接入 OpenTelemetry 1.17.0，覆盖 HTTP、HttpClient、.NET Runtime 和数据库链路。

新增 EF Core 数据库拦截器，记录耗时、失败数、慢查询数、TraceId、查询标签和 SQL 哈希；默认不记录完整 SQL及参数。
未配置 OTLP Collector 时不启动 SDK，避免无收益的性能开销。
为课表的作息、课程、灵活课程、考试、实验等六类查询增加稳定标签。
增加可配置的 500ms 慢查询阈值，以及生产环境变量示例。
README 补充 MySQL 慢查询与 EXPLAIN ANALYZE 操作规范。

src/Jiaowu.Api/Program.cs

@@ -7,6 +7,7 @@ using Jiaowu.Api.Infrastructure.Auth;
 using Jiaowu.Api.Infrastructure.Caching;
 using Jiaowu.Api.Infrastructure.Exams;
 using Jiaowu.Api.Infrastructure.Middleware;
+using Jiaowu.Api.Infrastructure.Observability;
 using Jiaowu.Api.Infrastructure.OfficialDocuments;
 using Jiaowu.Api.Infrastructure.Operations;
 using Jiaowu.Api.Infrastructure.Persistence;
@@ -19,6 +20,9 @@ using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Caching.Distributed;
 using Microsoft.IdentityModel.Tokens;
 using Microsoft.OpenApi.Models;
+using OpenTelemetry.Metrics;
+using OpenTelemetry.Resources;
+using OpenTelemetry.Trace;
 using System.Threading.RateLimiting;
 
 EnvironmentFile.Load();
@@ -78,6 +82,9 @@ var backgroundJobOptions = builder.Configuration
 var operationsOptions = builder.Configuration
     .GetSection(OperationsOptions.SectionName)
     .Get<OperationsOptions>() ?? new OperationsOptions();
+var observabilityOptions = builder.Configuration
+    .GetSection(ObservabilityOptions.SectionName)
+    .Get<ObservabilityOptions>() ?? new ObservabilityOptions();
 var rabbitMqOptions = builder.Configuration
     .GetSection(RabbitMqOptions.SectionName)
     .Get<RabbitMqOptions>() ?? new RabbitMqOptions();
@@ -110,6 +117,24 @@ if (databaseOptions.CommandTimeoutSeconds is < 5 or > 300)
         "Database:CommandTimeoutSeconds 必须在 5 到 300 秒之间。");
 }
 
+if (string.IsNullOrWhiteSpace(observabilityOptions.ServiceName) ||
+    observabilityOptions.ServiceName.Length > 100 ||
+    observabilityOptions.SlowQueryThresholdMilliseconds is < 1 or > 60000 ||
+    observabilityOptions.MaximumSqlTextLength is < 256 or > 20000)
+{
+    throw new InvalidOperationException(
+        "Observability 服务名、慢查询阈值或 SQL 文本长度超出允许范围。");
+}
+
+var otlpEndpoint = builder.Configuration["OTEL_EXPORTER_OTLP_ENDPOINT"];
+if (!string.IsNullOrWhiteSpace(otlpEndpoint) &&
+    (!Uri.TryCreate(otlpEndpoint, UriKind.Absolute, out var parsedOtlpEndpoint) ||
+     parsedOtlpEndpoint.Scheme is not ("http" or "https")))
+{
+    throw new InvalidOperationException(
+        "OTEL_EXPORTER_OTLP_ENDPOINT 必须是有效的 HTTP 或 HTTPS 绝对地址。");
+}
+
 if (cacheOptions.ReferenceExpirationMinutes is < 1 or > 1440 ||
     cacheOptions.TimetableExpirationMinutes is < 1 or > 1440 ||
     cacheOptions.AnalyticsExpirationMinutes is < 1 or > 1440 ||
@@ -193,11 +218,16 @@ builder.Services.AddSingleton(cacheOptions);
 builder.Services.AddSingleton(officialDocumentOptions);
 builder.Services.AddSingleton(backgroundJobOptions);
 builder.Services.AddSingleton(operationsOptions);
+builder.Services.AddSingleton(observabilityOptions);
 builder.Services.AddSingleton(rabbitMqOptions);
+builder.Services.AddSingleton<DatabaseCommandTelemetryInterceptor>();
 builder.Services.Configure<OfficialDocumentOptions>(
     builder.Configuration.GetSection(OfficialDocumentOptions.SectionName));
-builder.Services.AddDbContextPool<AppDbContext>(options =>
+builder.Services.AddDbContextPool<AppDbContext>((services, options) =>
 {
+    options.AddInterceptors(
+        services.GetRequiredService<DatabaseCommandTelemetryInterceptor>());
+
     if (databaseOptions.Provider.Equals("SQLite", StringComparison.OrdinalIgnoreCase))
     {
         var sqliteConnectionString = builder.Configuration.GetConnectionString("SQLite")
@@ -240,6 +270,28 @@ builder.Services.AddDbContextPool<AppDbContext>(options =>
         });
 });
 
+if (observabilityOptions.Enabled &&
+    !string.IsNullOrWhiteSpace(otlpEndpoint))
+{
+    builder.Services
+        .AddOpenTelemetry()
+        .ConfigureResource(resource =>
+            resource.AddService(observabilityOptions.ServiceName))
+        .WithMetrics(metrics => metrics
+            .AddAspNetCoreInstrumentation()
+            .AddHttpClientInstrumentation()
+            .AddRuntimeInstrumentation()
+            .AddMeter(DatabaseCommandTelemetryInterceptor.MeterName))
+        .WithTracing(tracing => tracing
+            .AddAspNetCoreInstrumentation(options =>
+                options.Filter = context =>
+                    !context.Request.Path.StartsWithSegments("/health/live"))
+            .AddHttpClientInstrumentation()
+            .AddSource(DatabaseCommandTelemetryInterceptor.ActivitySourceName))
+        .WithMetrics(metrics => metrics.AddOtlpExporter())
+        .WithTracing(tracing => tracing.AddOtlpExporter());
+}
+
 var redisConnectionString = builder.Configuration.GetConnectionString("Redis");
 if (cacheOptions.Enabled && !string.IsNullOrWhiteSpace(redisConnectionString))
 {