The existing markdown suite was strong on UTF-16 offsets and chunk
redistribution but had no coverage for nested or adjacent styles, no test
that an unmatched opener round-trips as plain text, and no test for the
blockquote/inline-code interaction. Add six cases including the
documented contiguous-BOLD output for `# **wrap** me`, which Signal
renders as one visual span.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>