fix(cognitive): separate reachability from quality evidence

cmd/cognitive-worker/task_evaluation.go

@@ -68,9 +68,10 @@ func (g cognitiveGateway) taskEvaluationHandler(w http.ResponseWriter, r *http.R
 			response, invokeErr := g.invokeAdmitted(r.Context(), string(invocation.RequestID), provider, invocation, int(request.MaxOutputBytes))
 			observation := capability.TaskCaseObservation{CaseID: item.CaseID, LatencyMicros: time.Since(started).Microseconds(), EvidenceArtifactRef: item.EvidenceArtifactRef}
 			if invokeErr == nil && response.FinishReason == cognitive.FinishCompleted && response.AdvisoryText != "" {
-				observation.Result = capability.EvaluationSupported
-				// Invocation success proves reachability/support for this case,
-				// not semantic answer quality. A verifier may score quality later.
+				// Invocation success proves reachability only. Without an
+				// independent verifier and answer evidence, semantic support and
+				// quality must remain UNKNOWN rather than becoming false evidence.
+				observation.Result = capability.EvaluationUnknown
 				observation.QualityScoreMillis = 0
 			} else {
 				observation.Result = capability.EvaluationUnknown

cmd/cognitive-worker/task_evaluation_test.go

@@ -47,7 +47,12 @@ func TestTaskEvaluationHandlerInvokesEveryBoundedCase(t *testing.T) {
 	if err := json.Unmarshal(recorder.Body.Bytes(), &response); err != nil {
 		t.Fatal(err)
 	}
-	if len(response.Observations) != 2 || response.Observations[0].Result != capability.EvaluationSupported || response.Observations[1].Result != capability.EvaluationSupported {
+	if len(response.Observations) != 2 || response.Observations[0].Result != capability.EvaluationUnknown || response.Observations[1].Result != capability.EvaluationUnknown {
 		t.Fatalf("unexpected observations: %+v", response.Observations)
 	}
+	for _, observation := range response.Observations {
+		if observation.QualityScoreMillis != 0 || observation.CriticalFailure {
+			t.Fatalf("reachability-only evidence must not carry quality or failure claims: %+v", observation)
+		}
+	}
 }