signed-daemon-health sliced detail at 512 UTF-16 units while the Rust owner
counts bytes, so 300 x "é" failed shape validation. truncateUtf8Bytes now
serves runtime presence and both daemon-health sites, replacing
truncateRuntimePresenceDetail. It makes the string well formed first, so a
lone surrogate becomes U+FFFD instead of invalid UTF-8 in msgpack. The
unsigned payload is extracted as unsignedDaemonHealthPayload so it can be
tested without a socket.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>