The ampersona-gates feature flag referenced ampersona_core and
ampersona_engine crates that do not exist, causing cargo check
--all-features to fail. Remove the feature flag and all gated code:
- Remove ampersona-gates from Cargo.toml [features]
- Delete src/sop/gates.rs (entire module behind cfg gate)
- Remove gated methods from audit.rs (log_gate_decision, log_phase_state)
- Remove gated MetricsProvider impl and tests from metrics.rs
- Simplify sop_status.rs gate_eval field and append_gate_status
- Update observability docs (EN + zh-CN)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
