Fix unicode corruption in agent downloading endpoint

[erayaydin]

When agent responses containing non-ASCII characters were sent, these characters were getting corrupted on the way through the proxy. We were decoding the body into a JS string and then re-encoding it as binary, which breaks UTF-8.

❓ What Changed?

• Removed binary/utf-8 toggle because it inferred from content-encoding header.
• Added received body chunks as-is to the body accumulator.
• Extra: typed the body accumulator as Buffer[] (from any[]).

⚙️ How This Works?

Keeping everything as raw buffers avoids issues and problems with string encodings. No assumptions about content-encoding. Compressed and uncompressed bodies are preserved byte by byte.

🧑‍🔬 How To Test?

1. Smoke

Build the new CloudFront worker from this branch and deploy it to your AWS environment. Try to use the agent downloading with a basic client. This test will ensure everything works fine (no breaking).

2. Use Mock Server

Use mock server and run agent response body integrity protected with 200 status code test with a CloudFront proxy integration (which points to your mock server). This test will ensure the new changes fix potential Unicode problems.

Shareable mock server form value (only test selected, empty fields):

eyJpbnRlZ3JhdGlvblVybCI6IiIsImluZ3Jlc3NQYXRoIjoiIiwiY2RuUGF0aCI6IiIsInRyYWZmaWNOYW1lIjoiIiwiaW50ZWdyYXRpb25WZXJzaW9uIjoiIiwidGVzdHNGaWx0ZXIiOlsiYWdlbnQgcmVzcG9uc2UgYm9keSBpbnRlZ3JpdHkgcHJvdGVjdGVkIHdpdGggMjAwIHN0YXR1cyBjb2RlIl19

✨ Potential Improvements

• Don't use Buffer.isBuffer and directly push chunks to the accumulator body. (response.on('data', (chunk) => data.push(chunk)))
• We can drop content-length from forwarded headers and let CloudFront handle the calculation.
• We can add a new mock server e2e test cases for gzip/br compression.
• Compressed/uncompressed test case content-length assertions.

[github-actions]

This PR will create a patch release 🚀

2.1.2 (2025-09-08)

Bug Fixes

• keep utf-8 intact (29090a4)

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	92.68% (+0.1% 🔼)	646/697
🟢	Branches	87.28% (+0.5% 🔼)	151/173
🟢	Functions	91.79%	123/134
🟢	Lines	92.87% (+0.11% 🔼)	612/659

Test suite run success

170 tests passing in 18 suites.

Report generated by 🧪jest coverage report action from 29090a4

Show full coverage report

St	File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
🟢	All files	92.68	87.28	91.79	92.86
🟢	mgmt-lambda	98.93	93.33	100	98.93
🟢	DefaultSettings.ts	100	100	100	100
🟢	app.ts	97.91	95	100	97.91	26
🟢	auth.ts	100	100	100	100
🟢	exceptions.ts	100	66.66	100	100	20
🟢	routing.ts	100	100	100	100
🟢	mgmt-lambda/handlers	87.22	72.5	93.33	87.15
🟢	errorHandlers.ts	100	71.42	100	100	22,41
🟡	statusHandler.ts	80	50	100	80	76-80,84-89
🟢	updateHandler.ts	87.21	75.86	87.5	87.12	50-51,67-68,139-142,214,219-228,290-291,319
🟢	mgmt-lambda/utils	81.25	88.88	66.66	100
🟢	cloudfrontUtils.ts	100	88.88	100	100	6
🔴	delay.ts	40	100	0	100
🟢	proxy/handlers	88.5	90.9	90.32	89.28
🟢	handleAgentDowloading.ts	100	75	100	100	29-34
🟡	handleResult.ts	76.74	100	76.92	78.04	90-105
🟢	handleStatus.ts	100	100	100	100
🟡	proxy/test	77.77	100	50	71.42
🟡	aws.ts	77.77	100	50	71.42	4-5
🟢	proxy/test/utils/customer-variables	100	100	100	100
🟢	in-memory-customer-variables.ts	100	100	100	100
🟢	proxy/utils	94.57	85.71	94.28	94.11
🟢	buffer.ts	100	100	100	100
🟢	cache-control.ts	100	100	100	100
🟢	cookie.ts	100	100	100	100
🟢	headers.ts	100	100	100	100
🔴	is-blob.ts	0	0	0	0	6-7
🟢	log.ts	85.71	33.33	100	83.33	11
🟢	request.ts	100	100	100	100
🟢	routing.ts	100	100	100	100
🔴	string.ts	14.28	100	0	14.28	2-8
🟢	traffic.ts	100	100	100	100
🟢	proxy/utils/customer-variables	100	100	100	100
🟢	customer-variables.ts	100	100	100	100
🟢	defaults.ts	100	100	100	100
🟢	header-customer-variables.ts	100	100	100	100
🟢	maybe-obfuscate-variable.ts	100	100	100	100
🟢	selectors.ts	100	100	100	100
🟢	types.ts	100	100	100	100
🟢	proxy/utils/customer-variables/secrets-manager	95.58	100	100	95.52
🟢	normalize-secret.ts	100	100	100	100
🟢	retrieve-secret.ts	100	100	100	100
🟢	secrets-manager-variables.ts	86.95	100	100	86.95	28,50-55
🟢	validate-secret.ts	100	100	100	100

[TheUnderScorer]

LGTM, but let's make sure that all E2E tests pass before merging :)