better concurrency debugging, --concurrency flag for npx quartz build

quartz/build.ts

@@ -1,19 +1,5 @@
 import sourceMapSupport from "source-map-support"
-sourceMapSupport.install({
-  retrieveSourceMap(source) {
-    // source map hack to get around query param
-    // import cache busting
-    if (source.includes(".quartz-cache")) {
-      let realSource = fileURLToPath(source.split("?", 2)[0] + ".map")
-      return {
-        map: fs.readFileSync(realSource, "utf8"),
-      }
-    } else {
-      return null
-    }
-  },
-})
-
+sourceMapSupport.install(options)
 import path from "path"
 import { PerfTimer } from "./perf"
 import { rimraf } from "rimraf"
@@ -23,14 +9,13 @@ import { parseMarkdown } from "./processors/parse"
 import { filterContent } from "./processors/filter"
 import { emitContent } from "./processors/emit"
 import cfg from "../quartz.config"
-import { FilePath, ServerSlug, joinSegments, slugifyFilePath } from "./path"
+import { FilePath, joinSegments, slugifyFilePath } from "./path"
 import chokidar from "chokidar"
 import { ProcessedContent } from "./plugins/vfile"
 import { Argv, BuildCtx } from "./ctx"
 import { glob, toPosixPath } from "./glob"
 import { trace } from "./trace"
-import { fileURLToPath } from "url"
-import fs from "fs"
+import { options } from "./sourcemap"
 
 async function buildQuartz(argv: Argv, clientRefresh: () => void) {
   const ctx: BuildCtx = {