Config schema validation errors show 'Unexpected server error' instead of field-level details #31954

Issue: Config schema validation errors show "Unexpected server error" instead of which fields are wrong

What happens

When opencode.json has fields in the wrong format, the app shows:

"Failed to reload — Unexpected server error. Check server logs for details."

What should happen

It should show the exact field errors, e.g.:

["formatter"]["typescript"] — Expected object, got "prettier"
["permission"]["bash"]["allow"] — Expected pattern map, got array

Breaking schema changes in v1.16.x (no migration, no warning)

Field: skill

• Old: {"skills": ["brainstorming"]}
• New: Key removed — use skills: {paths:[], urls:[]}

Field: formatter

• Old: {"typescript": "prettier"}
• New: true or {"typescript": {"command": [...]}}

Field: permission

• Old: {"bash": {"allow": ["npm *"]}}
• New: {"bash": {"npm *": "allow"}}

Field: model

• Old: {"provider": "deepseek", "model": "..."}
• New: "deepseek/model-id" (string)

Root cause (code location)

File: packages/opencode/src/config/config.ts line 601

// This converts ConfigInvalidError (which has field details) into an untyped defect
return yield* loadInstanceState(ctx).pipe(Effect.orDie)

File: packages/opencode/src/server/routes/instance/httpapi/middleware/error.ts

// This check fails for the loadInstanceState code path
if (ConfigErrorV1.InvalidError.isInstance(error)) {
  return Effect.succeed(HttpServerResponse.jsonUnsafe(error.toObject(), { status: 400 }))
}
// Falls through to generic 500 👇

The field-level errors ARE computed and logged to ~/.local/share/opencode/log/ — they just never reach the user.

Suggested fix

Surface the ConfigInvalidError cause in the HTTP response instead of swallowing it into a generic 500.