feat: add /compact slash command with PreCompact/PostCompact hooks

packages/agent-sdk/src/managers/hookManager.ts

@@ -400,6 +400,16 @@ export class HookManager {
         messageManager.addErrorBlock(errorMessage);
         return { shouldBlock: false };
 
+      case "PreCompact":
+        // Non-blocking for compaction, show error in error block
+        messageManager.addErrorBlock(errorMessage);
+        return { shouldBlock: false };
+
+      case "PostCompact":
+        // Non-blocking for compaction, show error in error block
+        messageManager.addErrorBlock(errorMessage);
+        return { shouldBlock: false };
+
       default:
         return { shouldBlock: false };
     }
@@ -606,7 +616,9 @@ export class HookManager {
         event === "WorktreeCreate" ||
         event === "WorktreeRemove" ||
         event === "SessionStart" ||
-        event === "SessionEnd") &&
+        event === "SessionEnd" ||
+        event === "PreCompact" ||
+        event === "PostCompact") &&
       context.toolName !== undefined
     ) {
       logger?.warn(
@@ -689,7 +701,9 @@ export class HookManager {
       event === "WorktreeRemove" ||
       event === "CwdChanged" ||
       event === "SessionStart" ||
-      event === "SessionEnd"
+      event === "SessionEnd" ||
+      event === "PreCompact" ||
+      event === "PostCompact"
     ) {
       return true;
     }
@@ -752,7 +766,9 @@ export class HookManager {
         event === "WorktreeCreate" ||
         event === "WorktreeRemove" ||
         event === "SessionStart" ||
-        event === "SessionEnd") &&
+        event === "SessionEnd" ||
+        event === "PreCompact" ||
+        event === "PostCompact") &&
       config.matcher
     ) {
       errors.push(`${prefix}: Event ${event} should not have a matcher`);
@@ -796,6 +812,8 @@ export class HookManager {
           CwdChanged: 0,
           SessionStart: 0,
           SessionEnd: 0,
+          PreCompact: 0,
+          PostCompact: 0,
         },
       };
     }
@@ -812,6 +830,8 @@ export class HookManager {
       CwdChanged: 0,
       SessionStart: 0,
       SessionEnd: 0,
+      PreCompact: 0,
+      PostCompact: 0,
     };
 
     let totalConfigs = 0;
@@ -977,4 +997,73 @@ export class HookManager {
 
     return results;
   }
+
+  /**
+   * Execute PreCompact hooks before compaction.
+   * Returns custom instructions from hook stdout.
+   */
+  async executePreCompactHooks(
+    sessionId: string,
+    transcriptPath: string,
+    customInstructions?: string,
+  ): Promise<{
+    results: HookExecutionResult[];
+    additionalInstructions?: string;
+  }> {
+    const context: ExtendedHookExecutionContext = {
+      event: "PreCompact",
+      projectDir: this.workdir,
+      timestamp: new Date(),
+      sessionId,
+      transcriptPath,
+      cwd: this.workdir,
+      compactInstructions: customInstructions,
+      env: Object.fromEntries(
+        Object.entries(process.env).filter((e) => e[1] !== undefined),
+      ) as Record<string, string>,
+    };
+
+    const results = await this.executeHooks("PreCompact", context);
+
+    let additionalInstructions: string | undefined;
+    for (const result of results) {
+      if (result.success && result.stdout?.trim()) {
+        const trimmed = result.stdout.trim();
+        additionalInstructions = additionalInstructions
+          ? additionalInstructions + "\n" + trimmed
+          : trimmed;
+      }
+    }
+
+    return { results, additionalInstructions };
+  }
+
+  /**
+   * Execute PostCompact hooks after compaction.
+   * Receives the compact summary text.
+   */
+  async executePostCompactHooks(
+    sessionId: string,
+    transcriptPath: string,
+    compactSummary: string,
+  ): Promise<HookExecutionResult[]> {
+    const context: ExtendedHookExecutionContext = {
+      event: "PostCompact",
+      projectDir: this.workdir,
+      timestamp: new Date(),
+      sessionId,
+      transcriptPath,
+      cwd: this.workdir,
+      compactSummary,
+      env:
+        this.container.get<Record<string, string>>("MergedEnv") ||
+        (process.env as Record<string, string>),
+    };
+
+    const results = await this.executeHooks("PostCompact", context);
+    if (results.length > 0) {
+      this.processHookResults("PostCompact", results);
+    }
+    return results;
+  }
 }

packages/agent-sdk/src/managers/slashCommandManager.ts

@@ -158,6 +158,23 @@ export class SlashCommandManager {
         }
       },
     });
+
+    // Register built-in compact command
+    this.registerCommand({
+      id: "compact",
+      name: "compact",
+      description: "Compact conversation history to reduce context usage",
+      handler: async (args?: string, signal?: AbortSignal) => {
+        this.aiManager.abortAIMessage();
+
+        const customInstructions = args?.trim() || undefined;
+
+        await this.aiManager.compactConversation({
+          customInstructions,
+          abortSignal: signal,
+        });
+      },
+    });
   }
 
   /**

packages/agent-sdk/src/services/aiService.ts

@@ -758,6 +758,7 @@ export interface CompactMessagesOptions {
   messages: ChatCompletionMessageParam[];
   abortSignal?: AbortSignal;
   model?: string;
+  customInstructions?: string;
 }
 
 export interface CompactMessagesResult {
@@ -835,7 +836,9 @@ export async function compactMessages(
           ...cleanedMessages,
           {
             role: "user",
-            content: `Please create a detailed summary of the conversation so far.`,
+            content: options.customInstructions
+              ? `Please create a detailed summary of the conversation so far. Pay special attention to these instructions: ${options.customInstructions}`
+              : `Please create a detailed summary of the conversation so far.`,
           },
         ],
       },

packages/agent-sdk/src/types/hooks.ts

@@ -24,7 +24,9 @@ export type HookEvent =
   | "WorktreeRemove"
   | "CwdChanged"
   | "SessionStart"
-  | "SessionEnd";
+  | "SessionEnd"
+  | "PreCompact"
+  | "PostCompact";
 
 // Individual hook command configuration
 export interface HookCommand {
@@ -117,6 +119,8 @@ export function isValidHookEvent(event: string): event is HookEvent {
     "CwdChanged",
     "SessionStart",
     "SessionEnd",
+    "PreCompact",
+    "PostCompact",
   ].includes(event);
 }
 
@@ -187,6 +191,8 @@ export interface HookJsonInput {
   source?: SessionStartSource; // Present for SessionStart events
   agent_type?: string; // Present for SessionStart events
   end_source?: SessionEndSource; // Present for SessionEnd events
+  compact_instructions?: string; // Present for PreCompact events
+  compact_summary?: string; // Present for PostCompact events
 }
 
 // Extended context interface for passing additional data to hook executor
@@ -205,6 +211,8 @@ export interface ExtendedHookExecutionContext extends HookExecutionContext {
   source?: SessionStartSource; // Session start source (SessionStart only)
   agentType?: string; // Agent type identifier (SessionStart only)
   endSource?: SessionEndSource; // Session end source (SessionEnd only)
+  compactInstructions?: string; // Custom instructions for PreCompact
+  compactSummary?: string; // Summary text for PostCompact
 }
 
 // Environment variables injected into hook processes