feat(scout-agent): wire compaction logging into buildStreamTextParams

This commit:
- Imports applyCompaction and createCompactionTool from ./compaction
- Applies compaction to messages before processing in buildStreamTextParams
- Logs when compaction is applied (showing message count reduction)
- Adds the compaction tool to the tools object so the model can call it
- Uses compacted messages for Slack metadata detection and model conversion
- Fixes isolated declarations issue in createCompactionTool by adding return type
- Fixes test assertion for execute method on Tool type

Author: blink-so[bot]

packages/scout-agent/lib/compaction.test.ts

@@ -198,7 +198,7 @@ describe("compaction", () => {
       const tools = createCompactionTool();
       const compactionTool = tools[COMPACT_CONVERSATION_TOOL_NAME];
 
-      const result = (await compactionTool!.execute(
+      const result = (await compactionTool.execute!(
         { summary: "Test summary content" },
         { abortSignal: new AbortController().signal } as any
       )) as { summary: string; compacted_at: string; message: string };

packages/scout-agent/lib/compaction.ts

@@ -1,4 +1,4 @@
-import { tool, type ModelMessage, APICallError } from "ai";
+import { tool, type Tool, type ModelMessage, APICallError } from "ai";
 import { z } from "zod";
 import type { Message } from "./types";
 
@@ -151,7 +151,10 @@ export function applyCompaction(messages: Message[]): Message[] {
  * Creates the compact_conversation tool.
  * This tool should be called by the model when the conversation is getting too long.
  */
-export function createCompactionTool() {
+export function createCompactionTool(): Record<
+  typeof COMPACT_CONVERSATION_TOOL_NAME,
+  Tool
+> {
   return {
     [COMPACT_CONVERSATION_TOOL_NAME]: tool({
       description: `Compact the conversation history to save context space. Call this tool when instructed that the conversation is approaching context limits. Provide a detailed and thorough summary that captures:

packages/scout-agent/lib/core.ts

@@ -29,6 +29,7 @@ import {
   githubAppContextFactory,
   handleGitHubWebhook,
 } from "./github";
+import { applyCompaction, createCompactionTool } from "./compaction";
 import { defaultSystemPrompt } from "./prompt";
 import { createSlackApp, createSlackTools, getSlackMetadata } from "./slack";
 import type { Message } from "./types";
@@ -346,7 +347,16 @@ export class Scout {
         )()
       : undefined;
 
-    const slackMetadata = getSlackMetadata(messages);
+    // Apply compaction if a compaction summary exists in the message history
+    const compactedMessages = applyCompaction(messages);
+    const wasCompacted = compactedMessages.length !== messages.length;
+    if (wasCompacted) {
+      this.logger.info(
+        `Applied conversation compaction: ${messages.length} messages -> ${compactedMessages.length} messages`
+      );
+    }
+
+    const slackMetadata = getSlackMetadata(compactedMessages);
     const respondingInSlack =
       this.slack.app !== undefined && slackMetadata !== undefined;
 
@@ -447,6 +457,7 @@ export class Scout {
     }
 
     const tools = {
+      ...createCompactionTool(),
       ...(this.webSearch.config
         ? createWebSearchTools({ exaApiKey: this.webSearch.config.exaApiKey })
         : {}),
@@ -473,7 +484,7 @@ ${slack.formattingRules}
 </formatting-rules>`;
     }
 
-    const converted = convertToModelMessages(messages, {
+    const converted = convertToModelMessages(compactedMessages, {
       ignoreIncompleteToolCalls: true,
       tools,
     });