fix: forward CHOIR_AGENT_TOKEN to codex mcp-stdio via env_vars

[brickfrog]

Summary

Codex leaves' choir mcp-stdio subprocesses launched with zero CHOIR_* env vars: codex's MCP stdio launcher builds each server's environment from scratch (env_clear() + a DEFAULT_ENV_VARS whitelist in rmcp-client's create_env_for_mcp_server; shell_environment_policy only governs shell/exec tool calls, not MCP subprocesses), and choir's codex MCP entry (codex_mcp_override_args) configured no per-server env forwarding. Registration then had no CHOIR_AGENT_TOKEN and the server rejected every codex leaf (choir-ghl9, P0). This adds a names-only mcp_servers.choir.env_vars=["CHOIR_AGENT_TOKEN"] override so codex forwards the token from its own environment — on this MCP override surface the token value never rides argv (the pre-existing token exports in launch_env_prefix/TL init command strings are a separate, out-of-scope surface).

Codex 0.144.0 config-schema findings (task step 1)

• codex mcp add --help exposes --env <KEY=VALUE> → the mcp_servers.<name>.env value map (rejected here: it would embed the secret in argv).
• Official docs (learn.chatgpt.com/docs/extend/mcp, the developers.openai.com/codex/mcp redirect target) document both: "env" (optional): Environment variables to set for the server. and "env_vars" (optional): Environment variables to allow and forward. — env_vars entries are names whose values are read from codex's local environment.
• Verified against the installed binary (codex-cli 0.144.0): codex mcp -c 'mcp_servers.x.env_vars=["CHOIR_AGENT_TOKEN"]' list accepts the field and shows CHOIR_AGENT_TOKEN=***** (value resolved from codex's env, masked). Also ran the exact full override shape choir now emits (command/args/env_vars/cwd) — parses clean. Unknown fields are silently ignored, so the masked-value display is the positive proof the field is live. TL audit additionally confirmed the mechanism against codex-rs source (rmcp-client/src/utils.rs + stdio_server_launcher.rs).

Why only CHOIR_AGENT_TOKEN (task step 3)

Audited the mcp-stdio registration path: agent identity, role, parent/branch/workspace, terminal target, and listen_uds all come from the per-leaf .choir/config.local.toml (written at spawn; mcp_servers.choir.cwd points at the worktree) plus the --role/--name args already in the server argv. The CHOIR_* env identity vars are only a fallback for when that file lacks identity (local_cfg_from_env_lookup), which never applies to spawned codex leaves. The token (format_registration_request, src/transport/transport.mbt:84) is the single env-only input, so it is the entire forward list — no blanket CHOIR_* glob.

What changed

• src/workspace/launch.mbt: codex_mcp_override_args emits -c mcp_servers.choir.env_vars=["CHOIR_AGENT_TOKEN"].
• src/workspace/workspace_test.mbt: new test asserts the env_vars entry is present for all roles and that no argv element carries a CHOIR_AGENT_TOKEN= assignment or an mcp_servers.choir.env./env= value map.
• .choir/config.toml: rewrote the [model.codex] comment — the outage was model-independent (not gpt-5.6-luna) and the scrub comes from codex's MCP launcher whitelist, not shell_environment_policy; model/effort values unchanged.

Verification

• moon test --target native: 2267 passed, 0 failed (RED first: the new test failed before the fix).
• moon run src/bin/choir_lint --target native: pass.
• End-to-end verification (spawning a real codex leaf and checking its mcp-stdio /proc environ / registration success) is for the TL after merge — leaves cannot fork_wave.

Verification

Generated by Choir from commands executed in the leaf workspace.

• moon test --target native
  • exit: 0
  • head: 4a52d6e
  • output tail:

----- BEG4
IN MOON TEST RESULT -----
{"type":"start","file":"exec_test.mbt","index":9}
----- END MOON TEST RESULT -----
Total tests: 2267, passed: 2267, failed: 0.

• moon run src/bin/choir_lint --target native
  • exit: 0
  • head: 4a52d6e

[brickfrog]

Choir: GitHub Actions rollup reports all checks successful on the latest head — re-check review/merge policy on GitHub (not an approval or merge signal by itself).

[brickfrog]

Choir: GitHub Actions rollup reports all checks successful on the latest head — re-check review/merge policy on GitHub (not an approval or merge signal by itself).