feat: Move parsing to worker threads for smooth progress animation

Offloads tree-sitter parsing to a dedicated worker thread, keeping the main thread unblocked so shimmer progress animations render smoothly during indexing. Refactors shimmer progress renderer into separate worker for consistent 50ms animation updates. Falls back to in-process parsing when worker compilation unavailable (e.g., tests).

src/ui/shimmer-worker.ts

@@ -0,0 +1,107 @@
+import { parentPort, workerData } from 'worker_threads';
+import type { ShimmerWorkerMessage } from './types';
+
+const SPINNER_GLYPHS = ['·', '✢', '✳', '✶', '✻', '✽'];
+const ANIM_INTERVAL = 150;
+const FRAMES_PER_GLYPH = 3;
+
+const RST = '\x1b[0m';
+const DM = '\x1b[2m';
+const GRN = '\x1b[32m';
+const BOLD = '\x1b[1m';
+
+const startTime: number = workerData.startTime;
+
+function animFrame(): number {
+  return Math.floor((Date.now() - startTime) / ANIM_INTERVAL);
+}
+
+function lerp(a: number, b: number, t: number): number {
+  return Math.round(a + (b - a) * t);
+}
+
+function shimmerColor(frame: number): string {
+  const t = (Math.sin(frame * 2 * Math.PI / 13) + 1) / 2;
+  const r = lerp(160, 251, t);
+  const g = lerp(100, 191, t);
+  const b = lerp(9, 36, t);
+  return `\x1b[38;2;${r};${g};${b}m${BOLD}`;
+}
+
+function formatNumber(n: number): string {
+  return n.toLocaleString();
+}
+
+function renderBar(frame: number, filled: number, empty: number): string {
+  if (filled === 0) return `${DM}${'░'.repeat(empty)}${RST}`;
+  const cycleFrames = 24;
+  const shimmerPos = ((frame % cycleFrames) / cycleFrames) * (filled + 6) - 3;
+  const shimmerWidth = 3;
+  let bar = '';
+  for (let i = 0; i < filled; i++) {
+    const dist = Math.abs(i - shimmerPos);
+    const t = Math.max(0, 1 - dist / shimmerWidth);
+    const r = lerp(160, 251, t);
+    const g = lerp(100, 191, t);
+    const b = lerp(9, 36, t);
+    bar += `\x1b[38;2;${r};${g};${b}m${BOLD}█`;
+  }
+  bar += `${RST}${DM}${'░'.repeat(empty)}${RST}`;
+  return bar;
+}
+
+// Mutable state
+let currentMessage = '';
+let currentPercent = -1;
+let currentCount = 0;
+
+function render(): void {
+  if (!currentMessage) return;
+  const frame = animFrame();
+  const glyphIdx = Math.floor(frame / FRAMES_PER_GLYPH) % SPINNER_GLYPHS.length;
+  const glyph = SPINNER_GLYPHS[glyphIdx] ?? '·';
+  const color = shimmerColor(frame);
+
+  let line: string;
+  if (currentPercent >= 0) {
+    const barWidth = 25;
+    const filled = Math.round(barWidth * currentPercent / 100);
+    const empty = barWidth - filled;
+    line = `${DM}│${RST}  ${color}${glyph}${RST} ${currentMessage}  ${renderBar(frame, filled, empty)}  ${currentPercent}%`;
+  } else if (currentCount > 0) {
+    line = `${DM}│${RST}  ${color}${glyph}${RST} ${currentMessage}... ${formatNumber(currentCount)} found`;
+  } else {
+    line = `${DM}│${RST}  ${color}${glyph}${RST} ${currentMessage}...`;
+  }
+
+  process.stdout.write(`\r\x1b[K${line}`);
+}
+
+function finishPhase(): void {
+  if (!currentMessage) return;
+  process.stdout.write(`\r\x1b[K`);
+  let detail = '';
+  if (currentPercent >= 0) detail = ' — done';
+  else if (currentCount > 0) detail = ` — ${formatNumber(currentCount)} found`;
+  process.stdout.write(`${DM}│${RST}  ${GRN}◆${RST} ${currentMessage}${detail}\n`);
+  currentMessage = '';
+  currentPercent = -1;
+  currentCount = 0;
+}
+
+// Render loop — independent of main thread
+const tickInterval = setInterval(render, 50);
+
+parentPort!.on('message', (msg: ShimmerWorkerMessage) => {
+  if (msg.type === 'update') {
+    currentMessage = msg.phaseName;
+    currentPercent = msg.percent;
+    currentCount = msg.count;
+  } else if (msg.type === 'finish-phase') {
+    finishPhase();
+  } else if (msg.type === 'stop') {
+    clearInterval(tickInterval);
+    finishPhase();
+    parentPort!.postMessage({ type: 'stopped' });
+  }
+});