perf(lsp): completion serves lock-free — never queues behind the cold build

Device logs: completion requests landing during the background rebuild waited
on stateLock (3s+ → sora dropped the popup). completion()/hover() now read the
atomically-published snapshot facade without the lock; mutations keep the lock.
setWorkspaceMetadata also moves its heavy rebuild to the background thread and
bumps the generation so the running/next background build picks up the new
metadata (the attempts-loop re-run already handles that).

Author: dingyi222666

src/jvmMain/kotlin/io/github/dingyi222666/luaparser/lsp/LuaLanguageService.kt

@@ -374,12 +374,23 @@ class LuaLanguageService(
         return result.affectedDocuments
     }
 
-    fun setWorkspaceMetadata(metadata: Map<String, String>): Unit = synchronized(stateLock) {
-        workspaceGeneration += 1
-        workspaceMetadata = metadata.toMap()
-        // Configuration that invalidates global metadata falls back to a full rebuild.
-        rebuildFull()
-        Unit
+    fun setWorkspaceMetadata(metadata: Map<String, String>): Unit {
+        // Store + bump generation under lock, then run the heavy rebuild on the
+        // background thread (scheduleBackgroundRebuild no-ops if one is already
+        // running; its post-build moved-check re-runs with the NEW metadata).
+        // A synchronous rebuild here blocked every completion/hover request for
+        // the whole 13-18s dex+corpus build on device.
+        val changed = synchronized(stateLock) {
+            val moved = workspaceMetadata != metadata.toMap()
+            if (moved) {
+                workspaceGeneration += 1
+                workspaceMetadata = metadata.toMap()
+            }
+            moved
+        }
+        if (changed) {
+            scheduleBackgroundRebuild()
+        }
     }
 
     /**