~anthropic/claude-sonnet-latest → B (6:4)

Side B fixes a real off-by-one/indexing bug (thread_post_index semantics), removing a fallback that masked an invariant violation with .expect() and documenting the 0-based vs 1-based confusion, plus adds regression tests asserting correct index values. Side A is purely cosmetic: dedenting HTML markup and tweaking CSS counter styling across theme files, which is low-risk but non-functional churn.