Rebuild: the worker joins stream pieces once per frame, gzips posts off its thread

decodeFrames joined each network piece (~64 KB) onto the frame so far:
a chunk of MBs copied over and over, 5.4% of a worker's time in an
end-to-end profile (the bench reads files, so it never showed). Pieces
are now joined once a frame is complete. A batch post's gzip (1.6%) runs
on a thread-pool thread.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

commands/edge_node.ts

@@ -4,11 +4,12 @@ import { setTimeout as sleep } from 'node:timers/promises'
 import { spawn, type ChildProcess } from 'node:child_process'
 import { availableParallelism } from 'node:os'
 import { promisify } from 'node:util'
-import { gzipSync, unzip } from 'node:zlib'
+import { gzip, unzip } from 'node:zlib'
 import { RangeIndexer, decodeFrames, isKeepalive, toWire, type EdgeBatch, type Lease } from '#lib/edge/index'
 
 const IDLE_MS = 30_000
 const unzipAsync = promisify(unzip)
+const gzipAsync = promisify(gzip)
 const RETRIES = 8
 
 class LeaseLost extends Error {}
@@ -219,8 +220,8 @@ class Api {
   }
 
   async batch(rangeId: number, batch: EdgeBatch): Promise<{ releases: number; candidates: number; bytes: number }> {
-    // Gzipped: chunk payloads are compressed already, the rest (names, fragments, candidates) compresses well.
-    const body = gzipSync(JSON.stringify(toWire(batch)), { level: 1 })
+    // Gzipped (on a thread-pool thread): chunk payloads are compressed already, the rest compresses well.
+    const body = await gzipAsync(JSON.stringify(toWire(batch)), { level: 1 })
     const response = await this.request(`ranges/${rangeId}/batches`, { method: 'POST', body, headers: { 'Content-Encoding': 'gzip' } })
     if (!response.ok) throw new Error(`batch: HTTP ${response.status}`)
     return { ...((await response.json()) as { releases: number; candidates: number }), bytes: body.length }