Creates tests/graph/shared-anchor-production-path.test.js (36 tests, all pass).
Experiment 49 asks whether any sequence of real production updates via
applyValidatedProposal creates two or more active unknowns sharing the same
populated relationship anchor. Two sequential-update scenarios (Cases A & B)
consistently returned separate_anchors or insufficient_data — no shared
anchor observed in tested flows.
Control cases C–F confirm: diagnostic correctly distinguishes shared vs
separated patterns on controlled fixtures; all produced nodes/edges pass
schema validation; resolving one node does not mutate another (immunity);
decomposition children share parent anchor correctly.
Combined regression suite: 78 tests across Exp 47 (26), Exp 48 (16),
Exp 49 (36) — all passing, no production code modified.
