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Workflows/CityGateExecutor.cs

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+using MAF1.Agents.FileCity;
+using Microsoft.Agents.AI.Workflows;
+using Microsoft.Extensions.AI;
+
+namespace MAF1.Workflows;
+
+internal sealed class CityGateExecutor() : ChatProtocolExecutor(
+    "CityGate",
+    new ChatProtocolExecutorOptions { AutoSendTurnToken = false })
+{
+    protected override ProtocolBuilder ConfigureProtocol(ProtocolBuilder builder)
+    {
+        return base.ConfigureProtocol(builder)
+            .SendsMessage<ChatMessage>()
+            .SendsMessage<TurnToken>()
+            .YieldsOutput<string>();
+    }
+
+    protected override async ValueTask TakeTurnAsync(
+        List<ChatMessage> messages,
+        IWorkflowContext context,
+        bool? emitEvents,
+        CancellationToken cancellationToken)
+    {
+        string text = string.Join(
+            Environment.NewLine,
+            messages
+                .Where(message => !string.IsNullOrWhiteSpace(message.Text))
+                .Select(message => message.Text));
+
+        CityExtraction extraction = FileCityAgent.Parse(text);
+        if (!extraction.HasValidCities)
+        {
+            string reason = string.IsNullOrWhiteSpace(extraction.Reason)
+                ? "文件里没有可查询的城市。"
+                : extraction.Reason;
+            await context.YieldOutputAsync(
+                $"没有有效城市，工作流结束，不执行 WeatherAgent。{reason}",
+                cancellationToken);
+            return;
+        }
+
+        string prompt = $"请查询这些城市的天气：{string.Join("、", extraction.Cities)}";
+        await context.SendMessageAsync(new ChatMessage(ChatRole.User, prompt), cancellationToken: cancellationToken);
+        await context.SendMessageAsync(new TurnToken(emitEvents), cancellationToken: cancellationToken);
+    }
+}

Workflows/CityParseExecutor.cs

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+using MAF1.Agents.FileCity;
+using Microsoft.Agents.AI.Workflows;
+using Microsoft.Extensions.AI;
+
+namespace MAF1.Workflows;
+
+/// <summary>
+/// 边条件模式：这里只解析，不做 if。走哪条边由 AddEdge 的 condition 决定。
+/// </summary>
+internal sealed class CityParseExecutor() : ChatProtocolExecutor(
+    "CityParse",
+    new ChatProtocolExecutorOptions { AutoSendTurnToken = false })
+{
+    protected override ProtocolBuilder ConfigureProtocol(ProtocolBuilder builder)
+    {
+        return base.ConfigureProtocol(builder).SendsMessage<CityExtraction>();
+    }
+
+    protected override async ValueTask TakeTurnAsync(
+        List<ChatMessage> messages,
+        IWorkflowContext context,
+        bool? emitEvents,
+        CancellationToken cancellationToken)
+    {
+        string text = string.Join(
+            Environment.NewLine,
+            messages
+                .Where(message => !string.IsNullOrWhiteSpace(message.Text))
+                .Select(message => message.Text));
+
+        await context.SendMessageAsync(FileCityAgent.Parse(text), cancellationToken: cancellationToken);
+    }
+}

Workflows/CityWeatherWorkflow.cs

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+using Microsoft.Agents.AI;
+using Microsoft.Agents.AI.Workflows;
+using MAF1.Agents.FileCity;
+
+namespace MAF1.Workflows;
+
+public static class CityWeatherWorkflow
+{
+    public static Workflow BuildNodeCondition(AIAgent fileCityAgent, AIAgent weatherAgent)
+    {
+        (ExecutorBinding fileCity, ExecutorBinding weather) = BindAgents(fileCityAgent, weatherAgent);
+        CityGateExecutor gate = new();
+
+        return new WorkflowBuilder(fileCity)
+            .AddEdge(fileCity, gate)
+            .AddEdge(gate, weather)
+            .WithOutputFrom(gate, weather)
+            .WithName("CityWeather-Node")
+            .Build();
+    }
+
+    public static Workflow BuildEdgeCondition(AIAgent fileCityAgent, AIAgent weatherAgent)
+    {
+        (ExecutorBinding fileCity, ExecutorBinding weather) = BindAgents(fileCityAgent, weatherAgent);
+        CityParseExecutor parse = new();
+        ToWeatherPromptExecutor toWeather = new();
+        SkipWeatherExecutor skip = new();
+
+        return new WorkflowBuilder(fileCity)
+            .AddEdge(fileCity, parse)
+            .AddEdge<CityExtraction>(parse, toWeather, extraction => extraction is { HasValidCities: true })
+            .AddEdge<CityExtraction>(parse, skip, extraction => extraction is not { HasValidCities: true })
+            .AddEdge(toWeather, weather)
+            .WithOutputFrom(skip, weather)
+            .WithName("CityWeather-Edge")
+            .Build();
+    }
+
+    private static (ExecutorBinding FileCity, ExecutorBinding Weather) BindAgents(AIAgent fileCityAgent, AIAgent weatherAgent)
+    {
+        AIAgentHostOptions agentOptions = new()
+        {
+            ForwardIncomingMessages = false,
+            ReassignOtherAgentsAsUsers = true,
+            EmitAgentUpdateEvents = true,
+            EmitAgentResponseEvents = true,
+        };
+
+        return (fileCityAgent.BindAsExecutor(agentOptions), weatherAgent.BindAsExecutor(agentOptions));
+    }
+}

Workflows/SkipWeatherExecutor.cs

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+using MAF1.Agents.FileCity;
+using Microsoft.Agents.AI.Workflows;
+
+namespace MAF1.Workflows;
+
+/// <summary>
+/// 只有「没有城市」那条边会进到这里，所以这里不再判断。
+/// </summary>
+internal sealed class SkipWeatherExecutor() : Executor<CityExtraction>("SkipWeather")
+{
+    protected override ProtocolBuilder ConfigureProtocol(ProtocolBuilder builder)
+    {
+        return base.ConfigureProtocol(builder).YieldsOutput<string>();
+    }
+
+    public override async ValueTask HandleAsync(
+        CityExtraction extraction,
+        IWorkflowContext context,
+        CancellationToken cancellationToken = default)
+    {
+        string reason = string.IsNullOrWhiteSpace(extraction.Reason)
+            ? "文件里没有可查询的城市。"
+            : extraction.Reason;
+        await context.YieldOutputAsync(
+            $"没有有效城市，工作流结束，不执行 WeatherAgent。{reason}",
+            cancellationToken);
+    }
+}

Workflows/ToWeatherPromptExecutor.cs

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+using MAF1.Agents.FileCity;
+using Microsoft.Agents.AI.Workflows;
+using Microsoft.Extensions.AI;
+
+namespace MAF1.Workflows;
+
+/// <summary>
+/// 只有「有城市」那条边会进到这里，所以这里不再判断。
+/// </summary>
+internal sealed class ToWeatherPromptExecutor() : Executor<CityExtraction>("ToWeatherPrompt")
+{
+    protected override ProtocolBuilder ConfigureProtocol(ProtocolBuilder builder)
+    {
+        return base.ConfigureProtocol(builder)
+            .SendsMessage<ChatMessage>()
+            .SendsMessage<TurnToken>();
+    }
+
+    public override async ValueTask HandleAsync(
+        CityExtraction extraction,
+        IWorkflowContext context,
+        CancellationToken cancellationToken = default)
+    {
+        string prompt = $"请查询这些城市的天气：{string.Join("、", extraction.Cities)}";
+        await context.SendMessageAsync(new ChatMessage(ChatRole.User, prompt), cancellationToken: cancellationToken);
+        await context.SendMessageAsync(new TurnToken(emitEvents: true), cancellationToken: cancellationToken);
+    }
+}