Common terms like 'error'/'exception' were stealing BFS seed slots from
rare identifiers like 'FooBarService', burning the token budget on noise.
- _compute_idf: weights query terms by inverse document frequency, cached
on G.graph so cost is paid once per graph load not per query
- _score_nodes: multiplies each tier bonus by IDF weight
- _pick_seeds: replaces fixed top-3 with gap-ratio selection — stops adding
seeds when score drops below 20% of the top match
- _subgraph_to_text: truncation hint now tells Claude to narrow with
context_filter or use get_node instead of just saying 'truncated'
Fixes#897
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
SafiandClaude Sonnet 4.6
a316590adc