Review feedback: analyze_decision_influence(), trace_decision_causality(),
and find_precedents() had the same vocabulary split as get_causal_chain().
The first two read edge_type_index, which is keyed by the RAW edge_type
string, so they now filter index keys by normalized type; find_precedents()
accepts the analyzer's 'precedes' spelling alongside PRECEDENT_FOR.
Adds regression tests for all three call sites.