Shut down dynamic store watching after headless commands

The chokidar watchers and syncer poll timer kept the node event loop
alive forever after commands like --render and --build when a dynamic
store was configured. Add a startup module to the filesystem plugin
that runs after the commander completes: if no server was started
(detected via th-server-command-post-start), it closes the watchers,
stops advertising getUpdatedTiddlers so the syncer schedules no more
polls, and drains any pending sync tasks so saves still flush before
the process exits naturally.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

plugins/tiddlywiki/filesystem/teardown.js

@@ -0,0 +1,48 @@
+/*\
+title: $:/plugins/tiddlywiki/filesystem/teardown.js
+type: application/javascript
+module-type: startup
+
+Shut down dynamic store watching and syncer polling once all CLI commands
+have completed, unless a server was started. Otherwise the chokidar watchers
+and the syncer poll timer keep the node event loop alive forever after
+headless commands like --render and --build.
+
+\*/
+
+"use strict";
+
+exports.name = "filesystem-teardown";
+exports.platforms = ["node"];
+exports.after = ["commands"];
+exports.synchronous = true;
+
+var serverStarted = false;
+
+if($tw.node) {
+	$tw.hooks.addHook("th-server-command-post-start",function() {
+		serverStarted = true;
+	});
+}
+
+exports.startup = function() {
+	var adaptor = $tw.syncadaptor;
+	if(serverStarted || !adaptor || adaptor.name !== "filesystem") {
+		return;
+	}
+	// Stop advertising poll support so the syncer doesn't reschedule
+	adaptor.getUpdatedTiddlers = undefined;
+	if(typeof adaptor.close === "function") {
+		adaptor.close();
+	}
+	// Kick the syncer: a pending poll timer may be up to pollTimerInterval
+	// away. Clearing it and processing the queue directly drains any pending
+	// save tasks; with polling disabled, nothing is rescheduled afterwards.
+	if($tw.syncer) {
+		if($tw.syncer.taskTimerId) {
+			clearTimeout($tw.syncer.taskTimerId);
+			$tw.syncer.taskTimerId = null;
+		}
+		$tw.syncer.processTaskQueue();
+	}
+};