claude_mcp

claude_mcp is a local, stdio-only Model Context Protocol server that gives Codex a controlled Claude Opus 5 collaborator through the installed Claude Code CLI and the user's Claude subscription. Opus can inspect an allowed workspace, plan or review work without editing, or take a separately annotated write-capable task that can edit files and run focused tests.

Codex remains the orchestrator and final authority. This bridge does not call the Anthropic API directly, accept an Anthropic API key, scrape a terminal, create commits, or run a resident Claude session.

Collaboration model

The intended workflow is writer–verifier separation:

User
  -> Codex (GPT-5.6-sol, orchestrator)
  -> claude_mcp over MCP stdio
  -> claude -p --model claude-opus-5
  -> controlled access to one validated workspace
  -> structured Opus report + trusted bridge observations
  -> Codex inspects the real diff, reruns important checks, and answers the user

Useful patterns include:

• Codex implements a substantial change, then starts a fresh Opus review.

• Opus implements a bounded change, then Codex inspects the actual diff and independently verifies it.

• A read-only planning session is resumed into implementation in the same canonical workspace.

• Final independent review normally uses a fresh session rather than resuming the authoring session.

Only one operation may use a workspace at a time. Calls for different workspaces may run concurrently up to the configured global limit. Do not ask both models to write the same workspace concurrently, and skip Opus for trivial mechanical work.

Related MCP server: claude-consult-mcp

Why claude -p

Claude Code's non-interactive print mode provides an argument-vector interface, explicit tools and permission mode, structured JSON output, session IDs, and a normal subprocess lifecycle. That is substantially more auditable than PTY, tmux, terminal-control-sequence, or interactive-TUI scraping. The bridge uses asyncio.create_subprocess_exec with no shell and supplies all task content as JSON on stdin.

Public MCP tools

Version 0.1 exposes exactly three tools:

• opus_status: free local readiness diagnostics. It runs claude --version and claude auth status, but never a model completion.

• opus_consult: read-only plan, review, diagnose, or design work using only Read,Glob,Grep. Those tools are explicitly allowed in both CLI arguments and the per-call settings policy. Scrubbed Claude Code sessions use the effective default permission mode directly, avoiding a misleading forced-mode warning. Any observed workspace change is returned as a policy violation.

• opus_execute: destructive, non-idempotent implement, fix, refactor, test, or document work using Read,Glob,Grep,Edit,Write,Bash. Git is required by default.

Both collaboration tools return the validated Opus report separately from bridge-observed process, session, policy, and workspace metadata. Claude's own files_changed claim is advisory; the bridge's pre/post manifest is independent. Full source diffs are not returned because Codex already has local workspace access and should inspect them directly.

The public tools use reliable turn ceilings: 24 for read-only consultation and 64 for execution. These are maxima, not quotas, so Claude stops earlier when the task is complete. If Claude exhausts a ceiling, the bridge reports error_max_turns as a process failure with the selected ceiling and safe remediation; it does not mislabel the result as a non-Opus fallback or a broken structured-output contract.

Requirements

• Python 3.11 or newer

• uv

• Git

• macOS, Linux, or WSL2 (not native Windows)

• Claude Code at or above the configured minimum, currently 2.1.224

• Native Claude Code sandbox dependencies. On Linux and WSL2 this normally means bubblewrap (bwrap) and socat; macOS uses Seatbelt.

• A Claude subscription login through Claude Code, or a deliberately supplied CLAUDE_CODE_OAUTH_TOKEN

The bridge fails closed when the native sandbox, required security settings, supported CLI version, or allowed workspace roots are missing. Write-capable execution also requires a successful authentication status probe unless the operator deliberately supplied CLAUDE_CODE_OAUTH_TOKEN; in that case the actual bounded request validates the token. Because some Claude Code releases can report a stale status for a usable stored login, read-only consultation also lets the bounded model request make the final authentication determination and returns its redacted failure reason.

Installation

git clone git@github.com:catid/claude_mcp.git
cd claude_mcp
uv sync --all-groups

Verify the installed entry point without sending a model request by configuring the server in Codex and calling opus_status.

Authentication

Use the normal Claude Code subscription login:

claude auth login
claude auth status

CLAUDE_CODE_OAUTH_TOKEN is preserved if the operator deliberately supplies it. Version 0.1 does not support API-key billing or Bedrock, Vertex, Foundry, custom gateways, profiles, or alternate endpoints.

Before every diagnostic and task process, the bridge copies the parent environment and removes variables that could switch authentication, provider, endpoint, organization, profile, or model. This includes ANTHROPIC_*, CLAUDE_CODE_USE_BEDROCK, CLAUDE_CODE_USE_VERTEX, and CLAUDE_CODE_USE_FOUNDRY, plus selected cloud credentials. Interpreter/loader injection variables such as NODE_OPTIONS, PYTHONPATH, and LD_PRELOAD, all GIT_* variables, proxy and custom-CA variables, and CLAUDE_CONFIG_DIR are also removed. It forces CLAUDE_CODE_SUBPROCESS_ENV_SCRUB=1 so Bash children do not inherit Anthropic or cloud credentials. opus_status reports detected override and dangerous environment names, never values. Ordinary requirements such as HOME, PATH, SHELL, TMPDIR, and locale are retained. Version 0.1 intentionally does not inherit corporate proxies; explicit opt-in proxy support is future work. Current Claude Code may create known zero-byte scrub stubs and append matching .git/info/exclude blocks. The bridge records pre-existing state, removes only new zero-byte stubs, and atomically restores only exact scrub-mode append blocks; pre-existing or model-written content is preserved.

Configuration

Set at least CLAUDE_MCP_ALLOWED_ROOTS in the MCP server environment. Paths are separated with os.pathsep (: on POSIX) and are resolved canonically at server startup.

All values are validated. bypassPermissions and plan mode are not accepted as execute modes.

Codex MCP configuration

Add this to ~/.codex/config.toml, using absolute paths:

[mcp_servers.opus_collaborator]
command = "/absolute/path/to/claude_mcp/.venv/bin/claude-mcp"
enabled = true
required = false
startup_timeout_sec = 20
tool_timeout_sec = 7500
default_tools_approval_mode = "approve"

[mcp_servers.opus_collaborator.env]
CLAUDE_MCP_ALLOWED_ROOTS = "/absolute/path/to/repositories"
CLAUDE_MCP_MODEL = "claude-opus-5"
CLAUDE_MCP_REQUIRE_GIT_FOR_WRITES = "true"

Codex clients share this MCP configuration. Run codex mcp list to inspect configured servers, or use /mcp in the Codex terminal UI to confirm that opus_collaborator loaded and advertises exactly three tools. See the current Codex MCP documentation for client configuration and approval-mode details.

Usage patterns

Fresh architecture plan

Call opus_consult without a session ID:

{
  "workspace_path": "/repos/service",
  "task": "Design the new durable job scheduler",
  "mode": "design",
  "focus": "crash recovery, idempotency, and migration",
  "effort": "high"
}

Resume a plan into implementation

Pass the returned session ID to opus_execute for the same canonical workspace:

{
  "workspace_path": "/repos/service",
  "task": "Implement the approved scheduler design",
  "mode": "implement",
  "session_id": "00000000-0000-4000-8000-000000000000",
  "acceptance_criteria": [
    "Existing jobs migrate without data loss",
    "Focused unit and recovery tests pass"
  ]
}

The shown UUID is illustrative; use the actual bridge-returned value.

Codex implementation, fresh Opus review

After Codex writes a substantial change, call opus_consult with mode: "review" and omit session_id. Ask for concrete, evidenced findings. Codex should evaluate each finding against the repository rather than accepting it automatically.

Opus implementation, Codex verification

Delegate a bounded change with opus_execute, then have Codex inspect git diff, the bridge's observed_changed_paths, pre-existing dirty work, and important tests. The bridge never commits or pushes the result.

Recommended Codex instruction

Use the Opus collaborator proactively for substantial architecture, unfamiliar
repositories, difficult bugs, multi-file changes, algorithms, concurrency,
security-sensitive work, and independent review. Skip it for trivial mechanical
edits. Delegate a complementary role, never let both agents write the workspace
at once, inspect the actual diff after Opus writes, and use a fresh session for
final independent review unless continuity is specifically valuable.

Security model

Workspace paths are hostile input. The bridge expands ~, performs strict canonical resolution, rejects files and missing paths, checks path-aware allowed root containment, detects the Git top level, and rejects symlink, traversal, sibling-prefix, and Git-root escapes. Execution requires Git by default but does not require a clean tree; pre-existing tracked, staged, untracked, deleted, and renamed work is preserved as context.

Every operation acquires, in order, a per-canonical-workspace async lock, a global async semaphore, and a process-safe file lock whose filename is a SHA-256 digest. This prevents duplicate calls for one workspace from consuming global capacity needed by another workspace. Sessions are canonical UUIDs stored in an atomic, mode-0600 registry inside a mode-0700 state directory. A session is bound to one canonical workspace and one Opus model. A plan may resume into execution, but cross- workspace and cross-model resumes fail.

Successful output must prove Opus 5 through a validated authoritative model field or protocol-conformant positive Opus usage that exceeds aggregate Haiku auxiliary usage. Both modelUsage spellings are audited when present; malformed, conflicting, or unexpected model entries fail closed, and no fallback model is configured.

Before and after a call, the bridge independently captures Git HEAD/branch, NUL-safe porcelain status, tracked/staged/untracked/deleted/renamed paths, diff statistics, and a content state fingerprint. The returned snapshot explicitly notes that Git-ignored paths and .git internals are not observed; Codex must inspect those separately when they matter. Non-Git consultations receive a directory manifest with explicit entry and content-hash limits; beyond the hash budget, bounded first/last content samples plus size/mtime/ctime metadata remain observation evidence. Filenames with spaces, tabs, quotes, and newlines are supported. A failed or timed-out process still gets a post-operation observation when possible.

Claude starts in its own process session. Timeout, cancellation, output overflow, or shutdown sends SIGTERM to the full process group, waits the configured grace period, sends SIGKILL if needed, reaps the process, stops heartbeats, cleans owner-only temporary prompt/settings files outside the repository, and releases all locks. The bridge never retries a completion automatically; an ambiguous failure may already have changed files and consumed subscription usage.

Every model call uses --safe-mode, --strict-mcp-config, --no-chrome, no Web tools, a mandatory fail-closed native sandbox, an empty strict network allowlist, no local binding or Unix sockets, secret-path denies, and dangerous Git-command denies. Unsandboxed retry is disabled. Admin-managed Claude Code policy still applies and can affect the effective policy; inspect organization policy when opus_status or Claude Code reports a managed-setting conflict.

Important limitations:

• Workspace source and submitted task context are sent to Anthropic through the locally authenticated Claude Code process and consume subscription usage.

• opus_execute is deliberately write-capable and should be approval-gated by the MCP client.

• Native sandboxing is a strong boundary, not magic. Repository-contained secrets remain sensitive even when common secret paths are denied.

• Claude Code may persist normal local session transcripts in its own state. The bridge does not copy or expose transcript contents.

• Network access from Claude tools is denied by default. The model request itself necessarily reaches Anthropic through Claude Code.

• Common commit, push, reset, clean, restore, rebase, merge, and history-rewrite commands are denied by pattern; HEAD and workspace changes are independently observed. These are layered controls, not a substitute for Codex inspecting the actual diff and trusted manifest.

Troubleshooting

• CLI too old: opus_status reports the parsed and minimum versions. Run claude update, then verify claude --version.

• Authentication unavailable: run claude auth login, claude auth status, and a new claude -p call. A nonzero or malformed status fails execution preflight unless the operator deliberately supplied CLAUDE_CODE_OAUTH_TOKEN. Read-only consultation may still attempt its bounded call and reports the redacted Claude authentication error if that request also fails. opus_status reports whether the deliberate-token execution exception is active.

• API key overrides subscription: unset ANTHROPIC_API_KEY and related provider variables. Task processes strip them regardless; status reports names.

• Workspace outside allowed roots: add the complete canonical Git root's parent to CLAUDE_MCP_ALLOWED_ROOTS. Allowing only a nested subdirectory is rejected when the Git root would escape.

• Native sandbox unavailable: install bwrap and socat on Linux/WSL2, or use a supported macOS host. The bridge runs a real namespace-isolation probe, not just an executable check, and never falls back to unsandboxed Bash. Ubuntu 24.04 may additionally require an administrator-provided AppArmor profile for /usr/bin/bwrap with userns, permission; prefer the distribution's purpose-built bwrap profile when available rather than disabling the global user-namespace restriction.

• Session/workspace mismatch: omit session_id to start fresh in the new workspace. Sessions cannot move between repositories.

• Timeout after possible edits: do not blindly call again. Inspect status, actual files, Git diff, tests, and the error's pre/post metadata first.

• Malformed Claude result: update Claude Code if necessary and inspect the workspace. Locally invalid structured output is never trusted and execution is never automatically retried.

• Corrupt session registry: stop bridge processes, preserve the registry for diagnosis, and move it aside only after deciding that resumable sessions are no longer needed. Corruption is not silently discarded.

Development

The test suite is fully offline. tests/fixtures/fake_claude.py emulates Claude diagnostics, structured completions, mutations, malformed output, limits, timeouts, and process descendants. No test requires Anthropic credentials, network access, subscription usage, or a real Claude invocation.

uv sync --all-groups
uv run ruff check .
uv run ruff format --check .
uv run pytest
uv build

tests/test_protocol.py launches the installed claude-mcp entry point and performs a real stdio MCP initialize/list/call sequence against the fake CLI.

Version 0.1 scope

Version 0.1 uses direct, synchronous access to one validated workspace per call. It intentionally has no PTY/TUI scraping, tmux integration, resident background agent, remote MCP transport, direct Anthropic API path, alternate provider, automatic worktree, automatic Git operation, arbitrary child MCP server, or background job that outlives an MCP call.

Possible later work includes opt-in isolated Git worktrees and richer progress streaming. Those features should preserve the writer–verifier and fail-closed security invariants established here.