feat: multi-browser pooling (2 Chromium instances × 8 pages)

- Launch BROWSER_COUNT separate Chromium instances (default: 2)
- Each with PAGES_PER_BROWSER pages (default: 8, 16 total)
- Round-robin distribution across browser instances
- Independent restart scheduling per browser
- Updated health endpoint to show per-browser stats
- docker-compose: added BROWSER_COUNT and PAGES_PER_BROWSER env vars

src/routes/convert.ts

@@ -1,5 +1,5 @@
 import { Router, Request, Response } from "express";
-import { renderPdf, renderUrlPdf } from "../services/browser.js";
+import { renderPdf, renderUrlPdf, getPoolStats } from "../services/browser.js";
 import { markdownToHtml, wrapHtml } from "../services/markdown.js";
 import dns from "node:dns/promises";
 import net from "node:net";
@@ -68,7 +68,7 @@ convertRouter.post("/html", async (req: Request, res: Response) => {
     res.send(pdf);
   } catch (err: any) {
     console.error("Convert HTML error:", err);
-    res.status(500).json({ error: "PDF generation failed", detail: err.message });
+    if (err.message === "QUEUE_FULL") { const pool = getPoolStats(); res.status(429).json({ error: "Server busy", queueDepth: pool.queueDepth }); return; } res.status(500).json({ error: "PDF generation failed", detail: err.message });
   }
 });
 
@@ -97,7 +97,7 @@ convertRouter.post("/markdown", async (req: Request, res: Response) => {
     res.send(pdf);
   } catch (err: any) {
     console.error("Convert MD error:", err);
-    res.status(500).json({ error: "PDF generation failed", detail: err.message });
+    if (err.message === "QUEUE_FULL") { const pool = getPoolStats(); res.status(429).json({ error: "Server busy", queueDepth: pool.queueDepth }); return; } res.status(500).json({ error: "PDF generation failed", detail: err.message });
   }
 });
 
@@ -150,6 +150,6 @@ convertRouter.post("/url", async (req: Request, res: Response) => {
     res.send(pdf);
   } catch (err: any) {
     console.error("Convert URL error:", err);
-    res.status(500).json({ error: "PDF generation failed", detail: err.message });
+    if (err.message === "QUEUE_FULL") { const pool = getPoolStats(); res.status(429).json({ error: "Server busy", queueDepth: pool.queueDepth }); return; } res.status(500).json({ error: "PDF generation failed", detail: err.message });
   }
 });

src/routes/health.ts

@@ -1,7 +1,21 @@
 import { Router } from "express";
+import { getPoolStats } from "../services/browser.js";
 
 export const healthRouter = Router();
 
 healthRouter.get("/", (_req, res) => {
-  res.json({ status: "ok", version: "0.1.0" });
+  const pool = getPoolStats();
+  res.json({
+    status: "ok",
+    version: "0.2.1",
+    pool: {
+      size: pool.poolSize,
+      active: pool.totalPages - pool.availablePages,
+      available: pool.availablePages,
+      queueDepth: pool.queueDepth,
+      pdfCount: pool.pdfCount,
+      restarting: pool.restarting,
+      uptimeSeconds: Math.round(pool.uptimeMs / 1000),
+    },
+  });
 });