MCP tools bypassed our agent's approval gate—here's the fail-closed fix
GapNew4766 · reddit · 2026-10-13
Atomic Agent, an MIT-licensed agent that doubles as an MCP client, disclosed an embarrassing hole: built-in file writes and shell commands required user approval, but the same writes proxied through an MCP server executed silently. The culprit was the default trust: "approvalgated" config, which read like consent but was only a scheduling constraint. An outside contributor found it in v0.3.1 (issue #132); the fix landed Aug 31.
The new rule
- A tool runs without approval only if its discovery-time annotation is exactly readOnlyHint === true. Missing, malformed, or string "true" all fail closed.
- The verdict is made once at registration and never revised, so servers can't flip tools to read-only mid-session.
- Deliberately narrower than destructiveHint === false: a tool that destroys nothing can still post messages or open tickets in your name.
- Wire flags are also ignored when batching parallel calls, since it's third-party code.
Composio integration
Instead of stuffing thousands of schemas into a local model's prompt, one POST to Composio's tool router returns a Streamable HTTP MCP URL exposing four meta-tools: SEARCHTOOLS and GETTOOLSCHEMAS (read-only, run free) vs MANAGECONNECTIONS and MULTIEXECUTETOOL (mutating, ask first). Caveats: requires your own Composio key, and it's hosted, so OAuth tokens flow through Composio's servers.
Migration & extras
atomic-agent import claude-code picks up MCP servers (they live in /.claude., not the directory), skills, memory, and sessions, with --dry-run and explicit --migrate-secrets for API keys. In Fusion mode, the planner treats every MCP tool as mutating regardless of annotations.
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