Config.update() writes runtime local config to ignored project-root config.json

[ReqX]

Description

Runtime local config updates made through Config.update() do not round-trip through instance disposal/reload correctly.

Config.update() writes to project-root config.json, but fresh project config loading reads the normal opencode.json / opencode.jsonc paths and local .opencode/opencode.json[c] overlays instead.

Because of that mismatch, a runtime config update can appear to work immediately, then disappear after the instance is disposed and reloaded.

I have a PR prepared for this.

Plugins

alvinunreal/oh-my-opencode-slim

OpenCode version

Observed on v1.15.7 and v1.15.10, and traced on current dev before fix.

Steps to reproduce

1. Start with a project where a runtime config update changes agent config through the config update path
2. Trigger the config update
3. Let the instance get disposed/reloaded
4. Use the updated config again after reload

Screenshot and/or share link

No response

Operating System

Linux

Terminal

No response

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Expected behavior

Runtime local config updates should be persisted to the local config overlay that fresh reload already reads, so they survive disposal/reload.

Actual behavior

Runtime local updates are written to project-root config.json, which fresh project config loading does not read, so runtime-added config can disappear after reload.

Root cause

• Config.update() writes config.json
• project config loading uses opencode.json / opencode.jsonc + .opencode overlays
• the reload path itself appears fine; the persisted file target is wrong

Proposed fix

Write runtime local updates to the managed local overlay instead:

• prefer existing .opencode/opencode.jsonc
• else existing .opencode/opencode.json
• else create .opencode/opencode.jsonc

This matches the normal local reload path and keeps runtime-managed overrides out of the project root.

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