fix(ai): disable OpenCode long cache retention for rejecting routes

closes #5702

packages/ai/test/cache-retention.test.ts

@@ -1,4 +1,5 @@
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { MODELS } from "../src/models.generated.ts";
 import { getModel } from "../src/models.ts";
 import { streamAnthropic } from "../src/providers/anthropic.ts";
 import { streamOpenAICompletions } from "../src/providers/openai-completions.ts";
@@ -13,6 +14,11 @@ class PayloadCaptured extends Error {
 	}
 }
 
+interface OpenAICompletionsCachePayload {
+	prompt_cache_key?: string;
+	prompt_cache_retention?: string;
+}
+
 function stopAfterPayload<TPayload>(capture: (payload: TPayload) => void): (payload: unknown) => never {
 	return (payload: unknown): never => {
 		capture(payload as TPayload);
@@ -455,5 +461,39 @@ describe("Cache Retention (PI_CACHE_RETENTION)", () => {
 			expect(capturedPayload.prompt_cache_key).toBeUndefined();
 			expect(capturedPayload.prompt_cache_retention).toBeUndefined();
 		});
+
+		it.each([
+			MODELS.opencode["deepseek-v4-flash"],
+			MODELS.opencode["deepseek-v4-pro"],
+			MODELS.opencode["kimi-k2.5"],
+			MODELS.opencode["kimi-k2.6"],
+			MODELS.opencode["minimax-m2.7"],
+			MODELS["opencode-go"]["kimi-k2.6"],
+		] as const)("should omit long cache retention for $provider/$id", async (metadata) => {
+			const model = metadata as Model<"openai-completions">;
+			let capturedPayload: OpenAICompletionsCachePayload | undefined;
+
+			try {
+				const s = streamOpenAICompletions(model, context, {
+					apiKey: "fake-key",
+					cacheRetention: "long",
+					sessionId: "session-opencode-long-cache-unsupported",
+					onPayload: stopAfterPayload<OpenAICompletionsCachePayload>((payload) => {
+						capturedPayload = payload;
+					}),
+				});
+
+				for await (const event of s) {
+					if (event.type === "error") break;
+				}
+			} catch {
+				// Expected to fail
+			}
+
+			expect(model.compat?.supportsLongCacheRetention).toBe(false);
+			expect(capturedPayload).toBeDefined();
+			expect(capturedPayload?.prompt_cache_key).toBeUndefined();
+			expect(capturedPayload?.prompt_cache_retention).toBeUndefined();
+		});
 	});
 });