feat: context window management — sliding window with auto-summarization

Author: DorianZheng

src/agent/context-compressor.test.ts

@@ -13,15 +13,39 @@ function buildMessages(count: number): FormattedMessage[] {
   }));
 }
 
+function createAnthropicMock(summary = 'compact summary'): Anthropic {
+  return {
+    messages: {
+      create: vi.fn(async () => ({
+        content: [{ type: 'text', text: summary }],
+      })),
+    },
+  } as unknown as Anthropic;
+}
+
 describe('ContextCompressor', () => {
-  it('needsCompression uses the 80% threshold', () => {
-    const compressor = new ContextCompressor({} as Anthropic);
+  it('returns false for null utilization', () => {
+    const compressor = new ContextCompressor(createAnthropicMock());
 
     expect(compressor.needsCompression(null)).toBe(false);
+  });
+
+  it('returns false below 80% utilization', () => {
+    const compressor = new ContextCompressor(createAnthropicMock());
+
     expect(compressor.needsCompression(0.79)).toBe(false);
+  });
+
+  it('returns true at 80% utilization', () => {
+    const compressor = new ContextCompressor(createAnthropicMock());
+
     expect(compressor.needsCompression(0.8)).toBe(true);
-    expect(compressor.needsCompression(0.85)).toBe(true);
-    expect(compressor.needsCompression(1.0)).toBe(true);
+  });
+
+  it('returns true above 80% utilization', () => {
+    const compressor = new ContextCompressor(createAnthropicMock());
+
+    expect(compressor.needsCompression(0.95)).toBe(true);
   });
 
   it('compress keeps the most recent 20% and summarizes the rest', async () => {
@@ -58,6 +82,22 @@ describe('ContextCompressor', () => {
     );
   });
 
+  it('compress keeps a single message and skips summarization', async () => {
+    const anthropic = createAnthropicMock();
+    const compressor = new ContextCompressor(anthropic);
+
+    const result = await compressor.compress([
+      { sender: 'User', content: 'one' },
+    ]);
+
+    expect(result).toEqual({
+      summary: '',
+      messagesCompressed: 0,
+      messagesKept: 1,
+    });
+    expect(anthropic.messages.create).not.toHaveBeenCalled();
+  });
+
   it('formatSummaryBlock wraps and escapes summary content', () => {
     const compressor = new ContextCompressor({} as Anthropic);
 
@@ -71,4 +111,20 @@ describe('ContextCompressor', () => {
     expect(block).toContain('Use <tags> & "quotes"');
     expect(block).toContain('</context_summary>');
   });
+
+  it('calls Haiku with the expected model', async () => {
+    const anthropic = createAnthropicMock();
+    const compressor = new ContextCompressor(anthropic);
+
+    await compressor.compress([
+      { sender: 'user', content: 'old context' },
+      { sender: 'assistant', content: 'new context' },
+    ]);
+
+    expect(anthropic.messages.create).toHaveBeenCalledWith(
+      expect.objectContaining({
+        model: 'claude-haiku-4-5-20251001',
+      }),
+    );
+  });
 });

src/agent/context-compressor.ts

@@ -7,11 +7,14 @@ export interface CompressResult {
   messagesKept: number;
 }
 
-export interface FormattedMessage {
-  sender: string;
+export interface CompressMessage {
+  role?: string;
+  sender?: string;
   content: string;
 }
 
+export type FormattedMessage = CompressMessage;
+
 function isTextBlock(block: { type: string }): block is TextBlock {
   return block.type === 'text' && 'text' in block;
 }
@@ -35,7 +38,7 @@ export class ContextCompressor {
     return utilization !== null && utilization >= ContextCompressor.THRESHOLD;
   }
 
-  async compress(messages: FormattedMessage[]): Promise<CompressResult> {
+  async compress(messages: CompressMessage[]): Promise<CompressResult> {
     if (messages.length === 0) {
       return { summary: '', messagesCompressed: 0, messagesKept: 0 };
     }
@@ -62,16 +65,23 @@ export class ContextCompressor {
     return `<context_summary type="compressed" compressed_at="${escapeXml(compressedAt)}">\nEarlier conversation summary (auto-generated):\n${escapeXml(summary)}\n</context_summary>`;
   }
 
+  buildSummaryBlock(summary: string): string {
+    return this.formatSummaryBlock(summary);
+  }
+
   private getAnthropic(): Anthropic {
     if (!this.anthropic) {
       this.anthropic = new Anthropic();
     }
     return this.anthropic;
   }
 
-  private async callHaiku(messages: FormattedMessage[]): Promise<string> {
+  private async callHaiku(messages: CompressMessage[]): Promise<string> {
     const transcript = messages
-      .map((message) => `[${message.sender}]: ${message.content}`)
+      .map(
+        (message) =>
+          `[${message.role ?? message.sender ?? 'unknown'}]: ${message.content}`,
+      )
       .join('\n');
     const anthropic = this.getAnthropic();
     const response = await anthropic.messages.create({

src/agent/message-processor.ts

@@ -541,7 +541,7 @@ export class MessageProcessor {
     try {
       const result = await this.contextCompressor.compress(
         recentMessages.map((message) => ({
-          sender: message.sender_name || message.sender,
+          role: message.sender_name || message.sender,
           content: message.content,
         })),
       );
@@ -555,8 +555,8 @@ export class MessageProcessor {
       const compressedAt = new Date().toISOString();
 
       delete this.ctx.sessions[group.folder];
-      this.ctx.db.setSession(group.folder, '');
-      this.ctx.db.setContextUtilization(chatJid, null);
+      this.ctx.db.clearSession(group.folder);
+      this.ctx.db.clearContextUtilization(chatJid);
       this.ctx.emit('context_compressed', {
         agentId: this.ctx.id,
         jid: chatJid,
@@ -566,7 +566,7 @@ export class MessageProcessor {
         timestamp: compressedAt,
       });
 
-      return `${this.contextCompressor.formatSummaryBlock(result.summary, compressedAt)}\n${formatMessages(
+      return `${this.contextCompressor.formatSummaryBlock(result.summary, compressedAt)}\n\n${formatMessages(
         keptMessages,
         this.ctx.runtimeConfig.timezone,
       )}`;

src/db.ts

@@ -575,7 +575,7 @@ export class AgentDb {
       .run(
         this.contextUtilizationKey(groupJid),
         utilization,
-        utilization === null ? null : Date.now(),
+        utilization !== null ? Date.now() : null,
       );
   }
 
@@ -588,6 +588,10 @@ export class AgentDb {
     return row?.context_utilization ?? null;
   }
 
+  clearContextUtilization(groupJid: string): void {
+    this.setContextUtilization(groupJid, null);
+  }
+
   // --- Sessions ---
 
   getSession(groupFolder: string): string | undefined {
@@ -605,6 +609,12 @@ export class AgentDb {
       .run(groupFolder, sessionId);
   }
 
+  clearSession(groupFolder: string): void {
+    this.db
+      .prepare('DELETE FROM sessions WHERE group_folder = ?')
+      .run(groupFolder);
+  }
+
   getAllSessions(): Record<string, string> {
     const rows = this.db
       .prepare('SELECT group_folder, session_id FROM sessions')

src/run-stream-events.test.ts

@@ -44,6 +44,10 @@ vi.mock('./agent/context-compressor.js', () => ({
     compress(messages: Array<{ sender: string; content: string }>) {
       return contextCompressionMocks.compress(messages);
     }
+
+    formatSummaryBlock(summary: string, compressedAt: string) {
+      return `<context_summary type="compressed" compressed_at="${compressedAt}">\nEarlier conversation summary (auto-generated):\n${summary}\n</context_summary>`;
+    }
   },
 }));