fix: recognize content ownership within prefixed error chains

internal/logging/text.go

@@ -115,6 +115,7 @@ func redactForm(body string) (string, bool) {
 }
 
 var textFieldLine = regexp.MustCompile(`^\s*([A-Za-z_][A-Za-z0-9_.-]*)\s*[:=]`)
+var textFieldLabel = regexp.MustCompile(`\b([A-Za-z_][A-Za-z0-9_.-]*)\s*[:=]`)
 
 func redactConversationLines(body string) string {
 	lines := strings.SplitAfter(body, "\n")
@@ -133,14 +134,20 @@ func redactConversationLines(body string) string {
 			}
 			hiding = false
 		}
-		if len(field) > 0 && sensitive(field[1]) {
-			lines[i] = "[REDACTED_FIELD]"
+		// Labels establish ownership wherever they occur in an error chain, not
+		// only at line start. Preserve the preceding actual failure description.
+		for _, span := range textFieldLabel.FindAllStringSubmatchIndex(line, -1) {
+			key := line[span[2]:span[3]]
+			if !sensitive(key) {
+				continue
+			}
+			lines[i] = line[:span[0]] + "[REDACTED_FIELD]"
 			if strings.HasSuffix(line, "\n") {
 				lines[i] += "\n"
 			}
-			// Credentials/header fields own their single line, not unrelated
-			// following diagnostics. Only conversational fields own continuation.
-			hiding = conversationField(field[1])
+			// Credentials own only this line; content owns the following paragraphs.
+			hiding = conversationField(key)
+			break
 		}
 	}
 	return strings.Join(lines, "")

internal/logging/text_security_test.go

@@ -61,6 +61,31 @@ func TestContentFieldClassificationAndEveryLoggingPathAgree(t *testing.T) {
 	}
 }
 
+func TestPrefixedContentLabelsKeepReasonAndOwnFollowingDialogue(t *testing.T) {
+	for _, prefix := range []string{"upstream failed: ", "wrapped error: upstream failed: ", "upstream failed; ", "上游失败：upstream failed: "} {
+		for _, field := range []string{"conversation", "history", "messages", "system_message", "prompt", "final_transcript"} {
+			value := prefix + field + ":\n\nuser: private-user-turn\n\nassistant: private-assistant-turn\nstatus=retry_pending\nattempts=2"
+			for _, debug := range []bool{false, true} {
+				out := installTestLogger(t, debug)
+				slog.Error("request failed", "error", errors.New(value), "detail", value)
+				slog.Info(value, "stage", "failure_observed")
+				TextBody(t.Context(), "HTTP text observed", []byte(value), "transport", "http")
+				text := out.String()
+				for _, secret := range []string{"private-user-turn", "private-assistant-turn"} {
+					if strings.Contains(text, secret) {
+						t.Fatalf("prefix %q field %s debug %v leak: %s", prefix, field, debug, text)
+					}
+				}
+				for _, keep := range []string{"upstream failed", "retry_pending", "attempts=2"} {
+					if !strings.Contains(text, keep) {
+						t.Fatal("business reason lost", text)
+					}
+				}
+			}
+		}
+	}
+}
+
 func TestConversationOwnershipPersistsAcrossBlankLines(t *testing.T) {
 	for _, gap := range []string{"\n", "\n\n", "\n \n\t\n", "\r\n\r\n"} {
 		for _, label := range []string{"messages", "prompt", "transcript", "content"} {