fix(skills): stabilize compression across zlib versions

src/main/skills/skill-package-creation.test.ts

@@ -125,7 +125,7 @@ describe('skill package creation and extraction', () => {
       archiveSha256: created.archiveSha256,
       packageDigest: created.manifest.packageDigest
     }).toEqual({
-      archiveSha256: '4a62b276b1e8100f0b437f2f0aa182d844768160ba30c5f76afd027acfe50ac8',
+      archiveSha256: '2abf449e92650f03b749631547c22e0f28facf6da9c36f0e77d6f8cc7df8e47a',
       packageDigest: '3bb1fc63cfea2f2b7f2cf80e539735eebd5bfb6aa65f47cf0db7e9fd35297f57'
     })
   })

src/main/skills/skill-package-tar.ts

@@ -4,7 +4,7 @@ import { once } from 'node:events'
 import type { Readable, Writable } from 'node:stream'
 import { Transform } from 'node:stream'
 import { pipeline } from 'node:stream/promises'
-import { createGunzip, createGzip } from 'node:zlib'
+import { constants as zlibConstants, createGunzip, createGzip } from 'node:zlib'
 import { SKILL_PACKAGE_MAX_COMPRESSED_BYTES } from '../../shared/skill-package-manifest'
 
 const TAR_BLOCK_BYTES = 512
@@ -103,7 +103,7 @@ export async function writeSkillTarGzip(
 ): Promise<{ archiveSha256: string; compressedBytes: number }> {
   const archiveHash = createHash('sha256')
   let compressedBytes = 0
-  const gzip = createGzip({ level: 9 })
+  const gzip = createGzip({ level: 9, strategy: zlibConstants.Z_FIXED })
   const hashTransform = new Transform({
     transform(chunk: Buffer, _encoding, callback) {
       compressedBytes += chunk.length