Support multiple installations via --config-dir flag

[aliwatters]

Problem

Currently gsuite-mcp uses a single global config directory (~/.config/gsuite-mcp/), which means one client_secret.json → one GCP project. This makes it impossible to simultaneously serve different Google accounts that require different GCP projects (e.g., a work Workspace account on one GCP project and a personal account on another).

Each GCP project has its own OAuth consent screen, test user list, and client credentials. A single global config can't accommodate multiple GCP projects.

Solution

Add --config-dir flag and GSUITE_MCP_CONFIG_DIR env var so each installation gets its own self-contained config directory.

Repo-local layout (gitignored)

gsuite-mcp/
├── .installations/              # gitignored
│   ├── work/
│   │   ├── client_secret.json   # Work GCP project
│   │   ├── config.json
│   │   └── credentials/
│   │       └── user@work.com.json
│   └── personal/
│       ├── client_secret.json   # Personal GCP project
│       ├── config.json
│       └── credentials/
│           └── user@gmail.com.json

CLI usage

gsuite-mcp --config-dir .installations/work init
gsuite-mcp --config-dir .installations/work auth
gsuite-mcp --config-dir .installations/work          # MCP server mode

MCP client config

{
  "mcpServers": {
    "gsuite-work": {
      "command": "/path/to/gsuite-mcp",
      "args": ["--config-dir", ".installations/work"]
    },
    "gsuite-personal": {
      "command": "/path/to/gsuite-mcp",
      "args": ["--config-dir", ".installations/personal"]
    }
  }
}

Implementation

~25 lines of code:

1. internal/config/config.go — Add configDirOverride var + SetConfigDir(). All path functions (DefaultConfigDir(), ConfigPath(), ClientSecretPath(), CredentialsDir()) already derive from DefaultConfigDir(), so they automatically respect the override.

2. cmd/gsuite-mcp/main.go — Parse --config-dir flag (or GSUITE_MCP_CONFIG_DIR env) before subcommand dispatch, call config.SetConfigDir().

3. .gitignore — Add .installations/

Design properties

• Backward compatible — no flag = ~/.config/gsuite-mcp/ (existing behavior)
• Each installation fully independent — own GCP project, client_secret, config, credentials
• No profile registry — directory name IS the profile
• MCP clients namespace by server name — no tool name conflicts between instances
• One binary, many configs

Motivation

Running gsuite-mcp for a work Google Workspace account requires a GCP project within the Workspace org (for domain-wide access, verified consent screen). A personal account uses a separate GCP project. Today this requires maintaining separate config directories manually.