feat: built-in AI Assistant with BYO endpoint (v0.6.0, Phase 10)

Add a GUI AI Assistant view (✨ rail) that drives serial + PDU in plain
language, without depending on Claude/Kiro. In-process function calling
(no MCP hop): Ai/OpenAiChatClient (minimal OpenAI-compatible client) +
Ai/AgentHost (hand-written agent loop) + Ai/AiTools (serial via the
existing SerialBridge with [AI] echo; PDU via ETTerms.PduCore).

BYO endpoint: Base URL / Model / API Key set in Settings → AI Assistant,
blank by default = disabled. No private endpoint ships in the app; API
key lives in Windows Credential Manager, never in settings.json or code.

Safety: destructive PDU actions (outlet off / power-cycle) require a GUI
confirmation; every tool call is written to AppLogger. Existing Serial/
PDU MCP servers (Settings → AI MCP) are unaffected and keep serving
external AI CLIs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/ETTerms/Ai/AgentHost.cs

@@ -0,0 +1,89 @@
+using System.Text.Json.Nodes;
+using ETTerms.Infrastructure;
+
+namespace ETTerms.Ai;
+
+/// <summary>
+/// 內建 AI Assistant 的 agent 迴圈：維護對話歷史,呼叫 <see cref="OpenAiChatClient"/>,
+/// 模型回 tool_calls 時執行 <see cref="AiTools"/> 再把結果餵回,直到模型給出最終文字回應。
+///
+/// UI 事件（Status / AssistantText / ToolActivity）皆在背景緒觸發,訂閱者需自行 Invoke 回 UI thread。
+/// </summary>
+public sealed class AgentHost
+{
+    private readonly OpenAiChatClient _client;
+    private readonly AiTools _tools;
+    private readonly JsonArray _messages = new();
+    private const int MaxToolRounds = 8;
+
+    public event Action<string>? AssistantText;   // 最終文字回應
+    public event Action<string>? ToolActivity;     // 「呼叫 serial_write …」之類過程
+    public event Action<string>? Status;           // thinking / done
+
+    private static string DefaultSystemPrompt =>
+        "你是 ETTerms 內建的硬體工程助理。可透過工具收發序列埠（serial）與控制 PDU 電源插座。" +
+        "回答用繁體中文、簡潔。動手操作前先說明你要做什麼。" +
+        "破壞性動作（關插座 / power-cycle）會由使用者在 GUI 確認,你只需正常呼叫工具。" +
+        "serial 操作前必須先 serial_attach 到 GUI 已開啟的 session。";
+
+    public AgentHost(OpenAiChatClient client, AiTools tools, string? systemPrompt)
+    {
+        _client = client;
+        _tools = tools;
+        _messages.Add(new JsonObject
+        {
+            ["role"] = "system",
+            ["content"] = string.IsNullOrWhiteSpace(systemPrompt) ? DefaultSystemPrompt : systemPrompt
+        });
+    }
+
+    /// <summary>送出一句使用者訊息,跑完 agent 迴圈（含工具呼叫）。</summary>
+    public async Task SendAsync(string userText, CancellationToken ct)
+    {
+        _messages.Add(new JsonObject { ["role"] = "user", ["content"] = userText });
+        var tools = _tools.GetSchemas();
+
+        for (int round = 0; round < MaxToolRounds; round++)
+        {
+            Status?.Invoke("thinking");
+            var msg = await _client.CompleteAsync(_messages, tools, ct);
+            _messages.Add((JsonObject)msg.DeepClone());
+
+            var toolCalls = msg["tool_calls"]?.AsArray();
+            if (toolCalls == null || toolCalls.Count == 0)
+            {
+                var content = msg["content"]?.GetValue<string>() ?? "";
+                AssistantText?.Invoke(content);
+                Status?.Invoke("done");
+                return;
+            }
+
+            // 執行每個 tool call,把結果以 role=tool 加回歷史
+            foreach (var tcNode in toolCalls)
+            {
+                var tc = tcNode!.AsObject();
+                string id = tc["id"]?.GetValue<string>() ?? "";
+                var fn = tc["function"]?.AsObject();
+                string fname = fn?["name"]?.GetValue<string>() ?? "";
+                string argStr = fn?["arguments"]?.GetValue<string>() ?? "{}";
+
+                JsonObject args;
+                try { args = JsonNode.Parse(string.IsNullOrWhiteSpace(argStr) ? "{}" : argStr)!.AsObject(); }
+                catch { args = new JsonObject(); }
+
+                ToolActivity?.Invoke($"{fname}({argStr})");
+                string result = await _tools.InvokeAsync(fname, args, ct);
+
+                _messages.Add(new JsonObject
+                {
+                    ["role"] = "tool",
+                    ["tool_call_id"] = id,
+                    ["content"] = result
+                });
+            }
+        }
+
+        AssistantText?.Invoke("（已達工具呼叫上限,停止。請縮小問題或分步再試。）");
+        Status?.Invoke("done");
+    }
+}

src/ETTerms/Ai/AiTools.cs

@@ -0,0 +1,229 @@
+using System.Text;
+using System.Text.Json.Nodes;
+using ETTerms.Infrastructure;
+using ETTerms.PduCore;
+using ETTerms.Sessions;
+
+namespace ETTerms.Ai;
+
+/// <summary>
+/// 內建 AI Assistant 的工具集：serial 收發（重用 GUI 持有的 <see cref="SerialBridge"/> session，
+/// AI 的 TX 照樣以 [AI] 標色顯示在終端機）＋ PDU 電源控制（<see cref="PduController"/>）。
+///
+/// 全部 in-process 直呼——不經 MCP 子行程 / named pipe（那是給外部 AI CLI 用的）。
+/// 破壞性 PDU 動作（關插座 / power-cycle）一律經 <see cref="ConfirmAsync"/> 由 GUI 彈確認框；
+/// 每筆工具呼叫寫 AppLogger 留跡。
+/// </summary>
+public sealed class AiTools : IDisposable
+{
+    /// <summary>破壞性動作確認：回 true 才執行。由 UI 提供（彈 MessageBox）。</summary>
+    public Func<string, Task<bool>> ConfirmAsync { get; set; } = _ => Task.FromResult(false);
+
+    // ── serial attach 狀態（供 serial_read 累積 RX）──
+    private SerialBridgeEndpoint? _attached;
+    private readonly StringBuilder _rxBuffer = new();
+    private readonly object _rxLock = new();
+    private Action<byte[]>? _rxHandler;
+    private readonly System.Text.Decoder _dec = Encoding.UTF8.GetDecoder();
+
+    // ── PDU 連線登錄（本 AI session 內，IP → controller）──
+    private readonly Dictionary<string, PduController> _pdus = new(StringComparer.OrdinalIgnoreCase);
+    private const int PduPortCount = 12;
+
+    /// <summary>OpenAI tools schema（function calling 用）。</summary>
+    public JsonArray GetSchemas()
+    {
+        JsonObject Fn(string name, string desc, JsonObject props, params string[] required)
+        {
+            var req = new JsonArray();
+            foreach (var r in required) req.Add(r);
+            return new JsonObject
+            {
+                ["type"] = "function",
+                ["function"] = new JsonObject
+                {
+                    ["name"] = name,
+                    ["description"] = desc,
+                    ["parameters"] = new JsonObject
+                    {
+                        ["type"] = "object",
+                        ["properties"] = props,
+                        ["required"] = req
+                    }
+                }
+            };
+        }
+        JsonObject Str(string d) => new() { ["type"] = "string", ["description"] = d };
+        JsonObject Int(string d) => new() { ["type"] = "integer", ["description"] = d };
+        JsonObject Bool(string d) => new() { ["type"] = "boolean", ["description"] = d };
+
+        return new JsonArray
+        {
+            Fn("serial_list", "List the serial sessions currently open in the ETTerms GUI (name + baud).",
+                new JsonObject()),
+            Fn("serial_attach", "Bind to an open GUI serial session by name (e.g. COM3). Required before write/read.",
+                new JsonObject { ["session"] = Str("Session name / COM port, e.g. COM3") }, "session"),
+            Fn("serial_write", "Send text to the attached serial session (echoes to the terminal tagged [AI]).",
+                new JsonObject { ["text"] = Str("Text to send"), ["appendNewline"] = Bool("Append the session newline (default true)") }, "text"),
+            Fn("serial_read", "Read accumulated RX from the attached serial session; optionally wait for a substring.",
+                new JsonObject { ["waitFor"] = Str("Optional substring to wait for"), ["timeoutMs"] = Int("Max wait ms (default 3000)") }),
+            Fn("pdu_connect", "Connect to an SNMP PDU by IP and verify it responds. Required before other pdu_* calls.",
+                new JsonObject { ["ip"] = Str("PDU IP address") }, "ip"),
+            Fn("pdu_status", "Read all outlets' state / current(mA) / power(W) of a connected PDU.",
+                new JsonObject { ["ip"] = Str("PDU IP address") }, "ip"),
+            Fn("pdu_set_port", "Turn a PDU outlet on or off (turning OFF requires user confirmation).",
+                new JsonObject { ["ip"] = Str("PDU IP"), ["port"] = Int("Outlet number"), ["on"] = Bool("true=on, false=off") }, "ip", "port", "on"),
+            Fn("pdu_power_cycle", "Power-cycle a PDU outlet (off → wait → on). Requires user confirmation.",
+                new JsonObject { ["ip"] = Str("PDU IP"), ["port"] = Int("Outlet number"), ["offSeconds"] = Int("Off duration seconds (default 5)") }, "ip", "port"),
+        };
+    }
+
+    /// <summary>執行一個工具呼叫,回傳給模型的 JSON 字串（統一 {ok, result/error}）。</summary>
+    public async Task<string> InvokeAsync(string name, JsonObject args, CancellationToken ct)
+    {
+        AppLogger.Info($"[AI tool] {name} {args.ToJsonString()}");
+        try
+        {
+            return name switch
+            {
+                "serial_list" => SerialList(),
+                "serial_attach" => SerialAttach(Str(args, "session")),
+                "serial_write" => SerialWrite(Str(args, "text"), Bool(args, "appendNewline", true)),
+                "serial_read" => await SerialRead(Str(args, "waitFor"), Int(args, "timeoutMs", 3000), ct),
+                "pdu_connect" => PduConnect(Str(args, "ip")),
+                "pdu_status" => PduStatus(Str(args, "ip")),
+                "pdu_set_port" => await PduSetPort(Str(args, "ip"), Int(args, "port", 0), Bool(args, "on", false)),
+                "pdu_power_cycle" => await PduPowerCycle(Str(args, "ip"), Int(args, "port", 0), Int(args, "offSeconds", 5), ct),
+                _ => Err($"unknown tool '{name}'")
+            };
+        }
+        catch (Exception ex)
+        {
+            AppLogger.LogWarning($"[AI tool] {name} failed: {ex.Message}");
+            return Err(ex.Message);
+        }
+    }
+
+    // ── serial ──
+    private string SerialList()
+    {
+        var arr = new JsonArray();
+        foreach (var e in SerialBridge.All) arr.Add(new JsonObject { ["name"] = e.Name, ["baud"] = e.BaudRate });
+        return Ok(new JsonObject { ["sessions"] = arr });
+    }
+
+    private string SerialAttach(string session)
+    {
+        DetachRx();
+        var ep = SerialBridge.Find(session);
+        if (ep == null) return Err($"no open serial session '{session}' in the GUI — open it first");
+        _attached = ep;
+        lock (_rxLock) _rxBuffer.Clear();
+        _rxHandler = data =>
+        {
+            lock (_rxLock)
+            {
+                var chars = new char[data.Length];
+                int n = _dec.GetChars(data, 0, data.Length, chars, 0);
+                if (n > 0) _rxBuffer.Append(chars, 0, n);
+                if (_rxBuffer.Length > 1_000_000) _rxBuffer.Remove(0, _rxBuffer.Length - 1_000_000);
+            }
+        };
+        ep.Rx += _rxHandler;
+        return Ok(new JsonObject { ["attached"] = ep.Name });
+    }
+
+    private string SerialWrite(string text, bool appendNewline)
+    {
+        if (_attached == null) return Err("not attached — call serial_attach first");
+        _attached.Write(text, appendNewline);
+        return Ok(new JsonObject { ["sent"] = text });
+    }
+
+    private async Task<string> SerialRead(string? waitFor, int timeoutMs, CancellationToken ct)
+    {
+        if (_attached == null) return Err("not attached — call serial_attach first");
+        var deadline = Environment.TickCount64 + Math.Clamp(timeoutMs, 0, 120_000);
+        while (true)
+        {
+            string cur;
+            lock (_rxLock) cur = _rxBuffer.ToString();
+            if (string.IsNullOrEmpty(waitFor) || cur.Contains(waitFor)) { lock (_rxLock) _rxBuffer.Clear(); return Ok(new JsonObject { ["data"] = cur }); }
+            if (Environment.TickCount64 >= deadline) { lock (_rxLock) _rxBuffer.Clear(); return Ok(new JsonObject { ["data"] = cur, ["timedOut"] = true }); }
+            await Task.Delay(80, ct);
+        }
+    }
+
+    private void DetachRx()
+    {
+        if (_attached != null && _rxHandler != null) _attached.Rx -= _rxHandler;
+        _attached = null; _rxHandler = null;
+    }
+
+    // ── PDU ──
+    private PduController GetOrThrow(string ip) =>
+        _pdus.TryGetValue(ip, out var c) ? c : throw new InvalidOperationException($"PDU {ip} not connected — call pdu_connect first");
+
+    private string PduConnect(string ip)
+    {
+        if (_pdus.ContainsKey(ip)) return Ok(new JsonObject { ["ip"] = ip, ["already"] = true });
+        var c = new PduController(ip, m => AppLogger.Info(m), m => AppLogger.LogWarning(m));
+        var model = c.GetModelName();
+        if (string.IsNullOrEmpty(model)) { c.Dispose(); return Err($"PDU {ip} did not respond to SNMP"); }
+        _pdus[ip] = c;
+        return Ok(new JsonObject { ["ip"] = ip, ["model"] = model });
+    }
+
+    private string PduStatus(string ip)
+    {
+        var c = GetOrThrow(ip);
+        var all = c.GetAllPortsStatus(PduPortCount);
+        var arr = new JsonArray();
+        for (int i = 0; i < all.Length; i++)
+            arr.Add(new JsonObject
+            {
+                ["port"] = i + 1,
+                ["state"] = all[i].State is bool b ? (b ? "on" : "off") : "unknown",
+                ["mA"] = all[i].CurrentMilliAmps,
+                ["W"] = all[i].PowerWatts
+            });
+        return Ok(new JsonObject { ["ip"] = ip, ["ports"] = arr });
+    }
+
+    private async Task<string> PduSetPort(string ip, int port, bool on)
+    {
+        var c = GetOrThrow(ip);
+        if (!on && !await ConfirmAsync($"AI 要求關閉 PDU {ip} 的 outlet {port}。確定?"))
+            return Err("user declined");
+        bool ok = on ? c.SetPortOn(port) : c.SetPortOff(port);
+        return ok ? Ok(new JsonObject { ["ip"] = ip, ["port"] = port, ["state"] = on ? "on" : "off" }) : Err("SNMP set failed");
+    }
+
+    private async Task<string> PduPowerCycle(string ip, int port, int offSeconds, CancellationToken ct)
+    {
+        var c = GetOrThrow(ip);
+        offSeconds = Math.Clamp(offSeconds, 1, 60);
+        if (!await ConfirmAsync($"AI 要求 power-cycle PDU {ip} 的 outlet {port}（關 {offSeconds}s 再開）。確定?"))
+            return Err("user declined");
+        if (!c.SetPortOff(port)) return Err("SNMP set (off) failed");
+        await Task.Delay(offSeconds * 1000, ct);
+        if (!c.SetPortOn(port)) return Err("SNMP set (on) failed");
+        return Ok(new JsonObject { ["ip"] = ip, ["port"] = port, ["cycled"] = true, ["offSeconds"] = offSeconds });
+    }
+
+    // ── helpers ──
+    private static string Ok(JsonObject result) => new JsonObject { ["ok"] = true, ["result"] = result }.ToJsonString();
+    private static string Err(string msg) => new JsonObject { ["ok"] = false, ["error"] = msg }.ToJsonString();
+
+    private static string Str(JsonObject a, string k) => a[k]?.GetValue<string>() ?? "";
+    private static string? Str(JsonObject a, string k, string? def) => a[k]?.GetValue<string>() ?? def;
+    private static int Int(JsonObject a, string k, int def) { try { return a[k]?.GetValue<int>() ?? def; } catch { return def; } }
+    private static bool Bool(JsonObject a, string k, bool def) { try { return a[k]?.GetValue<bool>() ?? def; } catch { return def; } }
+
+    public void Dispose()
+    {
+        DetachRx();
+        foreach (var c in _pdus.Values) c.Dispose();
+        _pdus.Clear();
+    }
+}

src/ETTerms/Ai/OpenAiChatClient.cs

@@ -0,0 +1,75 @@
+using System.Net.Http;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+
+namespace ETTerms.Ai;
+
+/// <summary>
+/// 極簡 OpenAI 相容 chat-completions client（非串流）。
+/// 只依賴 HttpClient + System.Text.Json，不引入 SDK——因為端點是使用者自帶（BYO），
+/// 任何 OpenAI 相容 gateway（Ollama / LiteLLM / 公司內部 gateway / OpenAI…）皆可接。
+///
+/// ⚠️ Base URL 與 API key 皆由使用者於 Settings 設定,不寫死於程式碼（見 AppSettings 註解）。
+/// </summary>
+public sealed class OpenAiChatClient : IDisposable
+{
+    private readonly HttpClient _http;
+    private readonly string _model;
+
+    public OpenAiChatClient(string baseUrl, string apiKey, string model)
+    {
+        // baseUrl 例："http://localhost:11434/v1" → endpoint = baseUrl + "/chat/completions"
+        var root = baseUrl.TrimEnd('/');
+        _http = new HttpClient { Timeout = TimeSpan.FromSeconds(300) };
+        _http.BaseAddress = new Uri(root + "/");
+        if (!string.IsNullOrEmpty(apiKey))
+            _http.DefaultRequestHeaders.Authorization =
+                new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", apiKey);
+        _model = model;
+    }
+
+    /// <summary>
+    /// 送出一輪對話（含歷史 messages 與可用 tools），回傳 assistant 的回應訊息節點
+    /// （可能含 content 或 tool_calls）。呼叫端負責 agent loop。
+    /// </summary>
+    public async Task<JsonObject> CompleteAsync(JsonArray messages, JsonArray? tools, CancellationToken ct)
+    {
+        var body = new JsonObject
+        {
+            ["model"] = _model,
+            ["messages"] = messages.DeepClone(),
+            ["temperature"] = 0.2,
+        };
+        if (tools != null && tools.Count > 0)
+        {
+            body["tools"] = tools.DeepClone();
+            body["tool_choice"] = "auto";
+        }
+
+        using var req = new HttpRequestMessage(HttpMethod.Post, "chat/completions")
+        {
+            Content = new StringContent(body.ToJsonString(), Encoding.UTF8, "application/json")
+        };
+        using var resp = await _http.SendAsync(req, HttpCompletionOption.ResponseContentRead, ct);
+        var text = await resp.Content.ReadAsStringAsync(ct);
+        if (!resp.IsSuccessStatusCode)
+            throw new InvalidOperationException($"AI endpoint HTTP {(int)resp.StatusCode}: {Trunc(text, 400)}");
+
+        JsonObject root;
+        try { root = JsonNode.Parse(text)!.AsObject(); }
+        catch (Exception ex) { throw new InvalidOperationException($"AI response parse error: {ex.Message}\n{Trunc(text, 400)}"); }
+
+        var choices = root["choices"]?.AsArray();
+        if (choices == null || choices.Count == 0)
+            throw new InvalidOperationException($"AI response has no choices: {Trunc(text, 400)}");
+        var msg = choices[0]?["message"]?.AsObject();
+        if (msg == null)
+            throw new InvalidOperationException($"AI response has no message: {Trunc(text, 400)}");
+        return (JsonObject)msg.DeepClone();
+    }
+
+    private static string Trunc(string s, int n) => s.Length <= n ? s : s.Substring(0, n) + "…";
+
+    public void Dispose() => _http.Dispose();
+}

src/ETTerms/App/AboutView.cs

@@ -183,6 +183,15 @@ public sealed class AboutView : UserControl
 
     private static readonly ChangelogEntry[] Changelog =
     [
+        new("0.6.0", new DateOnly(2026, 7, 5), "Built-in AI Assistant — drive serial & PDU in plain language",
+        [
+            "New ✨ AI Assistant view: chat in plain language to send serial commands and control PDU outlets — e.g. \"attach to COM3, send help and show me the reply\" or \"connect to the PDU and power-cycle outlet 3\".",
+            "Bring your own AI endpoint: point it at any OpenAI-compatible server (a local Ollama, a LiteLLM gateway, your company's gateway, or OpenAI). Set it up in Settings → AI Assistant; leave it blank and the assistant simply stays off.",
+            "Your API key is stored in Windows Credential Manager, never in a settings file — and no endpoint ships inside the app, so a copy you hand to someone else has the assistant disabled by default.",
+            "The AI drives your existing open Serial session, and everything it sends shows up in that terminal tagged [AI] so you always see what it did.",
+            "Turning an outlet off or power-cycling always pops up a confirmation first — the AI can't cut power on its own. Every tool call is written to the app log.",
+            "This is separate from the existing Serial/PDU MCP servers (Settings → AI MCP), which keep working for external AI CLIs like Claude Code / Kiro.",
+        ]),
         new("0.5.0", new DateOnly(2026, 7, 2), "Search, keyword alerts & a much bigger scripting language",
         [
             "Press Ctrl+F in any terminal to search everything you've scrolled past — all hits are highlighted, Enter jumps between them.",

src/ETTerms/App/ActivityRail.cs

@@ -10,7 +10,7 @@ namespace ETTerms.App;
 /// </summary>
 public sealed class ActivityRail : UserControl
 {
-    public enum RailView { Terminal, Status, Settings, About }
+    public enum RailView { Terminal, Ai, Status, Settings, About }
 
     public event EventHandler<RailView>? ViewSelected;
 
@@ -23,6 +23,7 @@ public sealed class ActivityRail : UserControl
     private static readonly (RailView view, string glyph, string tip)[] Items =
     {
         (RailView.Terminal, "▤", "Terminal"),
+        (RailView.Ai, "✨", "AI Assistant"),
         (RailView.Status, "⚡", "Status"),
         (RailView.Settings, "⚙", "Settings"),
         (RailView.About, "ℹ", "About"),

src/ETTerms/App/AiChatView.cs

@@ -0,0 +1,170 @@
+using System.Drawing;
+using System.Windows.Forms;
+using ETTerms.Ai;
+using ETTerms.Connections;
+using ETTerms.Infrastructure;
+
+namespace ETTerms.App;
+
+/// <summary>
+/// 內建 AI Assistant 檢視（Activity Rail 的一個 view）。自然語言驅動 serial + PDU。
+/// Provider 未設定（Base URL 空）時顯示提示,引導到 Settings → AI Assistant。
+///
+/// ⚠️ 端點 / 金鑰皆由使用者設定,程式不含任何預設私人端點。
+/// </summary>
+public sealed class AiChatView : UserControl
+{
+    private readonly RichTextBox _log;
+    private readonly TextBox _input;
+    private readonly Button _send;
+    private readonly Label _hint;
+
+    private AgentHost? _agent;
+    private OpenAiChatClient? _client;
+    private AiTools? _tools;
+    private CancellationTokenSource? _cts;
+
+    public AiChatView()
+    {
+        Dock = DockStyle.Fill;
+        BackColor = Theme.WorkspaceBack;
+
+        _log = new RichTextBox
+        {
+            Dock = DockStyle.Fill, ReadOnly = true, BorderStyle = BorderStyle.None,
+            BackColor = Color.FromArgb(28, 28, 32), ForeColor = Theme.Text,
+            Font = new Font("Cascadia Mono", 10f), DetectUrls = false
+        };
+
+        var bottom = new Panel { Dock = DockStyle.Bottom, Height = 92, BackColor = Theme.RailBack, Padding = new Padding(10, 8, 10, 8) };
+        _input = new TextBox
+        {
+            Dock = DockStyle.Fill, Multiline = true, BackColor = Theme.TabBack, ForeColor = Theme.Text,
+            Font = Theme.UiFont, BorderStyle = BorderStyle.FixedSingle
+        };
+        _input.KeyDown += (_, e) =>
+        {
+            if (e.KeyCode == Keys.Enter && !e.Shift) { e.Handled = e.SuppressKeyPress = true; OnSend(); }
+        };
+        _send = new Button
+        {
+            Text = "Send  ⏎", Dock = DockStyle.Right, Width = 90, FlatStyle = FlatStyle.Flat,
+            ForeColor = Theme.Text, BackColor = Theme.TabBack, Font = Theme.UiFont, Cursor = Cursors.Hand
+        };
+        _send.FlatAppearance.BorderColor = Theme.Accent;
+        _send.Click += (_, _) => OnSend();
+        bottom.Controls.Add(_input);
+        bottom.Controls.Add(_send);
+
+        _hint = new Label
+        {
+            Dock = DockStyle.Top, Height = 40, BackColor = Color.FromArgb(60, 50, 30), ForeColor = Theme.Text,
+            Font = Theme.UiFont, TextAlign = ContentAlignment.MiddleCenter, Visible = false,
+            Text = "尚未設定 AI Provider — 到 Settings → AI Assistant 填入 Base URL / API Key / Model。"
+        };
+
+        Controls.Add(_log);      // Fill
+        Controls.Add(_hint);     // Top
+        Controls.Add(bottom);    // Bottom
+
+        AppendSystem("ETTerms AI Assistant — 用自然語言操作 serial 與 PDU。\n" +
+                     "例：「列出目前的 serial session」/「接上 COM3,送 help 看回應」/「連上 PDU 192.168.1.50,把 outlet 3 重開」\n");
+    }
+
+    /// <summary>每次切到本檢視時呼叫,依最新設定重建 client（Provider 改了會生效）。</summary>
+    public void RefreshProvider()
+    {
+        var s = AppSettings.Instance;
+        bool configured = !string.IsNullOrWhiteSpace(s.AiBaseUrl) && !string.IsNullOrWhiteSpace(s.AiModel);
+        _hint.Visible = !configured;
+        _input.Enabled = _send.Enabled = configured;
+
+        _client?.Dispose(); _client = null;
+        _tools?.Dispose(); _tools = null;
+        _agent = null;
+
+        if (!configured) return;
+
+        var key = CredentialVault.Get("ETTerms/AiApiKey") ?? "";
+        _client = new OpenAiChatClient(s.AiBaseUrl, key, s.AiModel);
+        _tools = new AiTools { ConfirmAsync = ConfirmOnUiAsync };
+        _agent = new AgentHost(_client, _tools, s.AiSystemPrompt);
+        _agent.AssistantText += t => Ui(() => AppendAssistant(t));
+        _agent.ToolActivity += t => Ui(() => AppendTool(t));
+        _agent.Status += st => Ui(() => { if (st == "thinking") AppendDim("…thinking"); });
+    }
+
+    private Task<bool> ConfirmOnUiAsync(string message)
+    {
+        var tcs = new TaskCompletionSource<bool>();
+        Ui(() =>
+        {
+            var r = MessageBox.Show(this, message, "AI 動作確認",
+                MessageBoxButtons.YesNo, MessageBoxIcon.Warning, MessageBoxDefaultButton.Button2);
+            tcs.SetResult(r == DialogResult.Yes);
+        });
+        return tcs.Task;
+    }
+
+    private async void OnSend()
+    {
+        if (_agent == null) return;
+        var text = _input.Text.Trim();
+        if (text.Length == 0) return;
+        _input.Clear();
+        AppendUser(text);
+        _send.Enabled = false;
+        _cts = new CancellationTokenSource();
+        try { await _agent.SendAsync(text, _cts.Token); }
+        catch (OperationCanceledException) { AppendDim("（已取消）"); }
+        catch (Exception ex) { AppendError(ex.Message); }
+        finally { _send.Enabled = true; }
+    }
+
+    // ── 輸出 helpers ──
+    private void AppendUser(string t) => Append("你", t, Theme.Accent);
+    private void AppendAssistant(string t) => Append("AI", t, Theme.SerialColor);
+    private void AppendTool(string t) => Append("⚙ tool", t, Color.FromArgb(190, 170, 120));
+    private void AppendSystem(string t) => Append("", t, Theme.TextDim);
+    private void AppendError(string t) => Append("錯誤", t, Color.FromArgb(235, 120, 120));
+
+    private void AppendDim(string t)
+    {
+        _log.SelectionStart = _log.TextLength;
+        _log.SelectionColor = Theme.TextDim;
+        _log.AppendText(t + "\n");
+        _log.ScrollToCaret();
+    }
+
+    private void Append(string who, string text, Color color)
+    {
+        _log.SelectionStart = _log.TextLength;
+        if (who.Length > 0)
+        {
+            _log.SelectionColor = color;
+            _log.SelectionFont = new Font(_log.Font, FontStyle.Bold);
+            _log.AppendText($"{who}: ");
+        }
+        _log.SelectionColor = who.Length > 0 ? Theme.Text : color;
+        _log.SelectionFont = _log.Font;
+        _log.AppendText(text + "\n");
+        _log.ScrollToCaret();
+    }
+
+    private void Ui(Action a)
+    {
+        if (IsDisposed || !IsHandleCreated) return;
+        if (InvokeRequired) BeginInvoke(a); else a();
+    }
+
+    protected override void Dispose(bool disposing)
+    {
+        if (disposing)
+        {
+            _cts?.Cancel();
+            _client?.Dispose();
+            _tools?.Dispose();
+        }
+        base.Dispose(disposing);
+    }
+}

src/ETTerms/App/MainForm.cs

@@ -14,6 +14,7 @@ public partial class MainForm : Form
     private readonly ActivityRail _rail = new();
     private readonly ConnectionSidebar _sidebar = new();
     private readonly WorkspaceView _workspace = new();
+    private readonly AiChatView _aiView = new();
     private readonly StatusView _statusView = new();
     private readonly SettingsView _settings = new();
     private readonly AboutView _about = new();
@@ -46,12 +47,14 @@ public partial class MainForm : Form
     private void BuildLayout()
     {
         Controls.Add(_workspace);   // Fill
+        Controls.Add(_aiView);      // Fill (hidden)
         Controls.Add(_statusView);  // Fill (hidden)
         Controls.Add(_settings);    // Fill (hidden)
         Controls.Add(_about);       // Fill (hidden)
         Controls.Add(_sidebar);     // Left (內側)
         Controls.Add(_rail);        // Left (最外側)
 
+        _aiView.Visible = false;
         _statusView.Visible = false;
         _settings.Visible = false;
         _about.Visible = false;
@@ -71,9 +74,11 @@ public partial class MainForm : Form
             _statusLabel.Text = $"View: {view}";
             _sidebar.Visible = view == ActivityRail.RailView.Terminal;
             _workspace.Visible = view == ActivityRail.RailView.Terminal;
+            _aiView.Visible = view == ActivityRail.RailView.Ai;
             _statusView.Visible = view == ActivityRail.RailView.Status;
             _settings.Visible = view == ActivityRail.RailView.Settings;
             _about.Visible = view == ActivityRail.RailView.About;
+            if (view == ActivityRail.RailView.Ai) _aiView.RefreshProvider();
             AppLogger.LogInfo($"View selected: {view}");
         };
 

src/ETTerms/App/SettingsView.cs

@@ -1,10 +1,11 @@
 using System.Drawing;
 using System.Windows.Forms;
+using ETTerms.Connections;
 using ETTerms.Infrastructure;
 
 namespace ETTerms.App;
 
-/// <summary>Settings page with tabs: Terminal / AI MCP.</summary>
+/// <summary>Settings page with tabs: Terminal / Highlight / AI Assistant / AI MCP.</summary>
 public sealed class SettingsView : UserControl
 {
     public SettingsView()
@@ -53,6 +54,7 @@ public sealed class SettingsView : UserControl
         var termBtn = MakeTab("Terminal", BuildTerminalTab());
         tabBar.Controls.Add(termBtn);
         tabBar.Controls.Add(MakeTab("Highlight", BuildHighlightTab()));
+        tabBar.Controls.Add(MakeTab("AI Assistant", BuildAiAssistantTab()));
         tabBar.Controls.Add(MakeTab("AI MCP", BuildAiMcpTab()));
 
         Controls.Add(body);
@@ -290,6 +292,100 @@ public sealed class SettingsView : UserControl
         return page;
     }
 
+    // ═══ AI Assistant Tab（內建 agent 的 BYO endpoint 設定）═══
+    private Panel BuildAiAssistantTab()
+    {
+        var page = new Panel { BackColor = Theme.WorkspaceBack, Padding = new Padding(20) };
+        var s = AppSettings.Instance;
+
+        var flow = new FlowLayoutPanel
+        {
+            Dock = DockStyle.Fill, FlowDirection = FlowDirection.TopDown,
+            WrapContents = false, BackColor = Theme.WorkspaceBack, AutoScroll = true
+        };
+
+        flow.Controls.Add(new Label
+        {
+            Text = "Built-in AI Assistant", AutoSize = true,
+            ForeColor = Theme.Accent, Font = Theme.UiFontBold, Margin = new Padding(0, 0, 0, 4)
+        });
+        flow.Controls.Add(new Label
+        {
+            Text = "Bring your own OpenAI-compatible endpoint (Ollama / LiteLLM / a company gateway / OpenAI…).\n" +
+                   "Leave blank to keep the AI Assistant disabled. The model must support function calling.\n" +
+                   "The API key is stored in Windows Credential Manager, never in settings.json or the app.",
+            AutoSize = false, Width = 620, Height = 54,
+            ForeColor = Theme.TextDim, Font = Theme.UiFont, Margin = new Padding(0, 0, 0, 10)
+        });
+
+        var baseUrl = new TextBox
+        {
+            Width = 380, BackColor = Theme.TabBack, ForeColor = Theme.Text, Font = Theme.UiFont,
+            BorderStyle = BorderStyle.FixedSingle, Text = s.AiBaseUrl,
+            PlaceholderText = "http://localhost:11434/v1"
+        };
+        var model = new TextBox
+        {
+            Width = 260, BackColor = Theme.TabBack, ForeColor = Theme.Text, Font = Theme.UiFont,
+            BorderStyle = BorderStyle.FixedSingle, Text = s.AiModel,
+            PlaceholderText = "e.g. a function-calling model name"
+        };
+        var apiKey = new TextBox
+        {
+            Width = 380, BackColor = Theme.TabBack, ForeColor = Theme.Text, Font = Theme.UiFont,
+            BorderStyle = BorderStyle.FixedSingle, UseSystemPasswordChar = true,
+            Text = CredentialVault.Get("ETTerms/AiApiKey") ?? "",
+            PlaceholderText = "(stored in Credential Manager)"
+        };
+        var sysPrompt = new TextBox
+        {
+            Width = 560, Height = 70, Multiline = true, BackColor = Theme.TabBack, ForeColor = Theme.Text,
+            Font = Theme.UiFont, BorderStyle = BorderStyle.FixedSingle, Text = s.AiSystemPrompt,
+            PlaceholderText = "(optional) override the assistant persona / system prompt"
+        };
+
+        flow.Controls.Add(MakeRow("Base URL (with /v1)", baseUrl));
+        flow.Controls.Add(MakeRow("Model", model));
+        flow.Controls.Add(MakeRow("API Key", apiKey));
+        flow.Controls.Add(MakeSpacer(4));
+        flow.Controls.Add(new Label
+        {
+            Text = "System prompt (optional):", AutoSize = true,
+            ForeColor = Theme.Text, Font = Theme.UiFont, Margin = new Padding(0, 4, 0, 2)
+        });
+        flow.Controls.Add(sysPrompt);
+        flow.Controls.Add(MakeSpacer(6));
+
+        flow.Controls.Add(new Label
+        {
+            Text = "Tools the assistant can call: serial send/read (via the GUI's open Serial session, shown as [AI]),\n" +
+                   "and PDU control over SNMP. Turning an outlet off / power-cycling always asks you to confirm.",
+            AutoSize = false, Width = 620, Height = 36,
+            ForeColor = Theme.TextDim, Font = Theme.UiFont, Margin = new Padding(0, 0, 0, 8)
+        });
+
+        var save = MakeButton("Save", Theme.Accent);
+        save.Click += (_, _) =>
+        {
+            s.AiBaseUrl = baseUrl.Text.Trim();
+            s.AiModel = model.Text.Trim();
+            s.AiSystemPrompt = sysPrompt.Text.Trim();
+            s.Save();
+            var key = apiKey.Text;
+            if (string.IsNullOrEmpty(key)) CredentialVault.Delete("ETTerms/AiApiKey");
+            else CredentialVault.Set("ETTerms/AiApiKey", key);
+            MessageBox.Show(this,
+                string.IsNullOrWhiteSpace(s.AiBaseUrl) || string.IsNullOrWhiteSpace(s.AiModel)
+                    ? "Saved. AI Assistant stays disabled until Base URL and Model are both set."
+                    : "Saved. Open the AI Assistant view (✨ in the rail) to start.",
+                "AI Assistant", MessageBoxButtons.OK, MessageBoxIcon.Information);
+        };
+        flow.Controls.Add(save);
+
+        page.Controls.Add(flow);
+        return page;
+    }
+
     // ═══ AI MCP Tab ═══
     private Panel BuildAiMcpTab()
     {

src/ETTerms/ETTerms.csproj

@@ -10,7 +10,7 @@
     <AssemblyName>ETTerms</AssemblyName>
 
     <!-- 版本資訊 -->
-    <Version>0.5.0</Version>
+    <Version>0.6.0</Version>
     <Product>ETTerms</Product>
     <Company>ETTerms Project</Company>
 

src/ETTerms/Infrastructure/AppSettings.cs

@@ -30,6 +30,16 @@ public sealed class AppSettings
     public string ShellType { get; set; } = "PowerShell";       // PowerShell, Bash, Cmd
     public string ShellStartupDir { get; set; } = "";
 
+    // ── AI Assistant（BYO endpoint）──
+    // ⚠️ 預設全空白＝內建 AI 停用。任何私人端點 / 金鑰不得寫死於此或程式碼——
+    // 使用者自己在 Settings → AI Assistant 填。API key 存 Credential Manager（ETTerms/AiApiKey），不在此檔。
+    /// <summary>OpenAI 相容端點,含 /v1（例：http://localhost:11434/v1）。空＝AI 停用。</summary>
+    public string AiBaseUrl { get; set; } = "";
+    /// <summary>模型名（需支援 function calling）。</summary>
+    public string AiModel { get; set; } = "";
+    /// <summary>系統提示詞（人設）；空則用內建預設。</summary>
+    public string AiSystemPrompt { get; set; } = "";
+
     // ── Keyword highlight（終端機關鍵字標色 + 分頁警示；Settings → Highlight 分頁設定）──
     public bool KeywordHighlightEnabled { get; set; } = true;
     public List<KeywordRule> KeywordRules { get; set; } = new();