Unexpected silent merge of opencode.json and opencode.jsonc — partial overrides without warning

[escoffie]

Description

When both opencode.json and opencode.jsonc exist in the config directory, OpenCode silently merges them. A partial .jsonc can override specific keys from a full .json without any indication to the user.

In my case, opencode.json had the correct MCP config for Engram:

"engram": {
  "command": ["/usr/local/bin/engram", "mcp", "--tools=agent"]
}

But opencode.jsonc (leftover from a previous setup) had:

"engram": {
  "command": ["/usr/local/Cellar/engram/1.16.1/bin/engram", "mcp", "--tools=agent"]
}

This caused a confusing ENOENT error pointing to a path that didn't exist (1.16.1), even though the .json file was correct.
Expected
Either:

1. Document the precedence/merge behavior clearly (which file wins when both exist?)
2. Warn when a partial config overrides specific keys from the other file
3. Or discourage having two config files with conflicting MCP entries
   Additional context
   The error message (ENOENT: no such file or directory, posix_spawn '/usr/local/Cellar/engram/1.16.1/bin/engram') didn't hint that the problem was a stale config file or a merge conflict — it looked like a missing binary.

Plugins

engram.ts, model-variants.ts, skill-registry.ts, gentle-logo.tsx

OpenCode version

1.17.7

Steps to reproduce

1. Create ~/.config/opencode/opencode.json with a correct MCP entry:

"mcp": {
  "engram": {
    "command": ["/usr/local/bin/engram", "mcp"],
    "type": "local"
  }
}

2. Create ~/.config/opencode/opencode.jsonc with a partial override of the same MCP server pointing to a non-existent path:

"mcp": {
  "engram": {
    "command": ["/usr/local/Cellar/engram/1.16.1/bin/engram", "mcp"],
    "type": "local"
  }
}

3. Launch OpenCode.
4. Observed: the MCP server silently fails with ENOENT. No warning that a second config file exists, no indication of the merge happening, and no hint about which file takes precedence.

Screenshot and/or share link

Operating System

MacOS 26.5.1

Terminal

iTerm2 Build 3.6.11

[github-actions]

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

• v1.15.13 upward config loading causes local mcp sections to shadow/replace global MCP servers instead of merging #30415: Similar issue where local MCP config sections silently replace/shadow global MCP servers instead of merging — related config merge behavior without warning