Config update writes config.json, which config discovery never reads

[EthanZhao0710]

Description

Config.update — the code path behind PATCH /config — writes <project>/config.json, but project config discovery only reads opencode.json / opencode.jsonc (ConfigPaths.files("opencode", ...)). The update lands in a file that is never loaded again, so it has no effect and leaves a stray config.json in the project.

This was reported in #4194 and fixed in #4205; that PR was closed as stale and the issue was auto-closed for inactivity, with the note to open a new one if it is still relevant. It still reproduces on dev.

I have a fix + tests ready and can open a PR.

Steps to reproduce

1. Project with opencode.json containing "model": "anthropic/claude-sonnet-4-5"
2. opencode serve --port 4199

3. curl -X PATCH http://127.0.0.1:4199/config \
     -H 'content-type: application/json' \
     -H "x-opencode-directory: $PROJECT" \
     -d '{"model":"anthropic/claude-opus-4-5"}'
   

Response is 200 {"model":"anthropic/claude-opus-4-5"}, but on disk:

$ ls $PROJECT
config.json      opencode.json

$ cat $PROJECT/opencode.json      # still the old model
{ "$schema": "https://opencode.ai/config.json", "model": "anthropic/claude-sonnet-4-5" }

$ cat $PROJECT/config.json        # written, but never read back
{ "model": "anthropic/claude-opus-4-5" }

Restarting keeps the old model.

OpenCode version

dev @ b155b15 (v1.18.19)

Operating System

macOS (Darwin 25.5)

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Config.update() writes runtime local config to ignored project-root config.json (re-open) #42276: Same root cause — Config.update() writes to config.json but config discovery only reads opencode.json / opencode.jsonc, so the update never persists across restarts.

[EthanZhao0710]

Duplicate of #42276 — closing this one. #42257 already has a fix open.