feat: add token usage tracking, context display, and dynamic context length (#132)

* fix: specify TS_NODE_PROJECT for dev:server script

ts-node/register resolves tsconfig from the entry file upward,
finding the root solution-style tsconfig.json (no compilerOptions).
This causes target to default to ES3, breaking MapIterator spread
syntax (TS2802). Set TS_NODE_PROJECT env var to point to the server
tsconfig which targets ES2024.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add token usage tracking, context display, and dynamic context length

- Intercept SSE proxy to capture run.completed events and persist token
  usage (input_tokens, output_tokens) per session to SQLite/JSON store
- Display context usage bar in ChatInput showing used/total/remaining tokens
- Resolve actual context length from Hermes models_dev_cache.json based
  on the active profile's default model (fallback 200K), with 5min in-memory cache
- Move sessions-db.ts to db/hermes/ for unified database layer
- Add usage store with SQLite + JSON fallback (auto-migration via ensureTable)
- Fix proxy SSE path regex to match rewritten upstream path
- Fix route ordering: /sessions/usage before /sessions/:id to avoid 404
- Fetch per-session usage on session enter instead of batch
- Add unit tests for usage-store, db index, and proxy SSE interception

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/server/src/db/index.ts

@@ -0,0 +1,136 @@
+import { DatabaseSync } from 'node:sqlite'
+import { mkdirSync, readFileSync, writeFileSync, existsSync } from 'fs'
+import { resolve } from 'path'
+import { homedir } from 'os'
+
+const DB_DIR = resolve(homedir(), '.hermes-web-ui')
+const DB_PATH = resolve(DB_DIR, 'hermes-web-ui.db')
+const JSON_PATH = resolve(DB_DIR, 'hermes-web-ui.json')
+
+// --- SQLite availability check ---
+
+const SQLITE_AVAILABLE = (() => {
+  const [major, minor] = process.versions.node.split('.').map(Number)
+  return major > 22 || (major === 22 && minor >= 5)
+})()
+
+export function isSqliteAvailable(): boolean {
+  return SQLITE_AVAILABLE
+}
+
+// --- SQLite backend ---
+
+let _db: DatabaseSync | null = null
+
+export function getDb(): DatabaseSync | null {
+  if (!SQLITE_AVAILABLE) return null
+  if (!_db) {
+    mkdirSync(DB_DIR, { recursive: true })
+    _db = new DatabaseSync(DB_PATH)
+    _db.exec('PRAGMA journal_mode=WAL')
+    _db.exec('PRAGMA foreign_keys=ON')
+  }
+  return _db
+}
+
+/**
+ * Ensure a table's schema matches the expected definition.
+ * - Creates the table if it does not exist
+ * - Adds missing columns (ALTER TABLE ADD COLUMN)
+ * - Drops extra columns (ALTER TABLE DROP COLUMN, SQLite 3.35+)
+ *
+ * No-op when SQLite is not available.
+ */
+export function ensureTable(tableName: string, schema: Record<string, string>): void {
+  const db = getDb()
+  if (!db) return
+
+  const colDefs = Object.entries(schema)
+    .map(([col, def]) => `"${col}" ${def}`)
+    .join(', ')
+
+  db.exec(`CREATE TABLE IF NOT EXISTS "${tableName}" (${colDefs})`)
+
+  const rows = db.prepare(`PRAGMA table_info("${tableName}")`).all() as Array<{ name: string }>
+  const existingCols = new Set(rows.map(r => r.name))
+  const expectedCols = new Set(Object.keys(schema))
+
+  for (const col of expectedCols) {
+    if (!existingCols.has(col)) {
+      db.exec(`ALTER TABLE "${tableName}" ADD COLUMN "${col}" ${schema[col]}`)
+    }
+  }
+
+  for (const col of existingCols) {
+    if (!expectedCols.has(col)) {
+      db.exec(`ALTER TABLE "${tableName}" DROP COLUMN "${col}"`)
+    }
+  }
+}
+
+// --- JSON fallback backend ---
+
+type JsonData = Record<string, Record<string, Record<string, any>>>
+
+function readJsonStore(): JsonData {
+  if (!existsSync(JSON_PATH)) return {}
+  try {
+    return JSON.parse(readFileSync(JSON_PATH, 'utf-8'))
+  } catch {
+    return {}
+  }
+}
+
+function writeJsonStore(data: JsonData): void {
+  mkdirSync(DB_DIR, { recursive: true })
+  writeFileSync(JSON_PATH, JSON.stringify(data, null, 2), 'utf-8')
+}
+
+/**
+ * Get a record from the JSON store.
+ * @param table  Table name (namespace)
+ * @param key    Primary key
+ */
+export function jsonGet(table: string, key: string): Record<string, any> | undefined {
+  const data = readJsonStore()
+  return data[table]?.[key]
+}
+
+/**
+ * Set a record in the JSON store.
+ * @param table  Table name (namespace)
+ * @param key    Primary key
+ * @param value  Record data
+ */
+export function jsonSet(table: string, key: string, value: Record<string, any>): void {
+  const data = readJsonStore()
+  if (!data[table]) data[table] = {}
+  data[table][key] = value
+  writeJsonStore(data)
+}
+
+/**
+ * Get all records from a table in the JSON store.
+ */
+export function jsonGetAll(table: string): Record<string, Record<string, any>> {
+  const data = readJsonStore()
+  return data[table] || {}
+}
+
+/**
+ * Delete a record from the JSON store.
+ */
+export function jsonDelete(table: string, key: string): void {
+  const data = readJsonStore()
+  if (data[table]) {
+    delete data[table][key]
+    writeJsonStore(data)
+  }
+}
+
+/**
+ * Get the storage path for debugging.
+ */
+export function getStoragePath(): string {
+  return SQLITE_AVAILABLE ? DB_PATH : JSON_PATH
+}