId (child). The Navigator keeps the parent page mounted but offstage.

SelectableRegion (behind SelectionArea) does not use the render tree's hit-testing -- it iterates its own list of registered selectables. The offstage page's Text widgets remain registered with valid bounding boxes that overlap the current page's content, intercepting selection events.

Branches

• main: Reproduces the bug with published go_router: ^17.1.0
• fix/offstage-selection-disabler: Fix using a local go_router fork that wraps offstage page content in SelectionContainer.disabled

See INVESTIGATION.md for the full analysis.