architecture: introduce investigation narrative layer

docs/design-evolution-log.md

@@ -647,13 +647,95 @@ Confirmed.
 - Resolved unknowns and assumptions are factual answers to previously unanswered questions — they should appear in the known section with an epistemic label ("Not yet established" / "To be tested") if their status hasn't been explicitly set.
 - The translation adapter is the right place for this work: it is a single deterministic function, testable in isolation, and its output contracts are stable.
 
+#### Result
+
+Confirmed.
+
+#### What did we learn?
+
+- Semantic filtering significantly improved Version C.
+- The remaining limitations are architectural rather than visual.
+- Graph nodes still do not naturally map to facilitator language.
+- Users think in investigation progress rather than graph structure.
+- Version C proved the need for an intermediate narrative model.
+
 #### Decision
 
-Keep the semantic projection approach. The facilitator view now routes by meaning, suppresses structural noise, deduplicates observations, and prefers concrete findings. Experiment 13 is closed.
+Keep the semantic projection approach.
+
+Do not continue improving graph projection indefinitely.
+
+Proceed to designing an Investigation Narrative layer. Experiment 13 is closed.
 
 ---
 
-## Emerging Direction
+### Experiment 14 — Investigation Narrative Layer
+
+#### Hypothesis
+
+The graph should remain the internal reasoning model.
+
+A separate narrative model should become the presentation model.
+
+The facilitator UI should consume narrative state rather than graph nodes.
+
+#### Questions
+
+- What information belongs in a narrative?
+- What belongs only in the graph?
+- Which narrative elements can be derived deterministically?
+- What should remain hidden?
+- Can every facilitator panel consume the same narrative object?
+
+#### Status
+
+Architectural experiment.
+
+#### Evaluation
+
+Pending.
+
+---
+
+## Emerging Direction — Investigation Narrative
+
+The Confidence Engine architecture is becoming:
+
+User
+
+↓
+
+Facilitated Conversation
+
+↓
+
+Reasoning Graph
+
+↓
+
+Investigation Narrative
+
+↓
+
+Workspace Projection
+
+↓
+
+User
+
+The reasoning graph becomes the machine representation.
+
+The investigation narrative becomes the human representation.
+
+The UI simply renders whichever projection is appropriate.
+
+This is an emerging architectural direction.
+
+It is intentionally recorded before implementation so future experiments remain aligned.
+
+---
+
+## Emerging Direction — Graph as Source of Truth
 
 The first UX experiments focused on workspace structure.
 
@@ -698,3 +780,16 @@ Dark mode is intentionally deferred.
 Once the information architecture and visual hierarchy stabilise we will investigate whether an "Investigation Mode" (rather than a conventional dark mode) improves concentration.
 
 This should be treated as a future UX experiment rather than an accessibility feature.
+
+## Backlog — Investigation Narrative (Potential Future Work)
+
+These are observations, not implementation tasks.
+
+- Narrative adapter
+- Narrative quality heuristics
+- Narrative progression
+- Narrative completion state
+- Narrative confidence wording
+- Narrative testing
+- Narrative localisation
+- Multiple narrative projections