Fix build: platform_apis, missing AIDL import, private-scope leak

- Android.bp: sdk_version is empty (platform APIs) but platform_apis
  wasn't set, which Soong doesn't just reject cleanly -- it panics.
- PawletCacheService.kt was missing the pawletos.cache.IPawletCacheService
  import (different package than the file's own os.pawlet.cache).
- CacheToken.isExpired called CacheTokenVerifier's private parseIso8601,
  invisible outside that object; moved it to file scope so both can use it.

Android.bp

@@ -23,6 +23,7 @@ android_app {
     // No hidden-API/privileged-permission surface needed — just platform-signed
     // so BgUpd (also platform-signed) can hold the signature-level BIND_RESOLVER
     // permission this app defines.
+    platform_apis: true,
     certificate: "platform",
     system_ext_specific: true,
 

src/os/pawlet/cache/PawletCacheService.kt

@@ -10,6 +10,7 @@ import android.net.Uri
 import android.os.IBinder
 import android.util.Log
 import os.pawlet.cache.discovery.DiscoveredCache
+import pawletos.cache.IPawletCacheService
 import java.util.concurrent.Executors
 import java.util.concurrent.TimeUnit
 import java.util.concurrent.atomic.AtomicReference

src/os/pawlet/cache/trust/CacheToken.kt

@@ -16,6 +16,17 @@ import java.text.SimpleDateFormat
 import java.util.Locale
 import java.util.TimeZone
 
+private fun parseIso8601(value: String): Long? = try {
+    SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", Locale.US).apply {
+        timeZone = TimeZone.getTimeZone("UTC")
+    }.parse(value)?.time
+        ?: SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.US).apply {
+            timeZone = TimeZone.getTimeZone("UTC")
+        }.parse(value)?.time
+} catch (e: Exception) {
+    null
+}
+
 /**
  * A verified, parsed CacheToken — the central authority's attestation that a
  * given TLS public key belongs to a legitimately registered cache server.
@@ -115,15 +126,4 @@ object CacheTokenVerifier {
         }
         return sb.append('}').toString()
     }
-
-    private fun parseIso8601(value: String): Long? = try {
-        SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", Locale.US).apply {
-            timeZone = TimeZone.getTimeZone("UTC")
-        }.parse(value)?.time
-            ?: SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.US).apply {
-                timeZone = TimeZone.getTimeZone("UTC")
-            }.parse(value)?.time
-    } catch (e: Exception) {
-        null
-    }
 }