From 467736a1b4d8a57da1476195d6568bfcc0a46ac1 Mon Sep 17 00:00:00 2001
From: Jan Leon <Jan.gaschler@gmail.com>
Date: Tue, 30 Jun 2026 02:56:23 +0200
Subject: [PATCH] chore(dead-code): remove unused prompt cache control helper
 (#5466)

---
 src/lib/promptCache/index.ts                  |  2 +-
 src/lib/promptCache/prefixAnalyzer.ts         |  4 ---
 .../unit/prompt-cache-prefix-analyzer.test.ts | 30 +++++++++++++++++++
 3 files changed, 31 insertions(+), 5 deletions(-)
 create mode 100644 tests/unit/prompt-cache-prefix-analyzer.test.ts

diff --git a/src/lib/promptCache/index.ts b/src/lib/promptCache/index.ts
index 2d1446f864..4fa4e6a03f 100644
--- a/src/lib/promptCache/index.ts
+++ b/src/lib/promptCache/index.ts
@@ -1 +1 @@
-export { analyzePrefix, shouldInjectCacheControl, generatePromptCacheKey } from "./prefixAnalyzer";
+export { analyzePrefix, generatePromptCacheKey } from "./prefixAnalyzer";
diff --git a/src/lib/promptCache/prefixAnalyzer.ts b/src/lib/promptCache/prefixAnalyzer.ts
index 6f8e86e12e..b3aef53680 100644
--- a/src/lib/promptCache/prefixAnalyzer.ts
+++ b/src/lib/promptCache/prefixAnalyzer.ts
@@ -72,10 +72,6 @@ export function analyzePrefix(messages: Message[]): PrefixAnalysis {
   };
 }
 
-export function shouldInjectCacheControl(analysis: PrefixAnalysis, minTokens = 1024): boolean {
-  return analysis.prefixTokens >= minTokens && analysis.confidence >= 0.7;
-}
-
 export function generatePromptCacheKey(messages: Message[]): string {
   const analysis = analyzePrefix(messages);
   if (analysis.prefixHash) {
diff --git a/tests/unit/prompt-cache-prefix-analyzer.test.ts b/tests/unit/prompt-cache-prefix-analyzer.test.ts
new file mode 100644
index 0000000000..2e5978e7ef
--- /dev/null
+++ b/tests/unit/prompt-cache-prefix-analyzer.test.ts
@@ -0,0 +1,30 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+
+import { analyzePrefix, generatePromptCacheKey } from "../../src/lib/promptCache";
+
+describe("prompt cache prefix analyzer", () => {
+  it("captures stable system prefixes and derives a cache key", () => {
+    const messages = [
+      { role: "system", content: "You are helpful." },
+      { role: "user", content: "Hello" },
+    ];
+
+    const analysis = analyzePrefix(messages);
+
+    assert.equal(analysis.prefixEndIdx, 0);
+    assert.equal(analysis.prefixType, "system_only");
+    assert.equal(analysis.confidence, 0.9);
+    assert.ok(analysis.prefixTokens > 0);
+    assert.match(generatePromptCacheKey(messages), /^omni-[a-f0-9]{32}$/);
+  });
+
+  it("keeps the legacy empty-content key when there is no prefix", () => {
+    const messages = [{ role: "user", content: "Hello" }];
+
+    const analysis = analyzePrefix(messages);
+
+    assert.equal(analysis.prefixEndIdx, -1);
+    assert.equal(generatePromptCacheKey(messages), "omni-e3b0c44298fc1c149afbf4c8996fb924");
+  });
+});