feat(gateway): add system.sessionAnalytics usage snapshot RPC

src/session/index.ts

@@ -1,4 +1,5 @@
 export { SessionStore, parseDuration } from './store.js';
+export type { SessionAnalyticsSnapshot, SessionDailyAnalyticsRow, SessionTopAnalyticsRow } from './store.js';
 export { SessionManager, ManagedSession, type Session } from './manager.js';
 export { SessionIndexer, tokenize } from './indexer.js';
 export type { HistoryMetadata, HistoryIndexerConfig } from './indexer.js';

src/session/manager.ts

@@ -1,5 +1,6 @@
 import type { Message } from '../models/types.js';
 import type { SessionStore } from './store.js';
+import type { SessionAnalyticsSnapshot } from './store.js';
 import { auditLogger } from '../audit/index.js';
 import { SessionIndexer } from './indexer.js';
 import { SessionSearch, type HistorySearchResult } from './search.js';
@@ -206,4 +207,14 @@ export class SessionManager {
     }
     return rows.length;
   }
+
+  getSessionAnalytics(opts?: { days?: number; topLimit?: number; nowMs?: number }): SessionAnalyticsSnapshot {
+    const nowMs = opts?.nowMs ?? Date.now();
+    const days = opts?.days ?? 30;
+    const sinceTimestamp = Math.floor((nowMs - (days * 86_400_000)) / 1000);
+    return this.store.getSessionAnalytics({
+      sinceTimestamp,
+      topLimit: opts?.topLimit ?? 10,
+    });
+  }
 }

src/session/store.test.ts

@@ -74,6 +74,29 @@ describe('SessionStore', () => {
     expect(sessions).toContain('session-b');
   });
 
+  it('computes session analytics snapshot', () => {
+    const nowMs = Date.parse('2026-02-16T12:00:00.000Z');
+    const nowSec = Math.floor(nowMs / 1000);
+    const yesterdaySec = nowSec - 86_400;
+
+    store.addMessage('session-a', { role: 'user', content: 'A1', timestamp: nowMs });
+    store.addMessage('session-a', { role: 'assistant', content: 'A2', timestamp: nowMs + 1000 });
+    store.addMessage('session-b', { role: 'user', content: 'B1', timestamp: nowMs });
+    store.addMessage('session-c', { role: 'user', content: 'C1', timestamp: yesterdaySec * 1000 });
+
+    const snapshot = store.getSessionAnalytics({
+      sinceTimestamp: yesterdaySec,
+      topLimit: 2,
+    });
+
+    expect(snapshot.totalSessions).toBe(3);
+    expect(snapshot.totalMessages).toBe(4);
+    expect(snapshot.averageMessagesPerSession).toBeCloseTo(1.33, 2);
+    expect(snapshot.topSessions).toHaveLength(2);
+    expect(snapshot.topSessions[0]?.sessionId).toBe('session-a');
+    expect(snapshot.daily.length).toBeGreaterThan(0);
+  });
+
   it('stores and retrieves message metadata for indexed history', () => {
     const indexer = new SessionIndexer({ maxKeywords: 5 });
     const metadata = indexer.indexText('deploy backend release');

src/session/store.ts

@@ -12,6 +12,26 @@ export function parseDuration(s: string): number | null {
   return unit === 'h' ? Number(n) * 3600_000 : Number(n) * 86_400_000;
 }
 
+export interface SessionDailyAnalyticsRow {
+  day: string;
+  sessions: number;
+  messages: number;
+}
+
+export interface SessionTopAnalyticsRow {
+  sessionId: string;
+  messages: number;
+  lastActivity: number;
+}
+
+export interface SessionAnalyticsSnapshot {
+  daily: SessionDailyAnalyticsRow[];
+  topSessions: SessionTopAnalyticsRow[];
+  averageMessagesPerSession: number;
+  totalSessions: number;
+  totalMessages: number;
+}
+
 export class SessionStore {
   private db: Database.Database;
 
@@ -267,4 +287,66 @@ export class SessionStore {
   updateMessageMetadata(messageId: number, metadata: HistoryMetadata): void {
     this.db.prepare('UPDATE messages SET metadata = ? WHERE id = ?').run(JSON.stringify(metadata), messageId);
   }
+
+  getSessionAnalytics(opts: { sinceTimestamp: number; topLimit?: number }): SessionAnalyticsSnapshot {
+    const since = opts.sinceTimestamp;
+    const topLimit = opts.topLimit ?? 10;
+
+    const dailyRows = this.db.prepare(`
+      SELECT
+        date(created_at, 'unixepoch') AS day,
+        COUNT(DISTINCT session_id) AS sessions,
+        COUNT(*) AS messages
+      FROM messages
+      WHERE created_at >= ?
+      GROUP BY day
+      ORDER BY day DESC
+    `).all(since) as Array<{ day: string; sessions: number; messages: number }>;
+
+    const topRows = this.db.prepare(`
+      SELECT
+        session_id,
+        COUNT(*) AS messages,
+        MAX(created_at) AS last_activity
+      FROM messages
+      WHERE created_at >= ?
+      GROUP BY session_id
+      ORDER BY messages DESC, last_activity DESC
+      LIMIT ?
+    `).all(since, topLimit) as Array<{ session_id: string; messages: number; last_activity: number }>;
+
+    const totalMessagesRow = this.db.prepare(`
+      SELECT COUNT(*) AS total_messages
+      FROM messages
+      WHERE created_at >= ?
+    `).get(since) as { total_messages: number };
+
+    const totalSessionsRow = this.db.prepare(`
+      SELECT COUNT(DISTINCT session_id) AS total_sessions
+      FROM messages
+      WHERE created_at >= ?
+    `).get(since) as { total_sessions: number };
+
+    const totalMessages = totalMessagesRow.total_messages ?? 0;
+    const totalSessions = totalSessionsRow.total_sessions ?? 0;
+    const averageMessagesPerSession = totalSessions > 0
+      ? Math.round((totalMessages / totalSessions) * 100) / 100
+      : 0;
+
+    return {
+      daily: dailyRows.map((row) => ({
+        day: row.day,
+        sessions: row.sessions,
+        messages: row.messages,
+      })),
+      topSessions: topRows.map((row) => ({
+        sessionId: row.session_id,
+        messages: row.messages,
+        lastActivity: row.last_activity,
+      })),
+      averageMessagesPerSession,
+      totalSessions,
+      totalMessages,
+    };
+  }
 }