refactor(backend): downgrade lock (#8135)

* refactor(updater): drop write-only pending_* slots

* refactor(notify): fold sequence counter into entries lock

* refactor(port): fold startup-core-blocked flag into reason slot

* refactor(service): drop redundant provider sync serial lock

* refactor(port): store startup block reason in a OnceLock

* refactor(core): replace macOS network monitor slot with armed latch

src-tauri/src/core/service.rs

@@ -1045,7 +1045,8 @@ fn decode_hex(encoded: &str) -> Result<Vec<u8>> {
 }
 
 static PROVIDER_SYNC_QUEUED: AtomicBool = AtomicBool::new(false);
-static PROVIDER_SYNC_SERIAL: Lazy<tokio::sync::Mutex<()>> = Lazy::new(|| tokio::sync::Mutex::new(()));
+// Serializing the whole read-and-publish pass prevents an older cache from replacing a newer one.
+static PROVIDER_SYNC_SERIAL: tokio::sync::Mutex<()> = tokio::sync::Mutex::const_new(());
 static SYNC_TEMP_SEQUENCE: AtomicU64 = AtomicU64::new(0);
 const RUNTIME_PROVIDER_SYNC_ATTEMPTS: u32 = 4;
 const CONTENT_COMPARE_CHUNK: usize = 64 * 1024;