~x-ai/grok-latest → A (3:1)

A replaces .map(i+1).unwrap_or(0) with .expect(...) (plus doc/comment and test updates) to enforce 0-based thread_post_index invariants matching /t/tag/N routes; B churns ~3600 lines by deleting legacy/parser.rs then duplicating it verbatim into server/src/parser.rs plus voluminous boilerplate/tests/UI wiring whose commit message is merely 'nice'.