Enable model switching for active sessions

PolyPilot.Tests/ModelSelectionTests.cs

@@ -361,4 +361,184 @@ public void EndToEnd_LegacyDisplayNameEntry_IsNormalizedOnResume()
         Assert.Equal("claude-opus-4.5", resumeModel);
         Assert.Equal("/some/worktree", entry.WorkingDirectory);
     }
+
+    // === ChangeModelAsync behavior tests ===
+
+    [Fact]
+    public void ChangeModel_NewModelIsNormalized()
+    {
+        // ChangeModelAsync normalizes before use — display names from UI must become slugs
+        var userSelection = "Claude Opus 4.6";
+        var normalized = ModelHelper.NormalizeToSlug(userSelection);
+        Assert.Equal("claude-opus-4.6", normalized);
+    }
+
+    [Fact]
+    public void ChangeModel_SameModel_IsNoOp()
+    {
+        // If current model == requested model, ChangeModelAsync should be a no-op
+        var currentModel = "claude-opus-4.5";
+        var requested = "claude-opus-4.5";
+        var normalizedRequested = ModelHelper.NormalizeToSlug(requested);
+        Assert.Equal(currentModel, normalizedRequested); // Would trigger no-op guard
+    }
+
+    [Fact]
+    public void ChangeModel_DifferentModel_UpdatesInfo()
+    {
+        // Simulates what ChangeModelAsync does to AgentSessionInfo after successful resume
+        var info = new AgentSessionInfo
+        {
+            Name = "TestSession",
+            Model = "claude-sonnet-4.5",
+            SessionId = "some-guid",
+            WorkingDirectory = "/some/worktree"
+        };
+
+        var newModel = ModelHelper.NormalizeToSlug("claude-opus-4.6");
+        Assert.NotEqual(info.Model, newModel); // Different model → would proceed
+
+        // After successful resume, model is updated
+        info.Model = newModel;
+        Assert.Equal("claude-opus-4.6", info.Model);
+
+        // Working directory must NOT change during model switch
+        Assert.Equal("/some/worktree", info.WorkingDirectory);
+    }
+
+    [Fact]
+    public void ChangeModel_PreservesSessionIdentity()
+    {
+        // Model switch reconnects the same session ID — history is preserved server-side
+        var info = new AgentSessionInfo
+        {
+            Name = "MySession",
+            Model = "gpt-5.1-codex",
+            SessionId = "fixed-guid-123",
+            WorkingDirectory = "/my/worktree"
+        };
+        info.History.Add(ChatMessage.UserMessage("hello"));
+        info.History.Add(new ChatMessage("assistant", "hi there", DateTime.Now));
+
+        var originalSessionId = info.SessionId;
+        var originalHistory = info.History.Count;
+        var originalName = info.Name;
+        var originalWorkDir = info.WorkingDirectory;
+
+        // Simulate model switch
+        info.Model = ModelHelper.NormalizeToSlug("claude-opus-4.6");
+
+        // Everything except model must be unchanged
+        Assert.Equal(originalSessionId, info.SessionId);
+        Assert.Equal(originalHistory, info.History.Count);
+        Assert.Equal(originalName, info.Name);
+        Assert.Equal(originalWorkDir, info.WorkingDirectory);
+        Assert.Equal("claude-opus-4.6", info.Model);
+    }
+
+    [Fact]
+    public void ChangeModel_DisplayNameFromDropdown_NormalizesToSlug()
+    {
+        // The UI dropdown shows display names but passes slugs.
+        // If somehow a display name gets through, ChangeModelAsync must normalize it.
+        var displayNames = new Dictionary<string, string>
+        {
+            { "Claude Opus 4.6 (fast mode)", "claude-opus-4.6-fast" },
+            { "Gemini 3 Pro (Preview)", "gemini-3-pro-preview" },
+            { "GPT-5.1-Codex-Max", "gpt-5.1-codex-max" },
+        };
+
+        foreach (var (display, expectedSlug) in displayNames)
+        {
+            var normalized = ModelHelper.NormalizeToSlug(display);
+            Assert.Equal(expectedSlug, normalized);
+            Assert.False(ModelHelper.IsDisplayName(normalized));
+        }
+    }
+
+    // --- PrettifyModel tests ---
+    // The prettifier is duplicated in ExpandedSessionView.razor and ModelSelector.razor.
+    // We test the logic inline here to catch regressions like the "Opus-4.5" bug.
+
+    /// <summary>
+    /// Mirror of the PrettifyModel logic from ExpandedSessionView.razor / ModelSelector.razor.
+    /// </summary>
+    private static string PrettifyModel(string modelId)
+    {
+        var display = modelId
+            .Replace("claude-", "Claude ")
+            .Replace("gpt-", "GPT-")
+            .Replace("gemini-", "Gemini ");
+        display = display.Replace("-", " ");
+        display = display.Replace("GPT ", "GPT-");
+        return string.Join(' ', display.Split(' ', StringSplitOptions.RemoveEmptyEntries).Select(s =>
+            s.Length > 0 ? char.ToUpper(s[0]) + s[1..] : s));
+    }
+
+    [Theory]
+    [InlineData("claude-opus-4.5", "Claude Opus 4.5")]
+    [InlineData("claude-opus-4.6-fast", "Claude Opus 4.6 Fast")]
+    [InlineData("claude-sonnet-4.5", "Claude Sonnet 4.5")]
+    [InlineData("claude-haiku-4.5", "Claude Haiku 4.5")]
+    [InlineData("gpt-5.1-codex-max", "GPT-5.1 Codex Max")]
+    [InlineData("gpt-5.1-codex-mini", "GPT-5.1 Codex Mini")]
+    [InlineData("gpt-5.2-codex", "GPT-5.2 Codex")]
+    [InlineData("gpt-5-mini", "GPT-5 Mini")]
+    [InlineData("gemini-3-pro-preview", "Gemini 3 Pro Preview")]
+    public void PrettifyModel_ProducesReadableNames(string slug, string expected)
+    {
+        Assert.Equal(expected, PrettifyModel(slug));
+    }
+
+    [Theory]
+    [InlineData("claude-opus-4.5")]
+    [InlineData("gpt-5.1-codex")]
+    [InlineData("gemini-3-pro-preview")]
+    public void PrettifyModel_NoDuplicateHyphens(string slug)
+    {
+        var pretty = PrettifyModel(slug);
+        // Should not contain stray hyphens (except GPT- prefix)
+        var withoutGpt = pretty.Replace("GPT-", "GPT");
+        Assert.DoesNotContain("-", withoutGpt);
+    }
+
+    [Fact]
+    public void PrettifyModel_DoesNotProduceDuplicateEntries()
+    {
+        // Regression: "claude-opus-4.5" was prettified to "Claude Opus-4.5"
+        // which didn't match the display name "Claude Opus 4.5", causing duplicates in the dropdown
+        var slugs = new[] { "claude-opus-4.5", "claude-sonnet-4.5", "gpt-5.1-codex-max" };
+        foreach (var slug in slugs)
+        {
+            var pretty = PrettifyModel(slug);
+            Assert.DoesNotContain("-", pretty.Replace("GPT-", "GPT"));
+            // Prettifying twice should be stable
+            Assert.Equal(pretty, PrettifyModel(slug));
+        }
+    }
+
+    [Fact]
+    public void RecreateSession_UsesNormalizedModel()
+    {
+        // When RecreateSessionAsync is called, the model should be normalized
+        // before being passed to CreateSessionAsync
+        var displayName = "Claude Opus 4.5";
+        var normalized = ModelHelper.NormalizeToSlug(displayName);
+        Assert.Equal("claude-opus-4.5", normalized);
+        // The recreated session should use the slug, not the display name
+        Assert.False(ModelHelper.IsDisplayName(normalized));
+    }
+
+    [Theory]
+    [InlineData("claude-opus-4.5")]
+    [InlineData("gpt-5.1-codex-max")]
+    [InlineData("gemini-3-pro-preview")]
+    [InlineData("claude-opus-4.6-fast")]
+    public void RoundTrip_NormalizeAndPrettify_AreConsistent(string slug)
+    {
+        // Prettify a slug, then normalize back — should return the original slug
+        var pretty = PrettifyModel(slug);
+        var backToSlug = ModelHelper.NormalizeToSlug(pretty);
+        Assert.Equal(slug, backToSlug);
+    }
 }

PolyPilot/Components/ExpandedSessionView.razor

@@ -19,7 +19,7 @@
             <div class="info-popover">
                 <span class="info-trigger">ℹ︎</span>
                 <div class="info-panel">
-                    <div class="info-row"><span class="info-label">Model</span><span class="info-value">@CurrentModel</span></div>
+                    <div class="info-row"><span class="info-label">Model</span><span class="info-value">@PrettifyModel(CurrentModel)</span></div>
                     @if (!string.IsNullOrEmpty(Session.WorkingDirectory))
                     {
                         <div class="info-row"><span class="info-label">Directory</span><span class="info-value">@Session.WorkingDirectory</span></div>
@@ -133,14 +133,14 @@
                 <button class="mode-btn @(PlanMode ? "active" : "")" @onclick="() => OnSetPlanMode.InvokeAsync(true)">Plan</button>
             </div>
             <span class="status-sep">·</span>
-            <select class="inline-model-select" value="@CurrentModel" @onchange="e => OnSetModel.InvokeAsync(e.Value?.ToString())" disabled="@(Session.History.Count > 0)" title="@(Session.History.Count > 0 ? "Model cannot be changed during an active session" : "Select model")">
+            <select class="inline-model-select" value="@CurrentModel" @onchange="e => OnSetModel.InvokeAsync(e.Value?.ToString())" disabled="@Session.IsProcessing" title="@(Session.IsProcessing ? "Wait for response to complete" : "Switch model")">
                 @if (!AvailableModels.Contains(CurrentModel))
                 {
-                    <option value="@CurrentModel">@CurrentModel</option>
+                    <option value="@CurrentModel">@PrettifyModel(CurrentModel)</option>
                 }
                 @foreach (var m in AvailableModels)
                 {
-                    <option value="@m">@m</option>
+                    <option value="@m">@PrettifyModel(m)</option>
                 }
             </select>
             <span class="status-extra">
@@ -214,6 +214,21 @@
 
     private void LoadMore() => OnLoadMore.InvokeAsync();
 
+    private static string PrettifyModel(string modelId)
+    {
+        var display = modelId
+            .Replace("claude-", "Claude ")
+            .Replace("gpt-", "GPT-")
+            .Replace("gemini-", "Gemini ");
+        // Replace remaining hyphens with spaces (e.g. "opus-4.5" → "opus 4.5")
+        // but preserve hyphens within the GPT- prefix (already handled above)
+        display = display.Replace("-", " ");
+        // Re-insert hyphen for GPT prefix
+        display = display.Replace("GPT ", "GPT-");
+        return string.Join(' ', display.Split(' ', StringSplitOptions.RemoveEmptyEntries).Select(s =>
+            s.Length > 0 ? char.ToUpper(s[0]) + s[1..] : s));
+    }
+
     private void OpenSessionFolder(string sessionId)
     {
         try

PolyPilot/Components/ModelSelector.razor

@@ -73,9 +73,13 @@
             .Replace("claude-", "Claude ")
             .Replace("gpt-", "GPT-")
             .Replace("gemini-", "Gemini ");
+        // Replace remaining hyphens with spaces (e.g. "opus-4.5" → "opus 4.5")
+        display = display.Replace("-", " ");
+        // Re-insert hyphen for GPT prefix
+        display = display.Replace("GPT ", "GPT-");
 
         // Capitalize segments
-        display = string.Join(' ', display.Split(' ').Select(s =>
+        display = string.Join(' ', display.Split(' ', StringSplitOptions.RemoveEmptyEntries).Select(s =>
             s.Length > 0 ? char.ToUpper(s[0]) + s[1..] : s));
 
         return new ModelDisplayInfo(display, icon);

PolyPilot/Components/Pages/Dashboard.razor

@@ -1868,6 +1868,7 @@
     private async Task SetExpandedModel(AgentSessionInfo session, string? model)
     {
         if (string.IsNullOrEmpty(model)) return;
+
         // If the session has no history, recreate it to "switch" the model effectively
         if (session.History.Count == 0)
         {
@@ -1877,8 +1878,13 @@
             return;
         }
 
-        // SDK doesn't support changing model mid-session; update local state only.
-        session.Model = model;
+        // For active sessions with history, resume with the new model
+        var success = await CopilotService.ChangeModelAsync(session.Name, model);
+        if (success)
+        {
+            sessions = CopilotService.GetAllSessions().ToList();
+            await InvokeAsync(SafeRefreshAsync);
+        }
     }
 
     private void SetPlanMode(string sessionName, bool enabled) => planModeBySession[sessionName] = enabled;

PolyPilot/Services/CopilotService.cs

@@ -1066,6 +1066,64 @@ ALWAYS run the relaunch script as the final step after making changes to this pr
         return await CreateSessionAsync(name, newModel, workingDir);
     }
 
+    /// <summary>
+    /// Switch the model for an active session by resuming it with a new ResumeSessionConfig.
+    /// The session history is preserved server-side (same session ID); we just reconnect
+    /// asking for a different model.
+    /// </summary>
+    public async Task<bool> ChangeModelAsync(string sessionName, string newModel, CancellationToken cancellationToken = default)
+    {
+        if (!_sessions.TryGetValue(sessionName, out var state)) return false;
+        if (state.Info.IsProcessing) return false;
+        if (string.IsNullOrEmpty(state.Info.SessionId)) return false;
+
+        var normalizedModel = Models.ModelHelper.NormalizeToSlug(newModel);
+        if (string.IsNullOrEmpty(normalizedModel)) return false;
+
+        // Already on this model — no-op
+        if (state.Info.Model == normalizedModel) return true;
+
+        Debug($"Switching model for '{sessionName}': {state.Info.Model} → {normalizedModel}");
+
+        try
+        {
+            // Dispose old session connection
+            await state.Session.DisposeAsync();
+
+            if (_client == null)
+                throw new InvalidOperationException("Client is not initialized");
+
+            // Resume the same session ID with the new model
+            var resumeConfig = new ResumeSessionConfig
+            {
+                Model = normalizedModel,
+                WorkingDirectory = state.Info.WorkingDirectory
+            };
+            var newSession = await _client.ResumeSessionAsync(state.Info.SessionId, resumeConfig, cancellationToken);
+
+            // Build replacement state, preserving info/history
+            state.Info.Model = normalizedModel;
+            var newState = new SessionState
+            {
+                Session = newSession,
+                Info = state.Info
+            };
+            newSession.On(evt => HandleSessionEvent(newState, evt));
+            _sessions[sessionName] = newState;
+
+            Debug($"Model switched for '{sessionName}' to {normalizedModel}");
+            SaveActiveSessionsToDisk();
+            OnStateChanged?.Invoke();
+            return true;
+        }
+        catch (Exception ex)
+        {
+            Debug($"Failed to switch model for '{sessionName}': {ex.Message}");
+            OnError?.Invoke(sessionName, $"Failed to switch model: {ex.Message}");
+            return false;
+        }
+    }
+
     public async Task<string> SendPromptAsync(string sessionName, string prompt, List<string>? imagePaths = null, CancellationToken cancellationToken = default)
     {
         // In demo mode, simulate a response locally