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docs/adr/coherence-engine/ADR-CE-012-gate-refusal-witness.md

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+# ADR-CE-012: Gate = Refusal Mechanism with Witness
+
+**Status**: Accepted
+**Date**: 2026-01-22
+**Parent**: ADR-014 Coherence Engine Architecture
+
+## Context
+
+When coherence energy exceeds threshold, the system must refuse action. This refusal needs to be:
+- Deterministic (same inputs → same decision)
+- Auditable (why was it refused?)
+- Provable (cryptographic witness)
+
+## Decision
+
+**Gate = refusal mechanism with witness - every refusal is provable.**
+
+Gate evaluation produces:
+```rust
+pub struct GateDecision {
+    pub allow: bool,
+    pub lane: ComputeLane,
+    pub witness: WitnessRecord,
+    pub denial_reason: Option<String>,
+}
+```
+
+The WitnessRecord includes:
+- Energy snapshot at decision time
+- Policy bundle that defined thresholds
+- Hash chain to previous witness
+- Content hash for integrity
+
+## Consequences
+
+### Benefits
+- Every refusal has cryptographic proof
+- Can reconstruct exactly why any decision was made
+- Compliance-ready audit trail
+
+### Risks
+- Witness storage overhead
+- Must handle witness retrieval at scale
+
+## References
+
+- ADR-014: Coherence Engine Architecture, Section 3
+- ADR-CE-005: First-Class Governance Objects