Avoid stale reply gesture context

[Xare123]

Problem

A delayed reply gesture callback could retain a stale widget context after the message row was rebuilt or unmounted.

Change

Resolve the current context at callback time and guard the action when the row is no longer mounted.

Validation

• one-file defensive change
• git diff --check passes
• focused analyzer reports only two pre-existing informational findings

Scope

No reply-thread assembly, keyboard, transport, or message-storage changes.