drop tasks, drop thrashing bandaid

src/widget-batcher.ts

@@ -0,0 +1,92 @@
+import type { ExtensionContext } from "@earendil-works/pi-coding-agent";
+
+/**
+ * Batches widget updates from multiple parallel tasks into a single
+ * render cycle, preventing TUI thrashing when agents update independently.
+ *
+ * Uses microtask debouncing: updates within the same event-loop tick
+ * are coalesced into one flush. No artificial interval — updates hit the
+ * screen as soon as the current tick yields, but never duplicatively.
+ */
+export class WidgetBatcher {
+	/** Pending widget updates keyed by widget key. */
+	private pending: Map<string, string[]> = new Map();
+
+	/** Widget keys scheduled for removal. */
+	private pendingRemovals: Set<string> = new Set();
+
+	/** Whether a microtask flush is already queued. */
+	private scheduled = false;
+
+	/** Whether a flush is currently executing (prevents re-entry). */
+	private flushing = false;
+
+	constructor(private ctx: ExtensionContext) {}
+
+	/**
+	 * Schedule a widget update. Flushed asynchronously at end of the
+	 * current event-loop tick; multiple calls in the same tick coalesce.
+	 */
+	schedule(key: string, lines: string[]): void {
+		this.pending.set(key, lines);
+		this.scheduleFlush();
+	}
+
+	/**
+	 * Remove a widget (e.g., when a task completes).
+	 * Flushed asynchronously at end of the current tick.
+	 */
+	scheduleRemove(key: string): void {
+		this.pending.delete(key);
+		this.pendingRemovals.add(key);
+		this.scheduleFlush();
+	}
+
+	/** Synchronously flush all pending updates. */
+	flush(): void {
+		this.doFlush();
+	}
+
+	/** Flush remaining updates then stop scheduling. */
+	stop(): void {
+		this.doFlush();
+	}
+
+	// ── Internal ────────────────────────────────────────────────────────
+
+	private scheduleFlush(): void {
+		if (this.scheduled) return;
+		this.scheduled = true;
+		queueMicrotask(() => {
+			this.scheduled = false;
+			this.doFlush();
+		});
+	}
+
+	private doFlush(): void {
+		if (this.flushing) return;
+		this.flushing = true;
+
+		// Atomically swap — new schedule()/scheduleRemove() calls land on fresh
+		// collections, so the batch we iterate stays immutable and nothing is lost.
+		const toRender = this.pending;
+		const toRemove = this.pendingRemovals;
+		this.pending = new Map();
+		this.pendingRemovals = new Set();
+
+		// Apply removals first
+		for (const key of toRemove) {
+			this.ctx.ui.setWidget(key, undefined);
+		}
+
+		// Sort by key for deterministic, stable ordering across every flush.
+		// Task IDs are zero-padded ("008", "012", "013") so alpha sort = numeric order.
+		const sortedKeys = Array.from(toRender.keys()).sort();
+		for (const key of sortedKeys) {
+			// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+			this.ctx.ui.setWidget(key, toRender.get(key)!);
+		}
+
+		this.flushing = false;
+	}
+}