~anthropic/claude-sonnet-latest → B (8:2)

Side B is a substantial feature refactor converting entity fetch from a fire-and-forget JS morph into a proper SSE streaming flow with job-result signaling (oneshot channels, FetchJobResult enum, worker notifications), plus richer tracing, module reorganization (new fetch module), client-side SSE parsing, and updated integration tests. Side A is a small but real bugfix (moving a zero-ratio guard earlier) with a corresponding test update, which is correct and valuable but far narrower in scope and impact than B's architectural improvement to a core interaction flow.