Keep the advanced CDict estimator and its private workspace sizing inputs in C, but route the public estimate through a Rust policy bridge. Rust now selects unknown-source/create-CDict parameters and the public by-copy load mode before invoking the opaque C estimator. Focused tests verify callback ordering, selected parameters, and the missing-policy-input guard.
Test Plan: Not run in this atomic commit; the capped serial Rust, native, smoke, and original test-suite verification follows.
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