Feature request: transient checkmark feedback on code-block copy buttons #1000

Is your feature request related to a problem? Please describe.

The native GitHub-flavor code-block header has a copy button, but its icon does not acknowledge a successful copy. Applications can show a toast or trigger haptics through onCopyPress, but cannot update the built-in button itself. Feedback at the tapped control would confirm the action without requiring a separate overlay.

Describe the solution you'd like

Temporarily replace the code-block header's copy icon with a checkmark after a successful copy, then restore the copy icon after a short interval, for example 1.5 seconds.

• Support the native header on Android and iOS, and macOS where applicable.
• Repeated copies should restart the feedback interval.
• Reset feedback and cancel pending work when the block's code/language changes, it becomes pending during streaming, or the view is detached/recycled.
• Preserve the current icon sizing, theme colors, and accessibility behavior.
• Keep the documented onCopyPress contract unchanged: it should not start firing for Copy as Markdown as a side effect of adding visual feedback.

Whether feedback is enabled by default or exposed as an option is open to discussion. This request does not require a new copy-event API, toast, or haptics implementation.

Describe alternatives you've considered

An application-owned toast/haptic through onCopyPress works today, but does not acknowledge the action on the button. Replacing the entire native code-block header solely to change its icon is a larger customization than this behavior needs.

Additional context

We currently carry a downstream patch against react-native-enriched-markdown 1.0.2 that adds transient native checkmarks. We would like to contribute this independently of search highlighting or font changes, with lifecycle and repeated-copy coverage.