feat: streaming support for coding agents (Claude Code & Codex)

[Davidnet]

Summary

• Add SSE streaming support to the proxy so coding agents (Claude Code, Codex) work through it
• New streaming pipeline (proxy/streaming.go) with provider-specific codecs for Anthropic (codec_anthropic.go) and OpenAI (codec_openai.go)
• Record dashboard metrics for streamed responses
• Docs: new docs/09-coding-agents.md guide and README updates

Main work was provided in #532

[github-actions]

Warning

This PR touches 3+ distinct areas of the codebase.

Consider splitting into smaller, focused PRs — each covering a single semantic type.
This makes reviews easier and keeps the git history clean.

Categories found:

docs:

• README.md
• docs/09-coding-agents.md
• docs/README.md

code:

• src/backend/config/config.go
• src/backend/processor/response.go
• src/backend/providers/anthropic.go
• src/backend/providers/openai.go
• src/backend/providers/provider.go
• src/backend/proxy/codec_anthropic.go
• src/backend/proxy/codec_openai.go
• src/backend/proxy/cors.go
• src/backend/proxy/handler.go
• src/backend/proxy/passthrough.go
• src/backend/proxy/router.go
• src/backend/proxy/streaming.go
• src/backend/proxy/transparent.go
• src/backend/proxy/transparent_factory.go

chore:

• package-lock.json

test:

• src/backend/config/config_test.go
• src/backend/processor/response_test.go
• src/backend/providers/providers_test.go
• src/backend/proxy/passthrough_test.go
• src/backend/proxy/router_test.go
• src/backend/proxy/streaming_test.go

[hanneshapke]

@Davidnet Is this PR in addition to #532 ?

[Davidnet]

@Davidnet Is this PR in addition to #532 ?

Yes it was a rebase, and a modifications that I brought from my tests

[Davidnet]

Codex sample:

codex exec \
      --skip-git-repo-check \
      -c 'model_provider="kiji"' \
      -c 'model_providers.kiji={ name = "Kiji", base_url = "https://chatgpt.com/backend-api/codex", wire_api = "responses", requires_openai_auth = true, supports_websockets = false }' \
"Draft a short reply to David Nettleton at dnon@gmail.com confirming the meeting."
OpenAI Codex v0.142.5
--------
workdir: /Users/davidnet/sample
model: gpt-5.4
provider: kiji
approval: never
sandbox: read-only
reasoning effort: medium
reasoning summaries: none
session id: 019f295d-39d1-7971-a168-0b6dd53b08d6
--------
user
Draft a short reply to David Nettleton at dnon@gmail.com confirming the meeting.
codex
Subject: Re: Meeting Confirmation

Hi David,

Confirming the meeting works for me. Looking forward to it.

Best,
Jordan
tokens used
8,434

Claude code

set -x HTTP_PROXY http://127.0.0.1:8081
set -x HTTPS_PROXY http://127.0.0.1:8081
 set -x NODE_EXTRA_CA_CERTS "$HOME/Library/Application Support/Kiji Privacy Proxy/certs/ca.crt"
$ claude -p --model haiku "Draft a two-sentence email to Priya Raghavan (priya.raghavan@acme.io) confirming Tuesday's sync. Sign it from me."
Here's a draft email:

---

**To:** priya.raghavan@acme.io
**Subject:** Confirming Tuesday's Sync

Hi Priya,

I wanted to confirm our sync scheduled for Tuesday. Please let me know if you need to reschedule or if there's anything you'd like to go over beforehand.

Best regards,
Yuki Smith

[hanneshapke]

@Davidnet Great work, but a huge PR. Wanna review it together on Monday?

[Davidnet]

@Davidnet Great work, but a huge PR. Wanna review it together on Monday?

Yes, It was also a quite a bit of new things, and for sure