fix(providers): size prompt-cache gate on the larger of payload.system and request prompt

Gate on max(final payload.system, request.systemPrompt) so caching fires both
when the no-messages path blanks payload.system (size via the request prompt)
and when prompt-based structured output appends a large schema to payload.system
(size via the final system string). Add a test for the schema-appended case.

Caught by Cursor Bugbot.

Author: waleedlatif1

apps/sim/providers/anthropic/utils.test.ts

@@ -56,6 +56,17 @@ describe('applyAnthropicPromptCache', () => {
     expect(tools[0].cache_control).toEqual({ type: 'ephemeral' })
   })
 
+  it('caches when payload.system is large from appended schema text even if the request prompt is small', () => {
+    // Prompt-based structured output appends a large schema to payload.system,
+    // so the cacheable system block is large even though request.systemPrompt is small.
+    const payload: { system?: string | TextBlockParam[] } = { system: LARGE }
+
+    applyAnthropicPromptCache(payload, undefined, SMALL)
+
+    expect(Array.isArray(payload.system)).toBe(true)
+    expect((payload.system as TextBlockParam[])[0].cache_control).toEqual({ type: 'ephemeral' })
+  })
+
   it('leaves a small, tool-less prefix untouched (no write surcharge on one-shot calls)', () => {
     const payload: { system?: string | TextBlockParam[] } = { system: SMALL }
 

apps/sim/providers/anthropic/utils.ts

@@ -34,17 +34,25 @@ export function applyAnthropicPromptCache(
   tools: Tool[] | undefined,
   systemPrompt: string | null | undefined
 ): void {
+  const payloadSystem = typeof payload.system === 'string' ? payload.system : ''
+
+  // Size the gate on the LARGER of the final payload.system (which may include
+  // appended structured-output schema text) and the original request prompt
+  // (non-empty even when the no-messages path relocates it out of payload.system).
+  const gateSystem =
+    payloadSystem.length >= (systemPrompt?.length ?? 0) ? payloadSystem : systemPrompt
+
   const shouldCache = shouldCacheStaticPrefix({
-    systemPrompt,
+    systemPrompt: gateSystem,
     hasTools: !!tools?.length,
     toolsApproxChars: tools ? JSON.stringify(tools).length : 0,
   })
   if (!shouldCache) {
     return
   }
 
-  if (typeof payload.system === 'string' && payload.system.length > 0) {
-    payload.system = [{ type: 'text', text: payload.system, cache_control: { type: 'ephemeral' } }]
+  if (payloadSystem.length > 0) {
+    payload.system = [{ type: 'text', text: payloadSystem, cache_control: { type: 'ephemeral' } }]
   }
 
   if (tools?.length) {