cache group chat fixed context usage (#925)

tests/server/group-chat-context-cache.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, it } from 'vitest'
+import { countTokens } from '../../packages/server/src/lib/context-compressor'
+import {
+  estimateGroupHistoryMessageTokens,
+  groupContextTokensWithFixedOverhead,
+} from '../../packages/server/src/services/hermes/group-chat/agent-clients'
+
+describe('group chat fixed context cache helpers', () => {
+  it('adds cached fixed context to group chat message tokens', () => {
+    const history = [
+      { role: 'user', content: '[Alice]: hello' },
+      { role: 'assistant', content: '[Bot]: hi there' },
+    ]
+
+    const messageTokens = estimateGroupHistoryMessageTokens(history)
+
+    expect(messageTokens).toBe(countTokens('[Alice]: hello') + countTokens('[Bot]: hi there'))
+    expect(groupContextTokensWithFixedOverhead(20_000, history)).toBe(20_000 + messageTokens)
+  })
+
+  it('signals fallback when fixed context is unavailable', () => {
+    expect(groupContextTokensWithFixedOverhead(undefined, [{ content: 'hello' }])).toBeUndefined()
+    expect(groupContextTokensWithFixedOverhead(null, [{ content: 'hello' }])).toBeUndefined()
+  })
+})