diff --git a/components/investigation-map.jsx b/components/investigation-map.jsx
index 213c49d..e220a83 100644
--- a/components/investigation-map.jsx
+++ b/components/investigation-map.jsx
@@ -84,10 +84,10 @@ export default function InvestigationMap({ turnCount = 0 }) {
   return (
     <div className="rounded-lg border border-gray-100 bg-gray-50/50 p-4" role="region" aria-label="Investigation map preview">
       <h2 className="mb-1 text-sm font-semibold tracking-tight text-gray-400">
-        Investigation Map Preview
+        Investigation Map
       </h2>
       <p className="mb-3 text-xs text-gray-400">
-        This preview shows where a future reasoning map may appear. Its final shape will emerge from the reasoning engine.
+        Active investigation topics and their status.
       </p>
 
       <div className="space-y-px border-t border-gray-100 pt-3" role="list" aria-label="Investigation topics">
diff --git a/components/reasoning-workspace.jsx b/components/reasoning-workspace.jsx
index 8021ccd..3e83656 100644
--- a/components/reasoning-workspace.jsx
+++ b/components/reasoning-workspace.jsx
@@ -669,72 +669,100 @@ export default function ReasoningWorkspace({
           {/* Post-update acknowledgement — only after success, never during loading */}
           {updateStatus === "success" && !isUpdating && <UpdateAcknowledgement updateResult={result} />}
 
-          {/* ── Active workspace (left) + Working memory (right) ─────── */}
-          <div className="grid grid-cols-1 gap-6 md:grid-cols-2">
-            {/* Left column — active workspace */}
-            <div className="space-y-6">
-              {/* ── Local update loading (always visible when updating) ─ */}
-              {isUpdating && (
-                <LoadingOverlay
-                  isLoading={true}
-                  elapsed={updateElapsed}
-                  currentMessage={updateMsg}
-                  variant="update"
-                />
-              )}
+          {/* ══════════════════════════════════════════════════════════
+              FACILITATED INVESTIGATION WORKSPACE — PHASE 4 EXPLORATION
+              ══════════════════════════════════════════════════════════
 
-              {/* ── Response form — hidden during update loading ─ */}
-              {!isUpdating && canAnswer && (
-                <form onSubmit={handleUpdateCaptureAndSubmit} className="space-y-4 rounded-lg border border-gray-200 bg-white p-5">
-                  <div>
-                    <label htmlFor="rw-answer" className="mb-2 block text-sm font-medium text-gray-700">
-                      Response
-                    </label>
-                    <textarea
-                      id="rw-answer"
-                      value={answer}
-                      onChange={(e) => setAnswer(e.target.value)}
-                      rows={4}
-                      disabled={updateStatus === "loading"}
-                      className="w-full rounded-lg border border-gray-300 px-4 py-3 text-sm focus:border-gray-500 focus:outline-none focus:ring-2 focus:ring-gray-400 disabled:cursor-not-allowed disabled:opacity-60"
-                      placeholder="Enter the answer to the selected question..."
-                    />
-                  </div>
-                  <div className="flex items-center justify-between">
-                    <p className="text-xs text-gray-400">
-                      One update turn only in this prototype.
-                    </p>
-                    <button
-                      type="submit"
-                      disabled={!answer.trim()}
-                      className="rounded-lg bg-blue-700 px-5 py-2.5 text-sm font-medium text-white transition hover:bg-blue-600 disabled:cursor-not-allowed disabled:opacity-40"
-                    >
-                      Update
-                    </button>
-                  </div>
-                </form>
-              )}
+              Layout metaphor: a workshop desk, not a document.
 
-              {/* ── Terminal state: outcome card — hidden during update loading ─ */}
-              {!isUpdating && status === "success" && !hasSelectedQuestion && graph && genuineCompletion && (
+              Desktop: wide work surfaces organised by cognitive activity.
+              Tablet: simplified two-zone layout.
+              Mobile: naturally stacked.
+              ══════════════════════════════════════════════════════════ */}
+
+          {hasSelectedQuestion ? (
+
+            <>
+              {/* ── Active workspace zone (Question + Response) ───────── */}
+              <div className="space-y-6">
+
+                {isUpdating && (
+                  <LoadingOverlay
+                    isLoading={true}
+                    elapsed={updateElapsed}
+                    currentMessage={updateMsg}
+                    variant="update"
+                  />
+                )}
+
+                {!isUpdating && canAnswer && (
+                  <form onSubmit={handleUpdateCaptureAndSubmit} className="space-y-4 rounded-lg border border-gray-200 bg-white p-5">
+                    <div>
+                      <label htmlFor="rw-answer" className="mb-2 block text-sm font-medium text-gray-700">
+                        Response
+                      </label>
+                      <textarea
+                        id="rw-answer"
+                        value={answer}
+                        onChange={(e) => setAnswer(e.target.value)}
+                        rows={4}
+                        disabled={updateStatus === "loading"}
+                        className="w-full rounded-lg border border-gray-300 px-4 py-3 text-sm focus:border-gray-500 focus:outline-none focus:ring-2 focus:ring-gray-400 disabled:cursor-not-allowed disabled:opacity-60"
+                        placeholder="Enter the answer to the selected question..."
+                      />
+                    </div>
+                    <div className="flex items-center justify-between">
+                      <p className="text-xs text-gray-400">
+                        One update turn only in this prototype.
+                      </p>
+                      <button
+                        type="submit"
+                        disabled={!answer.trim()}
+                        className="rounded-lg bg-blue-700 px-5 py-2.5 text-sm font-medium text-white transition hover:bg-blue-600 disabled:cursor-not-allowed disabled:opacity-40"
+                      >
+                        Update
+                      </button>
+                    </div>
+                  </form>
+                )}
+
+              </div>
+
+              {/* ── Supporting workspace (Understanding, Map, Situation) ─ */}
+              <div className="grid grid-cols-1 gap-6 lg:grid-cols-5">
+
+                {/* Understanding — wider surface (2 cols) */}
+                {hasCurrentSummaryCondition && (
+                  <div className="lg:col-span-2">
+                    <CurrentUnderstandingCard currentSummary={graph?.currentSummary || result?.updatedSituationGraph?.currentSummary} plainLanguage={propUnderstanding || null} />
+                  </div>
+                )}
+
+                {/* Investigation Map — workspace artefact (1.5 cols) */}
+                {hasSelectedQuestion && (
+                  <div className="lg:col-span-1">
+                    <InvestigationMap turnCount={investigationHistory.length} />
+                  </div>
+                )}
+
+              </div>
+
+            </>
+
+          ) : status === "success" ? (
+
+            <>
+              {/* Terminal state */}
+              {genuineCompletion && (
                 <CompletionCard summary={resolveCurrentSummary(propUnderstanding || graph?.currentSummary || result?.updatedSituationGraph?.currentSummary)} />
               )}
-              {!isUpdating && status === "success" && !hasSelectedQuestion && graph && !genuineCompletion && (
+              {!genuineCompletion && (
                 <EvidenceLimitCard summary={resolveCurrentSummary(propUnderstanding || graph?.currentSummary || result?.updatedSituationGraph?.currentSummary)} />
               )}
+            </>
 
-            </div>
+          ) : null}
 
-            {/* Right column — working memory: Understanding + Map */}
-            {hasSelectedQuestion && (
-              <div className="space-y-6">
-                {hasCurrentSummaryCondition && (
-                  <CurrentUnderstandingCard currentSummary={graph?.currentSummary || result?.updatedSituationGraph?.currentSummary} plainLanguage={propUnderstanding || null} />
-                )}
-                <InvestigationMap turnCount={investigationHistory.length} />
-              </div>
-            )}
-          </div>
 
           {/* ── Reference row — Situation + History side-by-side on desktop ─ */}
           <div className="grid grid-cols-1 gap-6 md:grid-cols-2">
diff --git a/docs/design-evolution-log.md b/docs/design-evolution-log.md
new file mode 100644
index 0000000..b6fcea9
--- /dev/null
+++ b/docs/design-evolution-log.md
@@ -0,0 +1,92 @@
+# Design Evolution Log
+
+A chronological record of why significant design decisions were made. This is NOT a changelog. It records the product's evolution of thinking.
+
+---
+
+## Phase 1
+Simple conversational investigation
+
+Question → Answer interaction.
+
+Purpose:
+Prove the reasoning loop.
+
+Learning:
+Conversation alone does not provide sufficient context during longer investigations.
+
+---
+
+## Phase 2
+Persistent investigation notebook
+
+Added:
+
+- current understanding
+- original situation
+- investigation history
+
+Learning:
+Users need persistent context rather than remembering previous answers.
+
+---
+
+## Phase 3
+Document workspace
+
+Created a coherent workspace with:
+
+- investigation status
+- current investigation
+- response
+- understanding
+- investigation map placeholder
+- situation
+- history
+
+Learning:
+The interface became usable but still behaved like a document rather than a workspace.
+
+---
+
+## Phase 4 (Current Exploration)
+Facilitated Investigation Workshop
+
+Status:
+Experimental.
+
+Hypothesis:
+
+The Confidence Engine is not:
+
+- a chatbot
+- a dashboard
+- a form
+
+It is a facilitated investigation workspace.
+
+The interface should resemble the environment in which structured thinking happens.
+
+Record discoveries rather than conclusions.
+
+Leave room for future phases.
+
+---
+
+## Phase 4 — Guiding Principles
+
+The Confidence Engine is a workspace, not a document.
+
+People think in multiple directions simultaneously.
+
+Useful context should be visible together.
+
+The interface should favour thinking over scrolling.
+
+The workspace should feel like a large desk or workshop rather than a narrow report.
+
+The engine facilitates thinking.
+
+The user contributes evidence.
+
+The workspace captures shared understanding.
\ No newline at end of file