feat: Implement auto compression feature for chat context (#250)

Author: ethanyhou

com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/events/CopilotEventConstants.java

@@ -176,4 +176,14 @@ public class CopilotEventConstants {
    * conversation templates on receipt.
    */
   public static final String TOPIC_CHAT_DID_CHANGE_CUSTOMIZATION_FILES = TOPIC_CHAT + "DID_CHANGE_CUSTOMIZATION_FILES";
+
+  /**
+   * Event when automatic conversation compression starts.
+   */
+  public static final String TOPIC_CHAT_COMPRESSION_STARTED = TOPIC_CHAT + "COMPRESSION_STARTED";
+
+  /**
+   * Event when automatic conversation compression completes.
+   */
+  public static final String TOPIC_CHAT_COMPRESSION_COMPLETED = TOPIC_CHAT + "COMPRESSION_COMPLETED";
 }

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

@@ -43,6 +43,8 @@
 import com.microsoft.copilot.eclipse.core.lsp.mcp.McpOauthRequest;
 import com.microsoft.copilot.eclipse.core.lsp.mcp.McpRuntimeLog;
 import com.microsoft.copilot.eclipse.core.lsp.protocol.ChatProgressValue;
+import com.microsoft.copilot.eclipse.core.lsp.protocol.CompressionCompletedParams;
+import com.microsoft.copilot.eclipse.core.lsp.protocol.CompressionStartedParams;
 import com.microsoft.copilot.eclipse.core.lsp.protocol.ConversationCapabilities;
 import com.microsoft.copilot.eclipse.core.lsp.protocol.ConversationContextParams;
 import com.microsoft.copilot.eclipse.core.lsp.protocol.CurrentEditorContext;
@@ -366,6 +368,26 @@ public void onQuotaWarning(QuotaWarningParams params) {
     }
   }
 
+  /**
+   * Notify when automatic conversation compression starts.
+   */
+  @JsonNotification("$/copilot/compressionStarted")
+  public void onCompressionStarted(CompressionStartedParams params) {
+    if (eventBroker != null) {
+      eventBroker.post(CopilotEventConstants.TOPIC_CHAT_COMPRESSION_STARTED, params);
+    }
+  }
+
+  /**
+   * Notify when automatic conversation compression completes.
+   */
+  @JsonNotification("$/copilot/compressionCompleted")
+  public void onCompressionCompleted(CompressionCompletedParams params) {
+    if (eventBroker != null) {
+      eventBroker.post(CopilotEventConstants.TOPIC_CHAT_COMPRESSION_COMPLETED, params);
+    }
+  }
+
   /**
    * Reads the contents and stats of a file given its URI.
    */

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

@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+package com.microsoft.copilot.eclipse.core.lsp.protocol;
+
+/**
+ * Parameters for the {@code $/copilot/compressionCompleted} notification sent by the language server when automatic
+ * conversation compression finishes. The {@code contextInfo} field is optional and may be {@code null}.
+ */
+public record CompressionCompletedParams(
+    String conversationId,
+    int archivedPartitionId,
+    int newPartitionId,
+    int summaryLength,
+    int turnCount,
+    int durationMs,
+    ContextSizeInfo contextInfo) {
+}

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

@@ -0,0 +1,11 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+package com.microsoft.copilot.eclipse.core.lsp.protocol;
+
+/**
+ * Parameters for the {@code $/copilot/compressionStarted} notification sent by the language server when automatic
+ * conversation compression begins.
+ */
+public record CompressionStartedParams(String conversationId, int partitionId, String reason) {
+}

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

@@ -17,6 +17,7 @@ public class CopilotAgentSettings {
   @SerializedName("maxToolCallingLoop")
   private int agentMaxRequests;
   private boolean enableSkills;
+  private boolean autoCompress;
 
   private String transcriptDirectory;
 
@@ -178,6 +179,14 @@ public String getTranscriptDirectory() {
     return transcriptDirectory;
   }
 
+  public boolean isAutoCompress() {
+    return autoCompress;
+  }
+
+  public void setAutoCompress(boolean autoCompress) {
+    this.autoCompress = autoCompress;
+  }
+
   public void setTranscriptDirectory(String transcriptDirectory) {
     this.transcriptDirectory = transcriptDirectory;
   }
@@ -212,7 +221,7 @@ public ToolsSettings getTools() {
 
   @Override
   public int hashCode() {
-    return Objects.hash(agentMaxRequests, enableSkills, transcriptDirectory,
+    return Objects.hash(agentMaxRequests, enableSkills, autoCompress, transcriptDirectory,
         editorHandlesAllConfirmation, autoApproveUnmatchedTerminal, autoApproveUnmatchedFileOp, tools);
   }
 
@@ -229,6 +238,7 @@ public boolean equals(Object obj) {
     }
     CopilotAgentSettings other = (CopilotAgentSettings) obj;
     return agentMaxRequests == other.agentMaxRequests && enableSkills == other.enableSkills
+        && autoCompress == other.autoCompress
         && Objects.equals(transcriptDirectory, other.transcriptDirectory)
         && editorHandlesAllConfirmation == other.editorHandlesAllConfirmation
         && autoApproveUnmatchedTerminal == other.autoApproveUnmatchedTerminal
@@ -241,6 +251,7 @@ public String toString() {
     ToStringBuilder builder = new ToStringBuilder(this);
     builder.append("agentMaxRequests", agentMaxRequests);
     builder.append("enableSkills", enableSkills);
+    builder.append("autoCompress", autoCompress);
     builder.append("transcriptDirectory", transcriptDirectory);
     builder.append("editorHandlesAllConfirmation", editorHandlesAllConfirmation);
     builder.append("autoApproveUnmatchedTerminal", autoApproveUnmatchedTerminal);

com.microsoft.copilot.eclipse.swtbot.test/test-plans/context-compress/context-compress.md

@@ -0,0 +1,163 @@
+# Auto Context Compression
+
+## Overview
+Verifies the **Auto Compress** feature that automatically compresses long
+conversations to keep context usage within the model's limit. Auto Compress
+is always enabled (no user-facing preference). While compression is in
+progress, the chat view shows a "Compacting conversation..." spinner below
+the latest Copilot turn, and the context size donut updates once it
+completes.
+
+Entry points:
+- **Copilot Chat view** → latest Copilot turn (spinner banner appears here).
+- **Copilot Chat view** → control bar **Context Size Donut** (updates after
+  compression completes).
+
+---
+
+## Prerequisites
+
+- Eclipse IDE with the GitHub Copilot for Eclipse plugin installed (built from
+  the branch containing the staged Auto Compress changes).
+- A valid GitHub Copilot subscription is active (authentication completed).
+- A model that supports a finite context window is selected (so the donut and
+  compression can be exercised — e.g. Claude Sonnet 4.6 or GPT-4.1).
+- The Copilot Chat view is open and visible.
+
+---
+
+## Test Cases
+
+### TC-001: Compacting banner appears when compression starts
+
+**Type:** `Happy Path`
+**Priority:** `P0`
+
+#### Preconditions
+- The Copilot Chat view is open with a new conversation.
+
+#### Steps
+1. Start a conversation and drive the context usage toward the model limit —
+   for example, attach several large files and/or run multiple tool-heavy
+   turns until the **Context Size Donut** approaches its warning threshold
+   (≥90 %).
+2. Continue sending messages until the conversation goes over the threshold
+   so the server initiates automatic compression.
+3. Observe the latest Copilot turn while the server processes the request.
+
+#### Expected Result
+- A small banner appears **below the latest Copilot turn** containing:
+  - An animated spinner.
+  - The status text **"Compacting conversation..."**.
+- The chat view layout refreshes so the banner is fully visible (not clipped).
+- No error dialogs are shown.
+
+#### 📸 Key Screenshots
+- [ ] **Compacting banner** — spinner + "Compacting conversation..." text
+  rendered under the latest Copilot turn.
+
+---
+
+### TC-002: Compacting banner is dismissed and context donut updates on completion
+
+**Type:** `Happy Path`
+**Priority:** `P0`
+
+#### Preconditions
+- TC-001 has been executed and the "Compacting conversation..." banner is
+  currently visible.
+
+#### Steps
+1. Wait for the server to finish compression (typically a few seconds).
+2. Observe the latest Copilot turn after compression completes.
+3. Hover the **Context Size Donut** in the chat view control bar.
+
+#### Expected Result
+- The "Compacting conversation..." banner is removed from the Copilot turn.
+- The chat view scroller relayouts cleanly (no leftover blank space, no
+  clipping).
+- The Context Size Donut updates to reflect the new, smaller token usage
+  (the ring's filled portion shrinks).
+- The **Context Window** popup shows the post-compression token breakdown
+  consistent with the new total.
+- The subsequent reply continues to stream normally on top of the freshly
+  compressed history.
+
+#### 📸 Key Screenshots
+- [ ] **After completion** — Copilot turn without the banner.
+- [ ] **Donut after compression** — Context Size Donut showing reduced usage.
+- [ ] **Context Window popup** — Token breakdown after compression.
+
+---
+
+### TC-003: Cancelling a chat hides the compacting banner
+
+**Type:** `Edge Case`
+**Priority:** `P1`
+
+#### Preconditions
+- A conversation is set up so the next send will trigger compression
+  (as in TC-001).
+
+#### Steps
+1. Send the message that triggers compression and wait for the
+   "Compacting conversation..." banner to appear.
+2. While the banner is showing, click the **Cancel** (stop) button in the
+   chat input action bar.
+
+#### Expected Result
+- The send button is restored from its stop/cancel state back to its normal
+  send state.
+- The "Compacting conversation..." banner is removed from the latest Copilot
+  turn.
+- Any buffered reply text that arrived just before cancellation is rendered
+  (no missing trailing line).
+- The chat view relayouts cleanly so the flushed reply is fully visible.
+- The user can immediately send a new message in the same conversation.
+
+#### 📸 Key Screenshots
+- [ ] **After cancel** — banner gone, send button reset, any buffered reply
+  visible.
+
+---
+
+### TC-004: Compacting banner only updates the matching conversation
+
+**Type:** `Edge Case`
+**Priority:** `P2`
+
+#### Preconditions
+- Two conversations exist in chat history: *Conversation A* (about to
+  trigger compression) and *Conversation B* (short, well under the limit).
+
+#### Steps
+1. In *Conversation A*, send a message that triggers compression and wait
+   for the "Compacting conversation..." banner to appear.
+2. Without waiting for completion, open chat history and switch to
+   *Conversation B*.
+3. Inspect *Conversation B* for any compaction banner.
+4. Switch back to *Conversation A*.
+
+#### Expected Result
+- *Conversation B* never shows a "Compacting conversation..." banner — the
+  compaction status is scoped to *Conversation A* only.
+- When you return to *Conversation A*, its state is consistent with the
+  compression outcome (banner cleared if it completed in the meantime; new
+  reply continues to stream if still in progress).
+- No errors or stale spinners are left behind in either conversation.
+
+#### 📸 Key Screenshots
+- [ ] **Conversation B during A's compaction** — no banner shown.
+
+---
+
+## Screenshots Checklist
+> Consolidated list of all key screenshot moments.
+
+- [ ] `TC-001` Compacting banner under latest Copilot turn.
+- [ ] `TC-002` Copilot turn after compaction completes (banner gone).
+- [ ] `TC-002` Context Size Donut after compaction (reduced usage).
+- [ ] `TC-002` Context Window popup with post-compaction token breakdown.
+- [ ] `TC-003` State after cancel — banner gone, send button reset, buffered
+  reply visible.
+- [ ] `TC-004` Conversation B during Conversation A's compaction (no banner).