MCP client compatibility

Support scope

• Supported OS for building/testing the Rust workspace: macOS 15+ and Linux 6.9+.
• visionOS build tools (validate_sandbox_policy, build_visionos_app, fetch_build_output) require macOS + Xcode 16 with visionOS SDK installed.
• On non-macOS environments, the server can compile and tests can run (using mocks), but real visionOS builds are not supported.

Compatibility policy

This repository treats the MCP surface as a contract:

• Tool names and input/output JSON shapes are stable.
• Error code values are stable and are considered part of the public API.
• Structured error metadata is stable:
  • code, remediation, retryable, sandbox_state
  • Additional fields may be added, but existing fields should not be removed or renamed.

What counts as a breaking change

• Renaming/removing a tool or changing required request fields.
• Changing the meaning of an existing error code, or replacing a code with another one.
• Removing or renaming structured error fields (code / retryable / sandbox_state / remediation).

Supported libraries / protocol

• Uses rmcp crate v0.8.5; compatible with Model Context Protocol as of 2024Q2.
• Supported workflow: local stdio MCP server launched as an MCP client child process.
• TCP is not part of the current supported runtime.

Verified clients

Model Context Protocol Inspector CLI

npx @modelcontextprotocol/inspector target/release/seiro-mcp

Pass MCP_CONFIG_PATH only when the project config is not the current directory’s seiro-mcp.toml.

Codex CLI

Generate the registration snippet:

seiro-mcp config mcp

Paste it into ~/.codex/config.toml:

[mcp_servers.seiro_mcp]
command = "/Users/<user>/.cargo/bin/seiro-mcp"

After restarting Codex CLI, mcp list shows the visionOS tools.

TCP reintroduction policy

TCP should not be restored by re-adding the old shared-token startup flow. If TCP is needed again, design it as a separate remote/server mode with:

• localhost as the default bind address
• explicit opt-in for external bind addresses
• connection-level authentication
• clear exposure guidance
• Inspector-specific verification steps
• compatibility and migration notes

Compatibility checklist

• Use target/release/seiro-mcp from cargo build --release; visionOS tools respond via Inspector over stdio.
• Codex CLI command points to the binary absolute path; tools register successfully without token setup.
• Missing project config and MCP_CLIENT_REQUIRED are reproduced by tests and documented in troubleshooting.

Known limitations

• Running cargo run directly exits immediately because no MCP client is attached (MCP_CLIENT_REQUIRED exit 44). Always launch via an MCP client.
• TCP, WebSocket, and other remote transports are not currently supported.
• Without visionOS SDK, validate_sandbox_policy returns sdk_missing; visionOS tools are unavailable on Linux.