[User Story] Build codex-dev-container (containerized Codex CLI environment)

[noahwhite]

Story Summary

As a developer, I want a containerized OpenAI Codex CLI environment (mirroring the pattern of claude-dev-container), so that I can run Codex in a reproducible, isolated environment with the same ergonomics already established for the Claude CLI.

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✅ Acceptance Criteria

• New repo noahwhite/codex-dev-container exists (private) — created: https://github.com/noahwhite/codex-dev-container
• Dockerfile builds an image that installs the Codex CLI via npm i -g @openai/codex
• Image entrypoint launches codex with the host's project directory mounted
• Launcher script (equivalent to claude-dev-container's) handles volume mounts, auth token passthrough, and sensible defaults
• README documents install, authentication, and usage
• Repo mirrors the structure and conventions of claude-dev-container (same branch model, CI pattern if applicable, commit signing policy)

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📝 Additional Context

• Install command: npm i -g @openai/codex
• Reference: https://github.com/noahwhite/claude-dev-container (existing mirror pattern to copy)
• Auth: Codex CLI uses an OpenAI API key — follow whatever passthrough pattern claude-dev-container uses for the Anthropic key
• Base image: whatever claude-dev-container uses, if reasonable; otherwise a slim Node image

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📦 Definition of Ready

• Acceptance criteria defined
• No blocking stories or unresolved external dependencies
• Story is estimated
• Team has necessary skills and access
• Priority is clear
• Business value understood

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✅ Definition of Done

• All acceptance criteria met
• Unit/integration tests written & passing
• Peer-reviewed
• Docs updated (if applicable)
• Verified in staging (if needed)
• No critical bugs/regressions

[linear]

GHO-130