retry + decompress: RetryController exposes read-only rawHeaders, causing TypeError

[jesusgalhub]

Bug Description

Composing the built-in retry interceptor before the built-in decompress
interceptor causes compressed responses to fail:

new Agent().compose([
  interceptors.retry(),
  interceptors.decompress()
])

RetryHandler passes a RetryController proxy to downstream handlers. That
proxy exposes rawHeaders through a getter, but it has no corresponding
setter. When DecompressHandler receives a compressed response, it removes
content-encoding and content-length from the raw header list by assigning a
new value to controller.rawHeaders. Because the proxy property is
getter-only, this assignment throws in strict mode:

TypeError: Cannot set property rawHeaders of #<RetryController> which has only a getter

The failure occurs even with maxRetries: 0, so no retry attempt is required
to trigger it.

Reproduction

Standalone reproduction script:

'use strict'

const assert = require('node:assert/strict')
const { once } = require('node:events')
const { createServer } = require('node:http')
const { test } = require('node:test')
const { gzipSync } = require('node:zlib')
const { Agent, interceptors, request } = require('undici')

test('retry can be composed before decompress', { timeout: 5000 }, async (t) => {
  const compressedBody = gzipSync('ok')
  const server = createServer((_req, res) => {
    res.writeHead(200, {
      'content-encoding': 'gzip',
      'content-length': String(compressedBody.length)
    })
    res.end(compressedBody)
  })

  t.after(() => {
    server.closeAllConnections?.()
    server.close()
  })

  server.listen(0, '127.0.0.1')
  await once(server, 'listening')

  const dispatcher = new Agent().compose([
    interceptors.retry({ maxRetries: 0 }),
    interceptors.decompress()
  ])
  t.after(() => dispatcher.close())

  const { statusCode, body } = await request(
    `http://127.0.0.1:${server.address().port}`,
    {
      dispatcher,
      headers: { 'accept-encoding': 'gzip' }
    }
  )

  assert.equal(statusCode, 200)
  assert.equal(await body.text(), 'ok')
})

Steps to reproduce (if not using the script above):

1. Save the script as test/repro-retry-decompress-rawheaders.js.
2. Install undici@8.10.0.
3. Run:

   node --test test/repro-retry-decompress-rawheaders.js

Expected Behavior

The request should resolve with status code 200, and the decompressed response
body should equal "ok". The documented built-in interceptors should compose
without throwing.

Actual Behavior

The request fails during response header processing, before the response is
delivered to the caller:

TypeError: Cannot set property rawHeaders of #<RetryController> which has only a getter

In a non-test process, cleanup can also emit the same error from the already
created Gunzip stream as an unhandled stream error.

Logs & Screenshots

✖ retry can be composed before decompress

TypeError: Cannot set property rawHeaders of #<RetryController> which has only a getter
    at DecompressHandler.onResponseStart (undici/lib/interceptor/decompress.js:201:31)
    at RetryHandler.onResponseStart (undici/lib/handler/retry-handler.js:364:37)
    at Request.onResponseStart (undici/lib/core/request.js:345:39)

tests 1
pass 0
fail 1

Environment

• OS: macOS 26.2 (arm64)
• Node.js version: v24.11.1
• undici version: 8.10.0

Additional context

• The official interceptor documentation shows retry before decompress in
  its composition examples:
  https://github.com/nodejs/undici/blob/main/docs/docs/api/Interceptors.md#composing-multiple-interceptors
• Reversing the order to decompress before retry avoids the exception,
  because DecompressHandler then receives the native RequestController,
  whose rawHeaders field is writable.
• RetryController was introduced in
  fix(retry): keep flow-control wired to the active connection across resumes #5405. It forwards reads of
  rawHeaders and rawTrailers, but not writes.
• The same getter-only proxy and controller.rawHeaders = filteredHeaders
  assignment are still present on the current main branch.
• Forwarding rawHeaders and rawTrailers setters to the active target appears
  to be one possible fix, together with a regression test for this documented
  interceptor order.