Update filesystem-cache.ts

Proposed fix from coderabbitai

Author: tcely

src/filesystem-cache.ts

@@ -8,10 +8,16 @@ import {
   mkdirSync,
 } from "node:fs";
 import { createHash } from "node:crypto";
+import { debug } from "@actions/core";
 
 const CACHE_DIR = process.env.RUNNER_TEMP || tmpdir();
 const FS_CACHE_TIMEOUT = 1000 * 60 * 60 * 12; // hours
 
+function cacheDebug(operation: string, key: string, error: unknown): void {
+  const message = error instanceof Error ? error.message : String(error);
+  debug(`filesystem-cache: ${operation} failed for key "${key}": ${message}`);
+}
+
 function getCachePath(key: string): string {
   const hash = createHash("sha1").update(key).digest("hex");
   return join(CACHE_DIR, `setup-bun-${hash}.json`);
@@ -29,8 +35,8 @@ export function getCache(key: string): string | null {
         return readFileSync(path, "utf8");
       }
     }
-  } catch {
-    // Fail silently; a cache miss is better than a crash
+  } catch (error) {
+    cacheDebug("getCache", key, error);
   }
   return null;
 }
@@ -45,7 +51,7 @@ export function setCache(key: string, value: string): void {
       mkdirSync(CACHE_DIR, { recursive: true });
     }
     writeFileSync(path, value, "utf8");
-  } catch {
-    // Fail silently
+  } catch (error) {
+    cacheDebug("setCache", key, error);
   }
 }