fix(chat): reject conflicting card update responses

internal/shortcut/chatmsg/card_update.go

@@ -131,9 +131,19 @@ func observeCardUpdateMap(value map[string]any, observation *cardUpdateObservati
 			}
 		}
 	}
+	errorCode, hasErrorCode := value["errorCode"]
+	errorCodeEmpty := hasErrorCode && cardUpdateErrorCodeEmpty(errorCode)
+	if hasErrorCode && !errorCodeEmpty {
+		setNegativeCardUpdateEvidence(observation, "errorCode=non-empty")
+	}
 	if success, ok := value["success"].(bool); ok {
 		if success {
-			setPositiveCardUpdateEvidence(observation, "success=true")
+			// Record success=true only when the same response envelope explicitly
+			// includes its business-error field. A non-empty code is already
+			// negative evidence above, so the two signals reject the conflict.
+			if hasErrorCode {
+				setPositiveCardUpdateEvidence(observation, "success=true")
+			}
 		} else {
 			setNegativeCardUpdateEvidence(observation, "success=false")
 		}
@@ -149,6 +159,14 @@ func observeCardUpdateMap(value map[string]any, observation *cardUpdateObservati
 	}
 }
 
+func cardUpdateErrorCodeEmpty(value any) bool {
+	if value == nil {
+		return true
+	}
+	code, ok := value.(string)
+	return ok && strings.TrimSpace(code) == ""
+}
+
 func setPositiveCardUpdateEvidence(observation *cardUpdateObservation, evidence string) {
 	if observation.positiveEvidence == "" {
 		observation.positiveEvidence = evidence

internal/shortcut/chatmsg/card_update_test.go

@@ -63,6 +63,11 @@ func TestCrossPlatformCoverageVerifyStreamingCardUpdate(t *testing.T) {
 		{name: "conflicting evidence", response: map[string]any{"updated": true, "applied": false}, wantErrIs: ErrCardUpdateUnverified},
 		{name: "zero affected", response: map[string]any{"affectedCount": 0}, wantErrIs: ErrCardUpdateNotApplied},
 		{name: "success acknowledgement", response: map[string]any{"success": true, "errorCode": nil}, wantProof: "success=true"},
+		{name: "success acknowledgement with empty error code", response: map[string]any{"success": true, "errorCode": "  "}, wantProof: "success=true"},
+		{name: "success without explicit error code", response: map[string]any{"success": true}, wantErrIs: ErrCardUpdateUnverified},
+		{name: "success conflicts with error code", response: map[string]any{"success": true, "errorCode": "InternalError"}, wantErrIs: ErrCardUpdateUnverified},
+		{name: "success conflicts with numeric error code", response: map[string]any{"success": true, "errorCode": float64(500)}, wantErrIs: ErrCardUpdateUnverified},
+		{name: "error code without success", response: map[string]any{"errorCode": "InternalError"}, wantErrIs: ErrCardUpdateNotApplied},
 		{name: "failed acknowledgement", response: map[string]any{"success": false}, wantErrIs: ErrCardUpdateNotApplied},
 		{name: "explicitly not updated", response: map[string]any{"result": map[string]any{"updated": false}}, wantErrIs: ErrCardUpdateNotApplied},
 		{name: "mismatched id", response: map[string]any{"result": map[string]any{"bizId": "biz-2", "updated": true}}, wantErrIs: ErrCardUpdateBizIDDrift},