feat(installer): OpenCode MCP support + fix silent merge-failure bug

[aniongithub]

Adds OpenCode (https://opencode.ai) as an installer-detected MCP client, alongside Claude / GitHub Copilot / VS Code / Cursor.

While wiring it in I also caught — and fixed — a silent-failure bug in the existing merge path that affected all clients, not just OpenCode.

OpenCode support

OpenCode's MCP config shape differs from the other four:

• top-level key is "mcp" (not "mcpServers")
• command is a JSON array, not a string + separate args
• entries carry "enabled": true
• includes a $schema pointer when we create the file

A new configure_opencode() function in install.sh (and a Set-OpenCodeMcpConfig in install.ps1) emits and merges this shape. Detection mirrors the other clients: the config file already exists, the config directory has been created, or the opencode binary is on PATH. Paths written:

OS	File
Linux/macOS	~/.config/opencode/opencode.json (or .jsonc if that's what exists)
Windows	%APPDATA%\opencode\opencode.json

SKILL.md also gets dropped into OpenCode's primary skill discovery path (~/.config/opencode/skills/mind-map/SKILL.md, %APPDATA%\opencode\skills\mind-map\SKILL.md). OpenCode would also discover the file via its ~/.claude/skills/ and ~/.agents/skills/ fallbacks — both of which the installer already writes — but writing the primary path is more explicit.

Pre-existing bug fixed

configure_mcp_client was building its python3 merge step by interpolating the JSON entry string into Python source code via shell quoting:

python3 -c "
…
entry = json.loads('${mcp_entry}')
…
"

That works for the empty-config "created file" branch, but for any existing config file the Python source becomes:

entry = json.loads('{"type": "local", "command": "/path", "args": [], …}')

…which is a SyntaxError on the embedded double-quotes. The error was redirected to /dev/null, and the script printed a generic ! could not update with no diagnostics. Net effect: anyone with a pre-existing Claude / Copilot / Cursor / VS Code MCP config — i.e. essentially all real-world users — was silently not getting mind-map added.

Fix: pass the JSON entry via an environment variable, which sidesteps the shell-into-Python quoting entirely:

MM_CFG=… MM_ENTRY=… MM_CLIENT=… python3 -c '
import json, os
…
servers["mind-map"] = json.loads(os.environ["MM_ENTRY"])
'

configure_opencode uses the same pattern from the start.

Verified

Ran end-to-end inside the devcontainer:

1. OpenCode fresh — creates opencode.json with $schema, mcp, and a clean mind-map entry.
2. OpenCode merge — pre-populates with a playwright entry and model: setting; both are preserved, mind-map is added alongside.
3. Claude-shape merge (regression for the silent-failure bug) — pre-populates mcpServers with a foo entry; foo is preserved, mind-map is added.

All three produce correctly-merged JSON.