feat: implement model persistence with per-session overrides

- Add session_config SQLite table for per-session settings
- Update routing to support session override → agent config → global default resolution chain
- Upgrade WebChat SessionBridge from NativeAgent to AgentOrchestrator
- Add /model, /local, /cloud commands to Telegram adapter
- Add /model command to WebChat gateway handlers
- Clear session overrides on /reset command
- Pass memoryStore and config through to SessionBridge
- Add comprehensive tests for all new functionality

Fixes model persistence bug where TUI model changes didn't affect WebChat/Telegram sessions. Now:
- TUI /model sets global default (persists across restarts, affects all new sessions)
- WebChat/Telegram /model sets session override (only that conversation, cleared on /reset)
- WebChat sessions gain AgentOrchestrator features (delegation, compaction, memory)

src/session/manager.ts

@@ -8,6 +8,9 @@ export interface Session {
   getHistory(): Message[];
   clear(): void;
   replaceHistory(messages: Message[]): void;
+  getConfig(key: string): string | undefined;
+  setConfig(key: string, value: string): void;
+  deleteConfig(key: string): void;
 }
 
 export class ManagedSession implements Session {
@@ -64,6 +67,18 @@ export class ManagedSession implements Session {
   setHistory(messages: Message[]): void {
     this.history = [...messages];
   }
+
+  getConfig(key: string): string | undefined {
+    return this.store.getSessionConfig(this.id, key);
+  }
+
+  setConfig(key: string, value: string): void {
+    this.store.setSessionConfig(this.id, key, value);
+  }
+
+  deleteConfig(key: string): void {
+    this.store.deleteSessionConfig(this.id, key);
+  }
 }
 
 export class SessionManager {
@@ -129,4 +144,22 @@ export class SessionManager {
       this.sessions.delete(id);
     }
   }
+
+  /** Get a session config value. */
+  getSessionConfig(frontend: string, userId: string, key: string): string | undefined {
+    const session = this.getSession(frontend, userId);
+    return session.getConfig(key);
+  }
+
+  /** Set a session config value. */
+  setSessionConfig(frontend: string, userId: string, key: string, value: string): void {
+    const session = this.getSession(frontend, userId);
+    session.setConfig(key, value);
+  }
+
+  /** Delete a session config value. */
+  deleteSessionConfig(frontend: string, userId: string, key: string): void {
+    const session = this.getSession(frontend, userId);
+    session.deleteConfig(key);
+  }
 }

src/session/store.ts

@@ -36,6 +36,13 @@ export class SessionStore {
         code_used TEXT NOT NULL,
         PRIMARY KEY (channel, sender_id)
       );
+      CREATE TABLE IF NOT EXISTS session_config (
+        session_id TEXT NOT NULL,
+        key TEXT NOT NULL,
+        value TEXT NOT NULL,
+        PRIMARY KEY (session_id, key)
+      );
+      CREATE INDEX IF NOT EXISTS idx_session_config_session ON session_config(session_id);
     `);
   }
 
@@ -78,8 +85,11 @@ export class SessionStore {
   }
 
   clearSession(sessionId: string): void {
-    const stmt = this.db.prepare('DELETE FROM messages WHERE session_id = ?');
-    stmt.run(sessionId);
+    const transaction = this.db.transaction(() => {
+      this.db.prepare('DELETE FROM messages WHERE session_id = ?').run(sessionId);
+      this.db.prepare('DELETE FROM session_config WHERE session_id = ?').run(sessionId);
+    });
+    transaction();
   }
 
   listSessions(): string[] {
@@ -98,10 +108,12 @@ export class SessionStore {
 
     if (stale.length === 0) {return [];}
 
-    const deleteStmt = this.db.prepare('DELETE FROM messages WHERE session_id = ?');
+    const deleteMessages = this.db.prepare('DELETE FROM messages WHERE session_id = ?');
+    const deleteConfig = this.db.prepare('DELETE FROM session_config WHERE session_id = ?');
     const transaction = this.db.transaction(() => {
       for (const { session_id } of stale) {
-        deleteStmt.run(session_id);
+        deleteMessages.run(session_id);
+        deleteConfig.run(session_id);
       }
     });
     transaction();
@@ -136,6 +148,49 @@ export class SessionStore {
     };
   }
 
+  /** Get a single config value for a session. */
+  getSessionConfig(sessionId: string, key: string): string | undefined {
+    const stmt = this.db.prepare(
+      'SELECT value FROM session_config WHERE session_id = ? AND key = ?',
+    );
+    const row = stmt.get(sessionId, key) as { value: string } | undefined;
+    return row?.value;
+  }
+
+  /** Get all config values for a session. */
+  getAllSessionConfig(sessionId: string): Record<string, string> {
+    const stmt = this.db.prepare(
+      'SELECT key, value FROM session_config WHERE session_id = ?',
+    );
+    const rows = stmt.all(sessionId) as Array<{ key: string; value: string }>;
+    const result: Record<string, string> = {};
+    for (const row of rows) {
+      result[row.key] = row.value;
+    }
+    return result;
+  }
+
+  /** Set a config value for a session. Upserts (INSERT OR REPLACE). */
+  setSessionConfig(sessionId: string, key: string, value: string): void {
+    this.db.prepare(
+      'INSERT OR REPLACE INTO session_config (session_id, key, value) VALUES (?, ?, ?)',
+    ).run(sessionId, key, value);
+  }
+
+  /** Delete a config value for a session. */
+  deleteSessionConfig(sessionId: string, key: string): void {
+    this.db.prepare(
+      'DELETE FROM session_config WHERE session_id = ? AND key = ?',
+    ).run(sessionId, key);
+  }
+
+  /** Delete all config for a session (used when session is cleared/pruned). */
+  clearSessionConfig(sessionId: string): void {
+    this.db.prepare(
+      'DELETE FROM session_config WHERE session_id = ?',
+    ).run(sessionId);
+  }
+
   close(): void {
     this.db.close();
   }