Summary

• Implement CodexCliRuntime extending CLIRuntimeBase for OpenAI's codex CLI (src/middleware/runtimes/codex.ts)
• Handle the two-level Codex event model: 8 top-level event types (thread/turn/item lifecycle) × 8 item sub-types (agent_message, command_execution, mcp_tool_call, etc.)
• Implement CodexMcpConfigManager with merge-restore pattern for ~/.codex/config.toml TOML config lifecycle
• Delta text computation from progressive item.updated events (Codex sends accumulated text, not incremental deltas)
• Cross-provider contamination prevention: strips ANTHROPIC_API_KEY from subprocess environment
• 48 unit tests covering argument construction, all event types, environment setup, TOML serialization, MCP config management, and done event enrichment

Test plan

• pnpm build passes
• pnpm check (format + typecheck + lint) passes clean
• 48 unit tests pass covering all acceptance criteria
• Full test suite (10,691 tests) passes — 1 pre-existing flaky failure in supervisor.test.ts unrelated to changes

Closes #12

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