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

Side B delivers a working, tested improvement to the dev fixture workflow (cargo-watch integration, persistent fixture-data, port reuse, summary rebasing) plus a small real cleanup in forum.rs, all functional and immediately useful. Side A is purely a planning document (plan.md) plus a thin, mostly-unused RouteContext wrapper that still delegates to the old CanonicalItemUrl/ThreadNav internals—no actual migration or bugfix, just scaffolding and prose that may become stale.