Block contains both @Hans-Peter Müller and @Hans Müller; the listener fires
a rename for Hans Müller → Hans Schmidt. The simple replace("@" + old,
"@" + new) hinges on the leading @-and-space anchor: "@Hans Müller" does
not appear inside "@Hans-Peter Müller" (hyphen interrupts), so only the
standalone mention rewrites. Sidecar mirrors the same — Hans Müller's
entry flips to Hans Schmidt while Hans-Peter Müller's entry is preserved.
Refs #362
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>