Codex MCP schema translation converts array[string] tool params into string for memory_store.tags

What version of Codex is running?

codex-cli 0.115.0

### What subscription do you have?

[fill in]

### Which model were you using?

gpt-5.4

### What platform is your computer?

macOS (Darwin), Apple Silicon / x86_64 as applicable

### What issue are you seeing?

Codex appears to mis-convert an MCP tool parameter that is advertised as array[string] into a plain string in the exposed
callable tool schema.

In my case, an MCP server exposes:

• memory_store.tags: array[string]
• memory_update.tags: array[string]

But the Codex tool wrapper exposed to the assistant runtime shows:

• memory_store(... tags?: string ...)
• memory_update(... tags?: string ...)

As a result, the first tool call sends tags as a string, and the MCP server correctly rejects it with a validation error
because the backend expects list[str].

### What steps can reproduce the bug?

1. Register an MCP server whose tools/list response includes a tool with a parameter like:

• "tags": { "type": "array", "items": { "type": "string" } }

1. Start Codex and let it use that MCP tool.
2. Ask Codex to call the tool with tags.
3. Observe that Codex’s first call sends tags as a string instead of an array.

In my concrete case:

• MCP server: AI Memory Vault
• Tool: memory_store
• Correct MCP schema: tags is array[string]
• Exposed Codex wrapper schema: tags?: string

### What is the expected behavior?

Codex should preserve the MCP schema exactly:

• array[string] in MCP tools/list
• list[str] / array-of-string in the exposed tool wrapper

The first call should send:
```json
"tags": ["aimemvault", "mcp"]

not:

"tags": "aimemvault,mcp"

### Additional information

I verified that the MCP server itself is correct.

Server-side evidence:

• The MCP tools/list response advertises tags as array[string].
• The backend validator expects list[str].
• The server correctly rejects a plain string with a validation error.

This appears to be a Codex MCP bridge/schema translation bug, not a bug in the MCP server.

The issue likely affects multiple tools, not just this one, wherever Codex maps array[string] parameters incorrectly to
string.