fix write coalescer

server/write-coalescer.js

@@ -1,21 +1,18 @@
 // Write coalescer for slow filesystems (rclone, FUSE, NFS, SMB).
 //
-// First write to a path goes to disk immediately. Subsequent writes within
-// the coalesce window are buffered; the timer resets on each write. After
-// the window elapses with no new writes, the buffered data is flushed.
+// First write to a path goes to disk immediately. Subsequent writes within the coalesce window are buffered and flushed when the debounce timer fires; the timer resets on each write.
 //
-// This prevents rapid-fire writes (e.g. workspace.json saved 20x/min)
-// from overwhelming network-mounted filesystems.
+// Buffered writes respond to the HTTP client right away with synthetic mtime/size. Otherwise the browser's per-host connection cap blocks unrelated reads while writes sit in the buffer.
 
 const fs = require("fs");
 const config = require("./config");
 
 const FLUSH_TIMEOUT_MS = 10000;
 
-// absPath -> timestamp of last completed write
+// absPath -> timestamp of last completed (or scheduled) write
 const lastWriteTime = new Map();
 
-// absPath -> { data, encoding, timer, resolvers: [{ resolve, reject }] }
+// absPath -> { data, encoding, timer }
 const pending = new Map();
 
 async function writeToDisk(absPath, data, encoding) {
@@ -41,18 +38,9 @@ function flushEntry(absPath) {
   clearTimeout(entry.timer);
   pending.delete(absPath);
 
-  writeToDisk(absPath, entry.data, entry.encoding).then(
-    (result) => {
-      for (const r of entry.resolvers) {
-        r.resolve(result);
-      }
-    },
-    (err) => {
-      for (const r of entry.resolvers) {
-        r.reject(err);
-      }
-    },
-  );
+  writeToDisk(absPath, entry.data, entry.encoding).catch((err) => {
+    console.error(`[write-coalesce] Flush failed for ${absPath}:`, err);
+  });
 }
 
 function scheduleFlush(absPath) {
@@ -66,18 +54,24 @@ function scheduleFlush(absPath) {
   entry.timer = setTimeout(() => flushEntry(absPath), config.writeCoalesceMs);
 }
 
+function estimateSize(data, encoding) {
+  if (typeof data === "string") {
+    return Buffer.byteLength(data, encoding === "binary" ? "utf-8" : encoding);
+  }
+
+  return data.length || data.byteLength || 0;
+}
+
 /**
  * Write file content, coalescing rapid writes.
- * The returned promise resolves with { mtime, size } once data hits disk.
+ * Fresh writes resolve with real mtime/size once data is on disk. Buffered writes resolve immediately with synthetic values; the disk flush happens later when the debounce timer fires.
  */
 async function writeCoalesced(absPath, data, encoding) {
   const windowMs = config.writeCoalesceMs;
-
-  // Coalescing disabled or first write to this path
   const last = lastWriteTime.get(absPath);
 
+  // Fast path: coalescing disabled or far enough from the last write.
   if (windowMs <= 0 || !last || Date.now() - last >= windowMs) {
-    // Resolve any pending write for this path first
     if (pending.has(absPath)) {
       clearTimeout(pending.get(absPath).timer);
       pending.delete(absPath);
@@ -86,28 +80,23 @@ async function writeCoalesced(absPath, data, encoding) {
     return writeToDisk(absPath, data, encoding);
   }
 
-  // Within the coalesce window: buffer the write
-  return new Promise((resolve, reject) => {
-    const existing = pending.get(absPath);
+  // Within the coalesce window: buffer the write and respond immediately.
+  const existing = pending.get(absPath);
 
-    if (existing) {
-      // Update data and add another resolver
-      existing.data = data;
-      existing.encoding = encoding;
-      existing.resolvers.push({ resolve, reject });
-      scheduleFlush(absPath);
-    } else {
-      const entry = {
-        data,
-        encoding,
-        timer: null,
-        resolvers: [{ resolve, reject }],
-      };
+  if (existing) {
+    existing.data = data;
+    existing.encoding = encoding;
+    scheduleFlush(absPath);
+  } else {
+    pending.set(absPath, {
+      data,
+      encoding,
+      timer: null,
+    });
+    scheduleFlush(absPath);
+  }
 
-      pending.set(absPath, entry);
-      scheduleFlush(absPath);
-    }
-  });
+  return { mtime: Date.now(), size: estimateSize(data, encoding) };
 }
 
 /**
@@ -136,7 +125,6 @@ async function flushAll() {
 
   console.log(`[write-coalesce] Flushing ${paths.length} pending write(s)...`);
 
-  // Clear all timers
   for (const entry of pending.values()) {
     clearTimeout(entry.timer);
   }
@@ -145,20 +133,9 @@ async function flushAll() {
     const entry = pending.get(absPath);
     pending.delete(absPath);
 
-    return writeToDisk(absPath, entry.data, entry.encoding).then(
-      (result) => {
-        for (const r of entry.resolvers) {
-          r.resolve(result);
-        }
-      },
-      (err) => {
-        console.error(`[write-coalesce] Failed to flush ${absPath}:`, err);
-
-        for (const r of entry.resolvers) {
-          r.reject(err);
-        }
-      },
-    );
+    return writeToDisk(absPath, entry.data, entry.encoding).catch((err) => {
+      console.error(`[write-coalesce] Failed to flush ${absPath}:`, err);
+    });
   });
 
   const timeout = new Promise((resolve) => {