autoresearch iter 6: reject negative cursor instead of silently using 0

parsePositiveInt reported invalidity through a bool that both call sites
discarded, and returned (false, nil) whenever Atoi succeeded on a negative
number. GetLogs therefore accepted ?cursor=-5 and served it as cursor 0
('latest') instead of the documented 400. Validity now travels through the
error result, which no caller can ignore.

backend/plugins/domain/admin/handler/logs.go

@@ -11,6 +11,7 @@ import (
 	"Wavelet/plugins/domain/admin/model"
 	"Wavelet/plugins/domain/admin/service"
 	"encoding/json"
+	"errors"
 	"net/http"
 	"strconv"
 
@@ -47,11 +48,11 @@ func GetLogs(c *gin.Context) {
 	limitStr := c.DefaultQuery("limit", "200")
 
 	var cursor, limit int
-	if _, err := parsePositiveInt(cursorStr, &cursor); err != nil {
+	if err := parsePositiveInt(cursorStr, &cursor); err != nil {
 		response.AbortWithError(c, http.StatusBadRequest, errs.InvalidCursorParam)
 		return
 	}
-	if _, err := parsePositiveInt(limitStr, &limit); err != nil || limit <= 0 {
+	if err := parsePositiveInt(limitStr, &limit); err != nil || limit <= 0 {
 		limit = defaultLimit
 	}
 	if limit > maxLimit {
@@ -183,15 +184,22 @@ func getUpgrader() *websocket.Upgrader {
 	}
 }
 
-func parsePositiveInt(s string, result *int) (bool, error) {
+// errNegativeParam 表示查询参数解析出了负数。
+var errNegativeParam = errors.New("parameter must not be negative")
+
+// parsePositiveInt 解析非负整数查询参数；返回错误时 result 保持调用前的值。
+func parsePositiveInt(s string, result *int) error {
 	if s == "" {
 		*result = 0
-		return true, nil
+		return nil
 	}
 	n, err := strconv.Atoi(s)
-	if err != nil || n < 0 {
-		return false, err
+	if err != nil {
+		return err
+	}
+	if n < 0 {
+		return errNegativeParam
 	}
 	*result = n
-	return true, nil
+	return nil
 }

backend/plugins/domain/admin/handler/logs_test.go

@@ -0,0 +1,41 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package handler
+
+import (
+	"testing"
+)
+
+func TestParsePositiveInt(t *testing.T) {
+	const untouched = 77
+
+	tests := []struct {
+		name    string
+		input   string
+		want    int
+		wantErr bool
+	}{
+		{name: "empty means zero", input: "", want: 0},
+		{name: "zero accepted", input: "0", want: 0},
+		{name: "positive accepted", input: "42", want: 42},
+		{name: "negative rejected", input: "-5", want: untouched, wantErr: true},
+		{name: "oversized rejected", input: "99999999999999999999", want: untouched, wantErr: true},
+		{name: "non numeric rejected", input: "abc", want: untouched, wantErr: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			got := untouched
+			err := parsePositiveInt(tt.input, &got)
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("parsePositiveInt(%q) error = %v, wantErr %v", tt.input, err, tt.wantErr)
+			}
+			if got != tt.want {
+				t.Errorf("parsePositiveInt(%q) left result %d, want %d", tt.input, got, tt.want)
+			}
+		})
+	}
+}