fix(confidence-engine): scope focused presentation to active question

- FocusedQuestionBody derives thread-local contribution subset using
  targetNodeId || originatingTargetNodeId matching
- hasCompletedContext, latest completed contrib, and all effective
  presentation fallbacks use scoped collection only
- scenario-wide focusedContributions history preserved in memory
- Fresh Question B no longer bleeds Question A's content across
  every presentation surface (Previously answered, What this tells us,
  Still unclear, Questions this raises, Assumptions, Connections)
- Reopening or revisiting Question A still uses its own history
- Targeted regression: 3 new Vitest cases pass
- Handoff docs updated with v0.52 correction record

components/reasoning-workspace.jsx

@@ -143,6 +143,12 @@ function FocusedQuestionBody({
   onUpdateFindingDisposition,
   onUpdateFindingProposition,
 }) {
+  // ── Active-thread contribution scoping (v0.52) ──
+  // focusedContributions is scenario-wide; present only the active node's contributions.
+  const threadContribs = (focusedContributions || []).filter(
+    (c) => c.targetNodeId === nodeId || c.originatingTargetNodeId === nodeId,
+  );
+
   const hasContent = focused?.question?.trim() || formulationStep === "active" || processingStep === "active" || focused?.error;
   const hasResult = Boolean(focused?.result);
   const hasAnswer = Boolean(focused?.answer);
@@ -151,7 +157,7 @@ function FocusedQuestionBody({
   // Completed context: result (primary) OR prior contributions (fallback during processing/error).
   // Processing and error are transient states — they must NOT collapse completed context.
   const hasCompletedContext = Boolean(focused?.result) || (() => {
-    const pc = [...(focusedContributions || [])].reverse().find((c) => c?.question && c?.answer);
+    const pc = [...threadContribs].reverse().find((c) => c?.question && c?.answer);
     return !!pc;
   })();
 
@@ -159,7 +165,7 @@ function FocusedQuestionBody({
   // After setFollowUpQuestion() mutates focused.question/answer, derive from the
   // latest completed Contribution so the narrative remains correct.
   // Active follow-up detection: primary via result (when result exists), fallback via priorContribs (error state may have null result).
-  const priorContribs = [...(focusedContributions || [])].reverse();
+  const priorContribs = [...threadContribs].reverse();
   // Follow-ups from result are primary; priorContribs is fallback when result is null.
   const followUpsFromResult = focused?.result?.possibleFollowUpQuestions || [];
   const hasActiveFollowUpFromResult =