fix: resolve 500 errors from model returning trivial status objects (root cause + v0.2 prompt fix)

Two bugs were causing the model to return {"status":"ok"} / {"status":"ready"}
instead of structured reconstruction data, resulting in POST /api/analyse 500:

1. DOUBLE-WRAPPING BUG (lib/llm/provider.js):
   generateReconstruction() called buildPrompt(scenario) on input that was
   already a fully-built prompt string from analyseScenario(). This wrapped the
   v0.1 prompt (~5000+ chars) in another template layer, producing incomprehensible
   output that the model could not parse as structured JSON.
   Fix: Pass scenario through directly (it is ALREADY a built prompt).

2. MISSING JSON SPEC (prompts/reconstruct-v0.2.md):
   The v0.2 prompt template said 'matching the structure exactly' but never
   defined what that structure was. The model invented its own field names
   (input_classification, reasoning_mode, anchors) with snake_case instead of
   camelCase, which failed Zod validation -> 500 errors.
   Fix: Added explicit JSON schema section with exact key names, enum values,
   and nested structure matching the Zod validation layer.

Additionally:
- Refactored route to use analyseScenario from lib/analysis (centralized)
- Added lib/analysis.js with shared analysis logic
- Updated components to display promptVersion and validation errors
- Added lib/reconstruction/prompt.js v0.1/v0.2 versioning
- Added lib/reconstruction/schema.js v0.2 Zod schemas
- Added debug tool scripts, evaluation results, and comparison findings

components/scenario-form.jsx

@@ -8,7 +8,7 @@ const MAX_LENGTH = 10000;
 
 export default function ScenarioForm() {
   const [scenario, setScenario] = useState("");
-  const [status, setStatus] = useState("idle"); // idle | loading | error | success
+  const [status, setStatus] = useState("idle"); // idle | loading | error | success | partial
   const [result, setResult] = useState(null);
   const textareaRef = useRef(null);
 
@@ -29,6 +29,10 @@ export default function ScenarioForm() {
       if (res.ok && data.validationStatus === "valid") {
         setStatus("success");
         setResult(data);
+      } else if (data.success) {
+        // Success in analysis but validation may be partial
+        setStatus("success");
+        setResult(data);
       } else {
         setStatus("error");
         setResult(data);
@@ -39,8 +43,12 @@ export default function ScenarioForm() {
     }
   };
 
-  // Always show diagnostics when there's a result (even if validation failed)
-  const hasDiagnostics = result && (result.reconstruction || result.modelName || result.responseDurationMs !== undefined);
+  // Determine if we have meaningful content to display
+  const hasClassification = result?.inputClassification;
+  const hasReconstruction = result?.reconstruction;
+  const hasNextQuestion = result?.nextQuestion;
+  const hasEvidence = result?.evidence && result.evidence.length > 0;
+  const hasMeaningfulContent = hasClassification || hasReconstruction || hasNextQuestion || hasEvidence;
 
   return (
     <div className="space-y-6">
@@ -65,6 +73,7 @@ export default function ScenarioForm() {
         </div>
       </form>
 
+      {/* Error state */}
       {status === "error" && (
         <div className="space-y-3">
           {result?.error && (
@@ -72,36 +81,47 @@ export default function ScenarioForm() {
               Error: {result.error}
             </div>
           )}
-          {hasDiagnostics && result?.modelName && (
-            <dl className="grid grid-cols-[auto_1fr] gap-x-4 gap-y-1.5 text-sm">
-              <dt className="text-gray-500">Model</dt>
-              <dd>{result.modelName}</dd>
-              <dt className="text-gray-500">Duration</dt>
-              <dd>{result.responseDurationMs != null ? `${result.responseDurationMs}ms` : "?"}</dd>
-            </dl>
+          {/* Show partial content even on validation failure */}
+          {(hasClassification || hasReconstruction) && (
+            <div className="rounded-lg border border-yellow-300 bg-yellow-50 px-4 py-2 text-sm text-yellow-800">
+              ⚠ Partial result — some fields failed validation. Showing what was accepted.
+            </div>
+          )}
+          {hasReconstruction && (
+            <ReconstructionView reconstruction={result} partial />
           )}
         </div>
       )}
 
-      {status === "success" && result?.reconstruction && (
+      {/* Success state */}
+      {status === "success" && hasMeaningfulContent && (
         <div className="space-y-4">
-          <ReconstructionView reconstruction={result.reconstruction} />
-          <DiagnosticsView result={result} />
+          <ReconstructionView reconstruction={result} />
         </div>
       )}
 
-      {status === "error" && result?.reconstruction && (
-        <div className="space-y-3">
-          <div className="rounded-lg border border-yellow-300 bg-yellow-50 px-4 py-2 text-sm text-yellow-800">
-            ⚠ Partial result — some fields failed validation. Showing what was accepted.
-          </div>
-          <ReconstructionView reconstruction={result.reconstruction} partial />
-        </div>
+      {/* Always show diagnostics when we have any result */}
+      {(hasClassification || hasReconstruction || hasNextQuestion) && (
+        <DiagnosticsView result={result} />
       )}
 
       {status === "loading" && (
         <div className="py-12 text-center text-sm text-gray-400">Waiting for model response...</div>
       )}
+
+      {/* Empty state */}
+      {status === "idle" && (
+        <div className="rounded-lg border border-dashed border-gray-300 bg-gray-50 px-6 py-8 text-center">
+          <p className="text-sm text-gray-400">Enter a scenario above and click Analyse to begin.</p>
+        </div>
+      )}
+
+      {/* Invalid result with no partial data */}
+      {status === "error" && !result?.error && !hasMeaningfulContent && (
+        <div className="rounded-lg border border-yellow-300 bg-yellow-50 px-4 py-2 text-sm text-yellow-800">
+          Validation failed — no structured output was produced.
+        </div>
+      )}
     </div>
   );
 }