feat: Enhance model picker with context window size selection

com.microsoft.copilot.eclipse.core.test/src/com/microsoft/copilot/eclipse/core/chat/UserPreferenceTests.java

@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+package com.microsoft.copilot.eclipse.core.chat;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+
+class UserPreferenceTests {
+
+  private static final Gson GSON = new Gson();
+
+  @Test
+  void testContextWindowPreference_deserializesLegacyStringAndSerializesNumber() {
+    UserPreference preference = GSON.fromJson(
+        "{\"contextWindowByModel\":{\"gpt-5\":\"1000000\"}}", UserPreference.class);
+
+    assertEquals(1_000_000, preference.getContextWindow("gpt-5"));
+
+    JsonObject serialized = JsonParser.parseString(GSON.toJson(preference)).getAsJsonObject();
+    assertTrue(serialized.getAsJsonObject("contextWindowByModel").get("gpt-5").getAsJsonPrimitive().isNumber());
+  }
+}

com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/chat/UserPreference.java

@@ -27,6 +27,12 @@ public class UserPreference {
    */
   private volatile Map<String, String> reasoningEffortByModel = Map.of();
 
+  /**
+   * User-selected context-window size (a price tier's {@code maxContext} token count) keyed by the composite model
+   * key (matching the {@link #chatModel} format).
+   */
+  private volatile Map<String, Integer> contextWindowByModel = Map.of();
+
   /**
    * Gets the id of the Chat model.
    *
@@ -166,9 +172,98 @@ public synchronized boolean setReasoningEfforts(Map<String, String> reasoningEff
     return true;
   }
 
+  /**
+   * Returns the user-selected context-window size for the given model key, or {@code null} when the user has not made
+   * an explicit selection.
+   *
+   * @param modelKey the composite model key (matching the {@link #getChatModel()} format)
+   * @return the previously selected context-window size, or {@code null}
+   */
+  public Integer getContextWindow(String modelKey) {
+    if (modelKey == null) {
+      return null;
+    }
+    return contextWindowByModel.get(modelKey);
+  }
+
+  /**
+   * Returns an immutable snapshot of the model-key to context-window map. Useful as an observable value that changes
+   * by equality whenever any individual entry is added, updated, or removed.
+   *
+   * @return an immutable snapshot of the current context-window map (never {@code null})
+   */
+  public Map<String, Integer> getContextWindowSnapshot() {
+    return contextWindowByModel;
+  }
+
+  /**
+   * Stores the user-selected context-window size for the given model key. Passing a {@code null} value clears any
+   * previously stored value for that key.
+   *
+   * <p>The underlying map is replaced atomically with a fresh immutable snapshot via {@link Map#copyOf}, so concurrent
+   * readers (including Gson reflectively serializing this preference on a background thread) always observe either
+   * the old or the new snapshot, never a partially mutated map.
+   *
+   * @param modelKey the composite model key (matching the {@link #getChatModel()} format)
+   * @param contextWindow the context-window size to store, or {@code null} to clear
+   * @return {@code true} when the stored context window changed, {@code false} otherwise
+   */
+  public synchronized boolean setContextWindow(String modelKey, Integer contextWindow) {
+    if (modelKey == null) {
+      return false;
+    }
+    Map<String, Integer> current = contextWindowByModel;
+    if (contextWindow == null) {
+      if (!current.containsKey(modelKey)) {
+        return false;
+      }
+      Map<String, Integer> next = new HashMap<>(current);
+      next.remove(modelKey);
+      contextWindowByModel = Map.copyOf(next);
+      return true;
+    }
+    if (contextWindow.equals(current.get(modelKey))) {
+      return false;
+    }
+    Map<String, Integer> next = new HashMap<>(current);
+    next.put(modelKey, contextWindow);
+    contextWindowByModel = Map.copyOf(next);
+    return true;
+  }
+
+  /**
+   * Atomically replaces the entire context-window map with the given snapshot, dropping any keys not present in
+   * {@code contextWindowsByModel}. {@code null} entries in the input map are ignored. Returns {@code true} when the
+   * new snapshot differs from the previous one (so callers can decide whether to persist or notify observers).
+   *
+   * @param contextWindowsByModel the new context-window map keyed by composite model key (matching the
+   *     {@link #getChatModel()} format); may be {@code null} or empty to clear all entries
+   * @return {@code true} when the stored map changed, {@code false} otherwise
+   */
+  public synchronized boolean setContextWindows(Map<String, Integer> contextWindowsByModel) {
+    Map<String, Integer> updatedContextWindows;
+    if (contextWindowsByModel == null || contextWindowsByModel.isEmpty()) {
+      updatedContextWindows = Map.of();
+    } else {
+      Map<String, Integer> copy = new HashMap<>();
+      for (Map.Entry<String, Integer> entry : contextWindowsByModel.entrySet()) {
+        if (entry.getKey() != null && entry.getValue() != null) {
+          copy.put(entry.getKey(), entry.getValue());
+        }
+      }
+      updatedContextWindows = Map.copyOf(copy);
+    }
+    if (updatedContextWindows.equals(this.contextWindowByModel)) {
+      return false;
+    }
+    this.contextWindowByModel = updatedContextWindows;
+    return true;
+  }
+
   @Override
   public int hashCode() {
-    return Objects.hash(chatModeName, chatModel, userInputs, skipGitHubJobConfirmDialog, reasoningEffortByModel);
+    return Objects.hash(chatModeName, chatModel, userInputs, skipGitHubJobConfirmDialog, reasoningEffortByModel,
+        contextWindowByModel);
   }
 
   @Override
@@ -186,7 +281,8 @@ public boolean equals(Object obj) {
     return Objects.equals(chatModeName, other.chatModeName) && Objects.equals(chatModel, other.chatModel)
         && Objects.equals(userInputs, other.userInputs)
         && skipGitHubJobConfirmDialog == other.skipGitHubJobConfirmDialog
-        && Objects.equals(reasoningEffortByModel, other.reasoningEffortByModel);
+        && Objects.equals(reasoningEffortByModel, other.reasoningEffortByModel)
+        && Objects.equals(contextWindowByModel, other.contextWindowByModel);
   }
 
   @Override
@@ -197,6 +293,7 @@ public String toString() {
     builder.append("userInputs", userInputs);
     builder.append("skipGitHubJobConfirmDialog", skipGitHubJobConfirmDialog);
     builder.append("reasoningEffortByModel", reasoningEffortByModel);
+    builder.append("contextWindowByModel", contextWindowByModel);
     return builder.toString();
   }
 }

com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/CopilotLanguageServerConnection.java

@@ -265,13 +265,13 @@ public CompletableFuture<Object> sendExceptionTelemetry(Throwable ex) {
   }
 
   /**
-   * Create a conversation with the given parameters, including an optional reasoning effort to forward to the server
-   * via {@code modelInfo}.
+   * Create a conversation with the given parameters, including an optional reasoning effort and context-window size to
+   * forward to the server via {@code modelInfo}.
    */
   public CompletableFuture<ChatCreateResult> createConversation(String workDoneToken, String message,
       List<IResource> files, IFile currentFile, Range currentSelection, List<Turn> turns, CopilotModel activeModel,
-      String reasoningEffort, String chatModeName, String customChatModeId, List<TodoItem> todos, String agentSlug,
-      String agentJobWorkspaceFolder, String conversationId, String restoreToTurnId,
+      String reasoningEffort, Integer contextSize, String chatModeName, String customChatModeId, List<TodoItem> todos,
+      String agentSlug, String agentJobWorkspaceFolder, String conversationId, String restoreToTurnId,
       List<WorkspaceFolder> workspaceFolders) {
 
     boolean supportVision = activeModel.getCapabilities().supports().vision();
@@ -282,7 +282,7 @@ public CompletableFuture<ChatCreateResult> createConversation(String workDoneTok
       param.setReferences(FileUtils.convertToChatReferences(files));
       param.setModel(getModelName(activeModel));
       param.setModelProviderName(activeModel.getProviderName());
-      param.setModelInfo(buildModelInfo(activeModel, reasoningEffort));
+      param.setModelInfo(buildModelInfo(activeModel, reasoningEffort, contextSize));
       param.setChatMode(chatModeName);
       param.setCustomChatModeId(customChatModeId);
 
@@ -323,13 +323,14 @@ public CompletableFuture<ChatCreateResult> createConversation(String workDoneTok
   }
 
   /**
-   * Create a conversation turn with the given parameters, including an optional reasoning effort to forward to the
-   * server via {@code modelInfo}.
+   * Create a conversation turn with the given parameters, including an optional reasoning effort and context-window
+   * size to forward to the server via {@code modelInfo}.
    */
   public CompletableFuture<ChatTurnResult> addConversationTurn(String workDoneToken, String conversationId,
       String message, List<IResource> files, IFile currentFile, Range currentSelection, CopilotModel activeModel,
-      String reasoningEffort, String chatModeName, String customChatModeId, List<TodoItem> todoList, String agentSlug,
-      String agentJobWorkspaceFolder, List<WorkspaceFolder> workspaceFolders) {
+      String reasoningEffort, Integer contextSize, String chatModeName, String customChatModeId,
+      List<TodoItem> todoList, String agentSlug, String agentJobWorkspaceFolder,
+      List<WorkspaceFolder> workspaceFolders) {
 
     boolean supportVision = activeModel.getCapabilities().supports().vision();
     Either<String, List<ChatCompletionContentPart>> messageWithImages = ChatMessageUtils
@@ -339,7 +340,7 @@ public CompletableFuture<ChatTurnResult> addConversationTurn(String workDoneToke
       param.setReferences(FileUtils.convertToChatReferences(files));
       param.setModel(getModelName(activeModel));
       param.setModelProviderName(activeModel.getProviderName());
-      param.setModelInfo(buildModelInfo(activeModel, reasoningEffort));
+      param.setModelInfo(buildModelInfo(activeModel, reasoningEffort, contextSize));
       param.setChatMode(chatModeName);
       param.setCustomChatModeId(customChatModeId);
 
@@ -741,11 +742,11 @@ private String getModelName(CopilotModel activeModel) {
    * prefers over the legacy {@code model} family field), since the family is not unique across models. Returns
    * {@code null} when no model id is available.
    */
-  private static ModelInfo buildModelInfo(CopilotModel activeModel, String reasoningEffort) {
+  private static ModelInfo buildModelInfo(CopilotModel activeModel, String reasoningEffort, Integer contextSize) {
     if (activeModel == null || StringUtils.isBlank(activeModel.getId())) {
       return null;
     }
     String effort = StringUtils.isBlank(reasoningEffort) ? null : reasoningEffort;
-    return new ModelInfo(activeModel.getId(), activeModel.getProviderName(), effort, null);
+    return new ModelInfo(activeModel.getId(), activeModel.getProviderName(), effort, contextSize);
   }
 }

com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/protocol/ModelInfo.java

@@ -15,7 +15,8 @@
  * @param id model identifier (optional)
  * @param providerName provider name (optional)
  * @param reasoningEffort user-selected reasoning effort (optional)
- * @param contextSize context size (optional)
+ * @param contextSize user-selected context-window size in tokens (optional). Sent as a JSON number to match the
+ *     language server's {@code modelInfo.contextSize} schema.
  */
-public record ModelInfo(String id, String providerName, String reasoningEffort, String contextSize) {
+public record ModelInfo(String id, String providerName, String reasoningEffort, Integer contextSize) {
 }

com.microsoft.copilot.eclipse.ui.test/src/com/microsoft/copilot/eclipse/ui/chat/ModelPickerGroupsBuilderTests.java

@@ -0,0 +1,28 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+package com.microsoft.copilot.eclipse.ui.chat;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import com.microsoft.copilot.eclipse.core.lsp.protocol.CopilotModel;
+import com.microsoft.copilot.eclipse.ui.swt.DropdownItemGroup;
+
+class ModelPickerGroupsBuilderTests {
+
+  @Test
+  void testBuild_selectedLabelIncludesContextWindowAndReasoningEffort() {
+    CopilotModel model = new CopilotModel();
+    model.setModelName("gpt-5");
+
+    List<DropdownItemGroup> groups = ModelPickerGroupsBuilder.build(Map.of("gpt-5", model), false, false,
+        ignored -> "high", ignored -> "1M");
+
+    assertEquals("gpt-5 - 1M - High", groups.get(0).getItems().get(0).getSelectedLabel());
+  }
+}

com.microsoft.copilot.eclipse.ui.test/src/com/microsoft/copilot/eclipse/ui/chat/services/ModelServiceTests.java

@@ -4,6 +4,7 @@
 package com.microsoft.copilot.eclipse.ui.chat.services;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -210,6 +211,26 @@ void testDefaultKeyCollisionSelectsModelFromCurrentInventory() throws IOExceptio
     assertSame(pickerModel.get(), activeModel.get());
   }
 
+  @Test
+  void testSetActiveModel_AlreadyActiveModelDoesNotPersistPreference() throws InterruptedException {
+    CopilotModel defaultModel = createModel("gpt-4o", "GPT-4o", true);
+    when(lsConnection.listModels())
+        .thenReturn(CompletableFuture.completedFuture(new CopilotModel[] { defaultModel }));
+
+    modelService = new ModelService(lsConnection, authStatusManager);
+    waitUntil(() -> defaultModel.getId().equals(getActiveModelId()));
+
+    AtomicReference<CopilotModel> activeModel = new AtomicReference<>();
+    Display.getDefault().syncExec(() -> {
+      modelService.setActiveModel(defaultModel.getModelName());
+      activeModel.set(modelService.getActiveModel());
+    });
+
+    assertSame(defaultModel, activeModel.get());
+    Thread.sleep(100);
+    assertFalse(Files.exists(getPreferenceFile()));
+  }
+
   private static CopilotModel createModel(String id, String name, boolean isChatDefault) {
     CopilotModel model = new CopilotModel();
     model.setId(id);