接续L4-TOOL-DB浏览器Provider协议

结论：浏览器 Worker 已支持可插拔 Python runtime provider 的 line I/O，缺真实 Python/WASM runtime 时仍保持阻塞不解锁。

wasm-port/runtime/sdk/README.md

@@ -577,7 +577,9 @@ private module paths:
   boundary. The bundled worker reports
   `blocked_browser_python_wasm_runtime_missing` until a real Python/WASM runtime
   is installed; the Worker shell alone must not mark `DB_PROGRAM` execution
-  ready.
+  ready. The Worker supports a provider protocol (`start`, `writeLine`,
+  `readLine`, `close`) so a future Python/WASM runtime can provide line-based
+  `DB_PROGRAM` I/O without changing `ToolDbProcessPort`.
 - `createLinuxCncToolDbNodeRuntimeAdapter()` in
   `runtime/sdk/src/tool-db-node-runtime-adapter.js` for Node/native verification
   of the real LinuxCNC `DB_PROGRAM` child process. This adapter is intentionally

wasm-port/runtime/sdk/src/tool-db-browser-worker-adapter.js

@@ -96,7 +96,14 @@ export function createLinuxCncToolDbBrowserWorkerAdapter({
       return result.line;
     },
 
-    close() {
+    async close() {
+      if (worker) {
+        try {
+          await request("close");
+        } catch {
+          // The worker may be blocked or already gone; termination below is authoritative.
+        }
+      }
       rejectPending(new Error("Tool DB browser worker closed."));
       worker?.terminate();
       worker = null;