Retire legacy caller-fact governance APIs

[rcs2153]

Summary

• retire the public preview authority-bearing caller-fact proportional-governance API surface
• keep caller-fact routing private for internal enforcement
• preserve selected project-validation and Core-owned public governance paths
• document the compatibility boundary, migration posture, implementation report, and independent maintainer review

Why

The retired surface allowed callers to supply authority-bearing runtime facts and optional activation directly. That preserved an alternate public authority model after the selected project-validation path became canonical. Removing it closes that ambiguity without changing private route enforcement or the supported Core-owned APIs.

Compatibility

This is an intentional preview compile-time retirement. No production repository call sites were found. Shared result vocabulary remains public. The posture-recording assessment API is unchanged because it does not enforce approval or denial.

Validation

• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test -p workflow-core --test local_executor (338 passed, 1 ignored)
• cargo test --workspace
• npm run check:docs
• npm run check:integrations
• npm run check
• git diff --check

Governed phase

• implementation: dg/implement, run run-1786538708341183000-2, approval granted with persisted presentation proof
• independent review: dg/review, run run-1786563980091071000-2, approval granted with persisted presentation proof
• review verdict: Phase accepted; proceed to the next runtime-composition phase