fix(token-meter): reject stale config (round 2)

packages/llm/token-meter/README.md

@@ -8,7 +8,7 @@ Replay-aware token measurement through the singleton `ctx.tokenMeter` service. I
 |---|---:|---|
 | `contextWindow` | `128000` | Positive integer service-wide context capacity. |
 
-The estimator intentionally uses one fixed heuristic: four characters per token plus structural overhead for roles, blocks, and request-envelope fields. `contextWindow` is the only deployment setting. Direct construction validates it; Loader mounts first apply the package's Schemastery shape validation.
+The estimator intentionally uses one fixed heuristic: four characters per token plus structural overhead for roles, blocks, and request-envelope fields. `contextWindow` is the only deployment setting. Direct construction validates it; Loader mounts first apply the package's Schemastery shape validation. Unrecognized top-level keys are rejected.
 
 ## Measurement contract
 

packages/llm/token-meter/src/index.ts

@@ -23,6 +23,9 @@ export type * from './types.ts'
 /** Default service-wide provider context capacity. */
 const DEFAULT_CONTEXT_WINDOW = 128_000
 
+/** Complete public configuration key set. */
+const TOKEN_METER_CONFIG_KEYS: ReadonlySet<string> = new Set(['contextWindow'])
+
 /** Fixed text-density estimate used until exact tokenization is needed. */
 const CHARS_PER_TOKEN = 4
 
@@ -69,8 +72,20 @@ function optionalHeaderEquals(
   return headerEquals(left, right)
 }
 
+/** Reject stale or misspelled keys before defaults can hide them. */
+function validateConfigKeys(config: TokenMeterConfig): void {
+  for (const key of Object.keys(config)) {
+    if (!TOKEN_METER_CONFIG_KEYS.has(key)) {
+      throw new Error(
+        `TokenMeterConfig: unknown key "${key}" (allowed: contextWindow)`,
+      )
+    }
+  }
+}
+
 /** Resolve and validate the one service-wide context capacity. */
 function resolveContextWindow(config: TokenMeterConfig): number {
+  validateConfigKeys(config)
   const contextWindow = config.contextWindow === undefined
     ? DEFAULT_CONTEXT_WINDOW
     : config.contextWindow

packages/llm/token-meter/tests/token-meter.spec.ts

@@ -81,6 +81,11 @@ describe('TokenMeterService configuration and registration', () => {
     expect(meter({ contextWindow: 32_000 }).contextWindow).toBe(32_000)
   })
 
+  it.each(['models', 'contextWidow'])('rejects unknown top-level config key %s', (key) => {
+    expect(() => meter({ [key]: {} }))
+      .toThrow(`TokenMeterConfig: unknown key "${key}"`)
+  })
+
   it.each([
     { contextWindow: 0 },
     { contextWindow: -1 },