feat: add P2 features — retry policy, prompt templating, usage tracking, tech debt cleanup

- Extract shared splitMessage() into channels/utils.ts (dedup 4 adapters)
- Add Slack user name resolution with caching (users.info API)
- Add withRetry() with exponential backoff + jitter, isRetryable() filter
- Wire retry config into ModelRouter.chat() (non-streaming only)
- Add assembleSystemPrompt() multi-file template system (SOUL/AGENTS/IDENTITY/USER/TOOLS.md)
- Add usage tracking accumulators in NativeAgent + AgentOrchestrator
- Add estimateCost() with per-model pricing table
- Add /usage TUI command with full usage report formatting
- Add retrySchema and promptSchema to config schema

Tests: 569 passing, typecheck clean

src/channels/slack/adapter.ts

@@ -13,6 +13,7 @@ import type {
   ChannelAdapter,
   ChannelStatus,
 } from '../types.js';
+import { splitMessage } from '../utils.js';
 
 /** Configuration for the Slack channel adapter. */
 export interface SlackAdapterConfig {
@@ -34,36 +35,6 @@ interface SlackMessageEvent {
   subtype?: string;
 }
 
-/**
- * Split a long message into chunks that respect Slack's readability limit.
- * Prefers splitting at newlines, then spaces, then hard-cuts.
- */
-function splitMessage(text: string, maxLength: number): string[] {
-  const chunks: string[] = [];
-  let remaining = text;
-
-  while (remaining.length > 0) {
-    if (remaining.length <= maxLength) {
-      chunks.push(remaining);
-      break;
-    }
-
-    // Try to split at a newline within the allowed window
-    let splitIndex = remaining.lastIndexOf('\n', maxLength);
-    if (splitIndex === -1 || splitIndex < maxLength / 2) {
-      splitIndex = remaining.lastIndexOf(' ', maxLength);
-    }
-    if (splitIndex === -1 || splitIndex < maxLength / 2) {
-      splitIndex = maxLength;
-    }
-
-    chunks.push(remaining.slice(0, splitIndex));
-    remaining = remaining.slice(splitIndex).trimStart();
-  }
-
-  return chunks;
-}
-
 /**
  * Slack channel adapter backed by @slack/bolt.
  *
@@ -77,6 +48,7 @@ export class SlackAdapter implements ChannelAdapter {
   private app: App | null = null;
   private messageHandler?: (msg: InboundMessage) => void;
   private config: SlackAdapterConfig;
+  private userNameCache: Map<string, string> = new Map();
 
   get status(): ChannelStatus {
     return this._status;
@@ -105,7 +77,7 @@ export class SlackAdapter implements ChannelAdapter {
 
       // Register message event handler
       this.app.message(async ({ message }) => {
-        this.handleMessage(message as unknown as SlackMessageEvent);
+        await this.handleMessage(message as unknown as SlackMessageEvent);
       });
 
       await this.app.start();
@@ -161,8 +133,23 @@ export class SlackAdapter implements ChannelAdapter {
     }
   }
 
+  /** Resolve a Slack user ID to a display name, with caching. */
+  private async resolveUserName(userId: string): Promise<string> {
+    const cached = this.userNameCache.get(userId);
+    if (cached) return cached;
+
+    try {
+      const result = await this.app!.client.users.info({ user: userId });
+      const name = result.user?.real_name || result.user?.name || userId;
+      this.userNameCache.set(userId, name);
+      return name;
+    } catch {
+      return userId;
+    }
+  }
+
   /** Internal: process an inbound Slack message event. */
-  private handleMessage(message: SlackMessageEvent): void {
+  private async handleMessage(message: SlackMessageEvent): Promise<void> {
     if (!this.messageHandler) return;
 
     // Ignore bot messages
@@ -187,9 +174,10 @@ export class SlackAdapter implements ChannelAdapter {
     // Strip bot mentions: <@U\w+> pattern
     let text = (message.text ?? '').replace(/<@U\w+>/g, '').trim();
 
-    // TODO: message.user is a Slack user ID (e.g. U0123ABC), not a display name.
-    // To resolve display names, use this.app.client.users.info() with caching.
-    const senderName = message.user;
+    // Resolve display name from Slack user ID
+    const senderName = message.user
+      ? await this.resolveUserName(message.user)
+      : undefined;
 
     // Detect reset command
     if (text === '!reset' || text === 'reset') {