feat(session): persist model tier overrides per session

Store per-session config in SQLite and route /model and /reset through command fast-paths so channel sessions keep independent model selection across reconnects and restarts.

src/session/manager.ts

@@ -1,6 +1,8 @@
 import type { Message } from '../models/types.js';
 import type { SessionStore } from './store.js';
 import { auditLogger } from '../audit/index.js';
+import { SessionIndexer } from './indexer.js';
+import { SessionSearch, type HistorySearchResult } from './search.js';
 
 export interface Session {
   id: string;
@@ -18,6 +20,7 @@ export class ManagedSession implements Session {
     public readonly id: string,
     private store: SessionStore,
     private history: Message[] = [],
+    private indexer?: SessionIndexer,
   ) {}
 
   addMessage(message: Message): Message {
@@ -26,16 +29,20 @@ export class ManagedSession implements Session {
       timestamp: Date.now(),
     };
     this.history.push(messageWithTimestamp);
-    this.store.addMessage(this.id, messageWithTimestamp);
-    
+    const content = typeof message.content === 'string'
+      ? message.content
+      : JSON.stringify(message.content);
+    const metadata = this.indexer?.indexText(content);
+    this.store.addMessage(this.id, messageWithTimestamp, metadata);
+
     auditLogger?.sessionMessage({
       session_id: this.id,
       role: message.role,
-      content_length: typeof message.content === 'string' 
-        ? message.content.length 
+      content_length: typeof message.content === 'string'
+        ? message.content.length
         : JSON.stringify(message.content).length,
     });
-    
+
     return messageWithTimestamp;
   }
 
@@ -47,7 +54,7 @@ export class ManagedSession implements Session {
     const messageCount = this.history.length;
     this.history = [];
     this.store.clearSession(this.id);
-    
+
     auditLogger?.sessionDelete({
       session_id: this.id,
       message_count: messageCount,
@@ -83,8 +90,25 @@ export class ManagedSession implements Session {
 
 export class SessionManager {
   private sessions: Map<string, ManagedSession> = new Map();
+  private indexer?: SessionIndexer;
+  private search?: SessionSearch;
 
-  constructor(private store: SessionStore) {}
+  constructor(private store: SessionStore, historyIndexConfig?: {
+    enabled: boolean;
+    maxKeywords: number;
+    searchLimit: number;
+    minScore: number;
+  }) {
+    if (historyIndexConfig?.enabled) {
+      this.indexer = new SessionIndexer({
+        maxKeywords: historyIndexConfig.maxKeywords,
+      });
+      this.search = new SessionSearch(store, {
+        limit: historyIndexConfig.searchLimit,
+        minScore: historyIndexConfig.minScore,
+      });
+    }
+  }
 
   private makeSessionId(frontend: string, userId: string): string {
     return `${frontend}:${userId}`;
@@ -96,9 +120,9 @@ export class SessionManager {
     let session = this.sessions.get(id);
     if (!session) {
       const history = this.store.getMessages(id);
-      session = new ManagedSession(id, this.store, history);
+      session = new ManagedSession(id, this.store, history, this.indexer);
       this.sessions.set(id, session);
-      
+
       auditLogger?.sessionCreate({
         session_id: id,
         frontend,
@@ -125,7 +149,7 @@ export class SessionManager {
     for (const message of history) {
       toSession.addMessage(message);
     }
-    
+
     auditLogger?.sessionTransfer(fromSession.id, toSession.id, history.length);
   }
 
@@ -162,4 +186,24 @@ export class SessionManager {
     const session = this.getSession(frontend, userId);
     session.deleteConfig(key);
   }
+
+  searchHistory(query: string, opts?: { limit?: number; sessionId?: string }): HistorySearchResult[] {
+    if (!this.search) {
+      return [];
+    }
+    return this.search.search(query, opts);
+  }
+
+  reindexHistory(): number {
+    if (!this.indexer) {
+      return 0;
+    }
+
+    const rows = this.store.getAllMessagesWithMetadata();
+    for (const row of rows) {
+      const metadata = this.indexer.indexText(row.content);
+      this.store.updateMessageMetadata(row.id, metadata);
+    }
+    return rows.length;
+  }
 }