architecture: define investigation turn cycle

docs/design-evolution-log.md

@@ -817,7 +817,22 @@ Architectural.
 
 #### Evaluation
 
-Pending.
+Confirmed.
+
+---
+
+## What did we learn?
+
+Document observations such as:
+
+- Investigation state is distinct from behaviour.
+- Behaviour should consume assessment rather than graph structure.
+- State assessment provides a stable contract between reasoning and facilitation.
+- The architecture is becoming layered rather than procedural.
+
+Decision:
+
+Proceed to documenting the investigation turn cycle.
 
 ---
 
@@ -871,6 +886,38 @@ This architecture emerged from observation, not top-down design. It may still ch
 
 ---
 
+### Experiment 17 — Investigation Turn Cycle
+
+#### Hypothesis
+
+A complete investigation can be described as a repeating turn cycle in which every architectural layer has a single responsibility.
+
+Status
+
+Architectural.
+
+Evaluation
+
+Pending.
+
+---
+
+## Phase Transition
+
+Record that the project has moved from:
+
+Interface Design
+→
+Facilitated Investigation
+→
+Behavioural Architecture
+→
+System Architecture
+
+Future work should validate these layers rather than introduce new ones.
+
+---
+
 ## Emerging Direction — Graph as Source of Truth
 
 The first UX experiments focused on workspace structure.