🤖 [codex] Add MCP config overlay support

[robmaceachern]

🤖 Drafted by my AI agent.

Summary

• Generate Codex .codex/config.toml from shared ai-rules/mcp.json, with optional ai-rules/codex-config.toml overlay support for repo-owned Codex settings.
• Merge generated MCP server tables with the Codex overlay before serializing TOML, so server-name collisions produce one valid table with overlay values taking precedence.
• Match Firebender's source-overlay model for supplemental agent config, including cleaning the generated Codex config file when MCP/config generation is removed.
• Update Codex MCP tests and docs for the overlay model.

Why

Codex project config can include more than MCP server definitions. Letting repositories define ai-rules/codex-config.toml gives them a source-controlled place for shared Codex settings while still deriving MCP server entries from the common ai-rules/mcp.json source.

If the overlay defines a server that is also generated from ai-rules/mcp.json, the overlay wins for overlapping fields. The generator resolves those tables before writing TOML, so .codex/config.toml remains parseable while still allowing project-specific overrides, such as customizing a generated rlib server.

Alternatives Considered

• Preserving arbitrary existing .codex/config.toml content and adding generated MCP server tables was considered, but it leaves shared Codex settings outside source control and can produce duplicate TOML tables when an existing target server name overlaps with ai-rules/mcp.json.

Validation

• cargo fmt --all --check
• ./scripts/clippy-check.sh
• cargo test
• Verified against ios-register origin/main ai-rules/mcp.json: generated Codex config includes actionable-ci-results and rlib, and parses with tomllib.

---

This PR description was drafted with AI assistance.

[robmaceachern]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

ai-rules/src/agents/codex.rs

Line 140 in 0c29551

let content = merge_generated_mcp_block(&base_content, &generated_block);

Avoid duplicating existing mcp_servers tables

When .codex/config.toml already contains a user-defined [mcp_servers.<name>] table and ai-rules/mcp.json contains the same server name, this merge path appends another [mcp_servers.<name>] in the generated block instead of reconciling/replacing it. TOML does not allow defining the same table twice, so the resulting config becomes invalid and Codex can fail to load MCP settings for that project. This is reproducible with any name collision between preserved user config and generated servers.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 0c29551e8b

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[robmaceachern]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 366dd72c08

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".