fix(ai): clamp OpenAI prompt cache keys

closes #4720

packages/ai/src/providers/openai-completions.ts

@@ -36,6 +36,7 @@ import { parseStreamingJson } from "../utils/json-parse.js";
 import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
 import { isCloudflareProvider, resolveCloudflareBaseUrl } from "./cloudflare.js";
 import { buildCopilotDynamicHeaders, hasCopilotVisionInput } from "./github-copilot-headers.js";
+import { clampOpenAIPromptCacheKey } from "./openai-prompt-cache.js";
 import { buildBaseOptions } from "./simple-options.js";
 import { transformMessages } from "./transform-messages.js";
 
@@ -516,7 +517,7 @@ function buildParams(
 		prompt_cache_key:
 			(model.baseUrl.includes("api.openai.com") && cacheRetention !== "none") ||
 			(cacheRetention === "long" && compat.supportsLongCacheRetention)
-				? options?.sessionId
+				? clampOpenAIPromptCacheKey(options?.sessionId)
 				: undefined,
 		prompt_cache_retention: cacheRetention === "long" && compat.supportsLongCacheRetention ? "24h" : undefined,
 	};